A critical perspective that questions the use of PtX₂ for the HER when we have a better performing Pt/C while analysing the potential ways in which PtX₂ can actually be better than Pt/C.

Electrocatalytic water splitting activity trend is mainly justified using two activity markers namely the electrochemical surface area measured in terms of double-layer capacitance (Cdl) and the charge transfer resistance (Rct). In general, a better active catalyst always tends to have higher Cdl and lower Rct. The non-Faradaic Cdl has so far been shown to match with the Faradaic catalytic activity trend. Nonetheless, emphasizing its non-Faradaic origin and the fact that all ion adsorption and desorption sites should not necessarily be electrocatalytically active sites, we show here a strong disagreement between non-Faradaic Cdl and Faradaic oxygen evolution reaction (OER) activity trend between stainless steel (SS) and bleached stainless steel (BSS). BSS apparently exhibited higher Cdl due to increased OER inactive iron oxide contents on the surface while significantly losing its OER activity. This study, therefore, questions the credibility of using non-Faradaic Cdl to justify the purely Faradaic electrocatalytic activity trend.

Most better performing water splitting electrocatalysts are scarce, and their use increases the cost of production of H viaelectrolysis. Among the best performing noble/precious metal electrocatalysts, Ru is most notable because it acts as an excellent electrocatalyst for both oxidation and reduction reactions of water responsible for the H production. In fact, Ru outperforms Pt/C as the state-of-the-art water reduction electrocatalyst in alkali. However, the cost-wise more expensive Ru (than Pt and Ir) could not be extensively used in water electrolysis to avoid further increase in the cost of H production. Recently, there has been a renewed interest in Ru and is being intensively investigated with various structural and chemical modifications at the nano-level for catalytic water electrolysis with and without other materials. However, there is no comprehensive review that summarizes and analyzes recent developments in water splitting electrocatalysts that are modulated with Ru. Hence, this review is devoted to bringing out the strategies involved in harvesting the best of water splitting electrocatalysts by Ru-tweaking. The same is also benchmarked against their performance at different conditions. Besides, a detailed note on water splitting electrocatalysis and mechanisms involving Ru are given with insights on the phenomena that make it an active interface for water electrolysis. 2 2 2

Non-oxide/hydroxide hydrogen evolution reaction (HER) catalysts undergo hydroxylation to a significant extent even under reductive condition when exposed to alkali. Actual role of such hydroxylation in alkaline HER electrocatalysis is not previously given any significance. In this study, we report an intriguing finding that nickel sulfide a well-known HER electrocatalyst when subjected to anodic potential cycling covering Ni and Ni redox couple led to accelerated hydroxylation accompanying surface amorphization. As a result, improved electrochemical surface, better HER kinetics, and better charge transfer were achieved that lowering the HER overpotential by 110 mV at 100 mA cm . This surface amorphized and hydroxylated nickel sulfide exhibited excellent stability upon both galvanostatic and potentiostatic electrolysis for over 50 h. Besides, it also showed a lower Tafel slope (120 mV dec ), higher relative ECSA in terms of 2C (3.85 µF cm ), and higher electrochemical accessibility for Ni sites (3.7 × 10 cm ) which further advocate the superiority of our way of improving HER activity of a non-oxide/hydroxide catalyst. Thus, this study open up new avenues for re-examining other non-oxide/hydroxide catalysts in alkaline HER for benefiting the energy and cost-efficient hydrogen generation. 2+ 3+ 2 -1 −2 17 −2 dl

Cellulose in various forms possesses high strength, low density, and high aspect ratio with a three-dimensional open network structure, making them ideal candidates as current collectors in energy conversion application. Herein, a surface rough-cellulose-based bamboo fiber with unique and naturally-convoluted morphology is adopted for the fabrication of catalytically active cobalt substrates for water splitting. For the efficient evolution of hydrogen and oxygen, cobalt-based bimetallic alloys, namely, cobalt-molybdenum and cobalt-iron, were electrodeposited. The proposed system possesses a highly macro-porous network of hexa-filament micro-fibrils that demonstrate exceptional catalytic activities. In quantitative terms, the anodic and cathodic current density of 50 and −10 mA cm at respective overpotentials (η) of 250 and 46 mV with a low activation energy (E ) of 28 kJ mol were achieved. Moreover, when operated under harsh industrial standards of 5 M KOH@343 K, electrodes demonstrate excellent water electrolyzing catalytic activities (η = 147 mV;η = 209 mV). This work, thus, promises a new strategy for designing electrode systems that are highly efficient as well as economical as the substrate was obtained from a ubiquitous earth-friendly material for energy conversion application. −2 −1 a -100(HER) 100(OER)

Electrocatalytic oxygen evolution reaction (OER) catalyzed by non-precious metals and their compounds in alkaline medium is an attractive area of energy research for the generation of hydrogen from water. The 3d transition metals, particularly, Ni and Co show better OER activity than others in alkaline medium. Ni and Co based oxygen-evolving catalysts (OECs) experience an enormous enhancement in the OER activity either by incidental or intentional Fe doping/incorporation. To account for this, different roles of Fe that it exerts when incorporated into these OECs are reported to be responsible. Unfortunately, the conclusions drawn in many related studies are often contradictory to one another. Important contradictory conclusions are: 1) a few studies claim Fe is the active site and Ni/Co are inactive while other studies claim Ni/Co and Fe act together in OER, 2) a few studies claim Fe stays unoxidized while a few shows evidence for the existence of Fe , and 3) a few studies suggest Fe is the faster site in Ni/Co OEC matrices for OER but fail to explain similar effects observed with other OER matrices. Many critical experimental and theoretical investigations have been made recently to reveal this magical Fe effect and the results of those studies are coherently presented here with critical discussion. This review is presented as it is inevitable to know the critical roles of Fe effect in Ni/Co based OECs to succeed in energy efficient hydrogen generation in alkaline medium. 3+ 4+ 3+

We recently reported the fastest anodization method (just 80 s) of all for accessing a denser array of Cu(OH)2-CuO nanoneedles on a Cu foil substrate by applying a constant potential of 0.864 V vs a reversible hydrogen electrode in 1.0 M KOH that delivered a better activity for the methanol oxidation reaction (MOR). In this study, we show that the strength of the KOH solution used for anodization alters the size, morphology, surface chemistry, electrochemical accessibility of Cu sites, and the subsequent MOR activity trend. Intriguingly, an increase in KOH solution strength shortens the time of anodization from 80 s (1.0 M KOH) to 20 s with 3.0 M KOH, which in turn drastically reduces to just 6 s with 6.0 M KOH. As of now, this is the shortest time ever achieved for the anodic growth of Cu-OH/O nanoneedles on a Cu substrate. A set of detailed and comparative physical and electrochemical characterizations reveal positive relationships between anodization pH and anodization current, the size of Cu-OH/O nanoneedles grown, rate of growth, electrochemical accessibility of Cu sites, and electrocatalytic MOR activity. Thus, this study provides a universal approach to control the size of Cu-OH/O nanoneedles, electrochemical accessibility of Cu sites, and their subsequent MOR activity.

<p>The feasibility of a solar-driven photoelectrochemical process to generate hydrogen fuel from metal mine polluted water while simultaneously recovering heavy metals has been explored.</p>

Transition metal hydroxides (M-OH) and their heterostructures (X|M-OH, where X can be a metal, metal oxide, metal chalcogenide, metal phosphide, etc.) have recently emerged as highly active electrocatalysts for hydrogen evolution reaction (HER) of alkaline water electrolysis. Lattice hydroxide anions in metal hydroxides are primarily responsible for observing such an enhanced HER activity in alkali that facilitate water dissociation and assist the first step, the hydrogen adsorption. Unfortunately, their poor electronic conductivity had been an issue of concern that significantly lowered its activity. Interesting advancements were made when heterostructured hydroxide materials with a metallic and or a semiconducting phase were found to overcome this pitfall. However, in the midst of recently evolving metal chalcogenide and phosphide based HER catalysts, significant developments made in the field of metal hydroxides and their heterostructures catalysed alkaline HER and their superiority have unfortunately been given negligible attention. This review, unlike others, begins with the question of why alkaline HER is difficult and will take the reader through evaluation perspectives, trends in metals hydroxides and their heterostructures catalysed HER, an understanding of how alkaline HER works on different interfaces, what must be the research directions of this field in near future, and eventually summarizes why metal hydroxides and their heterostructures are inevitable for energy-efficient alkaline HER.

Electrochemical hydrogen peroxide synthesis using two-electron oxygen electrochemistry is an intriguing alternative to currently dominating environmentally unfriendly and potentially hazardous anthraquinone process and noble metals catalysed direct synthesis. Electrocatalytic two-electron oxygen reduction reaction (ORR) and water oxidation reaction (WOR) are the source of electrochemical hydrogen peroxide generation. Various electrocatalysts have been used for the same and were characterized using several electroanalytical, chemical, spectroscopic and chromatographic tools. Though there have been a few reviews summarizing the recent developments in this field, none of them have unified the approaches in catalysts' design, criticized the ambiguities and flaws in the methods of evaluation, and emphasized the role of electrolyte engineering. Hence, we dedicated this review to discuss the recent trends in the catalysts' design, performance optimization, evaluation perspectives and their appropriateness and opportunities with electrolyte engineering. In addition, particularized discussions on fundamental oxygen electrochemistry, additional methods for precise screening, and the role of solution chemistry of synthesized hydrogen peroxide are also presented. Thus, this review discloses the state-of-the-art in an unpresented view highlighting the challenges, opportunities, and alternative perspectives.

In this study, we show a simple two-step surface engineering method that uses chemical oxidation (using KOH and NaClO in 1:2 M ratio)-assisted leaching of metals (Cr, Mn, and Ni) from the surface and an electrochemical potentiostatic activation enabled resurfacing of only catalytically active Ni and Mn of the alloy. Such surface-engineered stainless steel 304 (SS-304-Ox-ECA) foils rich in Ni(OH)2 and multivalent Mn oxides were found to have a coarse texture with uniform nanostructures. As a result of leached Cr, resurfaced catalytically active sites improved roughness with nanotexturing and enhanced the charge-transfer ability. The SS-304-Ox-ECA foil has become a high-performance HER electrocatalyst that delivered 400 mA cm-2 higher current density at -0.8 V versus RHE and demanded 210 mV lower overpotential for a current density of 100 mA cm-2 than pristine SS-304 foils in 1.0 M KOH. A smaller Tafel slope (90 mV dec-1) and a higher double-layer capacitance (2Cdl = 0.784 μF cm-2) further justified that the activity enhancement is also due to the improved HER kinetics and increased electrochemical surface area. This catalytic electrode of high abundance and low cost is a promising candidate for cost-efficient hydrogen production from water.

Oxygen evolution reaction (OER) is the bottleneck for realizing energy-efficient hydrogen production through water electrolysis in both acid and alkali. Alkaline OER electrocatalyzed by Ni and Co hydroxides are well known which showed unexpected enhancement with the addition of Fe. We found that the commercially procured Cu foam containing trace amount of Ni (~1.5 wt.%) upon anodization formed Cu(OH) –CuO nanowires with conceivable formation of Ni(OH) and experienced a notable enhancement in its OER activity. When sufficient amount of Fe was intentionally supplemented during anodization, OER activity of the same was further improved. Specifically, as a combined result of anodization in KOH and in Fe supplemented KOH, overpotential at 50 mA cm was lowered by 153 mV. Such an activation also improved the kinetics of OER by lowering the Tafel slope by 100 mV dec . With these, it has been shown here that a moderately active OER catalyst i.e., Cu(OH) –CuO/Cu formed upon the anodization of Cu foam can be turned into a highly active catalyst just by utilizing the trace Ni that it already contains and intentionally supplementing sufficient amount of Fe. 2 2 2 −2 −1

The biomolecule DNA with the presence of different functionalities found to interact with different kinds of metal ions and show relatively higher stability over a long period of time when optimized appropriately. With the presence of A-T and G-C pairs, sugar moieties, phosphate functional groups and the double-helical structure, it can assemble both cationic and anionic species and forms a perfect metal-DNA self-assembly. Depending upon the aspect ratio of metal-DNA self-assemblies, metal content and their morphological outcomes, they could deliver variance in the catalytic activities. Such differences can be brought out by varying the synthesis reaction parameters focusing on a specific electrocatalytic application. In this review, recent developments in DNA metallization is elaborated first highlighting the underlying interactions between DNA and cationic/anionic species of various metals following which application of metal-DNA assemblies in electrocatalytic water oxidation and reduction are discussed critically. Knowledge provided in this review thus acts as the guide to various DNA metallization strategies and their subsequent application to water electrolysis for hydrogen generation.

A swift potentiostatic anodization method for growing a 5-7 μm tall nanoneedle array of Cu(OH)2-CuO on Cu foil within 100 s has been developed. This catalytic electrode when screened for methanol oxidation electrocatalysis in 1 M KOH with 0.5 M methanol, delivered a current density as high as 70 ± 10 mA cm-2 at 0.65 V versus Hg/HgO which is superior to the performance of many related catalysts reported earlier. The observed activity enhancement is attributed to the formation of both Cu(OH)2-CuO nanoneedle arrays of high active surface area over the metallic Cu foil. In addition, the Cu(OH)2-CuO/Cu electrode had also exhibited excellent stability upon prolonged potentiostatic electrocatalytic oxidation of methanol while retaining the charge-transfer characteristics. Growth of such highly ordered assembly of Cu(OH)2-CuO nanoneedles within a minute has never been achieved before. When compared to its oxygen evolution reaction activity, the addition of 0.5 M methanol has lowered the overpotential at 10 mA cm-2 by 334 mV, which is significant. This encourages the use of methanol as a sacrificial anolyte for energy-saving production of H2 from water electrolysis.

Nickel selenide is an important class of nickel chalcogenide that has recently gained greater attention in electrochemical water splitting. Though other chalcogenides such as sulphides and tellurides have also been shown to possess appreciable electrocatalytic water splitting activity as both cathode and anode material, the electrocatalytic activity of nickel selenides in oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is unmatched by the former one. In the case of HER, nickel selenides are good electrocatalysts in both acid and alkali with some metal dissolution in acid and surface modification to nickel hydroxide in alkali. In the case of OER, nickel selenides have been shown to behave in a unique way in which it acted better than simple nickel hydroxides/oxyhydroxides. This is quite intriguing to researchers and many studies have been recently carried out. However, there is still no exclusive review summarizing the recent development of this material for OER electrocatalysis with highlights on challenges and opportunities. Hence, we have dedicated to discuss the same in this review. In addition, the significance of OER electrocatalysis has been briefly introduced. Finally, all the studies that reported the OER activity of nickel selenides are benchmarked based on the Tafel slope values. With the collective information provided in this review, readers would be updated with the recent trend in utilizing nickel selenides as OER electrocatalysts.

Mixed valence spinel oxides have emerged as an attractive and inexpensive anode electrocatalyst for water oxidation to replace noble metals based electrocatalysts. The present work demonstrates the facile synthesis of Zn substituted MnCo O supported on 3D graphene prepared by simple hydrothermal technique and its application as an electrocatalyst for water oxidation and methanol oxidation. The physico-chemical properties of the nanocatalyst were studied using various microscopic, spectroscopic and diffraction analyses confirming the formation of the composite. The electrocatalytic performance of the prepared electrocatalyst was evaluated using potentiodynamic, potentiostatic and impedance techniques. The synthesized Zn Mn Co O /rGO electrocatalyst with x = 0.2 and 0.4 offered the same onset potential and overpotential at 10 mA/cm . However, catalyst x = 0.4 delivered a higher current density indicating the superiority of the same over other compositions which is attributed to better kinetics that it possessed for OER as revealed by the smallest Tafel slope (80.6 mV dec ). The prepared electrocatalysts were tested for methanol oxidation in which electrocatalyst Zn Mn Co O /rGO with x = 0.4 shows a better electrochemical performance in oxidizing methanol with the higher current density of 142.3 mA/cm . The above catalyst also revealed excellent stability and durability during both MOR and OER, suggesting that it can be utilized in practical applications. 2 4 1-x x 2 4 1-x x 2 4 2 −1 2

Electrochemical impedance spectroscopy (EIS) is an efficient tool that reveals the electrochemical characteristics of catalysts, surfaces, interfaces, coatings, and so forth. Use of EIS in different areas of energy research wherever current, potential, and charge determine the performance has become inevitable. Electrocatalytic water splitting is one of such fields focused on generating high purity hydrogen, where EIS is used to correlate the activity trends measuring charge transfer resistances (R ). In doing so, different conventions are followed. A few perform EIS at the open circuit potential (OCP), a few perform at onset potential or at a potential before onset potential, a few perform at different potentials for different catalysts at which they deliver the same current density, and a large group of people choose a constant potential beyond onset, at which all the studied catalysts show appreciable catalytic activity. Existence of such different practices in using EIS to characterize water splitting electrocatalysts often lead to misinterpretation of the activity trends. Hence, to provide a clear view on the appropriate use of EIS in water splitting electrocatalysis, we have carried out a comparative EIS study on the oxygen evolution reaction (OER) activity trend of stainless steel 304 (SS-304), Co, Ni, and Cu foils in 1 M KOH at all the above-stated conditions and the results showed that the EIS carried out at constant potentials in the catalytic turnover region is appropriate. ct

Cobalt chalcogenides are excellent oxygen evolution reaction (OER) precatalysts in alkaline medium as they readily form O -evolving CoOOH entities in electrochemically accessible Co sites when subjected to anodic potential. A key factor that determines the efficiency of OER in cobalt chalcogenides is the number of electrochemically accessible Co sites. Here, an easy way of increasing the electrochemical accessibility of Co sites in CoSe has been identified, which is the simple preoxidation of selenide to selenite. When screened for OER in alkali, it was found that the electrochemical accessibility of Co after preoxidation of Se in CoSe was increased by 7.8 ± 2 times in the first cycle and 2-3 times after activation by potential sweeping and redox cycling. The corresponding OER activation energy lowered to ∼1/2 at overpotentials 450 mV or higher due to such preoxidation of Se. Irrespective of the lowering in the electrochemical accessibility of Co sites from the 1st cycle to the 100th cycle, the overall OER activity was maintained to be the same. This is quite relatable as a major portion of Co oxidized in the first cycle is shuttling between 3+ and 4+ states while evolving O . Altogether, preoxidation of Se in CoSe benefitted the realization of increased electrochemical accessibility for Co sites, improved ECSA, improved charge transfer at catalytic turnover conditions, and lowered OER activation energy. 2 2 2 2 2 2+ 2+ 2+ 2+ 2+ 2+ 2+

Electrochemical water splitting powered by electrical energy derived from renewable sources is a green and faster way of producing bulk hydrogen with the highest purity. Unfortunately, the cost-inefficiency associated with energy loss (as overpotential) and costs of electrode materials have been forbidding this technology to surpass the currently dominant industrial process (steam reforming of hydrocarbons). With the recent evolution of transition metal chalcogenides, efficient commercial electrochemical water splitting is not too far. Transition metal chalcogenides are better in the hydrogen evolution reaction (HER) than pristine metals as they have negatively polarized chalcogenide anions with relatively lower free energy for proton adsorption. Moreover, chalcogenides are relatively easy to prepare and handle. Several metal chalcogenides have been reported with good HER activity among which Ni chalcogenides are reported to be exceptional ones. In recent years, growth of the nickel chalcogenide catalysed HER is massive. This review is devoted to bringing out a comprehensive understanding of what had happened in the recent past of this field with highlights on future prospects. In addition, we have also briefed the key physico-chemical properties of these materials and highlighted what one should anticipate while screening an electrocatalyst for electrochemical water splitting.

Plasmon-induced hot-electron generation and its efficient transfer to the conduction band (CB) of neighboring metal oxides is an effective route to solar energy harvesting. However, until now, this process has been very inefficient due to the poor charge transfer rate from plasmonic metal nanoparticles (NPs) to the CB of the oxide semiconductor. In this work, an in situ grown synthesis method has been developed to grow plasmonic Ag NPs within a titanium oxide (TiO ) matrix. This synthesis method allows us to deposit Ag NPs surrounded by a TiO semiconductor, which results in an efficient charge transfer from the Ag NPs to the CB of TiO and has been utilized for highly enhanced electro-photocatalytic H generation. Photoelectrochemical measurement of optimized Ag(NPs)-TiO thin film photoanodes showed a high photocurrent generation at a density of 42 mA cm in 1 M KOH solution, which is three orders of magnitude higher than that of pure TiO , and stability for more than 1.5 h. These data indicates that it has excellent potential application for photoelectrochemical (PEC) water splitting. An intense photocurrent generation in the region of plasmonic absorption of Ag NPs with a peak position of 435 nm has been observed; this photocurrent generation reveals direct evidence of a strong contribution of plasmon-induced hot electrons for solar energy conversion. 2 2 2 2 2 2 -2

Organic conversions electrified by suitable catalytic electrodes is attracting ever-increasing attention as it possesses multiple advantages such as minimal waste production, high atom economy, use of clean and green reagents, high selectivity and ability to provide shorter pathways for many important multi-step organic reactions. Electrochemically driven fluorination, polymerizations, C-H or C-X (X=halide) activation and CO2 reduction are few examples in this regard. Although electrodes play a key role in these processes, acting as catalysts or synthons in many reactions, their activity has been often neglected or given negligible significance. This review critically analyses the use of different electrodes including Pt, Ni, Cu, stainless steel, sacrificial anodes, B-doped diamond and C-based electrodes in the broad context of organic synthesis while highlighting their potential and limitations. Besides, we also elaborated the electrocatalytic reactions associated with the solvents that are essential to bring out above-mentioned reactions. Thus, this review provides useful guidelines not only for driving typical organic reactions, but also to design new synthetic pathways which will improve our understanding of making organic conversions greener and will also help us realize sustainability in the field of electroorganic synthesis.

Catalyzing oxygen evolution reaction (OER) with the lowest possible overpotential is a key to ensure energy efficiency in the production of hydrogen from water electrochemically. In this report, we show the results that astonished us. Co hydroxide containing trivalent V was prepared chemically and screened for electrochemical water oxidation in rigorously Fe free 1 M KOH (pH 13.8). Overpotential of 198 mV at 10 mA cm was observed for the synthesized Co-V hydroxide with the optimal Tafel slope of 60 mV dec . This is the lowest overpotential at this current density ever reported for OER in alkaline conditions while utilizing Co based electrocatalysts. Density function theory (DFT) calculations showed that the third elementary step (oxyhydroxide formation and delivery of O ) was spontaneous on V site that is bridging two adjacent Co sites which was attributed to the observed enhancement. -2 -1 2

Technology for producing highly pure hydrogen (99.999%) by water electrolysis is a field of importance in terms of the planets' current energy scenario. A much needed transition from a carbon economy to a hydrogen economy further adds importance to the field of hydrogen generation from water for a sustainable future. To avoid energy losses in the production process, the use of highly acidic (Proton Exchange Membrane (PEM) water electrolyzer) and alkaline (alkaline water electrolyzer) electrolytes is conventional practice in this field. Unfortunately, there are several other issues associated with the use of acidic and alkaline electrolytes such as the requirement of specific ion exchanging membranes with good stability, acid or alkali stable catalysts and corrosive environment withstanding cell stacks, etc. To overcome these issues, researchers have shown interest in the field of electrochemical water splitting in neutral and near-neutral conditions. In this review, the chronological development of 3d transition-metal-based electrocatalysts for neutral and near-neutral water splitting is extensively discussed with emphases on screening methodologies, mechanisms, structure-activity correlations, and detailed catalyst specific evolution. In addition, catalysts reported so far, are also benchmarked based on their performance separately for different electrolytes used.

In the near future, sustainable energy conversion and storage will largely depend on the electrochemical splitting of water into hydrogen and oxygen. Perceiving this, countless research works focussing on the fundamentals of electrocatalysis of water splitting and on performance improvements are being reported everyday around the globe. Electrocatalysts of high activity, selectivity, and stability are anticipated as they directly determine energy- and cost efficiency of water electrolyzers. Amorphous electrocatalysts with several advantages over crystalline counterparts are found to perform better in electrocatalytic water splitting. There are plenty of studies witnessing performance enhancements in electrocatalysis of water splitting while employing amorphous materials as catalysts. The harmony between the flexibility of amorphous electrocatalysts and electrocatalysis of water splitting (both the oxygen evolution reaction [OER] and the hydrogen evolution reaction [HER]) is one of the untold and unsummarized stories in the field of electrocatalytic water splitting. This Review is devoted to comprehensively discussing the upsurge of amorphous electrocatalysts in electrochemical water splitting. In addition to that, the basics of electrocatalysis of water splitting are also elaborately introduced and the characteristics of a good electrocatalyst for OER and HER are discussed.

Understanding the inherent activity of an electrocatalyst is an effective way of studying its optimization conditions for harvesting better performance. In this, we studied the inherent electrocatalytic activity of nickel selenide catalysts of three different stoichiometry such as Ni Se, Ni Se and NiSe in which the Se:Ni ration varies as 1.176, 1.333 and 2.0 respectively. The hydrogen evolution reaction (HER) of these catalysts was found to increase with the increasing Se:Ni ratio due to which NiSe turned out to be the better one among others. Interestingly, the oxygen evolution reaction (OER) of these catalysts showed a different trend irrespective of Se:Ni ratio where the ease of formation of NiOOH was found to control the kinetic current. Such influences of stoichiometry in HER and ease of NiOOH formation in OER had never been revealed before for nickel selenide system. 0.85 3 4 2 2

Replacing precious water oxidation electrocatalysts used in proton exchange membrane (PEM) water electrolyzers with the nonprecious and abundant electrocatalysts is still a poorly addressed issue in the field of hydrogen generation in acidic medium through water electrolysis. Herein we report such an all-nonprecious binary spinel metal oxide the "cobalt titanate" (Co TiO ) as an efficient alternate to expensive IrO and RuO for PEM water electrolyzer. The synthesized Co TiO octahedral nanocrystals of size 50 to 210 nm showed excellent oxygen evolution reaction (OER) activity in 0.5 M H SO , which was comparable to IrO and better than spinel Co O when examined under identical experimental conditions. Overpotential of just 513 mV was sufficient enough to drive a kinetic current density of 10 mA cm , which is a significant figure of merit as far as acidic water oxidation electrocatalysis is concerned. 2 4 2 2 2 4 2 4 2 3 4 -2

Water electrolysis is a field growing rapidly to replace the limited fossil fuels for harvesting energy in future. In searching of non-noble and advanced electrocatalysts for the oxygen evolution reaction (OER), here we highlight a new and advanced catalyst, selenized Cu Sn@Cu foam, with overwhelming activity for OER under both alkaline (1 M KOH) and near-neutral (1 M NaHCO ) conditions. The catalysts were prepared by a double hydrothermal treatment where Cu Sn is first formed which further underwent for second hydrothermal condition for selenization. For comparison, Cu Se @Cu foam was prepared by a hydrothermal treatment under the same protocol. The as-formed Cu Sn@Cu foam, selenized Cu Sn@Cu foam, and Cu Se @Cu foam were utilized as electrocatalysts and showed their potentiality in terms of activity and stability. In 1 M KOH, for attaining the benchmarking current density of 50 mA cm , selenized Cu Sn@Cu foam required a low overpotential of 384 mV and increased charge transfer kinetics with a lower Tafel slope value of 177 mV/dec comparing Cu Sn@Cu foam, Cu Se @Cu foam, and pristine Cu foam. Furthermore, potentiostatic analysis (PSTAT) was carried out for 40 h for selenized Cu Sn@Cu foam and with minimum degradation in activity assured the long-term application for hydrogen generation. Similarly, under neutral condition selenized Cu Sn@Cu foam also delivered better activity trend at higher overpotentials in comparison with others. Therefore, the assistance of both Sn and Se in Cu foam ensured better activity and stability in comparison with only selenized Cu foam. With these possible outcomes, it can also be combined with other active, non-noble elements for enriched hydrogen generation in future. 3 3 3 7 4 3 3 7 4 3 3 7 4 3 3 -2

Hydrogen generation through water electrolysis is a promising way of storing excess energies obtained from intermittent sources. Many catalysts including have been evaluated for acidic or alkaline water electrolysers. Here, we propose the use of the Ni Se /Ni foam 3D electrode as anode for a membrane-free hybrid water electrolyser where the catholyte (0.5 M H SO ) and anolyte (1 M KOH) are separated by an acid and alkali stable silicate disc of diameter 1 cm and thickness 0.3 cm to achieve the combined benefit of splitting water below its reversible potential 1.23 V. We have realized the initiation of water splitting just with 0.62 V. Significantly, the benchmarking current density 10 mA cm was achieved at a cell voltage of 1.12 V which is far below the reversible potential of water oxidation (1.23 V) with the cell Ni Se /Ni|1 M KOH||0.5 M H SO |Pt. The expected issue of salt formation can be easily overcome just by refilling the anode and cathode compartments with fresh electrolytes. This novel approach of underpotential splitting of water with a membrane-free acid-base hybrid electrolyser will certainly lead to several innovative achievements in the field of hydrogen generation through water electrolysis in the future. 3 4 2 4 3 4 2 4 −2

Revealing the intrinsic catalytic properties and their dependence on other factors is always a desired challenge in the field of catalysis. Finding and fine-tuning of the inherent electrocatalytic properties of 3D nonprecious metal hydroxides and oxides by a foreign element doping is an attractive domain in the electrocatalysis of water oxidation. This report reveals such an effect of Mn doping on the electrocatalytic oxygen evolution reaction (OER) of Co O nanosheet arrays grown on nickel foam (NF) by the ammonia evaporation technique. The Mn doping induces the in situ conversion of Co(OH) into Co O during deposition. The strain generation during doping and the presence of metallic Mn are important factors for enhanced OER performance. Such a unique way of doping as well as in situ conversion of hydroxides into oxides offer an excellent electrocatalyst with superior performance compared to pristine Co O or Co(OH) nanoflakes. 3 4 2 3 4 3 4 2

Evaluation of unique catalysts of the iron group metals with activity in the OER region similar to that of scarce metals is of great importance to achieve sustainable production of H on a large scale. Herein, we report the unique nanosheets of nickel iron hydroxy carbonate hydrate (NiFeHCH) which were prepared through a wet-chemical route within 1 h of reaction time, acting as an efficient electrocatalyst for the oxygen evolution reaction (OER) in both alkaline and near-neutral media. The NiFeHCH was prepared with different concentrations of Fe in different ratios: 1:0.2, 1:0.4, 1:0.6, 1:0.8, and 1:1. Among them, nanosheets of NiFeHCH (1:0.2) were found to have superior OER activity, which required an overpotential of 250 mV to reach 20 mA cm with a very low Tafel slope value of 39 mV/decade in 1 M KOH. Nanosheets with other ratios also had comparable OER activity with overpotentials ranging from 256 to 290 mV with Tafel slope values from 39 to 49 mV/decade. Nanosheets of NiFeHCH electrocatalysts screened for the OER in 1 M NaHCO (pH ∼8.5) required overpotentials for all of the ratios ranging from 389 to 507 mV at 10 mA cm and Tafel slope values from 155 to 205 mV/decade, of which nanosheets of NiFeHCH (1:0.4) showed better activity by requiring an overpotential of 389 mV at 10 mA cm and Tafel slope value of 155 mV/decade. With these fruitful advantages, these prepared nanosheets of NiFeHCH can be a better alternative to scarce metals for industrial water electrolysis. 2 3 -2 -2 -2

Exploration of rare earth metals for the Surface Enhanced Raman Scattering (SERS) is greatly preferred to identify probe molecules even at nano molar level. Highly stable Rh nanoparticles (NPs) which are ultra-small size have been prepared within 20 min of reaction time as a colloidal solution using a bio-molecular scaffold DNA and NaBH as a reducing agent under room temperature. While keeping metal ion concentration fixed and by making difference in DNA concentration, three different sets of Rh@DNA such as 0.08, 0.085 and 0.09 M were formed as nanochains like structure with varying diameters. The average chain length of Rh NPs for varying concentrations of DNA is ∼98 nm and the Rh particles size is below 5 nm in all the cases. These ultra-small Rh NPs have been utilized for two distinct potential applications such as in catalysis and SERS studies. From the catalysis reaction, reduction of 4-Nitro benzaldehyde to 4-amino benzaldehyde, Rh@DNA (0.08 M) has shown rate constant value of 0.26 min which is highest among other concentrations studied. SERS study revealed that the calculated Enhancement Factor (EF) value was 1.19 × 10 for Rh@DNA (0.08 M) which is highest while compared with other concentrations. Apart from catalysis and SERS, the as-synthesized Rh NPs can find applications in other interdisciplinary fields such as organic catalysis, electro-catalysis and so on in near future. 4 −1 5

A material with interdisciplinary properties is of wide interest for use in environmental applications. Currently, hydrogen generation by electrolysis and formation of carbonyl derivatives from alcohols are two different fields that focus on energy and environmental applications. In this work, a new material, Cobalt Tungsten Oxide Hydroxide Hydrate (CTOHH) on deoxyribonucleic acid (DNA) scaffold having chain-like morphology has been prepared for the first time by a facile microwave heating method. The same CTOHH was also prepared without the DNA scaffold and resulted in irregular aggregated molecular structures. Further, both CTOHH-DNA and CTOHH were converted into CoWO -DNA and CoWO , respectively by annealing them at a temperature of 600 °C. All the four catalysts were used for electrocatalytic oxygen evolution reaction (OER) and for oxidation of aromatic alcohols. In OER, CTOHH-DNA delivered fruitful results compared to all other electrocatalysts. For attaining a current density of 10 mA cm , it just required an overpotential of 355 mV with a Tafel slope value of 47.5 mV dec . Similarly, all four catalysts were also analyzed for selective and controlled oxidation of aromatic alcohols to their respective aldehydes and ketones using molecular oxygen as a green oxidant where CTOHH-DNA showed better results. Chemo-selectivity has been observed for CTOHH-DNA in the co-presence of hydroxyl and cyano functional groups. The durability of CTOHH-DNA was analyzed and it showed excellent catalytic activity retention up to five cycles. 4 4 -2 -1

Advancements in the search for efficient H evolving electrocatalysts by engineering the structure and electronic properties of bulk materials at the nano regime have had a constructive impact on realizing better performance with ultralow catalyst loading. In this work, we investigate the electrochemical hydrogen evolution catalysis of WS quantum dots (QDs) synthesized electrochemically. WS QDs were evaluated for a hydrogen evolution reaction (HER) in 0.5 M H SO as a binder-less electrocatalyst, which necessitated a low HER onset of 190 mV and reached -200 mA cm at 473 mV. In contrast, the bulk WS exhibited a poor performance, which required 780 mV to drive -50 mA cm . The electrochemical disintegration of bulk WS into QDs is the key behind such activation. 2 2 2 2 4 2 2 -2 -2

One dimensional (1D) materials are highly desirable in current platforms of materials chemistry owing to their unique physico-chemical properties. Herein, we report an effective way to synthesize 1D Co-ZIF microfibers using an electrospinning method, where a zeolitic imidazole framework (ZIF) with CoCl ·6H O was prepared as the precursor for electrospinning. The synthesized microfibers were labeled after their post-spinning processing temperature as Co-ZIF-RT (without annealing), Co-ZIF-350 (annealed at 350 °C in air and a N atmosphere) and Co-ZIF-550 (annealed at 550 °C in air and a N atmosphere). All five microfibers were evaluated for the first time in electrocatalytic oxygen evolution reaction (OER) studies both in 0.5 M H SO and 1 M KOH electrolytes. For the OER in 0.5 M H SO , Co-ZIF-550-N delivered a superior activity and required an overpotential of 405 mV at a current density of 10 mA cm with a Tafel slope value of 281 mV dec . For the OER in 1 M KOH, Co-ZIF-350-air gave better activity and required an overpotential of 370 mV and a lower Tafel slope value of 55 mV dec . Fabricated materials showing promising activity for the OER both in acid and alkali implied that they can be adapted as a cost-efficient, cheaper alternative to commercially available IrO /C electrocatalysts. Moreover, in the future, the same synthetic protocol can be easily extended to the fabrication of other active metals incorporating ZIFs and the zeolite derived networks can also be utilized for other energy related applications. 2 2 2 2 2 4 2 4 2 2 -2 -1 -1

Self-assembly is one of the most used strategies in the controlled synthesis and design of well-organized nanomaterials for various applications in diverse realms namely catalysis, sensors, microelectronics, energy storage, and energy conversion. It is quite common to see reports on the synthesis and design of several self-assembled nanomaterials for the application in the catalysis of various chemical, photochemical, and electrochemical reactions and processes. Nevertheless, a combined overview on the synthetic strategies for self-assembled nanomaterials has not been reported in any form in literature. Owing to the current interest shown and the future significance on the self-assembled nanomaterials, it is highly essential to have such an elaborated review on the progress and perspectives of synthesis of self-assembled nanomaterials and their subsequent application to catalysis of various chemical, photochemical, and electrochemical reactions and processes. In this review, we have highlighted various synthetic methodologies used so far for fabricating the self-assembled nanomaterials that includes Langmuir–Blodgett method, layer-by-layer assembly, amphiphilic (artificial and bio) self-assembly, and template-free approach. Nanomaterials derived from the above mentioned methods in various catalysis reactions are also highlighted in detail with an emphasis on confronts and prospects in the field of materials self-assembling and its concomitant application to catalysis.

Copper and its oxides are among the best electrocatalysts for the electrochemical conversion of CO to value-added small organics because of its high hydrogen overvoltage, making the hydrogen evolution reaction (HER) a poor side reaction. Here we report an interesting finding that turned the nature of surface-oxidized Cu upside down in electrochemical H evolution. It is commonly known that the electrochemical reactivity of a metal ion is highly sensitive to the anion to which it is coordinated in the electrolyte. In the case of Cu, when it is in the form of copper oxide, the hydrogen overvoltage is huge. Nonetheless, we found that when Cu is in coordination with Se ions as Cu Se, the hydrogen overvoltage was shrunken by ∼1 V, imparting ultralow charge transfer resistance (R ) that varied from 0.32 to 0.61 Ω depending on the means by which selenization was carried out. Selenization was done by two different methods. In one method, conventional stirring was employed to selenize Cu foam in a preheated NaHSe solution at 90 °C for 20 min. In another method, hydrothermal treatment was employed to selenize Cu foam with NaHSe solution at 120 °C for 1 h. The wet-chemical method yielded honeycomb-like hierarchical arrays of Cu Se sheets on Cu foam (designated as Cu Se-ch/Cu), and the hydrothermal method yielded a uniform array of spiky rods of Cu Se (designated as Cu Se-ht/Cu). The HER electrocatalytic studies carried out in 0.5 M H SO showed that Cu Se-ch/Cu and Cu Se-ht/Cu had similar kinetics, with Tafel slopes of 32 to 35 mV dec , which is closer to the state-of-the-art Pt/C. Interestingly, the Cu Se-ch/Cu delivered a total kinetic current density of -1200 mA cm when polarized up to -0.85 V vs RHE, whereas Cu Se-ht/Cu delivered a maximum of -780 mA cm only. 2 2 2 CT 2 2 2 2 2 4 2 2 2 2 2- -1 -2 -2

The construction of cost-effective, efficient, and sustainable catalytic systems for electrocatalytic hydrogen generation by water splitting is extremely important for future fuels globally. Herein, we have prepared nickel orthoborate (NOB) via simultaneous oxidation and reduction of nickel precursors and studied their role in oxygen evolution reaction (OER) for water electrolysis. In addition, the specific role of microwave irradiation and conventional stirring in the formation of NOB was also investigated with comparative assessment of their catalytic ability in electrochemical water splitting. It was found that NOB nanoflowers prepared via microwave irradiation exhibited better OER electrocatalyst than the ones prepared by conventional heating. Interestingly, the NOB nanoflowers outperformed the commercial NiO nanopowder under the identical experimental conditions in catalyzing OER. Morphological hierarchy and high Brunauer-Emmett-Teller specific surface area were attributed for their enhanced OER activity. A long run of 6 h chronopotentiometry analysis showed a negligible degradation in activity signified the high stability and endurance of NOB nanoflowers. The numbers of merits from the electrochemical characterizations revealed that NOB nanoflowers could be an alternate, efficient, and abundant OER electrocatalyst for bulk water electrolysis.

Nonprecious metals based electrocatalysts are highly anticipated in electrocatalytic water splitting as the increasing energy demand can be handled by large scale H production with minimum expenses. Herein, a facile and faster nickelo-sulfurization of DNA in ambient conditions has been developed that resulted in NiS anchored wirelike assemblies of DNA. The effect of DNA concentration on material stability and electrocatalytic activity was studied, and it was found that, with DNA to Ni ratios of 0.048 and 0.072 M, the NiS anchored DNA colloidal solutions were stable. In addition, it was found that NiS(0.048) with a relatively lower DNA concentration showed better oxygen evolution reaction (OER) activity than NiS(0.072). Overpotentials of 352 and 401 mV were required by NiS(0.048) and NiS(0.072) to deliver a current density of 10 mA cm even with an ultralow quantity of NiS(0.0123 mg cm ) in both. The same trend was reflected in the Tafel slopes of NiS(0.048) and NiS(0.072) which showed 58.6 and 112.4 mV dec indicating that the optimum ratio for better OER activity is 0.048. In this study, DNA plays a versatile role such as acting as a stabilizer, scaffold, and a microstructural stage for NiS in solution. Moreover, DNA also acts as an efficient binder and as a conductor of both ions and electrons in its OER activity trend. The proposed method can be used for preparing stable colloids of other metal sulfide based nano-electro-catalysts and can directly be employed for water oxidation in alkaline conditions. 2 2+ -2 -2 -1

The number of research reports published in recent years on electrochemical water splitting for hydrogen generation is higher than for many other fields of energy research. In fact, electrochemical water splitting, which is conventionally known as water electrolysis, has the potential to meet primary energy requirements in the near future when coal and hydrocarbons are completely consumed. Due to the sudden and exponentially increasing attention on this field, many researchers across the world, including our group, have been exerting immense efforts to improve the electrocatalytic properties of the materials that catalyze the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode, aided by the recent revolutionary discovery of nanomaterials. However, the pressure on the researchers to publish their findings rapidly has caused them to make many unnoticed and unintentional errors, which is mainly due to lack of clear insight on the activity parameters. In this perspective, we have discussed the use and validity of ten important parameters, namely overpotential at a defined current density, iR-corrected overpotential at a defined current density, Tafel slope, exchange current density (j ), mass activity, specific activity, faradaic efficiency (FE), turnover frequency (TOF), electrochemically active surface area (ECSA) and measurement of double layer capacitance (C ) for different electrocatalytic materials that are frequently employed in both OER and HER. Experimental results have also been provided in support of our discussions wherever required. Using our critical assessments of the activity parameters of water splitting electrocatalysis, researchers can ensure precision and correctness when presenting their data regarding the activity of an electrocatalyst. 0 dl

Better hydrogen generation with nonprecious electrocatalysts over Pt is highly anticipated in water splitting. Such an outperforming nonprecious electrocatalyst, nickel telluride (NiTe ), has been fabricated on Ni foam for electrocatalytic hydrogen evolution in extreme pH conditions, viz., 0 and 14. The morphological outcome of the fabricated NiTe was directed by the choice of the Te precursor. Nanoflakes (NFs) were obtained when NaHTe was used, and nanowires (NWs) were obtained when Te metal powder with hydrazine hydrate was used. Both NiTe NWs and NiTe NFs were comparatively screened for hydrogen evolution reaction (HER) in extreme pH conditions, viz., 0 and 14. NiTe NWs delivered current densities of 10, 100, and 500 mA cm at the overpotentials of 125 ± 10, 195 ± 4, and 275 ± 7 mV in 0.5 M H SO . Similarly, in 1 M KOH, overpotentials of 113 ± 5, 247 ± 5, and 436 ± 8 mV were required for the same current densities, respectively. On the other hand, NiTe NFs showed relatively poorer HER activity than NiTe NWs, which required overpotentials of 193 ± 7, 289 ± 5, and 494 ± 8 mV in 0.5 M H SO for the current densities of 10 and 100 mA cm and 157 ± 5 and 335 ± 6 mV in 1 M KOH for the current densities of 10 and 100 mA cm , respectively. Notably, NiTe NWs outperformed the state-of-the-art Pt/C 20 wt % loaded Ni foam electrode of comparable mass loading. The Pt/C 20 wt % loaded Ni foam electrode reached 500 mA cm at 332 ± 5 mV, whereas NiTe NWs drove the same current density with 57 mV less. These encouraging findings emphasize that a NiTe NW could be an alternative to noble and expensive Pt as a nonprecious and high-performance HER electrode for proton-exchange membrane and alkaline water electrolyzers. 2 2 2 2 2 2 4 2 2 2 4 2 2 2 -2 -2 -2 -2

Sometimes, searching for a cost efficient bifunctional catalytic material for water splitting can be accomplished from a very unlikely place. In this work, we are reporting such a discovery of utilizing the stainless steel (SS) scrubber directly as a catalytic electrode for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) of water electrolysis in 1 M KOH. The iR corrected overpotential calculated at an areal current density of 10 mA cm for a SS scrubber in HER is 315 mV which is 273 mV higher than Pt/C. Similarly, the SS scrubber required 418 mV at 10 mA cm which is just 37 and 98 mV higher than Ni(OH) and RuO . Interestingly, the kinetic analysis revealed that the SS scrubber had facile kinetics for both HER and OER in 1 M KOH as reflected by their corresponding Tafel slope values viz., 121 and 63 mV dec , respectively. In addition, the two electrode cell fabricated using the same SS scrubber electrode delivered 10 mA cm at 1.98 V. Beyond everything, the SS scrubber had shown ultrahigh stability in both half-cell and full-cell studies for total water splitting. Further, as far as the cost of an electrode material per gram is concerned, the SS scrubber defeats all the best electrocatalysts of water splitting by having a price of just $0.012 USD which is $2.228 USD lower than pure Ni, $59.658 USD lower than RuO and $158.028 USD lower than Pt/C 20 wt % catalyst. The overall study specified that the SS scrubber can be adapted for cost-efficient large scale water electrolysis for bulk hydrogen production. -2 -2 -1 -2 2 2 2

The influence of noble metals in the fields of catalysis and surface enhanced Raman scattering (SERS) is an emerging and interesting area of applied materials research. The application of bio-scaffolds such as DNA for staging nanoparticles (NPs) could also give an immense enhancement in SERS. The chemical reduction (bottom-up approach) is proposed here for the synthesis of Pt NPs staged on DNA assemblies. Using NaBH to reduce Pt ions to metallic Pt and keeping the concentration of DNA fixed, Pt NP-DNA assemblies were synthesized by changing Pt concentration in the molar ratios of 0.003, 0.004, 0.005 and 0.006 M. The as-synthesised NPs show the average chain length of ∼103 nm and average particle size below 5 nm. The Pt NP-DNA assemblies gave better activity in both catalysis and SERS. In catalysis, various nitro compounds were tested using NaBH as a reducing agent, where we observed the high rate constant (k) of 6.45 × 10 min for 2-nitroaniline using the Pt NPs-DNA (0.006 M). In SERS, the enhancement factor (EF) was calculated to be 2.52 × 10 for Pt NP-DNA assemblies (0.003 M). Stability of the Pt NP-DNA assemblies was monitored, and they were found to be highly stable for more than six months when kept in the refrigerator. With the high activity in catalysis and SERS, the Pt NP-DNA assemblies also have the potential for application in other fields of research in the near future. 4 4 4+ −1 −1 5

The maximum allowed limits of chlorpromazine (CPZ) established by Food and Drug Administration (FDA) for children aged between 1 and 5 years is 0.125 mM and between 6 to 12 years is 0.235 mM. However, excess consumption of CPZ beyond these permissible limit cause adverse health effects. In order to detect CPZ, herein, we employ NiFe-layered double hydroxide sheets modified glassy carbon electrode (GC/NiFe LDH). The GC/NiFe LDH electrode exhibited a good electrocatalytic activity towards CPZ detection at a less working potential even in the presence of interferents such as ascorbic acid, uric acid, glucose, sucrose, fructose and acetaminophen. The anodic peak observed at 614 mV (vs. Ag/AgCl) corresponds to the oxidation of CPZ and the proposed platform exhibited an excellent linearity in the range 75 μM to 1.0 mM. Further, the GC/NiFe LDH electrode exhibited an excellent sensitivity (1.05 μA μM ), repeatability (0.86% RSD), reproducibility (1.54% RSD) and limit of detection (1.23 μM). −1

Electrocatalytic water oxidation which is otherwise recently popularized as the oxygen evolution reaction (OER) is the significant half-cell reaction in the field of hydrogen generation by water splitting. Being a multistep and a relatively more complex half-cell reaction than its counter hydrogen evolution reaction (HER), OER always requires higher overpotentials than HER. In order to minimize the associated energy loss as overpotentials, these electrochemical half-reactions of water splitting are to be catalyzed with appropriate materials. The recent evolution of transition metals based layered double hydroxides (LDH) as OER catalysts in electrochemical water splitting have lifted the field of H generation with the uttermost purity to a greater height. In addition, these materials possess a lot of advantages like being non-precious, gaining excellent catalytic activity and stability in high alkaline solution along with the ease of preparation methods. With all those LDH materials used in electrochemical and photoelectrochemical water splitting, the presence of any of the three iron group metals (Ni, Co and Fe) is essentially seen. In this review, a detailed view on the basics of OER electrocatalysis, evaluation perspectives, current trends in OER electrocatalysis, evolution of these LDH materials as OER catalysts, activity trends, relationship among structure, activity and mechanism, trends in the synthesis methodologies, dominance of Ni–Fe LDH materials in OER electrocatalysis and the challenges and opportunities have been elaborated in detail. 2

Improving the water oxidation performance of abundantly available materials, such as stainless steel (SS), with notable intrinsic electrocatalytic oxygen evolution reaction (OER) activity due to the presence of Ni and Fe is highly anticipated in water splitting. A new method for promoting the corrosion of stainless steel (304) was found which assisted the uniform formation of oxygen evolution reaction (OER) enhancing NiO incorporated Fe O nanocrystals with the simultaneous reduction in the surface distribution of OER inactive Cr. An equimolar combination of KOH and hypochlorite was used as the corroding agent at 180 °C. The effect of corrosion time on the OER activity was studied and found that better water oxidation performance was observed when the corrosion time was 12 h (SS-12). The SS-12 showed an abnormal enhancement in OER activity compared to the untreated SS and other optimized versions of the same by requiring very low overpotentials of 260, 302, and 340 mV at the current densities of 10, 100, and 500 mA cm along with a very low Tafel slope in the range of 35.6 to 43.5 mV dec . These numbers have certainly shown the high-performance electrocatalytic water oxidizing ability of SS-12. The comparative study revealed that the state-of-the-art IrO had failed to compete with our performance improved catalytic water oxidation anode "the SS-12". This fruitful finding indicates that the SS-12 has the potential to be an alternate anode material to precious IrO /RuO for alkaline water electrolyzers in future. 2 3 2 2 2 -2 -1

Formation of NiFe layered double hydroxide (LDH) with Pt NPs was achieved following a two-step reaction viz., the hydrothermal preparation of highly crystalline NiFe LDH sheets and the homogenous reduction of Pt ions with borohydride in a solution of homogenized NiFe LDH crystalline sheets. Chemically equivalent NiFe LDH material decorated with Pt NPs was prepared by co-precipitation for comparative studies. The synthesized catalysts were systematically screened for oxygen and hydrogen evolution reactions (OER and HER) in 1 M KOH. The intentional incorporation of Pt NPs on the LDH layers reduced the cell voltage and delivered high current densities with a lower loading of 0.205 mg cm . The NiFe LDH crystalline sheets had shown significantly enhanced activity, good stability, lower overpotential (90 mV) at 10 mA cm and lower Tafel slope (12 mV dec ) than the co-precipitated NiFe LDH in OER. Similarly, Pt NPs tethered NiFe LDH crystalline sheets showed better activity by having lower overpotential (27 mV) and Tafel slope (51 mV dec ) than the co-precipitated NiFe LDH with Pt NPs. Moreover, the state-of-the-art catalysts viz., IrO and Pt/C 20 wt% of OER and HER failed in competing with Pt NPs tethered NiFe LDH crystalline sheets. 4+ −2 −2 −1 −1 2

Background: Increasing demand on the large scale H generation with the uttermost purity as required by the fuel cells is now totally depending on water splitting. The major energy consuming reaction in water splitting is the thermodynamically un-favoured oxygen evolution reaction (OER) for which the noble metal oxides such as IrO and RuO have so far been extensively used as efficient electrocatalysts. However, the increased metal dissolution at high anodic overpotential and expenses associated with these materials render its implementation in large scale H production. This report provides an alternative way of reducing the total RuO content with concomitantly increased corrosion resistance by alloying with NaPO at nano-scale. Methods: A detailed research and review on the existing literature has been carried out. The synthesis was carried out utilizing conventional wet-chemical and thermal annealing routes. The same was then characterized in and screened as an electrocatalyst for OER in acidic electrolyte of pH 1. Results: The successful synthesis of RuO -NaPO nanocomposite was confirmed by various advanced characterizations such as XRD, HRTEM, XPS and EDS. Then the same was screened for acidic OER in comparison with the commercial catalyst RuO procured from Sigma. The results have shown that RuO -NaPO nanocomposite required a very low overpotential of 250 mV at a current density of 10 mAcm for which the commercial catalyst required 85 mV higher potential than RuO -NaPO nanocomposite. Comparatively lower Tafel slope (110 mVdec ) and minimum increase in overpotential at 10 mAcm after cycling test for RuO -NaPO nanocomposite had once again proven the advantages of alloying RuO with NaPO for harvesting synergistically enhanced OER activity with improved corrosion stability. Conclusion: A comparatively easier synthesis of RuO -NaPO nanocomposite enabled the use of RuO with comparatively reduced loading to harvest maximum catalytic efficiency. The intentionally incorporated NaPO had increased the catalytic performance of RuO and also increased the corrosion stability as revealed by the electrochemical characterizations. The proposed approach is undoubtedly adaptable for the fabrication of highly active other electrocatalysts for OER with improved corrosion stability. 2 2 2 2 2 3 2 3 2 2 3 2 3 2 3 2 3 2 3 2 3 2 -2 -1 -2

Water oxidation in alkaline medium was efficiently catalyzed by the self-assembled molecular hybrids of CoS-DNA that had 20 times lower Co loading than the commonly used loading. The morphological outcome was directed by varying the molar ratio of metal precursor Co(Ac) and DNA and three different sets of CoS-DNA molecular hybrids, viz. CoS-DNA(0.036), CoS-DNA(0.06), and CoS-DNA(0.084) were prepared. These morphologically distinct hybrids had shown similar electrocatalytic behavior, because of the fact that they all contained the same cobalt content. The CoS-DNA(0.036), CoS-DNA(0.06), and CoS-DNA(0.084) required very low overpotentials of 350, 364, and 373 mV at a current density of 10 mA cm (1 M KOH), respectively. The advantages of lower overpotential, lower Tafel slope (42.7 mV dec ), high Faradaic efficiency (90.28%), high stability and reproducibility after all, with a lower cobalt loading, have certainly shown the worth of these molecular hybrids in large-scale water oxidation. Moreover, since DNA itself a good binder, CoS-DNA molecular hybrids were directly casted on substrate electrodes and used after drying. It also showed minimum intrinsic resistance as DNA is a good ionic and electronic conductor. Besides, the present method may also be extended for the preparation of other active electrocatalysts for water splitting. 2 -2 -1

Molecular hydrogen (H ) generation through water splitting with minimum energy loss has become practically possible due to the recent evolution of high-performance electrocatalysts. In this study, we fabricated, evaluated, and presented such a high-performance catalyst which is the Ni Se nanoassemblies that can efficiently catalyze water splitting in neutral and alkaline media. A hierarchical nanoassembly of Ni Se was fabricated by functionalizing the surface-cleaned Ni foam using NaHSe solution as the Se source with the assistance of microwave irradiation (300 W) for 3 min followed by 5 h of aging at room temperature (RT). The fabricated Ni Se nanoassemblies were subjected to catalyze water electrolysis in neutral and alkaline media. For a defined current density of 50 mA cm , the Ni Se nanoassemblies required very low overpotentials for the oxygen evolution reaction (OER), viz., 232, 244, and 321 mV at pH 14.5, 14.0, and 13.0 respectively. The associated lower Tafel slope values (33, 30, and 40 mV dec ) indicate the faster OER kinetics on Ni Se surfaces in alkaline media. Similarly, in the hydrogen evolution reaction (HER), for a defined current density of 50 mA cm , the Ni Se nanoassemblies required low overpotentials of 211, 206, and 220 mV at pH 14.5, 14.0, and 13.0 respectively. The Tafel slopes for HER at pH 14.5, 14.0, and 13.0 are 165, 156, and 128 mV dec , respectively. A comparative study on both OER and HER was carried out with the state-of-the-art RuO and Pt under identical experimental conditions, the results of which revealed that our Ni Se is a far better high-performance catalyst for water splitting. Besides, the efficiency of Ni Se nanoassemblies in catalyzing water splitting in neutral solution was carried out, and the results are better than many previous reports. With these amazing advantages in fabrication method and in catalyzing water splitting at various pH, the Ni Se nanoassemblies can be an efficient, cheaper, nonprecious, and high-performance electrode for water electrolysis with low overpotentials. 2 3 4 3 4 3 4 3 4 3 4 3 4 2 3 4 3 4 3 4 -2 -1 -2 -1

We demonstrated a high-yield and easily reproducible synthesis of a highly active oxygen evolution reaction (OER) catalyst, “the core-oxidized amorphous cobalt phosphide nanostructures”. The rational formation of such core-oxidized amorphous cobalt phosphide nanostructures was accomplished by homogenization, drying, and annealing of a cobalt(II) acetate and sodium hypophosphite mixture taken in the weight ratio of 1:10 in an open atmosphere. Electrocatalytic studies were carried out on the same mixture and in comparison with commercial catalysts, viz., Co O -Sigma, NiO-Sigma, and RuO -Sigma, have shown that our catalyst is superior to all three commercial catalysts in terms of having very low overpotential (287 mV at 10 mA cm ), lower Tafel slope (0.070 V dec ), good stability upon constant potential electrolysis, and accelerated degradation tests along with a significantly higher mass activity of 300 A g at an overpotential of 360 mV. The synergism between the amorphous Co P shell with the Co O core is attributed to the observed enhancement in the OER performance of our catalyst. Moreover, detailed literature has revealed that our catalyst is superior to most of the earlier reports. 3 4 2 x y 3 4 -2 -1 -1

Herein, self-assembled Ir and IrO nanoparticles (NPs) were synthesized on DNA scaffolds for the first time in an organic medium using microwave irradiation just for 30 s. By tuning the DNA to Ir molar ratio, stable colloidal Ir and IrO NP solutions were obtained in ethanol via reduction with tetrabutylammonium borohydride (TBABH ). The same procedure was executed without DNA to obtain discrete Ir NPs and with DNA (of different Ir :DNA molar ratio) for getting chain-like nano-assemblies of IrO NPs. The average diameter of the Ir-assembled DNA chains was 40 ± 10 nm, and the average particle size was 3.3 ± 0.5 nm. The synthesized Ir NP@DNA was applied in two different applications: catalysis and surface enhanced Raman scattering (SERS). The catalytic study was conducted for the reduction of various nitro compounds. Ir NP@DNA showed better catalytic activity and recyclability (5-14 times) than Ir NPs obtained without DNA scaffolds. Ir NP@DNA and Ir NPs without DNA were applied to the SERS study by taking methylene blue (MB) dye as a Raman probe molecule. An enhancement factor (EF) value of 8 × 10 for Ir NP@DNA was observed, which was much better than that obtained for our synthesized un-stabilized Ir NPs (1.07 × 10 ) and other reported Ir NPs. The synthesized Ir NP@DNA and IrO NP@DNA were extremely stable for more than 3 months, whereas the Ir NPs synthesized without DNA were not. These stable colloidal solutions were readily re-dispersed in many organic solvents (protic and nonprotic) and could be employed for other potential organic catalysis reactions. 2 2 4 2 2 3+ 3+ 5 5

Ni(OH) is a useful electrode material for electrochemical capacitors, due to its high theoretical specific capacitance and low cost, but its application has been limited by poor electrical conductivity. Hence, we fabricated Ni(OH) nano sheets (NSs) with nickel metal NPs via the hydrothermal partial reduction of Ni(ii) salt by ethanol in basic medium. The significance of the basic medium (presence of KOH) and other reaction parameters and the mechanism for the formation of Ni/Ni(OH) NSs are elaborated. The Ni/Ni(OH) NSs have been used as a positive electrode in an asymmetric supercapacitor (ASC) with a larger voltage window using the activated carbon (AC) as a negative electrode, which resulted in high energy and power densities. By optimizing the mass ratio between AC and Ni/Ni(OH) NSs in the fabrication of electrodes, we found a maximum specific capacitance (C ) of 62 F g at 2 mA cm at a voltage of 1.65 V and observed the maximum energy and power densities of 23.45 W h kg and 4598 W kg , respectively. The galvanostatic charge-discharge study shows high capacity retention up to 90%, even after 6000 consecutive cycles, which is a noteworthy achievement, considering the ASCs. Moreover, we believe that the presence of nickel metal in Ni/Ni(OH) NSs helped to reduce the charge transfer resistance (R ), which resulted in better performance. These results certainly demonstrate that such Ni/Ni(OH) NSs with Ni metal NPs are promising materials for the construction of next generation aqueous ASCs with higher specific capacitance. The synthesis procedure can be applied to other transition metals to synthesize their metal/metal hydroxide composites and enhance their conductive nature, instead of using conductive substrates. 2 2 2 2 2 S 2 CT 2 -1 -2 -1 -1

Hydrogen generation via electrocatalytic water splitting is on the cutting edge of energy research. The kinetic burdens associated with the sluggish anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER) cause a large amount of energy loss. Hence, these reactions must be catalyzed. Therefore, an array of magnetic CoPt nanoparticle (NP)-decorated ultrathin Co(OH) nanosheets was synthesized and applied for electrocatalytic water splitting in 1 M KOH. CoPt@Co(OH) required a minimum overpotential of 334 mV at 10 mA cm in the OER and 226 mV at 50 mA cm in the HER in addition to possessing exceptional stability upon cycling and chronoamperometry. The advantages of the magnetic property of CoPt@Co(OH) have been utilized for the first time to improve its stability. The aging study carried out at the CoPt@Co(OH) -modified interface with and without magnetic support has shown that the magnetically co-stabilized interface was more stable even after 5 days of aging in 1 M KOH. This magnetism-assisted enhancement in the stability of a nanocatalyst-modified interface along with proper further developments will surely take the electrocatalysis of water splitting to a new level. 2 2 2 2 -2 -2

A facile way of recovering 3d transition metals of industrial importance from spent lithium-ion batteries (LIBs) without using any surfactants has been developed. Mn- and Co-rich spent LIBs were chosen as sustainable sources for recovering the oxides of the respective elements. The physical dismantling of Li-ion batteries, chemical leaching with 2 M acetic acid, precipitation with ammonium carbonate, hydrothermal conditioning and calcination at 650 °C led to the facile formation of spherical spinel MnCo O with very high morphological selectivity. The obtained spherical MnCo O was identified by various advanced characterization techniques. Detailed electrochemical characterization revealed that the recovered spheres of spinel MnCo O were effective in catalyzing the oxygen evolution reaction (OER) in 1 M KOH and required an overpotential of 358 and 400 mV to generate a current density of 5 and 10 mA cm , respectively, with a relatively low catalyst loading (0.001025 g cm ). Comparative electrocatalytic studies carried out with recovered LiCoO , recovered Li MnO and commercially available catalysts such as RuO (c-RuO ), Co O (c-Co O ) and MnO (c-MnO ) revealed that the recovered spheres of spinel MnCo O were more effective OER catalysts than the recovered LiCoO , recovered Li MnO , c-Co O and c-MnO and exhibited comparable activity to that of c-RuO with very little difference in overpotential (∼50 mV) at current densities of 5 and 10 mA cm . With such a low catalyst loading, the observed electrocatalytic performance in water oxidation of a material recovered from waste is highly significant and will surely attain greater industrial importance when the recycling of spent LIBs from electronic wastes is considered. 2 4 2 4 2 4 2 X X+1 2 2 3 4 3 4 2 2 2 4 2 X X+1 3 4 2 2 -2 -2 -2

A new class of metal hydroxyphosphates, to be used as an alternative to noble metal catalysts for better oxygen evolution reaction (OER), has been identified and in particular iron hydroxyphosphate (Fe (PO ) (OH) ·2H O, FeHP) has been used because of its performance in electrocatalytic water oxidation in an alkaline medium. To assist the coordination of -OH ligands with the metal center and also to weaken the M -OH bonding, which is desirable to enhance the OER behavior, tin (Sn) has been incorporated to form Sn entrapped iron hydroxyphosphate, otherwise known as Sn incorporated FeHP (Sn-FeHP) which is another new electrocatalyst, which has been identified and characterised in the current study. Symmetrical nanocrystals of FeHP and Sn-FeHP were prepared using a simple hydrothermal method with appropriate metal precursors at 220 °C for 48 h. Interestingly, the incorporated Sn does not lead to any change in the orthorhombic crystal structure of pristine FeHP. However, the effect of the added Sn is found to be reflected in the morphology by way of forming self-assembled needle-like crystals to ultimately form a star-like architecture. The ability of these nanocrystals to perform in electrocatalytic water oxidation in alkaline conditions as anode for the OER was studied in comparison with the state-of-art ruthenium(iv) oxide (RuO ) and with the best performing alkaline OER catalyst from 3d VIII group metals, i.e., nickel(ii) hydroxide [Ni(OH) ]. The results of the OER study suggest that the currently synthesized Sn-FeHP possesses better catalytic ability than that of pristine FeHP. The overpotential (η) required to achieve the benchmarking current density of 10 mA cm is 359 mV for Sn-FeHP and 442 mV for FeHP. Similarly, the Tafel slope of Sn-FeHP and FeHP is 81 and 91 mV dec , respectively, suggesting that the Sn-FeHP explored in this research is a better electrocatalyst for OER. The enhanced activity of Sn-FeHP compared to that of Fe-HP may be correlated to the morphology-based advantages and the effect of added Sn in altering the electronic structure of FeHP, which in turn favors the OER kinetics. The stability of the Sn-FeHP modified working electrode was supported by the constant i-t performance for more than 800 min at 1.65 V versus a reversible hydrogen electrode (RHE). Thus, Sn-FeHP could be considered as an efficient, cheaper and alternative futuristic anode material in comparison to the expensive nickel-based electrocatalysts, exploited commonly in water electrolysers. 5 4 4 3 2 2 2 - 3+ -2 -1

Enhancing the electrocatalytic water oxidation activity of an electrocatalyst by altering its solid state properties at the electrode/electrolyte interface is a promising way to minimize the energy loss in water splitting. Atomic layer thin films of biphasic spinels Co O and CoO were fabricated through pulsed laser deposition (PLD) and examined for the oxygen evolution reaction (OER). During this process, the biphasic thin film interface of cobalt oxides underwent significant activation after prolonged potentiostatic electrolysis at 1.59 V vs. RHE with pronounced enhancement in its OER activity. The biphasic thin film interface of cobalt oxides required 372 ± 5 mV to drive 10 mA cm which was reduced by 55 mV after activation. The associated lower Tafel slope (55 mV dec ) implies better kinetics on the activated thin film interface of cobalt oxides. This indicated that the thin film of cobalt oxides must have undergone significant surface reconstruction at the interface. To find out the same, a set of detailed pre- and post-activation material characterization studies were carried out where the results have evidenced that there had been a dominant formation of β-CoOOH along with some Co(OH) and KCoO as a result of the phenomenon of electrochemical phase (ECP) formation under potentiostatic/galvanostatic activation conditions. A comparative study under identical conditions with the state-of-the-art OER electrocatalyst RuO had revealed that the biphasic thin film interface of cobalt oxides had nearly parallel activity before activation and better activity after the construction of β-CoOOH along with some Co(OH) and KCoO via potentiostatic surface reconstruction of the catalytic interface. 3 4 2 2 2 2 2 -2 -1

Electrocatalytic water splitting by non-noble-metal-based catalysts is the focus of attention in energy conversion technology. Group VIII 3d metals and their compounds are the often chosen catalysts for the same. Herein, we have demonstrated an easy way to synthesize one such efficient catalyst from β-Ni(OH) , which has a petal-like morphology as a result of the formation of a 3D hierarchical array of interwoven ultra-thin β-Ni(OH) nanosheets decorated with β-Ni(OH) nanoburls. The electrocatalytic activity in the oxygen evolution reaction (OER) of the hierarchical array of ultra-thin β-Ni(OH) nanosheets decorated with β-Ni(OH) nanoburls displayed an unusual enhancement as a consequence of surface faceting of diffraction planes from (001) to (101) and (111) in addition to the formation of oxyhydroxide upon potential cycling. The solvothermally synthesized petal-like 3D hierarchical array of β-Ni(OH) nanosheets and nanoburls activated by faceting and the formation of oxyhydroxide exhibited a lower overpotential (η = 0.300 ± 0.003 V @ j = 10 mA cm ), a minimum Tafel slope (0.043 V dec ), and very high turnover frequency (TOF = 47.14 s @ 1.53 V vs. RHE) with very high faradaic efficiency when compared to earlier studies on Ni(OH) . Regardless of the type of polymorph, our catalyst have performed better than the state-of-the-art RuO catalyst under the same experimental conditions. 2 2 2 2 2 2 2 2 -2 -1 -1

Increasing demand for finding eco-friendly and everlasting energy sources is now totally depending on fuel cell technology. Though it is an eco-friendly way of producing energy for the urgent requirements, it needs to be improved to make it cheaper and more eco-friendly. Although there are several types of fuel cells, the hydrogen (H ) and oxygen (O ) fuel cell is the one with zero carbon emission and water as the only byproduct. However, supplying fuels in the purest form (at least the H ) is essential to ensure higher life cycles and less decay in cell efficiency. The current large-scale H production is largely dependent on steam reforming of fossil fuels, which generates CO along with H and the source of which is going to be depleted. As an alternate, electrolysis of water has been given greater attention than the steam reforming. The reasons are as follows: the very high purity of the H produced, the abundant source, no need for high-temperature, high-pressure reactors, and so on. In earlier days, noble metals such as Pt (cathode) and Ir and Ru (anode) were used for this purpose. However, there are problems in employing these metals, as they are noble and expensive. In this review, we elaborate how the group VIII 3d metal sulfide, selenide, and phosphide nanomaterials have arisen as abundant and cheaper electrode materials (catalysts) beyond the oxides and hydroxides of the same. We also highlight the evaluation perspective of such electrocatalysts toward water electrolysis in detail. (Chemical Equation Presented). 2 2 2 2 2 2 2

Highly Sensitive and ultra-small Rhenium (Re) metal nanoparticles (NPs) were successfully stabilized in water by the staging and fencing action of the versatile biomolecule DNA that resulted in two distinct aggregated chain-like morphologies with average grain sizes of 1.1 ± 0.1 nm and 0.7 ± 0.1 nm for the very first time within a minute of reaction time. Re NPs are formed by the borohydride reduction of ammonium perrhenate (NH ReO ) in the presence of DNA at room temperature (RT) under stirring. The morphologies were controlled by carefully monitoring the molar ratio of NH ReO and DNA. The synthesized material was employed in two potential applications: as a substrate for surface enhanced Raman scattering (SERS) studies and as a catalyst for the reduction of aromatic nitro compounds. SERS study was carried out by taking methylene blue (MB) as the probe and the highest SERS enhancement factor (EF) of 2.07 × 10 was found for the aggregated chain-like having average grain size of 0.7 ± 0.1 nm. Catalytic reduction of 4-nitro phenol (4-NP), 2-nitro phenol (2-NP) and 4-nitroaniline (4-NA) with a rate constant value of 6 × 10  min , 33.83 × 10  min and 37.4 × 10  min have testified the excellent catalytic performance of our Re NPs immobilized on DNA. The overall study have revealed the capability of DNA in stabilizing the highly reactive Re metal at nanoscale and made them applicable in practice. The present route can also be extended to prepare one dimensional (1-D), self-assembled NPs of other reactive metals, mixed metals or even metal oxides for specific applications in water based solutions. 4 4 4 4 7 −2 −1 −2 −1 −2 −1

An efficient electrocatalytic hydrogen evolution reaction (HER) with ultralow loading of Pt has been under intense investigation to make the state-of-the-art Pt economically affordable for water electrolyzers. Here, colloidally synthesized Pt nanoparticles of average size 3.5 ± 0.3 nm were successfully anchored on molecular self-assemblies of DNA. The synthesized Pt@DNA colloidal solution was directly assessed for the electrochemical hydrogen evolution reaction (HER) in 0.5 M H SO with a loading of 5 μL of Pt@DNA colloidal solution that corresponds to a Pt equivalent of 15 μg/cm . The excellent adhesion of DNA onto GC and FTO substrate electrodes, the conductivity of DNA, and its stability upon potentiostatic electrolysis and accelerated degradation have made the synthesized, stable Pt@DNA colloidal solution an advanced HER electrocatalyst. The Pt@DNA-GC interface without binder required overpotentials of -0.026 and -0.045 V for current densities of 10 and 20 mA/cm , respectively. The potentiostatic electrolysis and accelerated degradation tests did not affect the electrocatalytic activity, and the observed increase in overpotential was highly negligible. The extreme stability of the Pt@DNA-GC interface was witnessed during an aging study carried out by keeping the working electrode in the electrolyte solution for more than 10 days and acquiring linear sweep voltammograms (LSVs) at intervals of 24 h. Under the same experimental conditions, the commercial Pt/C 10 wt % catalyst with Nafion binder had failed to compete with our colloidal Pt@DNA. These findings certainly indicate the advantageous use of electrocatalyst-loaded DNA molecular self-assemblies for the HER which has never been observed before. 2 4 2 2

Highly stable Re nanoparticles (NPs) have been synthesized in an organic solvent for the first time through a homogeneous reduction route using DNA as a scaffold within 10 min at room temperature. Transfer of both (NH )ReO and DNA salts to the organic layer has been executed by a two phase extraction procedure using TOAB (phase transfer catalyst) followed by successive reduction with NaBH resulting in the formation of highly stable Re NPs. By changing the molar ratio of the starting reagents and by varying other reaction parameters, the diameter of the synthesized Re NPs can be tuned. The average diameter of the Re NPs is found to be 1.5 ± 0.7 nm and 6.5 ± 1.5 nm for two different morphologies. The as-synthesized Re organosol has been applied in two distinct potential applications such as catalysis and SERS studies. The catalysis reaction has been done for the reduction of hexavalent chromium ions in the presence of thiosulfate for which the catalytic rate was found to be faster compared to previous reports. SERS activity was monitored using methylene blue (MB) dye as a model SERS probe and the observed enhancement factor (EF) value was 3.35 × 10 using Re NPs having an average diameter of 1.5 ± 0.7 nm. This is the highest EF value for Re organosol ever reported. The synthesized Re organosol has been found to be extremely stable for more than six months when kept in a refrigerator in a sealed container. Moreover, the synthesized Re NPs can readily be re-dispersed in all protic and non-protic solvents which can be used for further applications in other interdisciplinary areas. 4 4 4 6 0

Seedless, surfactantless and support-free unprotected, metallic, interconnected nano-chain networks of ruthenium nanoparticles (NPs) were successfully synthesized via the reduction of ruthenium(iii) chloride (RuCl ) with sodium borohydride (NaBH ) at three different temperatures, viz. 30 °C, 45 °C and 60 °C. The molar ratio of RuCl solution and borohydride was optimized to be 1:1.5 to produce stable colloids with the optimum final solution pH of 9.7 ± 0.2. Average diameters of the interconnected nano-chain networks prepared at 30 °C (Ru-30), 45 °C (Ru-45) and 60 °C (Ru-60) were 3.5 ± 0.5 nm, 3.0 ± 0.2 nm and 2.6 ± 0.2 nm respectively. The morphology and composition dependent catalytic and electrocatalytic activities of these unprotected Ru nano-chain networks (Ru-30, Ru-45 and Ru-60) were studied in detail. The catalysis study was performed by investigating the transfer hydrogenation of several substituted aromatic nitro compounds. It was observed that Ru-60 was relatively more active compared to Ru-30 and Ru-45, which was reflected in their rate constant values. The electrocatalytic activities of Ru-30, Ru-45 and Ru-60 were screened for anodic water splitting in alkaline medium (0.1 M NaOH) and it was found that all of them showed almost the same activity which required an over-voltage of 308 ± 2 mV to obtain an anodic current density of 10 mA cm . The catalytic and electrocatalytic performances of these unprotected Ru networks were compared with Ru nanomaterials prepared under similar conditions with three different surfactants, viz. CTAB, SDS and TX-100, which revealed that unprotected Ru networks are better catalysts than those stabilized with surfactants. The superior catalytic and electrocatalytic performance is due to the availability of unprotected Ru surfaces. The present route may provide a new possibility of synthesizing other surfactant-free, unprotected metal colloids for enhanced catalytic and electrocatalytic applications. 3 4 3 -2 0 0 0 0

ZnWO nanoparticles (NPs) that are assembled and aggregated together as chain-like morphology have been synthesized via the reaction of Zn(II) salt solution with sodium tungstate in the presence of the DNA scaffold under 5 min of microwave heating. The reaction parameters have been tuned to control the size of the individual particles and diameter of the chains. The significance of different reaction parameters and specific growth mechanism for the formation of particles is elaborated. The DNA-ZnWO nanoassemblies have been used in two potential applications for the first time, namely, supercapacitor and catalysis studies. Supercapacitor study revealed that DNA-ZnWO nanoassemblies exhibited good electrochemical properties having high specific capacitance value ∼72 F/g at 5 mV s , and electrodes possessed a good cyclic stability with more than 1000 consecutive times of cycling. Catalysis studies have been done for benzyl alcohol oxidation, and it was observed that DNA-ZnWO nanoassemblies having smaller diameter gives better catalytic efficiency compared to other morphology. This is further authenticated from their BET surface area analysis. In the future, the self-assembled DNA-ZnWO nanoassemblies could be a promising candidate for the synthesis of other mixed metal oxides and should be applicable in various emerging fields like Li ion batteries or photocatalysis, or as luminescent materials. 4 4 4 4 4 -1

A DNA-encapsulated chain and wire-like β-MnO2 organosols have been synthesized utilizing a two-phase water-toluene extraction procedure at room temperature (RT). The β-MnO2 organosol was prepared by transferring KMnO4 and DNA from aqueous solution separately to an organic solvent (toluene) using a phase transfer catalyst, mixing both organic solutions together, and subsequent reduction with NaBH4. The eventual diameters of the MnO2 particles in chain-like and wire-like morphologies were ∼1-2 nm and ∼1.8 ± 0.2 nm, respectively, whereas the nominal length of the DNA-MnO2 chains was ∼2-3 μm. Different morphologies of the MnO2 organosol were synthesized by simply tuning the DNA to KMnO4 molar ratio. The synthesized particles were successfully re-dispersed in different organic solvents for application in various organic reactions. The potential of the DNA-MnO2 organosol as a catalyst has been tested in the organic catalytic reaction for the oxidative polymerization of pyrrole to polypyrrole, using the DNA-MnO2 organosol as a potential catalyst. The synthesis process was simple, reproducible and robust. In future, the present process might be utilized for the formation of other nanomaterials in organic solvents, with specific morphologies and uses in a variety of catalytic reactions and energy storage applications.

We report a new route for the self-assembled NiWO nanoparticles (NPs) in chain-like aggregates on a DNA scaffold by the reaction of nickel(II) acetate with sodium tungstate under continuous stirring and heating at 60 °C within 90 min of reaction. The size of the individual NiWO particles was found to be ∼20-30 nm and the diameter of the aggregates was in the ∼220 ± 30 nm range. The probable growth mechanisms of DNA-NiWO chain-like aggregates were elaborated. The potential of the NiWO chain-like aggregates was tested in catalytic reaction and in electrochemical supercapacitor studies. Catalysis study revealed that the NiWO aggregated structure acts as a suitable catalyst for the conversion of K [Fe(CN) ] to K [Fe(CN) ] in the presence of Na S O under UV-light illumination within a short time. Supercapacitor study signified that different morphologies of NiWO show different specific capacitance (C) values, and the highest C value of 173 F g at a scan rate of 5 mV s was observed while chain diameter was less. The supercapacitor study also revealed an excellent long cycle life along with 90% retention of C value even after 1000 consecutive times of cycling. The exploitation for the synthesis of mixed metal oxide on DNA scaffold might generate a new avenue for the successful formation of other oxides and can be useful for organic catalysis reactions and in future energy storage devices. 4 4 4 4 4 3 6 4 6 2 2 3 4 -1 -1

Size-selective, mono-dispersed spherical osmium (Os) nanoparticles (NPs) have been synthesized for the first time in a two-phase (water-toluene) extraction procedure in organic medium (in toluene) under ambient conditions. A simple wet chemical synthesis route was employed to prepare the Os organosol from the precursor osmium tetroxide (OsO ) and tetrabutylammonium borohydride (TBABH ). Tetraoctylammonium bromide (TOAB) was used as a phase transfer catalyst (PTC) which quantitatively transferred Os precursors to the organic medium from the aqueous medium. Four different spherical Os NP organosols with varying sizes of 1 ± 0.2 nm, 10-30 nm, 22 ± 2 nm and 31 ± 3 nm were synthesized just by changing the concentration ratio of the metal precursor and the amount of reductant added. The role of all the precursor concentrations in the size-selectivity was examined in-detail. The synthesized osmium organosol were stabilized by the extensive π-stacking intercalation effect offered by toluene as well as the interaction of tetrabutylammonium ions (TBA ) presented in the organic medium. The synthesized spherical Os NP organosols were utilized in two different applications such as in catalysis and in Surface Enhanced Raman Scattering (SERS) studies. The catalytic activity of osmium organosol was tested for the reduction of hexavalent chromium (Cr ) ions under UV light in the presence of sodium thiosulphate. The SERS activity was examined by taking methylene blue (MB) dye as a probe molecule. In the near future, the synthesized Os organosol might be utilized as a potential catalyst in organic catalysis reactions as well as in the field of fuel cells and sensors. 4 4 + 6+

Self-assembled IrO nanoparticles (NPs) of two distinct chain-like morphologies were successfully synthesized on a DNA scaffold at room temperature by the reduction of a hydrated iridium salt precursor under continuous stirring. Different morphologies of IrO NPs were formed by tuning the concentration ratio of DNA to iridium salt solution. The probable growth mechanisms of the IrO NPs on DNA were elaborated. The potentiality of the DNA@IrO NPs was tested in two important applications, one as a catalyst for the oxidation of 2-propanol to acetone and the other as an electrocatalyst for the oxygen evolution reaction (OER). The catalysis study revealed that the reaction completed in a short time with a higher product yield. The self-assembled, chain-like IrO NPs were screened as a potential electrocatalyst for the OER study that required an overpotential of 312 mV, to produce anodic current densities of 10 mA cm (0.1 M NaOH) with a turnover frequency (TOF) of 7.88 s . This is one among the lowest oxygen overpotentials reported for IrO alone. The presence of phosphorous on the DNA-phosphate backbone on the IrO NP surface is the key factor for the enhancement of OER activity. Though the conductivity of DNA@IrO NPs modified GC is lower than that of bare GC, the synergism assisted enhancement by PO from DNA in the overall OER activity makes it worthier still. The overall processes are simple, less time consuming, reproducible, occur at room temperature and can be extended to the synthesis of other important nano-catalysts at a short time scale for their applications in different interdisciplinary fields like organic catalysis and electrocatalysis. 2 2 2 2 2 2 2 2 4 -2 -1 3-

Osmium (Os) organosol on DNA scaffold has been synthesized by utilizing a homogeneous reduction route. The synthesis was done by the reduction of OsO with tetrabutylammonium borohydride (TBABH ) in the presence of DNA in acetone within 10 min of stirring at room temperature. Different morphologies were synthesized by varying the DNA to OsO molar ratio and controlling the other reaction parameters. The eventual diameters of the individual Os particles in organosol were ∼1-3 nm, and the nominal lengths of the wires were ∼1-2 μm. The potentiality of the Os organosol was tested in two different applications: one is the catalytic hydrogenation of cyclohexene to cyclohexane and other is the surface enhanced Raman scattering (SERS) studies. The SERS study has been examined using MB as a Raman probe, and the EF value is found to be the highest in the case of Os organosol having aggregated wires (short size) compared to longer wires. The fast synthesis of Os organosol on DNA and their potential catalytic and SERS activity will be found to be very useful in the near future for the catalytic applications of various organic reactions and in the fields of sensors, electronic devices, and fuel cells. 4 4 4

A new approach is developed for the aqueous phase formation of flake-like and wire-like β-MnO nanomaterials on a DNA scaffold at room temperature (RT) within a shorter time scale. The β-MnO nanomaterials having a band gap energy ∼3.54 eV are synthesized by the reaction of Mn(ii) salt with NaOH in the presence of DNA under continuous stirring. The eventual diameter of the MnO particles in the wire-like and flake-like morphology and their nominal length can be tuned by changing the DNA to Mn(ii) salt molar ratio and by controlling other reaction parameters. The synthesized β-MnO nanomaterials exhibit pronounced catalytic activity in organic catalysis reaction for the spontaneous polymerization of aniline hydrochloride to emeraldine salt (polyaniline) at RT and act as a suitable electrode material in electrochemical supercapacitor applications. From the electrochemical experiment, it was observed that the β-MnO nanomaterials showed different specific capacitance (C ) values for the flake-like and wire-like structures. The C value of 112 F g at 5 mV s was observed for the flake-like structure, which is higher compared to that of the wire-like structure. The flake-like MnO nanostructure exhibited an excellent long-term stability, retaining 81% of initial capacitance even after 4000 cycles, whereas for the wire-like MnO nanostructure, capacitance decreased and the retention value was only 70% over 4000 cycles. In the future, the present approach can be extended for the formation of other oxide-based materials using DNA as a promising scaffold for different applications such as homogeneous and heterogeneous organic catalysis reactions, Li-ion battery materials or for the fabrication of other high performance energy storage devices. © the Partner Organisations 2014. 2 2 2 2 2 s s 2 2 -1 -1