Water Oxidation Activity Research Articles

Resorcin[4]arene-based [Co12] supermolecule cage functionalized by bio-inspired [Co4O4] cubanes for visible light-driven water oxidation

The design and assembly of efficient water oxidation catalysts (WOCs) is quite desirable, but still remains a synthetic challenge. Herein, we researched remarkable calix[4]resorcinarene-based [Co12] coordination cages with bio-inspired [Co4O4] cubanes. Markedly, the coordination cage features efficient visible light-driven water oxidation activity, and represents a unique example of calix[4]resorcinarene-based [Co4O4] cubane WOC. It afforded an optimal turnover number (TON) of 119, corresponding to a quite high turnover frequency (TOF) of 793 h−1 and an oxygen yield of 17.0%. A possible mechanism for the water oxidation reaction was also proposed by means of density functional theory (DFT) calculations.

A Binuclear Cobalt Complex in the Electrochemical Water Oxidation Reaction

AbstractThe water splitting reaction represents an appealing approach to store solar energy. The 4e−/4H+ oxidation of water generating O2 is considered as the bottleneck in this reaction and usually requires a rather large over potential. We report on the synthesis and application of a binuclear cobalt(III) complex, 1, with two μ‐OH ligands and tripodal triazole ligands, L, in the electrochemical water oxidation reaction (WOR; L=tris((1‐phenyl‐1H‐1,2,3‐triazol‐4‐yl)methyl)amine). The cobalt(III) centres in the complex exhibit an octahedral coordination geometry and the complex is stable in water. Electrochemical studies revealed that solutions of 1NO3 catalyse the WOR in phosphate or borate buffer. However, further analysis showed, that 1NO3 is a precursor and decomposes under the applied potential. A smooth deposit is formed on the electrode surface, which is a highly active water oxidation catalysis. The deposit consists of mainly cobalt oxide/hydroxide, which accounts for the catalytic activity, and small amounts of 1NO3.

Hierarchical palladium catalyst for highly active and stable water oxidation in acidic media.

Acidic water electrolysis is of great importance for boosting the development of renewable energy. However, it severely suffers from the trade-off between high activity and long lifespan for oxygen evolution catalysts on the anode side. This is because the sluggish kinetics of oxygen evolution reaction necessitates the application of a high overpotential to achieve considerable current, which inevitably drives the catalysts far away from their thermodynamicequilibrium states. Here we demonstrate a new oxygen evolution model catalyst-hierarchical palladium (Pd) whose performance even surpasses the benchmark Ir- and Ru-based materials. The Pd catalyst displays an ultralow overpotential (196mV), excellent durability and mitigated degradation (66μVh-1) at 10mAcm-2 in 1M HClO4. Tensile strain on Pd (111) facets weakens the binding of oxygen species on electrochemical etching-derived hierarchical Pd and thereby leads to two orders of magnitudes of enhancement of mass activity in comparison to the parent Pd bulk materials. Furthermore, the Pd catalyst displays the bifunctional catalytic properties for both oxygen and hydrogen evolutions and can deliver a current density of 2Acm-2 at a low cell voltage of 1.771V when fabricated into polymer electrolyte membrane electrolyser.

In Situ Imaging of Catalytic Reactions on Tungsten Oxide Nanowires Connects Surface-Ligand Redox Chemistry with Photocatalytic Activity.

Semiconductor nanocrystals are promising candidates for generating chemical feedstocks through photocatalysis. Understanding the role of ligands used to prepare colloidal nanocrystals in catalysis is challenging due to the complexity and heterogeneity of nanocrystal surfaces. We use in situ single-molecule fluorescence imaging to map the spatial distribution of active regions along individual tungsten oxide nanowires before and after functionalizing them with ascorbic acid. Rather than blocking active sites, we observed a significant enhancement in activity for photocatalytic water oxidation after treatment with ascorbic acid. While the initial nanowires contain inactive regions dispersed along their length, the functionalized nanowires show high uniformity in their photocatalytic activity. Spatial colocalization of the active regions with their surface chemical properties shows that oxidation of ascorbic acid during photocatalysis generates new oxygen vacancies along the nanowire surface. We demonstrate that controlling surface-ligand redox chemistry during photocatalysis can enhance the active site concentration on nanocrystal catalysts.

Single‐Metal Atoms and Ultra‐Small Clusters Manipulating Charge Carrier Migration in Polymeric Perylene Diimide for Efficient Photocatalytic Oxygen Production

AbstractLimited by the retarded charge carrier migration and the sluggish four‐electron reaction kinetics, it is still a great challenge for polymeric semiconductors to achieve efficient photocatalytic water oxidation. Herein, single Co atoms and ultra‐small CoOx clusters are simultaneously introduced into polymeric perylene diimide (PDI) through a facile impregnation‐calcination two‐step method. The obtained Co‐PDI exhibits excellent photocatalytic water oxidation activity under visible‐light irradiation, with an oxygen evolution rate reaching as high as 5.53 mmol h–1 g–1 (λ > 420 nm). The apparent quantum yield for oxygen evolution is determined to be 8.17% at 450 nm, and remains 0.77% at even longer visible light wavelength of 700 nm without redundant co‐catalysts, indicating that Co‐PDI may serve as an excellent oxygen evolution photocatalyst for water splitting. Theoretical calculations and experimental results demonstrate that single Co atoms act as the electron mediators connecting adjacent PDI layers to build directional channels for rapid charge transfer, while ultra‐small CoOx clusters as hole collectors and reaction sites to accelerate oxygen evolution reaction kinetics. The study presents a facile and reliable strategy to effectively activate polymeric semiconductors for efficient photocatalysis by rationally modulating atomic structures and active sites for promoted charge carrier transfer and surface reaction kinetics.

Direct and indirect role of Fe doping in NiOOH monolayer for water oxidation catalysis.

Water oxidation activity of pristine NiOOH is greatly enhanced by doping it with Fe. However, the precise role of Fe is still being debated. Using a first-principles DFT+U approach, we investigate the direct and indirect roles of Fe in enhancing the oxygen evolution reaction (OER) activity of NiOOH monolayers. Considering two Mars-Van-Krevelen mechanisms of OER based on the source of O-O bond formation, we show that a mechanism involving the coupling of lattice oxygen is generally more favorable than water nucleophilic attack on lattice oxygen. On doping with Fe, the overpotential of NiOOH is reduced by 0.33 V, in excellent agreement with experimental findings. Introducing Fe at active sites results in different potential determining steps (PDS) in the two mechanisms. The Ni sites in pristine and Fe-doped NiOOH have the same PDS regardless of the mechanism. The Fe sites not only have the lowest overpotential but also decrease the overpotential for Ni sites.

Protocol for Screening Water Oxidation or Reduction Electrocatalyst Activity in a Three-Electrode Cell for Alkaline Exchange Membrane Electrolysis

Accurate and reproducible screening of the electrocatalytic activity of novel materials for Oxygen Evolution Reaction (OER) and Hydrogen Evolution Reaction (HER) requires establishing an easily adoptable harmonized testing protocol. Herein, we describe a robust, instrumentation-independent testing technique utilizing a three-electrode cell with a fully immersed working electrode. Compared to rotating disk electrode (RDE) techniques, this protocol produces current densities close to those obtained in real electrolyzers and eliminates the usage of the expensive RDE apparatus.

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.

NiPd nano-alloy film as a promising low overpotential electrocatalyst for high activity water oxidation reaction

Electrolytic water splitting is promising strategy for the production of Green Hydrogen (H2) but the sluggish kinetics during the oxygen evolution reaction (OER) is still a challenge. Herein, nickel palladium (NiPd) electrocatalyst has been presented for energy-efficient water oxidation. The catalyst films have been deposited on nickel foam (NF) substrate using a single-step aerosol-assisted chemical vapor deposition technique. The thickness of the deposited film is controlled by varying the deposition time from 60 to 180 min. The morphology and structure of the NiPd catalysts were characterized and directly employed for OER investigation in 1.0 M KOH. The catalyst made for 120 min initiates OER at an extremely low onset potential of 1.4 V vs. RHE (η = 170 mV), requires an overpotential of just 180 mV to approach the benchmark current density of 10 mA cm-2 and peak current density of > 1300 mA cm-2 is achieved at an overpotential of mere 370 mV. Moreover, the catalyst demonstrates excellent durability during prolonged water electrolysis experiments and imposing kinetics for OER. The catalytic performance of NiPd electrode is many folds better than the star catalyst (IrO2) investigated under similar circumstances. The superior OER activity of NiPd alloy at such low overpotentials is accredited to the mutual relevance of high electroactive sites at intermetallic catalyst surface, the favorable synergy created between intrinsically active 3d-transition metal Ni and noble metal, Pd grown over porous and conductive NF surface that cumulatively favors electronic communications and adsorption/desorption process at nano surfaces of the catalytic film.

Ammonium cobalt phosphate with asymmetric coordination sites for enhanced electrocatalytic water oxidation

Cobalt-based materials have been considered as promising candidates to electrocatalyze water oxidation. However, the structure-performance correlation remains largely elusive, due to the complex material structures and diverse performance-influencing factors in those Co-based catalysts. In this work, we designed two cobalt phosphates with distinct Co symmetry to explore the effect of coordination symmetry on electrocatalytic water oxidation. The two analogues have similar morphology, Co valence and 6-coordinated Co octahedron, but with different coordination symmetry. In contrast to symmetric Co 3 (PO 4 ) 2 ·8H 2 O, asymmetric NH 4 CoPO 4 ·H 2 O exhibited enhanced electrocatalytic water oxidation activity in a neutral aqueous solution. It is proven that, by experimental and theoretical studies, the asymmetric Co coordination sites can facilitate the surface reconstruction under anodic polarization to boost the electrocatalysis. Based on this contrastive platform with distinct symmetry differences, the preferred configuration in cobalt-oxygen octahedrons for water oxidation has been straightforwardly assigned. Two cobalt phosphates with distinct Co symmetry were obtained to explore the effect of coordination structure on the electrocatalytic oxygen evolution reaction. Asymmetric Co geometry can accelerate surface reconstruction to enhance OER activity.

Intramolecular hydroxyl nucleophilic attack pathway by a polymeric water oxidation catalyst with single cobalt sites

Exploration of efficient water oxidation catalysts (WOCs) is the primary challenge in conversion of renewable energy into fuels. Here we report a molecularly well-defined heterogeneous WOC with Aza-fused, π-conjugated, microporous polymer (Aza-CMP) coordinated single cobalt sites (Aza-CMP-Co). The single cobalt sites in Aza-CMP-Co exhibited superior activity under alkaline and near-neutral conditions. Moreover, the molecular nature of the isolated catalytic sites makes Aza-CMP-Co a reliable model for studying the heterogeneous water oxidation mechanism. By a combination of experimental and theoretical results, a pH-dependent nucleophilic attack pathway for O-O bond formation was proposed. Under alkaline conditions, the intramolecular hydroxyl nucleophilic attack (IHNA) process with which the adjacent -OH group nucleophilically attacks Co4+=O was identified as the rate-determining step. This process leads to lower activation energy and accelerated kinetics than those of the intermolecular water nucleophilic attack (WNA) pathway. This study provides significant insights into the crucial function of electrolyte pH in water oxidation catalysis and enhancement of water oxidation activity by regulation of the IHNA pathway.

Effect of SnO2 incorporation on the photoelectrochemical properties of α-Fe2O3–SnO2 nanocomposites prepared by hydrothermal method

In this work, we report the effect of tin oxide (SnO2) incorporation on the photoelectrochemical (PEC) water oxidation activity of hematite-tin oxide (α-Fe2O3–SnO2) nanocomposites prepared by hydrothermal method. During synthesis of α-Fe2O3–SnO2, the proportions of SnO2 in the composites were varied from 5 wt% to 50 wt%. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), and UV–visible spectroscopy. XRD results showed diffraction signals from both α-Fe2O3 and SnO2 in the composite structure. The surface morphology and size features of α-Fe2O3 altered drastically with addition of SnO2. TEM analysis revealed that small-sized SnO2 were coated on the surface of α-Fe2O3, forming heterogeneous grain boundary interfaces. The α-Fe2O3–SnO2 nanocomposites were tested as photoanode for PEC water oxidation under standard 1 Sun illumination condition in 1 M NaOH. Among the various compositions, α-Fe2O3–SnO2 (50 wt%) displayed promising water splitting photocurrent density of 0.32 mAcm−2 at 1.4 V versus RHE, which is a 5-fold higher as compared to the photocurrent density of pure α-Fe2O3 (0.06 mAcm−2). This enhancement in photocurrent density can be attributed to the reduced electron-hole recombination as a result of better charge separation at local heterojunction between α-Fe2O3 and SnO2 in the composite.

ZIF-8 derived NiFe hydroxide on nickel foam for robust water oxidation

Developing active water oxidation electrocatalysts with earth-abundant components is significant for bulk hydrogen supply via water electrolysis. Herein, nickel iron hydroxide nanosheets assembled particles on nickel foam are prepared through ion-assisted etching method with ZIF-8 as precursor. The sample achieves remarkable catalysis efficiency toward oxygen evolution reaction with ultralow overpotential of 259 mV at high current density of 100 mA cm−2. The superior catalysis efficiency is assigned to Ni/Fe synergisms of optimized intrinsic activity, abundant surface oxygen vacancies, enhanced charge flow, and increased active sites, as well as nanosheet structure benefits of approachable catalytic sites and shortened charge transform pathways.

In situ growth Fe and V co-doped Ni3S2 for efficient oxygen evolution reaction at large current densities

Industrial electrolysis of water is one of the effective strategies for green hydrogen production in the future. Nevertheless, the large-scale applications of water electrolysis are still intractable issues hindered by the high overpotentials and inferior reaction kinetics on the anode. Herein, a facile one-step hydrothermal method was applied to in situ growth the Fe and V co-doped Ni 3 S 2 electrocatalyst on nickel foam substrate (Fe, V–Ni 3 S 2 /NF). In 1 M KOH electrolyte, the as-prepared Fe, V–Ni 3 S 2 /NF electrode exhibited an improved water oxidation activity with ultralow overpotentials of 253 and 370 mV to realize large current densities of 100 and 1000 mA/cm 2 , respectively. More importantly, the Fe, V–Ni 3 S 2 /NF electrode existed an activation process during 100 h chronopotentiometry testing period. Detailed characterizations revealed that elements of V and S in the electrocatalyst were oxidized and dissolved into the electrolyte, making the electrocatalyst undergo surface reconstruction and resulting in a faster kinetic reaction rate, thus leading to enhanced oxygen evolution reaction activities. Collectively, the resultant Fe, V–Ni 3 S 2 /NF in this work provides new cogitation towards design and synthesis of low-cost electrocatalyst with large current densities for water oxidation. • Fe,V–Ni 3 S 2 /NF electrode was hydrothermal prepared and used as OER electrocatalyst. • Ni 3 S 2 is converted to NiOOH during the electrochemical oxidation process. • The electrode can attain 100 and 1000 mA/cm 2 with overpotentials of 253 and 370 mV. • The enhanced OER activity owned to the surface reconstruction by V, S etching.

Dual functions of heterometallic FeCo oxyhydroxides in borate-treated BiVO4 photoanodes toward boosted activity and photostability in photoelectrochemical water oxidation

• B-BiVO 4 /Fe x Co 1-x OOH photoanode is fabricated by a simple solution method. • B-BiVO 4 /Fe x Co 1-x OOH is used as photoanode for water oxidation. • B-BiVO 4 /Fe x Co 1-x OOH shows a high photocurrent density of 5.21 mA cm −2 . • B-BiVO 4 /Fe x Co 1-x OOH exhibits a sustainable photostability of 10 h. • The Fe and Co species in Fe x Co 1-x OOH as hole mediators help to the OER. Decorating a semiconductor photoanode with an oxygen evolution cocatalyst is an effective strategy for promoting the utilization efficiency of surface charge for oxygen evolution. Herein, a new hybrid catalyst i.e. heterometallic FeCo oxyhydroxides (Fe x Co 1-x OOH) decorated on borate-treated BiVO 4 photoanode (B-BiVO 4 ), is prepared via a simple immersion procedure. The obtained photoanode serves as a water oxidation catalyst capable of accelerating the transportation of the photo-generated holes from the B-BiVO 4 photoanode to the surface active sites of Fe x Co 1-x OOH nanoparticles, while the Fe and Co species in the Fe x Co 1-x OOH serve as hole shuttling mediators beneficial to the oxygen evolution reaction. Particuarly, introducing Co into BiVO 4 lattice boosts the photostability by inhibiting the photooxidation-coupled dissolution of V 5+ from BiVO 4 lattice. The B-BiVO 4 /Fe x Co 1-x OOH photoanode displays an extremely excellent photocurrent density of 5.21 mA cm −2 at 1.23 V RHE , with a 60% increase over the B-BiVO 4 (3.26 mA cm −2 ). Particularly, the photocurrent density of the B-BiVO 4 /Fe x Co 1-x OOH photoanode during consecutive illumination for 10 h shows a negligible decay, corresponding to more 95% of the initial photocurrent density. The improved PEC performance is attributed to the accelerated charge separation/transfer and surface water oxidation reaction occurring in the photoanode matrix and/or at the photoanode/electrolyte interface due to the synergistic effect of bifunctional Fe x Co 1-x OOH and B-BiVO 4 .

Effect of surface-deposited Ti3C2Tx MXene on the photoelectrochemical water-oxidation performance of iron-doped titania nanorod array

As a promising photoanode material, TiO2 confronts two challenges, weak visible light absorption and low catalytic activity for water oxidation, which limit its photoelectrochemical performance toward water oxidation. Doping and co-catalyst deposition provide effective ways to extending the light-absorption spectral range and accelerating the water-oxidation kinetics, respectively. Herein, an efficient TiO2-based photoelectrode for water oxidation is prepared by Fe doping and electrophoretic Ti3C2Tx deposition. The Fe doping effectively extends the light absorption of TiO2 toward visible region. Owing to the excellent water oxidation activity of Ti3C2Tx, its deposition greatly accelerates the water-oxidation kinetics, which in turn enhances the photocarrier separation and injection efficiencies. The well-designed Fe-TiO2/Ti3C2Tx exhibits a photoelectrochemical current density of 1.23 mA cm−2 at 1.23 V vs. RHE, which is much higher than those of Fe-TiO2. The maximum IPCE value is enhanced from 64.7% of Fe-TiO2 to 92.8% of Fe-TiO2/Ti3C2Tx at 380 nm. Our findings provide an effective way to fabricate efficient photoanode for water oxidation and are helpful to understanding the photoelectrochemical performance of hybrid nanostructures.

Light-Driven Water Oxidation with Ligand-Engineered Prussian Blue Analogues.

The elucidation of the ideal coordination environment of a catalytic site has been at the heart of catalytic applications. Herein, we show that the water oxidation activities of catalytic cobalt sites in a Prussian blue (PB) structure could be tuned systematically by decorating its coordination sphere with a combination of cyanide and bidentate pyridyl groups. K0.1[Co(bpy)]2.9[Fe(CN)6]2 ([Cobpy–Fe]), K0.2[Co(phen)]2.8[Fe(CN)6]2 ([Cophen–Fe]), {[Co(bpy)2]3[Fe(CN)6]2}[Fe(CN)6]1/3 ([Cobpy2–Fe]), and {[Co(phen)2]3[Fe(CN)6]2}[Fe(CN)6]1/3 Cl0.11 ([Cophen2–Fe]) were prepared by introducing bidentate pyridyl groups (phen: 1,10-phenanthroline, bpy: 2,2′-bipyridine) to the common synthetic protocol of Co–Fe Prussian blue analogues. Characterization studies indicate that [Cobpy2–Fe] and [Cophen2–Fe] adopt a pentanuclear molecular structure, while [Cobpy–Fe] and [Cophen–Fe] could be described as cyanide-based coordination polymers with lower-dimensionality and less crystalline nature compared to the regular Co–Fe Prussian blue analogue (PBA), K0.1Co2.9[Fe(CN)6]2 ([Co–Fe]). Photocatalytic studies reveal that the activities of [Cobpy–Fe] and [Cophen–Fe] are significantly enhanced compared to those of [Co–Fe], while molecular [Cobpy2–Fe] and [Cophen2–Fe] are inactive toward water oxidation. [Cobpy–Fe] and [Cophen–Fe] exhibit upper-bound turnover frequencies (TOFs) of 1.3 and 0.7 s–1, respectively, which are ∼50 times higher than that of [Co–Fe] (1.8 × 10–2 s–1). The complete inactivity of [Cobpy2–Fe] and [Cophen2–Fe] confirms the critical role of aqua coordination to the catalytic cobalt sites for oxygen evolution reaction (OER). Computational studies show that bidentate pyridyl groups enhance the susceptibility of the rate-determining Co(IV)-oxo species to the nucleophilic water attack during the critical O–O bond formation. This study opens a new route toward increasing the intrinsic water oxidation activity of the catalytic sites in PB coordination polymers.

Metal-free pristine halloysite nanotubes: Electrochemically active and stable oxygen evolution reaction

Halloysite nanotubes (HNT) are naturally occurring one-dimensional porous clay minerals and have a unique chemical structure of kaolinite. The presence of hydroxyl functional groups on the surface of HNT is more suitable for O2 evolution reaction (OER). The HNT based electrocatalyst coated on Ni foam substrate shows excellent water oxidation activity with an overpotential of 287 mV to reach a current density of 10 mA cm−2 and have excellent stability in alkaline electrolyte solution over 32 h without any decay. The adsorption of OH− species occurs on the surface of HNT from the alkaline electrolyte via one-electron transfer, the metal cation underwent repeated oxidation and reduction reactions during the OER. This result outperforms many of the transition metal-based electrocatalysts. This work provides a new platform to use naturally abundant clay minerals as an anode material in fuel cell applications.

Trimetallic oxide-hydroxide porous nanosheets for efficient water oxidation

Multimetallic systems have been the subject of intensive research for their promising electrocatalytic activities. Herein, we describe the synthesis ofbimetallic and trimetallic (Ni, Co and Mn) oxide-hydroxide nanosheets and evaluate their catalytic activity toward water oxidation. The catalytic activity of porous trimetallic nanosheets was found to be higher than that of bimetallic hybrids. In addition, the trimetallic systems also possess excellent stability. A current density of 10 mA/cm2is achieved for an overpotential of 287 mV and ∼0% loss even after 8000 cycles. The enhanced performance by the trimetallic system can be attributed to the large electrochemical surface area and better intrinsic activity. The electronic modulation in this three-element system is evident from the X-Ray Photoelectron Spectroscopy (XPS) study and Mott-Schottky analysis. The position of flat-band potential plays a significant role in determining the charge transfer kinetics, thereby affecting the water oxidation activity in the semiconductor-electrolyte system. Trimetallic system also offers better oxygen evolution reaction kinetics as evident from the least activation energy compared to the bimetallic counterparts. The local structure system is realized with the X-rayabsorption spectroscopy(XAS) analysis. The present study highlights the importance of intrinsic activity in designing efficient non-noble metal electrocatalysts.

Electrokinetic analysis of water oxidation on alumina supported silver oxide nanopowders

This research intended to synthesize γ-Al2O3 supported Ag2O nanopowders (xAg2O/Al2O3, x = 1–5%) in five different compositions for alkaline water electro-oxidation reaction (WEOR). Electrochemical investigations including cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) were performed to examine the electrocatalytic potential of the synthesized nanomaterials. Performed electrochemical (EC) studies designated Ag2O/γ-Al2O3 as a robust electrocatalyst for WEOR. Standard benchmarking protocols were employed to appraise the activity of synthesized catalysts. All catalyst materials exhibited comparable activities by achieving an overpotential of nearly 300 mV at 10 mAcm−2. Results demonstrated that an increase in Ag2O contents reduced the charge transfer resistance (Rct) and augmented EC surface area, ensuing in reduced onset potential (0.98 V vs. Ag/AgCl) and a small Tafel slope (TS) of 0.85 V dec−1. EC analysis revealed high WEOR performance at all Ag2O/γ-Al2O3 modified electrodes, however maximum diffusion coefficient (Do; 6.5 × 10−6 cm2s−1), mass transport coefficient (mt; 7.63 × 10−4 cm s−1), rate constant (ko; 2.4 × 10−4 cm s−1) and low Rct (101 Ω) was observed for 5% Ag2O/γ-Al2O3. This study scheme has proved to be cost-effective synthesis of Ag2O/γ-Al2O3 catalysts providing better fallouts for activity and stability for water oxidation at ambient conditions.