Tuning the Electronic Structure of a Ni-Vacancy-Enriched AuNi Spherical Nanoalloy via Electrochemical Etching for Water Oxidation Studies in Alkaline and Neutral Media.

Internal Ni-vacancy-enriched spherical AuNi nanoalloys (AuNi1-2-T) have been prepared via a noble electrochemical etching method. AuNi1.5-T showed the highest oxygen evolution reaction (OER) activity compared to bare AuNi1.5, and it demands only 239 mV overpotential, which was 134 mV lesser than the overpotential required by commercial RuO2 at 10 mA cm-2 current density in a 1 M KOH solution (pH = 14). The calculated turnover frequency (TOF) value for AuNi1.5-T (0.0229 s-1) was 11.74 times higher than that of AuNi1.5 (0.00195 s-1). Also, the electrochemically activated AuNi1.5-T showed superior neutral water oxidation activity by demanding only 335 mV overpotential with a TOF value of 0.000135 s-1 in a 1 M Na2SO4 solution (pH = 7) at 10 mA cm-2. The long-term stability studies (over 60 h) reveal the excellent robustness of an electrochemically treated alloy system. Density functional theory based electronic structure calculations showed that in the case of AuNi and AuNi1.5, Au d, Au s, and Ni d orbitals have significant contributions, whereas in the Ni-vacant systems, the density of states is mainly governed by d orbitals of Au and Ni. Also, the Ni-vacant system possesses a work function value of 4.96 eV, which is lower than that of the pristine system (5.27 eV) and thereby favored OH- binding with an optimum adsorption energy. This result is in reasonable agreement with the experimental outcome of an accelerated OER in a vacancy-enriched Ni-rich AuNi alloy system. Also, mechanistic analysis reveals that the creation of a Ni vacancy can effectively alter the overall mechanism of the OER and thereby facilitate the same with a lower applied energy.

Enabling and Inducing Oxygen Vacancies in Cobalt Iron Layer Double Hydroxide via Selenization as Precatalysts for Electrocatalytic Hydrogen and Oxygen Evolution Reactions.

Production of hydrogen by water electrolysis is an environment-friendly method and comparatively greener than other methods of hydrogen production such as stream reforming carbon, hydrolysis of metal hydride, etc. However, sluggish kinetics of the individual half-cell reactions hinders the large-scale production of hydrogen. To minimize this disadvantage, finding an appropriate, competent, and low-cost catalyst has attracted attention worldwide. Layer double hydroxide (LDH)-based materials are promising candidates for oxygen evolution reaction (OER) but not fruitful and their hydrogen evolution reaction (HER) activity is very poor, due to the lack of ionic conductivity. The inclusion of chalcogenide and generation of inherent oxygen vacancies in the lattice of LDH lead to improvement of both OER and HER activities. The presence of rich oxygen vacancies was confirmed using both the Tauc plot (1.11 eV, vacancy induction) and the photoluminescence study (peak at 426 nm, photoregeneration of oxygen). In this work, we have developed vacancy-enriched, selenized CoFe-LDH by the consequent wet-chemical and hydrothermal routes, respectively, which was used for OER and HER applications in 1 M KOH and 0.5 M H2SO4 electrolytes, respectively. For OER, the catalyst required only 251 mV overpotential to reach a 50 mA/cm2 current density with a Tafel slope value of 47 mV/dec. For HER, the catalyst demanded only 222 mV overpotential for reaching a 50 mA/cm2 current density with a Tafel slope value of 126 mV/dec. Hence, generating oxygen vacancies leads to several advantages from enhancing the exposed active sites to high probability in obtaining electrocatalytically active species and subsequent assistance in oxygen and hydrogen molecule cleavage.

In Situ Decorated Ni Metallic Layer with CoS2-Layered Thin Films via a Layer-by-Layer Strategy Using Pulsed Laser Deposition for Enhanced Electrocatalytic OER.

The catalytic activity of 3d-transition-metal-based electrocatalysts has exhibited considerable enhancements in electrocatalytic water splitting via pioneering modulations in the active sites. To overcome the energy loss because of the mechanic steps involved in a complex oxygen evolution reaction (OER), the electrode surface with only a few layers would be an advantage over multilayers for the ease of the electrolyte interaction and gas evolution. Here, for the first time, thin films of CoS2 are prepared on a carbon cloth via a pulsed laser deposition (PLD) technique via layer-by-layer deposition of Ni that tend to give Ni-CoS2 thin films. Based on varying the ablation of metallic Ni followed by CoS2 as a layer-by-layer assembly using PLD, three catalysts, namely, Ni5-CoS2, Ni10-CoS2, and Ni15-CoS2, were prepared. In OER, to achieve a benchmarking current density of 10 mA cm-2 in 1 M KOH, Ni10-CoS2 required a lesser overpotential of 304 mV, whereas others, namely, Ni5-CoS2, Ni15-CoS2, and CoS2, required overpotentials of 328, 336, and 373 mV, respectively, to attain the same current density. The charge transfer kinetics associated with all of the catalysts were analyzed, and the corresponding Tafel slope values for Ni5-CoS2 and Ni10-CoS2 were 75 and 98 mV/dec, respectively, ensuring the facile transfer of electrons at the interface. The assistance of metallic Ni sites also ensured stability for long-term applications. These findings will give a way for other earth-abundant catalysts for the increased electrocatalytic activity toward energy needs in future.

Surface Decoration of DNA-Aided Amorphous Cobalt Hydroxide via Ag+ Ions as Binder-Free Electrodes toward Electrochemical Oxygen Evolution Reaction.

Out of various available methods, generation of hydrogen by electrocatalytic water splitting is the most accepted one which consists of two half-cell reactions, viz, oxygen evolution reaction (OER) at the anode and hydrogen evolution reaction at the cathode. OER is a complex four-electron transfer process, and to sustain the spontaneous generation of hydrogen at the cathode, it is urgent to develop some earth-abundant, low-cost electrode materials. Recently, use of cobalt-based hydroxide as the electrode substrate has taken much consideration and has been fabricated over various substrates. Because of various structural disorders, internal resistance, and dependence on the electrode, the binder substrate makes their applications limited. Here, in this work, to remove structural disorder and to increase electrical conductivity, we have incorporated silver ions into amorphous Co(OH)2, which turns to be a highly active OER electrocatalyst. Also, for the first time, we have developed hydroxide-based materials by using DNA as a stabilizer, and most importantly, using DNA gives an immense opportunity to run long-term OER applications without using an external binder such as nafion. Moreover, for the first time, these DNA-based materials were coated on nickel foam mainly to eliminate the low conductive nature of Ag2O. The synthesized catalyst showed a very high OER activity, and to reach 50 mA/cm2 current density, it needs only 260 mV as overpotential. The amorphous nature of hydroxide-based materials gives a higher opportunity toward the electrolyte to bind on the surface of a catalyst to run the OER with less applied overpotentials.

Metallic Gold-Incorporated Ni(OH)2 for Enhanced Water Oxidation in an Alkaline Medium: A Simple Wet-Chemical Approach.

The development of a highly efficient electrocatalyst for the oxygen evolution reaction (OER) with a lower overpotential and high intrinsic activity is highly challenging owing to its sluggish kinetic behavior. As an alternative to the state-of-the-art OER catalyst, recently, transition-metal-based hydroxide materials have been shown to play important roles for the same. Owing to the high earth abundance of various Ni-based hydroxide and its derivatives, these are known to be highly studied materials for the OER. Herein, we report a simple wet-chemical synthesis of metallic gold-incorporated (by varying the concentration of Au3+ ions) Ni(OH)2 nanosheets as an active and stable electrocatalyst for the OER in 1 M KOH medium. The Au-Ni(OH)2 (2) catalyst demanded a low overpotential of 288 mV to attain a geometric current density of 10 mA/cm2 with a lower Tafel value of 55 mV/dec compared to bare Ni(OH)2 with a lower mass loading of only 0.1 mg/cm2. Tafel slope analysis reveals that the incorporation of metallic gold on the hydroxide surfaces could alter the mechanistic pathways of the overall OER reaction. It has been proposed that the incorporation of metallic gold over the Ni(OH)2 surfaces led to a change in the electronic structure of the electroactive nickel sites (Jahn-Teller distortion), which favors the OER by electronic aspects.

Electrospun Cobalt-Incorporated MOF-5 Microfibers as a Promising Electrocatalyst for OER in Alkaline Media.

Metal-organic framework (MOF)-based materials have attracted attention in recent times owing to their remarkable properties such as regulatable pore size, high specific surface area, and elasticity in their network topology, geometry, dimension, and chemical functionality. It is believed that the incorporation of a MOF network into a fibrous matrix results in the improvement of the electrocatalytic properties of the material. Herein, we have synthesized a Co-incorporated MOF-5-based fibrous material by a simple wet-chemical method, followed by an electrospinning (ES) process. The as-prepared Co-incorporated MOF-5 microfibers were employed as an electrocatalyst for the oxygen evolution reaction (OER) in 1 M KOH electrolyte. The catalyst demands a lower overpotential of 240 mV to attain a current density of 10 mA/cm2 with a lower Tafel slope value of 120 mV/dec along with a charge transfer resistance value of 2.9 Ω from electron impedance spectroscopy (EIS) analysis. From these results, it has been understood that the incorporation of Co metal into the MOF-5 microfibrous network has significantly improved the OER performance, which made them a potential entrant in other energy-related applications also.

Temperature-Controlled Structural Variations of Meticulous Fibrous Networks of NiFe-Polymeric Zeolite Imidazolate Frameworks for Enhanced Performance in Electrocatalytic Water-Splitting Reactions.

Developing non-noble, earth-ample, and stable electrocatalysts are highly anticipated in oxygen-evolution reaction (OER) and hydrogen-evolution reaction (HER) at unique pH conditions. Herein, we have synthesized bimetallic (nickel and iron) zeolite imidazolate framework (ZIF)-based nanofibrous materials via a simple electrospinning (ES) process. The structural stability of the fibrous material is subjected to various calcination conditions. We have elaborated the structural importance of the one-dimensional (1D) fibrous materials in electrocatalytic water-splitting reactions. As a result, NiFe-ZIF-NFs (Nanofibers)-RT (Room Temperature) have delivered a small overpotential of 241 mV at 10 mA cm-2 current density in OER and 290 mV at a fixed current density of 50 mA cm-2 in HER at two different pH conditions with 1 M KOH and 0.5 M H2SO4, respectively. Furthermore, it exposes the actual surface area of 27.270 m2 g-1 and a high electrochemical active surface area (ECSA) of 50 µF in OER and 55 µF in HER, which is responsible for the electrochemical performance with better stability. This exceptional activity of the materials is mainly attributed to the structural dependency of the fibrous network through the polymeric architecture.

Enhancement of the OER Kinetics of the Less-Explored α-MnO2 via Nickel Doping Approaches in Alkaline Medium.

Development of a low-cost transition metal-based catalyst for water splitting is of prime importance for generating green hydrogen on an industrial scale. Recently, various transition metal-based oxides, hydroxides, sulfides, and other chalcogenide-based materials have been synthesized for developing a suitable anode material for the oxygen evolution reaction (OER). Among the various transition metal-based catalysts, their oxides have received much consideration for OER, especially in lower pH condition, and MnO2 is one of the oxides that have widely been used for the same. The large variation in the structural disorder of MnO2 and internal resistance at the electrode-electrolyte interfaces have limited its large-scale application. By considering the above limitations of MnO2, here in this work, we have designed Ni-doped MnO2 via a simple wet-chemical synthetic route, which has been successfully applied for OER application in 0.1 M KOH solution. Doping of various quantities of Ni into the MnO2 lattices improved the OER properties, and for achieving 10 mA/cm2 current density, the Ni-doped MnO2 containing 0.02 M of Ni2+ ions (coined as MnO2-Ni0.002(M)) demands only 445 mV overpotential, whereas the bare MnO2 required 610 mV overpotential. It has been proposed that the incorporation of nickel ions into the MnO2 lattices leads to an electron transfer from the Ni3+ ions to Mn4+, which in turn facilitates the Jahn-Teller distortion in the Mn-O octahedral unit. This electron transfer and the creation of a structural disorder in the Mn sites result in the improvization of the OER properties of the MnO2 materials.

V3+ Incorporated ß-Co(OH)2: A Robust and Efficient Electrocatalyst for Water Oxidation.

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-2 was observed for the synthesized Co-V hydroxide with the optimal Tafel slope of 60 mV dec-1. 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 O2) was spontaneous on V site that is bridging two adjacent Co sites which was attributed to the observed enhancement.

Tuning Cu Overvoltage for a Copper-Telluride System in Electrocatalytic Water Reduction and Feasible Feedstock Conversion: A New Approach.

Highly efficient and earth-abundant elements capable of water reduction by electrocatalysis and are attractive for the sustainable generation of fuels. Among the earth-abundant metals, copper is one of the cheapest but often the most neglected choice for the hydrogen evolution reaction (HER) due to its high overvoltage. Herein, for the first time we have tuned the overpotential of copper by tellurizing it by two different methodologies, viz. hydrothermal and wet chemical methods, which form copper telluride nanochains and aggregates. The application of copper telluride as an electrocatalyst for the HER gave fruitful results in terms of both activity and stability. The hydrothermally synthesized catalyst Cu2-xTe/hyd shows a low overpotential (347 mV) at 10 mA cm-2 toward the HER. In addition, the catalyst showed a very low charge transfer resistance (Rct) of 24.4 Ω and, as expected, Cu2-xTe/hyd exhibited a lower Tafel slope value of 188 mV/dec in comparison to Cu2-xTe/wet (280 mV/dec). A chronoamperometry study reveals the long-term stability of both catalysts even up to 12 h. The Faradaic efficiency of Cu2-xTe/hyd was calculated and found to be 95.06% by using gas chromatographic (GC) studies. Moreover, with the idea of utilizing produced hydrogen (H2) from electrocatalysis, for the first time we have carried out feedstock conversion to platform chemicals in water under eco-friendly green conditions. We have chosen cinnamaldehyde, 2-hydroxy-1-phenylethanone, 4-(benzyloxy)benzaldehyde, and 2-(3-methoxyphenoxy)-1-phenylethanone (ß-O-4) as model compounds for feedstock conversion by hydrogenation and/or hydrogenolysis reactions in aqueous medium using external hydrogen pressure. This protocol could also be scaled up for large-scale conversion and the catalyst is likely to find industrial application since it requires an inexpensive catalyst and an easily available, mild reducing agent. The robustness of the developed catalyst is proven by recyclability experiments and its possibility of use in real-life applications.

Cubic Nanostructures of Nickel-Cobalt Carbonate Hydroxide Hydrate as a High-Performance Oxygen Evolution Reaction Electrocatalyst in Alkaline and Near-Neutral Media.

Catalyst development for the efficient direction of electrocatalytic water splitting with much less overpotential is crucial for meeting large-scale hydrogen generation. Being highly abundant and cost-effective, 3d transition-metal-based catalysts show promising activities in alkaline conditions. In this work, bimetallic nickel-cobalt carbonate hydroxide hydrate (NiCoCHH) was prepared by a co-precipitation method with varying molar ratios of Ni/Co of 0.5:1, 1:1, and 1.5:1, which were analyzed for oxygen evolution reaction (OER) study in both alkaline (1 M KOH) and near-neutral (1 M NaHCO3) media. For OER in 1 M KOH, NiCoCHH 1:1 required overpotential of just 238 mV at 10 mA cm-2 current density compared to other ratios of 0.5:1 and 1.5:1, which required 290 and 308 mV, respectively. Similarly, in 1 M NaHCO3, NiCoCHH 1:1 required an overpotential of 623 mV to reach 10 mA cm-2. A post-OER study confirmed the formation of NiOOH during OER. The observed faradaic efficiency was nearly 95.21% for the NiCoCHH 1:1 catalyst. A two-electrode setup with NiCoCHH 1:1∥Pt required just 312 mV as an overpotential at 10 mA cm-2. These kinds of comparative studies can be used in other 3d transition-metal-based catalysts for OER in the future.

Enhancing Hydrogen Evolution Reaction Activities of 2H-Phase VS2 Layers with Palladium Nanoparticles.

Effective hydrogen (H2) production with surface engineering of less active catalysts by an innovative approach is followed here. In this work, a non-noble 2H phase of VS2 layers, which showed poor activity for hydrogen evolution reaction (HER) in 0.5 M H2SO4, was made highly active by decorating palladium (Pd) nanoparticles (NPs) over VS2 layers. A density functional theory (DFT) study confirmed the successful binding of Pd with VS2, and the bond length in a Pd4 tetrahedron was measured to be 2.60 Å. In VS2-Pd, Pd as a Pd4 tetrahedron is pointed toward the VS2 layer, and the calculated Pd-S bond distance is 2.42 Å with some expansion of three Pd-Pd bonds (2.85 Å). From the density of states, it was confirmed that the band gap was too high for VS2 (0.2 eV; 2H phase) and was reduced to nearly zero in VS2-Pd (0.05 eV). In the electrocatalytic HER part, the obtained ΔGH values from DFT were 0.05, -0.45, and 0.22 eV for VS2/Pd4, Pd4, and VS2, respectively, which imply that VS2-Pd4 had improved HER activity compared to pristine VS2 and Pd4. A concentration-dependent study was carried out with molar ratios of Pd at 0.01, 0.05, and 0.1 M with VS2 layers. From the HER polarization study, VS2-Pd (0.05 M) showed an overpotential of 157 mV at 20 mA cm-2, which is 373 mV less than only VS2 with a Tafel slope of 75 mV dec-1 with overwhelming stability. These highly promising results will be interesting to make less active stable phases by incorporating metal NPs for efficient and stable H2 production.

Spinel Cobalt Titanium Binary Oxide as an All-Non-Precious Water Oxidation Electrocatalyst in Acid.

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" (Co2TiO4) as an efficient alternate to expensive IrO2 and RuO2 for PEM water electrolyzer. The synthesized Co2TiO4 octahedral nanocrystals of size 50 to 210 nm showed excellent oxygen evolution reaction (OER) activity in 0.5 M H2SO4, which was comparable to IrO2 and better than spinel Co3O4 when examined under identical experimental conditions. Overpotential of just 513 mV was sufficient enough to drive a kinetic current density of 10 mA cm-2, which is a significant figure of merit as far as acidic water oxidation electrocatalysis is concerned.

In Situ Modified Nitrogen-Enriched ZIF-67 Incorporated ZIF-7 Nanofiber: An Unusual Electrocatalyst for Water Oxidation.

One-dimensional (1D) based carbonaceous materials have wider applicability owing to flexibility over their properties. Electrospinning is one of the pioneering techniques that is being utilized predominantly for the synthesis of fibers. Fibrous material has their own advantages like, high porosity over its surface, mechanical stability and fascinating physicochemical properties. With these many advantages, herein we have synthesized a distinctive nanofiber from a zeolite imidazolate framework (ZIF) based material. This powder has been mixed with PAN (polyacrylonitrile) which act as both a heteroatom source and a precursor material in the making of a fibrous material via electrospinning. The synthesized nitrogen-enriched ZIF-67 incorporated ZIF-7 microfibers were prepared under two different conditions (room temperature and N2 atmosphere) and labeled as CoZn-ZIF-RT and CoZn-ZIF-500, respectively. The newly developed materials were assessed for the first time in electrocatalytic oxygen evolution reaction (OER) studies have been carried out in a 1 M KOH electrolyte. CoZn-ZIF-500 delivered superior activity at a current density of 10 mA cm-2 with a kinetically facile Tafel slope and explicitly showed good long-term stability.

Evaluating DNA Derived and Hydrothermally Aided Cobalt Selenide Catalysts for Electrocatalytic Water Oxidation.

Electrocatalysts with engaging oxygen evolution reaction (OER) activity with lesser overpotentials are highly desired to have increased cell efficiency. In this work, cobalt selenide catalysts were prepared utilizing both wet-chemical route (CoSe and CoSe-DNA) and hydrothermal route (Co0.85Se-hyd). In wet-chemical route, cobalt selenide is prepared with DNA (CoSe-DNA) and without DNA (CoSe). The morphological results in the wet-chemical route had given a clear picture that, with the assistance of DNA, cobalt selenide had formed as nanochains with particle size below 5 nm, while it agglomerated in the absence of DNA. The morphology was nano networks in the hydrothermally assisted synthesis. These catalysts were analyzed for OER activity in 1 M KOH. The overpotentials required at a current density of 10 mA cm-2 were 352, 382, and 383 mV for Co0.85Se-hyd, CoSe, and CoSe-DNA catalysts, respectively. The Tafel slope value was lowest for Co0.85Se-hyd (65 mV/dec) compared to CoSe-DNA (71 mV/dec) and CoSe (80 mV/dec). The chronoamperometry test was studied for 24 h at a potential of 394 mV for Co0.85Se-hyd and was found to be stable with a smaller decrease in activity. From the OER study, it is clear that Co0.85Se was found to be superior to others. This kind of related study can be useful to design the catalyst with increased efficiency by varying the method of preparation.

Nanosheets of Nickel Iron Hydroxy Carbonate Hydrate with Pronounced OER Activity under Alkaline and Near-Neutral Conditions.

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 H2 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-2 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 NaHCO3 (pH ∼8.5) required overpotentials for all of the ratios ranging from 389 to 507 mV at 10 mA cm-2 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-2 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.

Advanced Cu3Sn and Selenized Cu3Sn@Cu Foam as Electrocatalysts for Water Oxidation under Alkaline and Near-Neutral Conditions.

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 Cu3Sn@Cu foam, with overwhelming activity for OER under both alkaline (1 M KOH) and near-neutral (1 M NaHCO3) conditions. The catalysts were prepared by a double hydrothermal treatment where Cu3Sn is first formed which further underwent for second hydrothermal condition for selenization. For comparison, Cu7Se4@Cu foam was prepared by a hydrothermal treatment under the same protocol. The as-formed Cu3Sn@Cu foam, selenized Cu3Sn@Cu foam, and Cu7Se4@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-2, selenized Cu3Sn@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 Cu3Sn@Cu foam, Cu7Se4@Cu foam, and pristine Cu foam. Furthermore, potentiostatic analysis (PSTAT) was carried out for 40 h for selenized Cu3Sn@Cu foam and with minimum degradation in activity assured the long-term application for hydrogen generation. Similarly, under neutral condition selenized Cu3Sn@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.

NiTe2 Nanowire Outperforms Pt/C in High-Rate Hydrogen Evolution at Extreme pH Conditions.

Better hydrogen generation with nonprecious electrocatalysts over Pt is highly anticipated in water splitting. Such an outperforming nonprecious electrocatalyst, nickel telluride (NiTe2), has been fabricated on Ni foam for electrocatalytic hydrogen evolution in extreme pH conditions, viz., 0 and 14. The morphological outcome of the fabricated NiTe2 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 NiTe2 NWs and NiTe2 NFs were comparatively screened for hydrogen evolution reaction (HER) in extreme pH conditions, viz., 0 and 14. NiTe2 NWs delivered current densities of 10, 100, and 500 mA cm-2 at the overpotentials of 125 ± 10, 195 ± 4, and 275 ± 7 mV in 0.5 M H2SO4. 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, NiTe2 NFs showed relatively poorer HER activity than NiTe2 NWs, which required overpotentials of 193 ± 7, 289 ± 5, and 494 ± 8 mV in 0.5 M H2SO4 for the current densities of 10 and 100 mA cm-2 and 157 ± 5 and 335 ± 6 mV in 1 M KOH for the current densities of 10 and 100 mA cm-2, respectively. Notably, NiTe2 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-2 at 332 ± 5 mV, whereas NiTe2 NWs drove the same current density with 57 mV less. These encouraging findings emphasize that a NiTe2 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.

Self-Assembled Molecular Hybrids of CoS-DNA for Enhanced Water Oxidation with Low Cobalt Content.

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)2 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-2 (1 M KOH), respectively. The advantages of lower overpotential, lower Tafel slope (42.7 mV dec-1), 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.

Melamine-Based Hydrogen-bonded Systems as Organoelectrocatalysts for Water Oxidation Reaction.

Applications of small organic molecules and hydrogen-bonded aggregates, instead of traditional transition-metal-based electrocatalysts, are gaining momentum for addressing the issue of low-cost generation of H2 to power a sustainable environment. Such systems offer the possibility to integrate desired functional moieties with predictive structural repetition for modulating their properties. Despite these advantages, hydrogen-bonded organic systems have largely remained unexplored, especially as electrocatalysts. Melamine and adipic acid-based hydrogen-bonded organic ionic (BMA) and co-crystal systems developed under varying temperatures are explored as electrocatalysts for water oxidation reaction (WOR). These systems are easily modifiable with precisely designed molecular architecture and judiciously positioned nitrogen atoms. Combined effect of charge-assisted hydrogen bonding stabilizes the ionic BMA system under corrosive alkaline conditions and augments its remarkable electrocatalytic WOR activity, achieving a current density of 10 mA cm-2 at an overpotential of 387 mV and Faradaic efficiency ∼94.5 %. The enhanced electrocatalytic ability of BMA is attributed to its hydrophilic nature, unique molecular composition with complementary hydrogen-bonded motifs and a high density of positively charged nitrogen atoms on the surface, that facilitates electrostatic interactions and accelerate charge and mass transport processes culminating in a turnover frequency of ∼0.024 s-1 . This work validates the potential of hydrogen-bonded molecular organo-electrocatalysts towards WOR.