Oxygen Evolution Catalysts Research Articles

Correction to “Mixed Silver–Bismuth Oxides: A Robust Oxygen Evolution Catalyst Operating at Low pH and Elevated Temperatures”

Correction to “Mixed Silver–Bismuth Oxides: A Robust Oxygen Evolution Catalyst Operating at Low pH and Elevated Temperatures”

Ligand-Tuning Metallic Sites in Molecular Complexes for Efficient Water Oxidation.

Metal-organic hybrid catalysts with highly tunable single-sites are promising for oxygen-evolution reaction (OER), but molecular-scale understanding of underlying reaction mechanisms still remain elusive on these bulk materials. Herein, we report a direct construction of heterogenized molecular complexes stabilized on carbon substrates via coordinating Fe-Ni sites with four aromatic carboxylate ligands (FeNi-Lx). The ligands-tuning π-π stacking interaction between aromatic carboxylate ligands and carbon supports promote the oxidative charge accumulation on Fe-Ni sites via fast electron transferring, thus the optimized FeNi-Lx rendering a mass activity of 6680 A gFe/Ni-1 at 0.3 V overpotential. In situ characteristics and theoretical analysis demonstrate that the OH- nucleophilic attack on hypervalent iron sites induce the reconstruction of active Fe-O-Ni species, accompanying with fast valence increasing. Whereas, during OER, the unexpected valence reduction of Fe-O-Ni sites would be attributed to the oxygen-generating from OOH* intermediates. These findings would establish an essential understanding of the origin of active centers in molecular complexes catalysts for oxygen-evolution.

Sulfur-doped FeCoNiOx nanosheets improve their catalytic oxygen evolution reaction performance

Developing efficient and easily synthesized oxygen evolution catalysts is crucial for generating clean energy. A low-sulfur (S) doped FeCoNiOx flower-like nanosheet (denoted as S-FeCoNiOx) grown on nickel foam (NF) is presented. The porous structure of the NF, combined with the electronic structure modification from S doping, results in the nanosheets featuring numerous active sites and optimal adsorption strength. Electrochemical tests reveal that the catalyst demonstrates outstanding performance in alkaline electrolytes, characterized by a low overpotential (221 mV @ 10 mA cm−2) and a small Tafel slope of 29.19 mV dec−1, indicating favorable reaction kinetics. A two-electrode system comprising S-FeCoNiOx and Pt/C for water splitting, it exhibits low voltage (1.49 V @ 10 mA cm−2) and superior stability over 40 h. This research emphasizes significant potential applications and offers fresh guidance for creating additional high-efficiency S-doped electrocatalysts for oxygen evolution reactions (OER).

Biochar from residues of anaerobic digestion and its application as electrocatalyst in Zn–air batteries

BackgroundBiochar, the product obtained by pyrolysis of biomass, is a new eco-friendly material with excellent properties and many promising applications. Among them it can be used as cathode in Zn-air batteries with very satisfactory results MethodsThe residue was obtained by anaerobic digestion of a mixture of corn silage (10%), malt (10%), and cattle manure (80%), aiming to biogas production. It was first freeze–dried and then it was subjected to pyrolysis up to 800oC. Significant findingsThe biochar was physicochemically characterized. It has moderate specific surface area, sufficient sp2/sp3 ratio and metal and non–metal surface chemical species. The biochar demonstrated satisfactory electrocatalytic performance, both as oxygen reduction and oxygen evolution catalyst. When applied as electrocatalyst in Zn–air batteries it reached an open–circuit potential of 1.45 V, a short–circuit current density of 200 mA cm–2 and maximum power density of around 62 mW cm–2. Its energy density was 927 Wh kg–1, (at 20 mA), and 518 Wh kg–1 (at 100 mA). In a charge–discharge mode at 10 mA, the potential varied between 1.35 and 1.90 V. These data, show that the waste biomass can be used as inexpensive material for Zn–air batteries and offers a useful approach to combine waste management with energy storage.

Reactivity and Stability of Reduced Ir-Weight TiO2-Supported Oxygen Evolution Catalysts for Proton Exchange Membrane (PEM) Water Electrolyzer Anodes.

Reducing the iridium demand in Proton Exchange Membrane Water Electrolyzers (PEM WE) is a critical priority for the green hydrogen industry. This study reports the discovery of a TiO2-supported Ir@IrO(OH)x core-shell nanoparticle catalyst with reduced Ir content, which exhibits superior catalytic performance for the electrochemical oxygen evolution reaction (OER) compared to a commercial reference. The TiO2-supported Ir@IrO(OH)x core-shell nanoparticle configuration significantly enhances the OER Ir mass activity from 8 to approximately 150 A gIr-1 at 1.53 VRHE while reducing the iridium packing density from 1.6 to below 0.77 gIr cm-3. These advancements allow for viable anode layer thicknesses with lower Ir loading, reducing iridium utilization at 70% LHV from 0.42 to 0.075 gIr kW-1 compared to commercial IrO2/TiO2. The identification of the Ir@IrO(OH)x/TiO2 OER catalyst resulted from extensive HAADF-EDX microscopic analysis, operando XAS, and online ICP-MS analysis of 30-80 wt % Ir/TiO2 materials. These analyses established correlations among Ir weight loading, electrode electrical conductivity, electrochemical stability, and Ir mass-based OER activity. The activated Ir@IrO(OH)x/TiO2 catalyst-support system demonstrated an exceptionally stable morphology of supported core-shell particles, suggesting strong catalyst-support interactions (CSIs) between nanoparticles and crystalline oxide facets. Operando XAS analysis revealed the reversible evolution of significantly contracted Ir-O bond motifs with enhanced covalent character, conducive to the formation of catalytically active electrophilic OI- ligand species. These findings indicate that atomic Ir surface dissolution generates Ir lattice vacancies, facilitating the emergence of electrophilic OI- species under OER conditions, while CSIs promote the reversible contraction of Ir-O distances, reforming electrophilic OI- and enhancing both catalytic activity and stability.

Coordination engineering of B/N-doped graphene with phosphorus-transition metal diatomic catalysts for enhanced oxygen bifunctionality electrocatalysis

The design of highly active and cost-effective bifunctional catalysts for oxygen evolution (OER) and oxygen reduction (ORR) reactions is critical for advancing energy storage and conversion, yet significant challenges remain. Inspired by the efficient bifunctionality of graphene-based single-atom and diatomic catalysts in OER/ORR, we designed 42 structural of TMPX4@graphene (X = B, N; TM = V-Pt) and A-BN, and assessed their OER and ORR catalytic performance using density functional theory (DFT). The sum of overpotentials (ηsum = ηOER + ηORR) was identified as an effective descriptor for predicting the bifunctional catalytic properties of the TMPX4@graphene system. The transferred electron count and d-orbital occupation of Co atoms were identified as key sources of catalytic activity in OER and ORR, as determined through Bader charge analysis and partial density of states (PDOS). Finally, constant potential method (CPM) calculations showed that CoPB4@graphene exhibits excellent catalytic activity under alkaline conditions, with ORR and OER overpotentials of 0.86 V and 1.38 V, respectively. This study highlights the importance of rationally designing the local coordination environment by regulating boron content to enhance catalytic activity. It further provides insights into the rational design of stable and efficient catalysts by considering electrode potential and pH effects in electrocatalytic systems.

Tailoring Carrier Dynamics of BiVO4 Photoanode via Dual Incorporation of Au and Co(OH)x Cooperative Modification for Photoelectrochemical Water Splitting

AbstractPhotoelectrochemical solar to hydrogen production is a promising way to achieve carbon neutrality, but severe charge recombination in photoanodes limits the conversion efficiency. Herein, Au nanoparticles and Co(OH)x co‐sensitized bismuth vanadate (BiVO4) to construct AuCo(OH)x/BiVO4 photoanode for significantly enhancing the performance of photoelectrochemical water splitting. This process significantly improves the bulk charge carrier separation efficiency, the surface kinetics of water oxidation, and the electron density of BiVO4 photoanode through Au surface plasmon resonance (SPR) and Co(OH)x oxygen evolution catalysts effect. Additionally, the enhancement of the *O and the *OOH generation accelerate the oxygen evolution reaction kinetics. Consequently, the constructed AuCo(OH)x/BiVO4 photoanode demonstrates an excellent photocurrent of 6.2 mA cm−2 at 1.23 V versus reversible hydrogen electrode and a stable continuous output within 42 h. This work contributes to developing high‐efficiency and high‐stability photoanodes for solar H2 production through SPR effect and oxygen evolution catalysts.

Alkali Metal Iridates as Oxygen Evolution Catalysts Via Thermal Transformation of Amorphous Iridium (oxy)hydroxides.

AbstractEfficient water‐splitting is severely limited by the anodic oxygen evolution reaction (OER). Iridium oxides remain one of the only viable catalysts under acidic conditions due to their corrosion resistance. We have previously shown that heat‐treating high‐activity amorphous iridium oxyhydroxide in the presence of residual lithium carbonate leads to the formation of lithium‐layered iridium oxide, suppressing the formation of low‐activity crystalline rutile IrO2. We now report the synthesis of Na‐IrOx and K‐IrOx featuring similarly layered crystalline structures. Electrocatalytic tests confirm Li‐IrOx retains similar electrocatalytic activity to commercial amorphous IrO2 ⋅ 2H2O and with increasing size of the intercalated cation, the activity towards the OER decreases. However, the synthesised electrocatalysts that contain layers show greater stability than crystalline rutile IrO2 and amorphous IrO2 ⋅ 2H2O, suggesting these compounds could be viable alternatives for industrial PEM electrolysers where durability is a key performance measure.

N,S‐Doped Zeolite‐Templated Carbon Like Supported NixFeySz as an Efficient Bifunctional Catalyst for Rechargeable Zinc Air Batteries

AbstractA still unexplored class of heterostructured bifunctional catalysts for oxygen evolution (OER) and reduction (ORR) reactions is investigated: Ni−Fe sulfides deposited onto a N,S‐co‐doped zeolite‐templated carbon (ZTC) substrate achieved upon the impregnation of a ZTC with thiourea and Ni and Fe precursors (Ni/Fe atomic ratio of 1). By heat‐treating the impregnated ZTC substrate at 700 °C under N2 atmosphere the efficient bifunctional catalyst is generated. A difference of only 0.76 V is measured between the potential required to drive an OER current density of 10 mA cm−2 and the ORR half‐wave potential. Using electrochemical measurements and physico‐chemical characterizations, it is evidenced that OER activity results from the presence of a sulfide containing both Fe and Ni whereas the ORR activity originates from the N,S‐doped ZTC substrate. The selectivity of the ORR process is improved through the presence of sulfide phases. Compared to more conventional carbon substrate such as N,S‐co‐doped reduced graphene oxide, high specific surface area ZTC favors high ORR performances. The functional ZTC material was further successfully implemented as bifunctional air electrode in a coin‐type Zn‐air battery.

TiO2 modified NiFe-LDH as photoanode to achieve high efficiency photochemical water oxidation reaction

With the semiconductor modified oxygen evolution (OER) catalyst as the photoanode, the solar energy can be fully utilized, and the synergistic reaction makes the OER catalyst play a great role in the photochemical (PEC) water decomposition. Herein, we adopted a one-step hydrothermal method to introduce TiO2 to form heterojunction as photoanode in a well-known NiFe-LDH electrocatalyst, which contributes to carrier separation and transfer efficiency, thereby speeding up the water oxidation reaction kinetics. Benefiting from the TiO2/Ni4Fe6-LDH heterojunctions, the TiO2/ Ni4Fe6-LDH shows an overpotential of 371 mV @30 mA cm−2 and a Tafel slope of 131.36 mV/dec under illumination, which is better than Ni4Fe6-LDH and TiO2. The comparison experiment of oxygen evolution efficiency showed that the polarization current density of TiO2/Ni4Fe6-LDH reached 12 mA cm−2 under the illumination voltage of 1.72 V, which was twice the current density under the non-illumination condition. Surface electronic structure analysis shows that these excellent OER performance are largely due to the introduction of TiO2, which not only enables Ni4Fe6-LDH surface to have more oxygen vacancy, increase photoanode conductivity and accelerate reaction electron conduction, but also accelerates hole capture and enhances OER reaction kinetics. This synergistic effect between semiconductor and OER catalyst provides more ideas for realizing efficient and stable photoelectrochemical water oxidation.

Electrodeposited Manganese Dioxides and Their Composites as Electrocatalysts for Energy Conversion Reactions.

Enhancing the efficiencies of electrochemical reactions for converting renewable energy into clean chemical fuels as well as generating clean energy is critical to achieving carbon neutrality. However, this enhancement can be achieved using materials that are not constrained by resource limitations and those that can be converted into devices in a scalable manner, preferably for industrial applications. This review explores the applications of electrochemically deposited manganese dioxides (MnO2) and their composites as electrochemical catalysts for oxygen evolution (OER) and hydrogen evolution reactions for converting renewable energy into chemical fuels. It also explores their applications as electrochemical catalysts for oxygen reduction reaction (ORR) and bifunctional OER/ORR for the efficient operation of fuel cells and metal-air batteries, respectively. Manganese is the second most abundant transition metal in the Earth's crust, and electrodeposition represents a binder-free and scalable technique for fabricating devices (electrodes). To propose an improved catalyst design, the studies on the electrodeposition mechanism of MnO2 as well as the fabrication techniques for MnO2-based nanocomposites accumulated in the development of electrodes for supercapacitors are also included in this review.

Porphyrin-Confined Supported Ultrasmall Ir Clusters as Oxygen Evolution Catalysts for Water Electrolysis.

Metalloporphyrin ligands themselves can participate in the redox process, making them beneficial in promoting the multielectron catalytic process of the oxygen evolution reaction (OER). However, OER catalysts synthesized by traditional chemical strategies face challenges in water electrolysis. We synthesized high-performance and stable alkaline and acidic OER electrocatalysts loaded with ultrasmall iridium clusters by taking advantage of the attraction and confinement of Ir atoms by the Ir-N bonds formed by the porphyrin cavity. The N in the porphyrin cavity forms an Ir-N bond with Ir so that Ir carries a negative charge and attracts Ir atoms to form ultrasmall Ir clusters above the cavity to adjust the electronic structure of the Ir clusters. The resulting catalyst Tpyp-Ir(IrOX) exhibits a small overpotential (242 and 259 mV) at a current density of 10 mA cm-2 in alkaline and acidic conditions and demonstrates good long-term operational stability. In addition, Tpyp-Ir(IrOX) exhibits a higher transition frequency (TOF) (1.69 O2 s-1 at 300 mV) in 1 M KOH, which is 7 times that of Ir/C.

In Situ Unraveling Surface Reconstruction of Ni‐CoP Nanowire for Excellent Alkaline Water Electrolysis

The surface reconstruction behavior of transition metal phosphides precursors is considered as an important method to prepare efficient oxygen evolution catalysts, but there are still significant challenges in guiding catalyst design at the atomic scale. Here, the CoP nanowire with excellent water splitting performance and stability is used as a catalytic model to study the reconstruction process. Obvious double redox signals and valence evolution behavior of the Co site are observed, corresponding to Co2+/Co3+ and Co3+/Co4+ caused by auto‐oxidation process. Importantly, the in situ Raman spectrum exhibits the vibration signal of Co–OH in the non‐Faradaic potential interval for oxygen evolution reaction, which is considered the initial step in reconstruction process. Density functional theory and ab initio molecular dynamics are used to elucidate this process at the atomic scale: First, OH− exhibits a lower adsorption energy barrier and proton desorption energy barrier at the configuration surface, which proposes the formation of a single oxygen (–O) group. Under a higher –O group coverage, the Co–P bond is destroyed along with the POx groups. Subsequently, lower P vacancy formation energy confirm that the Ni‐CoP configuration can fast transform into a highly active phase. Based on the optimized reconstruction behavior and rate‐limiting barrier, the Ni‐CoP nanowire exhibit an excellent overpotential of 1.59 V at 10 mA cm−2 for overall water splitting, which demonstrates low degradation (2.62%) during the 100 mA cm−2 for 100 h. This work provide systematic insights into the atomic‐level reconstruction mechanism of transition metal phosphides, which benefit further design of water splitting catalysts.

Porous and B‐site Substituted Y2[Mn0.2Ru0.8]2O7 Pyrochlore for Boosting Acidic Water Oxidation Activity and Stability

Boosting the reaction stability without sacrificing the activity and cost is extremely important but full of challenging for the RuO2‐based oxygen evolution catalysts. Herein, porous and B‐site substituted Y2[Mn0.2Ru0.8]2O7 (p‐Y2[Mn0.2Ru0.8]2O7) pyrochlore toward oxygen evolution reaction is innovatively synthesized. The formed meso/macro‐porous structure can increase the specific surface area and corresponding active sites, meanwhile, Mn‐substitution can modulate the electronic structure, stabilize the morphology, and reduce the dosage of Ru species. Excitingly, the p‐Y2[Mn0.2Ru0.8]2O7 performs 50 h stable operation, significantly outperforming the commercial RuO2(CM) counterpart with less than 2 h life. Furthermore, the required overpotential to achieve 10 mA cm‐2 is only 266 mV, accompanied with favorable reaction kinetics and catalyst utilization.

Nanoparticles of CoFeZn Supported on N-Doped Carbon as Bifunctional Catalysts for Oxygen Reduction and Oxygen Evolution

Nanoparticles of CoFeZn Supported on N-Doped Carbon as Bifunctional Catalysts for Oxygen Reduction and Oxygen Evolution

{Co4O4} Cubanes in a conducting polymer matrix as bio-inspired molecular oxygen evolution catalysts

Exploration of efficient molecular water oxidation catalysts for long-term application remains a key challenge for the conversion of renewable energy sources into fuels. Cuboidal {Co4O4} complexes keep attracting interest as molecular water oxidation catalysts as they combine features of both heterogeneous and homogeneous catalysis with bio-inspired motifs. However, the application of many cluster-based catalysts for the oxygen evolution reaction still requires new stabilization strategies. Drawing inspiration from the stabilizing effects of natural polymers, we introduce a conductive polymer-hybrid approach to covalently immobilize {Co4O4} cubane oxo clusters as oxygen evolution catalysts. Polypyrrole is applied as an efficient p-type conducting polymer that promotes hole transfer during the oxygen evolution reaction, resulting in higher turnover frequency compared to the pristine {Co4O4} oxo cluster and heterogeneous Co-oxide benchmarks. The asymmetric coordination of {Co4O4} not only mitigates catalyst decomposition pathways, but also increases the catalytic efficiency by exposing a directed cofacial dihydroxide motif during catalysis.

Probing the structural evolution of cobalt hydroxide in electrochemical water splitting.

Transition-metal hydroxides are a category of earth-abundant and stable electrocatalysts for energy storage and conversion devices involving sluggish oxygen evolution reaction (OER). Understanding dynamic evolution at the solid/liquid interface of transition-metal hydroxides is crucial for the rational design of high-performance OER electrocatalysts. This study implemented in situ electrochemical atomic force microscopy (EC-AFM) to directly image the dynamic structural evolution of α-Co(OH)2 platelets during the electrochemical OER. Reconstruction of α-Co(OH)2, accompanied by ion insertion from the electrolyte, results in a volume expansion, which can be well confirmed from the X-ray diffraction patterns. Our findings are important for the fundamental understanding of transition-metal hydroxide oxygen-evolution catalysts, illustrating the dynamic nature of Co-based nanostructures under electrochemical conditions.

Tethering Cobalt Ions to BiVO4 Surface via Robust Organic Bifunctional Linker for Efficient Photoelectrochemical Water Splitting.

In the quest for efficient and stable oxygen evolution catalysts (OECs) for photoelectrochemical water splitting, the surface modification of BiVO4 is a crucial step. In this study, a novel and robust OEC, based on 3-(bis(pyridin-2-ylmethyl) amino) propanoic acid bifunctional linker known as dipicolyl alanine acid (DPAA) and cobalt ions, is prepared and fully characterized. The DPAA is anchored to the surface of BiVO4 and utilized to tether cobalt ions. The Co-DPAA/BiVO4 photoanode exhibits remarkable stability and efficiency toward photoelectrochemical water oxidation. Specifically, it showed anodic photocurrent increase of 7.1, 5.0, 3.0, and 1.3-fold at 1.23VRHE as compared to pristine BiVO4, DPAA/BiVO4, Co-BiVO4, and Co-Pi/BiVO4 photoanodes, respectively. The photoelectrochemical and IMPS studies revealed that the Co-DPAA/BiVO4 photoanode exhibits a longer transient decay time for surface-trapped holes, higher charge transfer kinetics, and charge separation efficiency compared to Co-Pi/BiVO4 and pristine BiVO4 photoelectrodes. This indicates that the Co-DPAA effectively reduces surface recombination and facilitates charge transfer. Moreover, at 1.23VRHE, the Co-DPAA/BiVO4 photoanode achieved a faradic efficiency of 92% for oxygen evolution reaction and could retain a turnover frequency of 3.65s-1. The- exhibited effeciency is higher than most of the efficient molecular oxygen evolution catalyst based on Ru.

Preparation of nickel-manganese based bimetallic hydroxide nanosheets for enhanced electrocatalytic oxygen evolution reaction

Abstract This paper uses a common one-step hydrothermal method to prepare NiMn-LDH/NF (Layered Double Hydroxide, LDH) oxygen evolution catalyst with outstanding performance. The NiMn-LDH grows into a nanosheet array structure on nickel foam (NF) and it has a big surface area and exceptional ion transport function that could accelerate the diffusion rate of electrocatalytic products. It attempted to modulate the molar proportion of Ni and Mn to explore the oxygen evolution reaction (OER) performance of the NiMn-LDH/NF catalysts. It was found that when Ni:Mn=4:1 (molar ratio, hereinafter), the nanosheets grew more densely and had better OER performance and stability. The electrochemical test results show that the Ni4Mn-LDH/NF catalyst exhibits an overvoltage of 341 mV at a current density of 10 mA cm−2, and the Tafel slope is only 98.99 mV dec−1.

Iron-promoted rapid self-reconstruction of nickel-based catalysts for efficient oxygen evolution

High-performance oxygen evolution reaction (OER) catalyst is critical for improving the water splitting efficiency. In this work, an efficient self-supported OER catalyst was prepared by electrodeposition of nickel–iron layered double hydroxide nanosheets on titanium mesh substrate (NiFe-LDH/Ti-mesh). This self-supporting design exposes abundant active sites. At 100 mA cm−2, the NiFe-LDH/Ti-mesh shows a low overpotential of 310 mV in 1.0 M KOH. When assembled into an anion exchange membrane water electrolyzer, it can run stably over 200 h. In-situ Raman reveals that the NiFe-LDH/Ti-mesh surface was reconstructed into NiFeOOH active species. In-situ infrared shows that the introduction of Fe promotes the evolution of oxygen intermediates. Theoretical calculations reveal a weakened binding strength of *OH and accelerated formation of *O in OER by the introduction of Fe. This study provides a facile approach for developing self-supported high-performance OER electrocatalyst, and advances the understanding on the origin of NiFe-based catalysts as well.