Electrocatalyst For Water Oxidation Research Articles

Fishnet-like superstructures constructed from ultrafine and ultralong Ni-MOF nanowire arrays directionally grown on highly rough and conductive scaffolds: synergistic activating effect for efficient and robust alkaline water oxidation activity

The water oxidation efficiency driven by electrocatalysts is related to the energy conversion efficiency of water electrolysis and other systems. It is the key to expose active sites as possible, to fully and firmly contact with other components, and to deliver superior conductivity for the development of high-performance electrocatalysts. Herein, we have fabricated self-supporting Ni-MOF electrode containing three-dimensional (3D) fishnet-like superstructures, which are constructed from in-situ growth of amorphous or poor crystalline Ni-MOF nanowire arrays on highly rough and conductive scaffolds of metallic Ni/carbon cloth (Ni-MOF/Ni/CC). The Ni-MOF/Ni/CC electrode delivers an overpotential of 250 mV at the current density of 10 mA cm−2 (η10). The η10 is maintained at 240 mV after a constant current electrolysis for 32 h, which is much smaller than those of Ni-MOF/CC (423 mV) and Ni/CC (281 mV). The superior activity and robust durability can be attributed to the synergistic activating effect of each component in the superstructures with high density of coordination unsaturated active sites, intimate connection and excellent conductivity. This work can provide a new strategy to develop high-efficiency MOFs-based electrocatalysts for electrocatalytic water oxidation.

Carbon-based active support for water oxidation electrocatalyst: Making full use of the available surface area

Since the support of conventional electrocatalysts is mostly inert, certain parts of these supported electrocatalysts that have direct contact with the reactants do not have electrocatalytic function. Therefore, the surface area of these electrocatalysts is larger than their electrochemically active surface area. So as to make full use of the available surface area and release the activity potential of the electrocatalysts, this work synthesized a carbon-based active support with certain electrocatalytic activity for water oxidation reaction, providing a general route to prepare electrocatalysts with electrochemically active surface area close to their surface area. In detail, a cubic core-shell support was synthesized via an aqueous phase synthesis method for oxygen evolution reaction (OER). The carbon-based active support with a larger specific surface area (306 m2 g−1) is beneficial to the dispersion of the active sites. The support has appropriate OER catalytic activity which can synergistically catalyze OER together with NiFe (oxy)hydroxide on it during the reaction. Under the current density of 10 mA cm−2, the overpotential is as low as 214 mV for OER, which is better than those of most non-precious metal catalysts, suggesting that carbon-based active support could effectively reduce energy consumption via promoting surface area utilization ratio.

Construction of echinoids-like MoS2@NiS2 electrocatalyst for efficient and robust water oxidation

Boosting stability, durability, and intrinsic activity of electrocatalysts are the world’s concerns in promoting the application of oxygen evolution reaction (OER). Ni is averagely required in efficient electrocatalysts for OER, while Mo is familiar to hydrogen evolution reaction (HER). Herein, we introduce Mo into electrocatalysts for OER and synthesize an echinoids-like MoS2@NiS2 electrocatalyst with unique morphology, which demonstrates rapid reaction kinetics and impressive catalysis activity. Furthermore, the electrocatalyst shows low overpotentials of 356 mV at 100 mA cm−2 as well as a Tafel slope of 82.6 mV dec−1 in alkaline media. Meanwhile, the electrocatalyst has a large double-layer capability (Cdl) and electrochemically active surface areas (ECSA) values. The OER performances remarkably enhanced with the help of MoS2 affiliation. Owning to the Ni compounds as the substrate, the catalyst can maintain a good stability in alkaline solution even after 10 h of chronoamperometry test at 1.51 V. Our study proposes a feasible way to obtain a high-efficient and robust OER electrocatalyst for the practical application.

Bonding interface boosts the intrinsic activity and durability of NiSe@Fe2O3 heterogeneous electrocatalyst for water oxidation

The intrinsic activity and durability of oxygen evolution reaction (OER) electrocatalysts are mainly dominated by the surface and interface properties of active materials. Herein, a core-shell heterogeneous structure (NF/NiSe@Fe2O3) is fabricated via two-step hydrothermal method, which exhibits a low overpotential of 220 mV (or 282 mV) at 10 mA/cm2 (or 200 mA/cm2), a small Tafel slope of 36.9 mV/dec, and long-term stability (~230 h) in 1 mol/L KOH for OER. X-ray photoelectron spectroscopy and X-ray absorption spectroscopy reveal the (oxy)hydroxide-rich surface and strong coupling interface between NiSe and Fe2O3 via the Fe-Se bond. Density functional theory calculation suggests that the d-band center and electronic state of NiSe@Fe2O3 heterojunction are well optimized due to the formation of Fe-Se bond, which is favorable for the enhanced OER activity because of the easy adsorption of oxygen-containing intermediates and desorption of O2 in the OER process. In addition, the unique core-shell structure and robust bonding interface are responsible for the good stability for OER. This work provides fundamental insights on the bonding effect that determine the performance of OER electrocatalyst.

Urchin-Like Cobalt-Copper (Hydr)oxides as an Efficient Water Oxidation Electrocatalyst.

The development of efficient and low-cost oxygen evolution reaction (OER) catalysts is essential for the generation of clean hydrogen energy from water splitting. Herein, a novel hierarchical urchin-like cobalt-copper (hydr)oxide in situ grown on copper foam (CoCuOx Hy (S)/CF) was synthesized through the electrochemical transformation of cobalt-copper sulfides (Co9 S8 -Cu1.81 S) via anodization process. This CoCuOx Hy (S)/CF anode exhibited a low overpotential (η) of 274 mV at a current density of 100 mA cm-2 with a robust durability over a period of 40 h when operated at 10 mA cm-2 . Further investigations imply that the unique nanowires aggregated urchin-like structure of CoCuOx Hy (S) derived from the in situ anion exchange process could facilitate the exposure of active sites and accelerate electron transfer. More importantly, the incorporation of copper resulted in an electronic delocalization around the cobalt species, which contributed to reach a high-valent catalytically active cobalt species and further improved the OER performance.

Spinel-type ternary multimetal hybrid oxides with porous hierarchical structure grown on Ni foam as large-current-density water oxidation electrocatalyst

Abstract Transition metal oxides have been proved to be stable oxygen evolution reaction (OER) catalysts under alkaline conditions. However, their single component limits further improvement of elecatalytic activity. In this aspect, spinel oxides with adjustable composition show promising advantages. Herein, we report a spinel-type ternary multimetal hybrid oxides Co-doped NiO-Fe3O4@NiCo2O4 with porous hierarchical architecture grown on Ni foam. The obtained electrocatalyst has excellent electrocatalytic performance for OER 1 M KOH solution, which only needs overpotential of 280 mV to reach 10 mA cm−2. In practical industrial electrolyte (30 wt% KOH solution), this material just requires overpotential of 250 mV to reach a large-current-density of 1000 mA cm−2. Such superior high OER catalytic performance of this material should be related to the synergistic effect between metal elements of Ni, Co and Fe with intrinsically high OER activities; Hierarchical architecture exposes more catalytically active sites. Spinel oxides arrays with high conductivity can be used as fast electron transport pathways to effectively reduce resistance and thus improve catalytic activity. The unique hierarchical porous structure endows the catalyst with high mass transfer mobility. This work provides a new way to exploit spinel oxides OER electrocatalysts with high activity and stability. Such high activity and robust stability in concentrated KOH solution make it can be applied in commercial industrial electrolyzers.

Homogeneous Electrochemical Water Oxidation at Neutral pH by Water-Soluble NiII Complexes Bearing Redox Non-innocent Tetraamido Macrocyclic Ligands.

Water oxidation is the bottleneck reaction in artificial photosynthesis. Exploring highly active and stable molecular water oxidation catalysts (WOCs) is still a great challenge. In this study, a water-soluble NiII complex bearing a redox non-innocent tetraamido macrocyclic ligand (TAML) is found to be an efficient electrocatalyst for water oxidation in neutral potassium phosphate buffer. Controlled-potential electrolysis experiments show that it can sustain at a steady current of approximately 0.2 mA cm-2 for >7 h at 1.75 V versus normal hydrogen electrode (NHE) without the formation of NiOx . Electrochemical and spectroelectrochemical tests show that the redox-active ligand, as well as HPO4 2- in the buffer, participate in the catalytic cycle. More importantly, catalytically active intermediate [NiIII (TAML2- )-O. ] is formed via several proton-coupled electron transfer processes and reacts with H2 O with the assistance of base to release molecular oxygen. Thus, the employment of redox non-innocent ligands is a useful strategy for designing effective molecular WOCs.

3D freestanding flower-like nickel-cobalt layered double hydroxides enriched with oxygen vacancies as efficient electrocatalysts for water oxidation

Economic, efficient, and stable layered double hydroxides (LDHs) based oxygen evolution reaction (OER) electrocatalysts are recognized as promising substitutions of precious catalysts. While LDHs composites suffer from low intrinsic activity, which slightly impedes their wide utilization in energy conversion. Here, we demonstrate a kind of three-dimensional (3D) freestanding flower-like NiCo-LDHs materials with abundant oxygen vacancies are synthesized for electrocatalytic OER application. Simple solvent-thermal method is conducted in ethanol-N, N-dimethylformamide (DMF) mixed solution, which owns slight etching effect to obtain 3D open structures. The as-synthesized Ni1Co1-LDHs-E1D1 composite (in which molar ratio of nickel‑cobalt and volume ratio of ethanol-DMF are both 1:1) is characterized with abundant oxygen vacancies on surface and ultrathin nanosheets morphology with large surface area. It exhibits a relatively low overpotential (260 mV) to drive the current density of 10 mA cm−2 with a low Tafel slope of 72 mV dec−1, as well as high durability in alkaline solution. This work confirms an ingenious strategy for designing 3D vacancy-rich LDHs functional electrocatalytic materials.

Water Oxidation in Acidic Solutions: Beyond Noble Metals

Water oxidation, a kinetically demanding half-reaction, plays a vital role in hydrogen production through electrochemical water-splitting. Thus, the development of efficient and stable oxygen evolution reaction electrocatalysts has become a central theme for basic research in the field of renewable energy. Substantial progress has been made in developing robust and inexpensive noble metal-free heterogeneous electrocatalysts for water oxidation operating under alkaline and neutral pH conditions. There is, however, a scarcity of active and stable electrocatalysts for acidic water oxidation, which is an ideal pH condition for high purity hydrogen production and offers several other technological advantages. Low performance and poor stability of existing water oxidation electrocatalysts based on non-noble metals are mainly attributed to the dissolution of respective elements in acidic solution. Considering these challenging aspects, we constructed the water oxidations catalysts based on thermodynamically and acid-stable oxides, which are incorporated with catalytically active species (transition metal-based water oxidation catalysts). Specifically, the highly-disordered mixed metal oxide, based on cobalt, iron, and lead, produced in situ exhibits excellent OER performance with unprecedented stability, through self-healing mechanism, under harsh operating conditions of pH 0 and temperature 80 °C. Importantly, the Cobalt-iron-lead oxide demonstrates the capability of operating at industrially relevant rates of 0.5 A cm-2 at low OER overpotentials of 0.7 V. These findings highlight the new strategy to design highly active and acid-stable, noble metal-free, OER electrocatalysts that can essentially operate indefinitely. Our most recent developments focused on replacement of lead with alternative, less toxic components. The presentation will also highlight these new systems, some of which demonstrate outstanding stability even without a self-healing mechanism.

Macroporous Rgo Electrode Decorated with Co3O4 Nanoparticles for Selective Catalytic Electro-Oxidation of Water

OBJECTIVESThe electro-oxidation of H2O to O2 is a promising process to store energy into a green fuel. Its intrinsic high kinetic barrier requires the use of catalysts to lower the applied potential; moreover, it suffers the competition of side-reactions like Cl‒ oxidation to chlorine, an undesirable corrosive by-product. The high concentration of Cl‒ ions in seawater is one of the major obstacles which hinders the direct employment of such widely available resource as the electrolyte for O2 production (Adv. Mater., 2018, 30, 1707261).The benchmark electrocatalysts based on noble metals (Pt, IrO2) are not selective toward Cl‒, and their scarcity prevents their practical large-scale application. Earth-abundant oxides and (oxy)hydroxides of first-row transition metals (FeOOH, NiOOH, Co3O4) are robust and show even higher catalytic performances than Pt/IrO2. Unfortunately they are not selective against Cl‒ oxidation (ACS Catal., 2014, 4, 3701).In this work, we aim to suppress Cl‒ interference on heterogeneous catalysts through a carefully designed electrode architecture. We synthesize a free-standing, conducting, 3D macroporous reduced graphene oxide (rGO) composite with catalytic Co3O4 nanoparticles (NP) selectively deposited just on the internal walls of its closed, not interconnected pores (average diameter 100 µm). The pore walls act as membranes made of multiple stacked rGO nanosheets; the nanochannels between rGO layers have width < 1 nm which previous works have shown to be permeable to water and gases while preventing the diffusion of dissolved ions like Cl‒ (e.g. Nat. Mater., 2017, 16, 1198). Since the catalytic sites are accessible selectively to the substrates able to permeate through the rGO walls, the water electro-oxidation is expected to happen without suffering the competing Cl2 evolution.The most common method for synthesizing 3D rGO porous materials is through self-assembly of graphene oxide (GO) suspensions during hydrothermal reduction. However, this method leads to scaffolds with small open pores with diameters in the micrometer range (e.g. ACS Nano, 2010, 7, 4324). A macroporous closed structure, instead, allows for selectivity together with higher diffusion rates of the permeating species from the outer solution to the reaction sites. For this reason, in our strategy we synthesize the scaffolds starting from emulsions of hexane droplets in water stabilized by GO nanosheets as soft template for the macroporous structure.RESULTSWe modify the amphiphilicity of GO by adding different amounts of surfactants to produce so-called high internal phase emulsions (HIPE) stabilized by GO. These are single phase emulsions characterized by a high amount of emulsified phase (Hex:H2O ratio > 0.75), and a long-term stability (several months). Then, we convert the HIPE in the final 3D scaffolds by triggering the self-assembly of GO sheets through a hydrothermal reduction with slow temperature ramp, at the end of which hexane has entirely evaporated due to its low boiling point.Through this simple process we are able to control the architecture of the rGO scaffolds without polymerizations or post-modifications. We can control the pore size by tuning the templating HIPE droplet size, which we show depends on the GO concentration, hexane to water ratio, hexane to volume ratio, and emulsifying method (time and power). Because of its superior structural homogeneity compared to the conventional diluted emulsions previously reported (J. Mater. Chem. A, 2015, 3, 4018), a HIPE brings several advantages to the final material, i.e. better mechanical properties, very high surface area, and lower electrical resistivity (2.6±1.3 kΩcm).This is also the first study which reports the addition of a metal-organic precursor (of Co3+ in this specific case), or metal oxide NP (specifically Co3O4) functionalized with a hydrophobic layer, in the apolar phase during the preparation of the emulsion template, and then exploits the immiscible nature of the apolar and water phases to selectively decorate with catalytic NP only the internal wall of the closed pores. This feature requires the formation of highly stable initial GO HIPE and cannot be achieved by any other strategy previously reported.SIGNIFICANCE OF THE WORKThe rGO macroporous materials produced are currently under investigation as self-standing electrocatalysts for selective water oxidation with respect to chlorine evolution. We will then test these electrodes for water decontamination and as anodes in energy storage devices.While in this work we focus on Co3O4, our approach allows the encapsulation of any type of nanocatalyst (metal oxide/metal-based NP) inside the closed rGO macropores, just by changing the hydrophobic precursor. Such materials may exhibit electrocatalytic activity and selectivity towards a variety of substrates that can permeate through the rGO walls while suppressing any competitive reaction involving interfering species which are rejected by the rGO walls. Figure 1

Recent Progress in Electrocatalysts for Acidic Water Oxidation

AbstractHydrogen is a clean and renewable energy carrier for powering future transportation and other applications. Water electrolysis is a promising option for hydrogen production from renewable resources such as wind and solar energy. To date, tremendous efforts have been devoted to the development of electrocatalysts and membranes for water electrolysis technology. In principle, water electrolysis in acidic media has several advantages over that in alkaline media, including favorable reaction kinetics, easy product separation, and low operating pressure. However, acidic water electrolysis poses higher requirements for the catalysts, especially the ones for the oxygen evolution reaction. It is a grand challenge to develop highly active, durable, and cost‐effective catalysts to replace precious metal catalysts for acidic water oxidation. In this article, an overview is presented of the latest developments in design and synthesis of electrocatalysts for acidic water oxidation, emphasizing new strategies for achieving high electrocatalytic activity while maintaining excellent durability at low cost. In particular, the reaction pathways and intermediates are discussed in detail to gain deeper insight into the oxygen evolution reaction mechanism, which is vital to rational design of more efficient electrocatalysts. Further, the remaining scientific challenges and possible strategies to overcome them are outlined, together with perspectives for future‐generation electrocatalysts that exploit nanoscale materials for water electrolysis.

In-situ synthesis of free-standing FeNi-oxyhydroxide nanosheets as a highly efficient electrocatalyst for water oxidation

The design and synthesis of efficient and affordable electrocatalysts for water oxidation are essential to advance water splitting technology, which depends on developing earth-abundant catalytic materials with rational compositions and structures. Here, we propose a facile synthesis of FeNiOOH nanosheets grown on FeNi foam (FNF) by in-situ chemical oxidation as a novel 3D electrode for oxygen evolution reaction (OER). This FeNiOOH/FNF electrode shows outstanding electrocatalytic performance in alkaline electrolyte, including high OER activity that requires a small overpotential of 252 mV to achieve a current density of 10 mA cm−2, favourable OER kinetics with a low Tafel slope of 36.8 mV dec−1, and excellent operation stability for at least 50 h. The superior OER properties are resulted from the highly active FeNi-oxyhydroxide species and advantageous nanosheet array structure. This work presents an effective strategy to rationalize self-supporting electrodes consisting of nanostructured arrays on conductive substrates, creating new opportunities to search for more advanced materials towards a sustainable energy future.

Zn-substituted MnCo2O4 nanostructure anchored over rGO for boosting the electrocatalytic performance towards methanol oxidation and oxygen evolution reaction (OER)

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 MnCo2O4 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 Zn1-xMnxCo2O4/rGO electrocatalyst with x = 0.2 and 0.4 offered the same onset potential and overpotential at 10 mA/cm2. 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−1). The prepared electrocatalysts were tested for methanol oxidation in which electrocatalyst Zn1-xMnxCo2O4/rGO with x = 0.4 shows a better electrochemical performance in oxidizing methanol with the higher current density of 142.3 mA/cm2. The above catalyst also revealed excellent stability and durability during both MOR and OER, suggesting that it can be utilized in practical applications.

Recent progress of precious-metal-free electrocatalysts for efficient water oxidation in acidic media

The realization of efficient oxygen evolution reaction (OER) is critical to the development of multiple sustainable energy conversion and storage technologies, especially hydrogen production via water electrolysis. To achieve the massive application of hydrogen energy and mass-scale hydrogen production from water splitting drives the pursuit of competent precious-metal-free electrocatalysts in acidic media, where the hydrogen evolution reaction (HER) is more facilitated. However, the development of high-efficient and acid-stable OER electrocatalysts, which are robust to function stably at high oxidation potentials in the acidic electrolyte, remains a great challenge. This article contributes a focused, perceptive review of the up-to-date approaches toward this emerging research field. The OER reaction mechanism and fundamental requirements for oxygen evolution electrocatalysts in acid are introduced. Then the progress and new discoveries of precious-metal-free active materials and design concepts with regard to the improvement of the intrinsic OER activity are discussed. Finally, the existing scientific challenges and the outlooks for future research directions to the fabrication of emerging, earth-abundant OER electrocatalysts in acid are pointed out.

Nickel foam supported cobalt phosphate electrocatalyst for alkaline oxygen evolution reaction

Cobalt phosphate (CoPO) nanoflakes evenly grown on nickel foam (NF) substrate are triumphantly synthesized through a handy hydrothermal/solvothermal process. The morphology of the CoPO is regular circular nanoflakes with the diameter size of 2–5 μm. The nickel foam supported cobalt phosphate (CoPO/NF) which presents more prominent oxygen evolution reaction (OER) activity and stability shows an overpotential (116 mV at 10 mA cm−2) and Tafel slope (65.6 mV dec−1) superior to previously reported CoPO and commercial RuO2 catalysts. Furthermore, after 48 h current-time test, the CoPO/NF maintains 96.7% compared to initial current density. The maximum current densities of CoPO/NF in the linear sweep voltammetry (LSV) curves are basically stable from the 1st cyclic voltammetry (CV) cycle to the 20000th CV cycles. The prominent OER performance of CoPO/NF can be put down to the nickel foam substrate, which amplifies the electrochemically active superficial area of CoPO nanoflakes. The low-cost, simple and convenient preparation method, favorable catalytic activity and stability make this CoPO/NF material a hopeful OER electrocatalyst for electrochemical water oxidation.

Effect of Selenium Content on Nickel Sulfoselenide-Derived Nickel (Oxy)hydroxide Electrocatalysts for Water Oxidation.

An efficient and inexpensive electrocatalyst for the oxygen evolution reaction (OER) must be found in order to improve the viability of hydrogen fuel production via water electrolysis. Recent work has indicated that nickel chalcogenide materials show promise as electrocatalysts for this reaction and that their performance can be further enhanced with the generation of ternary, bimetallic chalcogenides (i.e., Ni1-aMaX2); however, relatively few studies have investigated ternary chalcogenides created through the addition of a second chalcogen (i.e., NiX2-aYa). To address this, we studied a series of Se-modified Ni3S2 composites for use as OER electrocatalysts in alkaline solution. We found that the addition of Se results in the creation of Ni3S2/NiSe composites composed of cross-doped metal chalcogenides and show that the addition of 10% Se reduces the overpotential required to reach a current density of 10 mA/cm2 by 40 mV versus a pure nickel sulfide material. Chemical analysis of the composites' surfaces shows a reduction in the amount of nickel oxide species with Se incorporation, which is supported by transmission electron microscopy; this reduction is correlated with a decrease in the OER overpotentials measured for these samples. Together, our results suggest that the incorporation of Se into Ni3S2 creates a more conductive material with a less-oxidized surface that is more electrocatalytically active and resistant to further oxidation. Importantly, oxidation does still occur, and the active catalyst is most likely a nickel (oxy)hydroxide surrounding a crystalline, conductive Ni3S2-xSex core.

FeCoNi Ternary Spinel Oxides Nanosheets as High Performance Water Oxidation Electrocatalyst

AbstractFeCoNi spinel oxides nanosheets array directly supported on the Ni foam substrate were prepared via a facile wet chemical method with 2‐methylimidazole as a structure directing agent and subsequently annealing. The as‐prepared 0.1Fe−CoNiO/NF offers high intrinsic catalytic activity, high surface area and good conductivity, resulting in enhanced activity for the oxygen evolution reaction (OER) in the alkaline solution. It demonstrates an ultralow overpotentials of 240 mV at 10 mA cm−2 and a small Tafel slope of 36.8 mV dec−1, with attractive durability during long‐term operation in 1 M KOH solution.

Neutral and alkaline chemical environment dependent synthesis of Mn3O4 for oxygen evolution reaction (OER)

Co-precipitation assisted hydrothermal synthesis was employed to prepare Mn3O4 electrocatalysts for efficient electrochemical water oxidation. Tetragonal structure of high crystalline and pure phase Mn3O4 nanostructures was confirmed by X-ray diffraction (XRD) spectra. Physical characteristics such as vibration, optical and morphology of the electro catalysts were examined and confirmed by Raman spectra, Fourier Transform Infrared Spectra (FTIR), photoluminescence spectra (PL) and ultra-violet diffuse reflection spectra (UV-DRS) respectively. Mn3O4 electro catalysts were deposited on GCE electrode for investigating the electrochemical behavior. The electrochemical water splitting application was demonstrated by the prepared Mn3O4 electro catalysts in conventional three electrode cell with Hg/HgO as a reference electrode and Pt mesh as a counter electrode. Higher current density of 1.31 mA/g with lowest Tafel slope value of 63 mV/dec was achieved for the prepared electro catalyst synthesized in base pH condition. Good stability of 55% over 12 h long time was achieved for the electro catalysts in alkaline medium under continuous electrochemical reaction with good retention in performance. Hence, the controlled alkaline environmentally synthesized Mn3O4 electro catalysts prepared in this work achieved the good standard of highly efficient electrode material for electrochemical water splitting applications.

A polyoxometalate supported copper dimeric complex: Synthesis, structure and electrocatalysis

A polyoxometalate (POM) supported copper dimeric complex, [Mo8O26{Cu2(2,2′-bpy)2 (CH3COO)2H2O}2]٠H4Mo8O26·16H2O (1) has been synthesized using conventional wet synthesis. The compound has been characterized using routine spectral techniques and its molecular structure has been elucidated using single crystal X-ray crystallography. The two copper(II) ions are bridged by acetate ions and each copper ion is also coordinated to 2,2′-bipyridine molecule. In each dimer, one of the copper ions is bonded to the POM anion from one side, whereas the other copper ion is bonded to a water molecule, hence acquiring a penta-coordinated square pyramidal structure around each copper center. The lattice water molecules play an important role to stabilize the system, by forming a water pentamer, which binds both the polyoxometalate supported transition metal complex and the other POM anion [Mo8O26]4–. Interestingly, compound 1 is found to function as a versatile heterogeneous electro-catalyst for water oxidation, proton reduction and hydrogen peroxide reduction.

Gold‐Supported Gadolinium Doped CoB Amorphous Sheet: A New Benchmark Electrocatalyst for Water Oxidation with High Turnover Frequency

AbstractElectrochemical water splitting has been considered a promising approach for green and sustainable hydrogen as a future energy carrier. However, the lack of high performance and inexpensive electrocatalysts for kinetically sluggish oxygen evolution reaction (OER) hinder the practical application. Here, the noteworthy enhancement of electrodeposited cobalt boride (CoB) nanosheets from the combined effect of using gadolinium as a dopant and thin film of gold as prudent support is demonstrated. The free‐standing Gd‐CoB@Au exhibits remarkable electrochemical performance, high intrinsic activity, and lower reaction resistance, which are confirmed by lower onset potential, small charge transfer resistance, lower Tafel slope value, and high turnover frequency. Furthermore, the post‐OER characterization signpost, no observable change in the chemical structure or morphology of nanosheets during the long‐lasting oxidation process. Because of the inexpensive, facile, and scalable one‐step preparation processes, the catalyst is highly encouraging for large‐scale practical applications.