High-performance Oxygen Evolution Reaction Catalysts Research Articles

Modifying d–p orbital hybridization of Ni/Fe[sbnd]O species by high-valence ruthenium doping to enhance oxygen evolution performance

The electron distribution of catalysts can be modulated by high-valence metal doping, thus enhancing the intrinsic activity. Herein, we adopt Ru modification to adjust the d–p orbital hybridization of Ni-Fe oxyhydroxides, significantly increasing the oxygen evolution reaction (OER) activity. The amorphous NiFe0.5Ru0.1OxHy catalyst synthesized by sol–gel method exhibits excellent OER activity, far superior to commercial RuO2. In situ Raman and XPS results confirm that the NiOOH/FeOOH active species gradually form with increasing applied voltage. Density functional theory (DFT) calculations reveal that high-valence Ru dopants can effectively regulate the hybridization of d–p orbital of Ni/FeO, significantly increase the electron density around Fermi level, promote charge transfer, make them have more anti-bonding orbitals, enhance the binding ability of active sites to intermediates, reduce the reaction energy barrier of the rate-determining step (H2O → *OH), and thus improve the OER activity. In addition, NiFeRuOxHy as a cathode catalyst in a rechargeable zinc-air battery shows an outstanding cycle life of 600 h. This study provides a promising hybrid orbital method for designing high-performance OER catalysts for water splitting and rechargeable zinc-air batteries.

Synergistic effects of feni bimetal-doped biochar on oxygen evolution reaction kinetics: A one-step, low-temperature pyrolysis approach

As the hydrogen energy sector progresses, water electrolysis technology played a crucial role in producing green hydrogen. A major challenge in this endeavor lied in the oxygen evolution reaction (OER), where the overpotential has consistently been high leading to an increase in the energy demand. This study developed a one-step pyrolysis technique to transform metal-supported biomass into FeNi/NC catalysts having enhanced crystallinity and defect sites. This process without activation step using strong acids or bases reduced the operational procedures and the treatment of intermediate products, which reduced the technical difficulty. As the pyrolysis temperature increases, the metal ions in the biochar gradually formed stable metal oxides, which catalyze the alkaline OER and markedly boosted catalytic efficiency. Crucially, the abundance of lattice oxygen and oxygen vacancies in the catalyst played a key role in enhancing the OER kinetics. Notably, the catalyst pyrolyzed at 750 °C demonstrated good performance, with an overpotential of 270 mV at a concentration of 10 mA cm−2 of the density of current, which was superior to RuO2(η10=315 mV) and IrO2(η10=300 mV). Overall, this study reported an approach for the fabrication of high-performance OER catalysts and the strategic utilization of biomass resources for application in clean energy technologies.

Fe-S dually modulated adsorbate evolution and lattice oxygen compatible mechanism for water oxidation.

Simultaneously activating metal and lattice oxygen sites to construct a compatible multi-mechanism catalysis is expected for the oxygen evolution reaction (OER) by providing highly available active sites and mediate catalytic activity/stability, but significant challenges remain. Herein, Fe and S dually modulated NiFe oxyhydroxide (R-NiFeOOH@SO4) is conceived by complete reconstruction of NiMoO4·xH2O@Fe,S during OER, and achieves compatible adsorbate evolution mechanism and lattice oxygen oxidation mechanism with simultaneously optimized metal/oxygen sites, as substantiated by in situ spectroscopy/mass spectrometry and chemical probe. Further theoretical analyses reveal that Fe promotes the OER kinetics under adsorbate evolution mechanism, while S excites the lattice oxygen activity under lattice oxygen oxidation mechanism, featuring upshifted O 2p band centers, enlarged d-d Coulomb interaction, weakened metal-oxygen bond and optimized intermediate adsorption free energy. Benefiting from the compatible multi-mechanism, R-NiFeOOH@SO4 only requires overpotentials of 251 ± 5/291 ± 1 mV to drive current densities of 100/500 mA cm-2 in alkaline media, with robust stability for over 300 h. This work provides insights in understanding the OER mechanism to better design high-performance OER catalysts.

Design and Optimization of Nanoporous Materials as Catalysts for Oxygen Evolution Reaction—A Review

With the growing demand for new energy sources, electrochemical water splitting for hydrogen production is a technology that must be vigorously promoted. Therefore, to improve the efficiency of the oxygen evolution reaction (OER) at the anode, high-performance OER catalysts are essential. Given their advantages in electrocatalysis, nanoporous materials have garnered considerable attention in previous studies for OER applications. This review provides a comprehensive overview of various strategies to optimize active site utilization in nanoporous materials. These strategies include regulating pore size and porosity, constructing hierarchical nanoporous structures, and enhancing material conductivity. Additionally, it covers approaches to boost the intrinsic OER activity of nanoporous materials, such as tuning the composition of anions and cations, creating vacancies, constructing interfaces, and forming boundary active sites. While nanoporous materials offer significant potential for advancing OER, challenges remain, including difficulties in quantifying activity within nanopores, the unclear impact of nanoporous material morphology, challenges in accessing nanopore interiors with in situ techniques, and a lack of theoretical calculations on pore structure. However, these challenges also present opportunities, and we hope this review provides a fresh perspective to inspire future research.

Hierarchical design of self-standing FeNi-based metallic glass by in-situ surface amorphous oxide construction for durable and efficient oxygen evolution

As the driving force to accelerate water electrolysis in commercialization, electrocatalysts concurrently satisfying electrocatalytic activity, mechanical flexibility and low cost are essential in the design to lower the kinetic barriers of oxygen evolution reaction (OER). Herein, we present a strategy to in situ construct amorphous metal oxide nanolayers on different compositions of self-standing non-precious FexNiyP20 (at.%) metallic glasses (AMO-MG). With the mechanical flexibility, the processed FexNiyP20 MGs, particularly at Fe30Ni50P20, reaches low OER overpotentials of 238 at a current density of 10 mA cm−2 and a Tafel slope of 33 mV dec−1 in 1.0 M KOH solution while preserving a long-term durability exceeding 60 h. Further studies indicate these robust OER activities appear to be directly linked with the unique surface patterns of the in situ formed AMO nanolayer providing abundant active sites, low charge transfer resistance and superior structural-integration. Modelling analysis further shows that both Fe and Ni sites in the AMO nanolayer act as active sites leading to a strong charge transfer for effective H2O adsorption and an optimization of rate-determining step of OER process. Such in situ AMO-MG hierarchical structure therefore provides a novel structure-integration strategy and win–win situation to design and commercialize high-performance alloy catalysts for OER.

S-doped amorphous multi-metal borophosphates for efficient alkaline seawater oxidation with a high corrosion resistance

Direct seawater splitting is a promising strategy for the production of green hydrogen to address water shortage and environmental concerns. However, the primary obstacle in direct seawater splitting is directly related to the high selectivity and durability of oxygen evolution reaction (OER) electrocatalysts. In this study, we developed sulfur-doped multimetal (Ni, Fe, and Co) borophosphates (BPOs) as high-performance OER catalysts for alkalized seawater electrolytes. The incorporated sulfur atoms act as precursors to enhance the corrosion resistance, as they form negatively charged polyanionic surface layers that block the chloride ions. The best catalyst demonstrates an overpotential of 278 mV in alkaline freshwater and 292 mV in alkalized seawater electrolytes when subjected to a current density of 100 mA cm−2. The overpotential disparity between the two media was only 14 mV, suggesting that the material has substantial resistance to chloride corrosion. Furthermore, excellent electrochemical durability was attained for the sulfurized and amorphized multi-metal BPOs, highlighting their high potential as promising catalysts for seawater oxidation.

Amorphous P-CoOX Promotes the Formation of Hypervalent Ni Species in NiFe LDHs by Amorphous/Crystalline Interfaces for Excellent Catalytic Performance of Oxygen Evolution Reaction.

Water electrolysis has become an attractive hydrogen production method. Oxygen evolution reaction (OER) is a bottleneck of water splitting as its four-electron transfer procedure presents sluggish reaction kinetics. Designing composite catalysts with high performance for efficient OER still remains a huge challenge. Here, the P-doped cobalt oxide/NiFe layered double hydroxides (P-CoOX/NiFe LDHs) composite catalysts with amorphous/crystalline interfaces are successfully prepared for OER by hydrothermal-electrodeposition combined method. The results of electrochemical characterizations, operando Raman spectra, and DFT theoretical calculations have demonstrated the electrons in the P-CoOX/NiFe LDHs heterointerfaces are easily transferred from Ni2+ to Co3+ because that the amorphous configuration of P-CoOX can well induce Ni-O-Co orbital coupling. The electron transfer of Ni2+ to the surrounding Fe3+ and Co3+ will lead to the unoccupied eg orbitals of Ni3+ that can promote water dissociation and accelerate *OOH migration to improve OER catalytic performance. The optimized P-CoOX/NiFe LDHs exhibit superior catalytic performance for OER with a very low overpotential of 265mV at 300mA cm-2 and excellent long-term stability of 500h with almost no attenuation at 100mA cm-2. This work will provide a new method to design high-performance NiFe LDHs-based catalysts for OER.

Modulating the valence states of transition metals in FeCoNiMnW high-entropy alloys for enhanced oxygen evolution reaction activity

Amorphous high-entropy alloys (HEA) are promising electrocatalysts with multi-element active sites and dense defect distribution, high valences of 3d transition metals (3d TMs) are beneficial for the oxygen evolution reaction (OER). However, it is still unknown how to enhance the 3d TMs valence state in amorphous HEA to improve OER catalytic activity. Herein, we successfully boosted the valence state of 3d TMs in HEA through electronegativity. The prepared FeCoNiMnW HEA exhibited significant amorphous characteristics. X-ray photoelectron spectroscopy analysis confirmed the formation of Ni3+ sites after adding electronegative W and the widespread occurrence of oxygen vacancies through amorphization. The enhanced oxidation state of Ni reduced the overpotential, while the abundant oxygen vacancies significantly facilitated electron transfer and thus boosting the rate of catalytic reactions. These characteristics lead to the amorphous FeCoNiMnW HEA exhibiting excellent OER performance. Amorphous FeCoNiMnW HEA films deposited on carbon cloth loaded with carbon nanotubes (FeCoNiMnW@CCC) only require an overpotential of 253 mV to generate a current density of 10 mA cm−2, which is much lower than RuO2 films (399 mV) and commercial RuO2 (309 mV), and shows excellent durability for 700 h at 20 mA cm−2 and 100 h at 200mA cm−2. This work provides a novel strategy for designing high-performance OER catalysts through structural and electronic modulation.

Metal vacancies and self-reconstruction of high entropy metal borates to boost the oxygen evolution reaction

Exploring highly efficient oxygen evolution reaction (OER) electrocatalysts is important for industrial water electrolysis. Herein, a new high entropy material was reported, i.e., an amorphous high entropy metal borate (CrMnCoNiFe)0.2BOx was synthesized by a new simple solvothermal method. The key of this new synthesis method was to obtain (CrMnCoNiFe)0.2BOx with a high specific surface area (446 m2/g) and porous structure, being expected to promote OER reaction. (CrMnCoNiFe)0.2BOx provided a low overpotential of 236 mV at 10 mA cm−2, a reduced Tafel slope of 64 mV dec–1, and good stability. The outstanding OER performance of (CrMnCoNiFe)0.2BOx was attributed to the high entropy structure, generation of metal vacancies, and self-reconstruction during OER. The Cr vacancies generated during the OER process have been demonstrated by Cr 2P XPS and EPR experiments. Various in situ and Ex-situ analyses such as In situ Raman, XPS, and TEM were used to investigate the self-reconstruction of the (CrMnCoNiFe)0.2BOx during the OER. The resulting metal (oxy)hydroxide was believed to be the true active center for OER. The DFT calculation showed the high entropy structure can reduce the adsorption and conversion energy barriers of oxygen-containing intermediates, matching well with the catalytic performance results. This study provided a new simple strategy to construct high entropy metal borate (CrMnCoNiFe)0.2BOx and would inspire the design of high-performance OER catalysts.

Ti3C2 mediates the NiFe-LDH layered electrocatalyst to enhance the OER performance for water splitting

Oxygen evolution reaction (OER) is a very complex process with slow reaction kinetics and high overpotential, which is the main limitation for the commercial application of water splitting. Thus, it is of necessary to design high-performance OER catalysts. NiFe based layered double hydroxides (NiFe-LDHs) have recently gained a lot of attention due to their high reaction activity and simple manufacturing process. In this study, a novel electrocatalyst based on NiFe-LDH was constructed by introducing Ti3C2, which was utilized to modulate the structural and electronic properties of the electrocatalysts. Structural examinations reveal that the Ti3C2 of 2D structure successfully dope the NiFe-LDHs nanosheets, forming NiFe-LDH/Ti3C2 heterojunctions. Firstly, the heterojunction substantially reduces the charge transfer resistance, promoting the electron migration between the LDH nanosheets. Secondly, theoretical calculations demonstrate that the energy barrier between the rate-determining step from *OH to *O is lowered, favoring the formation of the reaction intermediates and thus the occurrence of OER. As a result, the composite electrocatalyst exhibits a low overpotential of 334 mV at a current density of 10 mA/cm2 and a small Tafel slope of 55 mV/dec, which are superior to those of the NiFe-LDH by 11.2 % and 38.5 %, respectively. This study provides inspiration for promoting the performances of NiFe based electrocatalysts by utilizing 2D materials.

Guided Design of Efficient Oxygen Evolution Catalysts Using Patent Analysis.

The facile and rapid design of efficient oxygen evolution reaction (OER) catalysts holds paramount significance for energy conversion devices, such as water electrolyzers and fuel cells. Despite substantial progress in catalyst synthesis and performance exploration, the design and selection processes remain inefficient. In this context, we integrate patent analysis with catalyst design, leveraging the scholarly research functionalities within patent analyses to aid in the design and synthesis of a NiFeRu-carbon catalyst as a high-performance OER catalyst. The results demonstrate that the NiFeRu-Carbon catalyst with low Ru loading (0.3 wt %) exhibits an overpotential of only 219 mV at 10 mA cm-2 under alkaline conditions, and after continuous operation for 200 h, the overpotential only attenuates by 15 mV. The incorporation of high-valence Ru dopants elevated the intrinsic activity of individual catalytic sites within NiFe-layered double hydroxides (LDHs). During the catalytic process, the partial dissolution of Ru might lead to the generation of numerous oxygen vacancies within NiFe- LDH, thereby enhancing the catalyst's activity and stability.

Theoretical study on oxygen evolution reaction mechanism of double rare earth europium-doped graphene under hydroxyl modification in alkaline environment

The development and design of high performance OER catalyst is the key to electrocatalysis technology. Herein, based on density functional theory (DFT), the oxygen evolution reaction mechanism of double rare earth europium-doped graphene under hydroxyl modification in alkaline environment has been systematically studied. Through thermodynamic and kinetic stability analysis, and the optimal reaction path and different adsorption sites of intermediates were compared. Four catalysts with good catalytic activity for OER reaction were selected. The results show that when the two hydroxyl groups are modified, the overpotentials on the optimal pathway for the four catalyst configurations are 0.54 V, 0.50 V, 0.54 V, and 0.61 V, respectively. These catalysts demonstrate excellent catalytic activity for the oxygen evolution reaction (OER). Moreover, these catalysts have good electrical conductivity, and the active site and adsorption intermediates can be stably bonded together. In addition, the scaling relationship between oxygen adsorption free energy and overpotential is described. This work may provide new insights and guidance for future research on rare-earth atom-based OER catalysts.

Cathodized Stainless Steel Mesh for Binder-Free NiFe<sub>2</sub>O<sub>4</sub>/NiFe Layer Double Hydroxides Oxygen Evolution Reaction Electrode

Oxygen evolution reaction (OER) is an essential reaction commonly applied in various energy storage and conversion technologies. One of the common issues of OER lies in its low kinetic activity. Therefore, developing durable, low-cost, and high-performance OER catalysts is critical. Recently, many attempts have used stainless steel mesh (SSM) as the substrate for OER electrodes because SSM is abundant, cheap, and durable. Nickel/iron-based materials, i.e., NiFe2O4/NiFe layer double hydroxides (LDHs), are regarded as one of the most excellent OER catalysts in alkaline electrolytes, making them attractive low-cost materials for OER catalysts. However, synthesizing NiFe2O4/NiFe LDHs directly on the surface of SSM is challenging. Modifying the SSM surface through cathodization has proved to enhance the adhesion and OER activity. Moreover, the cathodization technique is facile and cost-effective. In this work, the surface of SSM is modified by cathodization treatment. Subsequently, NiFe2O4/NiFe LDHs are deposited onto the surface of treated SSM via a low-temperature one-step chemical bath deposition technique. This synthesis is a binder-free method; the resulted electrodes show excellent OER performance without the binder effects. The as-prepared electrodes have a small Tafel slope of 125.4 mV/dec (1 M KOH) and high durability (10 mA/cm2 for 50 hours).

Recent advances in the synthesis of transition metal hydroxyl oxide catalysts and their application in electrocatalytic oxygen evolution reactions.

With the extensive use of fossil energy, people will face the depletion of fossil energy and increasingly severe problems. As a non-polluting, high specific energy density energy source, hydrogen energy is expected to solve this problem by producing hydrogen through electrolysis of water through renewable energy power generation. Water electrolysis technology involves two important half-reactions: the cathode hydrogen evolution reaction (HER) and anode oxygen evolution reaction (OER). The OER is a 4-electron transfer process with a high energy barrier. In order to achieve higher energy conversion, OER catalyst technology is a key part of the process. Researchers have conducted a lot of research into high-performance, high-stability, and highly economical OER catalysts, among which oxyhydroxide (MOOH), as an active substance for OER, has received particular attention. This article provides a timely follow-up to the research on oxyhydroxides, first introducing the two catalytic mechanisms of OER, namely the adsorbate evolution mechanism (AEM) and lattice-oxygen-mediated mechanism (LOM). Then, strategies are proposed to improve OER catalytic performance by increasing catalytic active surface area/active sites, optimizing intermediate adsorption energy based on the AEM, triggering the LOM, and enhancing catalyst stability. Finally, the challenges and future development directions of MOOH catalysts are analyzed, which provides guidance for the design and preparation of high-performance OER catalysts in the future.

Highly dispersed Ir/Fe nanoparticles anchored at nitrogen-doped activated pyrolytic carbon black as a high-performance OER catalyst for lead recovery.

The use of a methanesulfonic acid (MSA) electrolytic system is recommended as a green method for hydrometallurgical recovery of metallic Pb from waste lead-acid batteries (LABs), contributing to the sustainable protection of the ecosystem. Nevertheless, the system's high energy consumption is a current issue due to the substantial overpotential of the oxygen evolution reaction (OER) and competitive anodic oxidation of Pb2+. Herein, we propose an IrFe/nitrogen-doped pyrolytic carbon black (IrFe/NCBp) composite as a novel OER catalyst for the MSA electrolytic system, which demonstrates advanced OER catalytic efficiency and selectivity for H2O oxidation. This can be ascribed to the catalyst's thoughtful design, which enhances the number and uniformity of Ir and Fe species via increasing the specific surface area and employing NCBp as a sustainable substrate. The optimized IrFe/NCBp composite exhibits superior OER performance, with a low 252 mV@10 mA cm-2 overpotential and a 62 mV dec-1 Tafel slope, and excellent durability in a 1 M MSA electrolyte for 30 h operation compared to commercial Ir/C. In contrast to carbon paper (CP) and commercial Ir/C anodes, the anodic reaction of IrFe/NCBp is primarily OER-driven (97%) in 1 M MSA and 0.2 M Pb2+ electrolyte for Pb recovery. This effectively circumvents the high potential oxidation of Pb2+ into PbO2, reducing the electrolytic voltage to 488 kWh for the recovery of 1 ton Pb metal. This work provides a green, low-carbon footprint solution for the MSA electrolytic system, thereby promoting the commercialization of the hydrometallurgical Pb recovery.

Surface charge modulation boosts electrocatalytic water splitting over iridium catalysts on a polyimide support.

Developing high-performance iridium (Ir)-based catalysts with minimal precious Ir metal is a significant but challenging step towards the acidic oxygen evolution reaction (OER). Here, we report a high-performance OER catalyst with Ir nanoparticles on a polyimide support, where the polyimide support can effectively modulate the electronic structures of the Ir active sites for decreased thermodynamic barriers, but also enrich the local proton concentration near the Ir active sites, enhancing the OER rates.

Polyoxometalate-incorporated NiFe-based oxyhydroxides for enhanced oxygen evolution reaction in alkaline media.

NiFe-based oxyhydroxides are promising electrocatalysts for the oxygen evolution reaction (OER) in alkaline media, but further enhancing their OER performance remains a significant challenge. Herein, we in situ incorporated polyoxometalates into NiFe oxyhydroxides to form a homogeneous/heterogeneous hybrid material, which induces the electronic interaction between Ni, Fe and Mo sites, as revealed by a variety of characterization experiments and theoretical calculations. The resulting hybrid electrocatalyst delivers a low overpotential of 203 mV at 10 mA cm-2 and a TOF of 2.34 s-1 at 1.53 V in alkaline media. This work presents a critical step towards developing high-performance OER catalysts by constructing metal-POM hybrids.

Facile synthesis of FeNi alloy-supported N-doped Mo2C hollow nanospheres for the oxygen evolution reaction

The rapid depletion of fossil fuels results in significant environmental pollution. Consequently, researching environmentally friendly and cost-effective electrocatalysts with exceptional oxygen evolution reaction (OER) capabilities holds immense importance in enhancing the efficient utilization of resources. In this paper, a straightforward and cost-effective method was employed to produce Fe-Ni alloy-supported N-doped carbon hollow nanospheres (FeNi/Mo2C/NC) using self-assembled molybdenum dopamine spheres (Mo-PDA-HS) as a substrate. The inclusion of iron and nickel addressed the issue of aggregation and collapse in Mo-PDA-HS nanostructures at high temperatures, while adjusting the electronic structure of the composites to achieve efficient OER activity. The composite displayed a low overpotential (η10 mA = 304 mV) and a minimal Tafel slope (41.8 mV/dec-1). This study introduces a simple strategy for constructing structurally robust and non-aggregating Mo2C nanostructures, along with a direct method for designing cost-effective and high-performance catalysts for OER.

Density Functional Theory Optimization of Cobalt- and Nitrogen-Doped Graphene Catalysts for Enhanced Oxygen Evolution Reaction

The optimization and advancement of effective catalysts in the oxygen evolution reaction (OER) are integral to the evolution of diverse green power technologies. In this study, cobalt–nitrogen–graphene (Co-N-g) catalysts are analyzed for their OER contribution via density functional theory (DFT). The influence of vacancies and nitrogen doping on catalyst performance was probed via electronic features and related Frontier Molecular Orbitals. The research reveals that the double-vacancy nitrogen-doped catalyst (DV-N4) exhibits remarkable OER effectiveness, characterized by a notably low overpotential of 0.61 V. This is primarily attributed to enhanced metal–ligand bonding interactions, a diminished energy gap indicating augmented reactivity, and advantageous charge redistribution upon water adsorption. Additionally, nitrogen doping is found to facilitate electron loss from Co, thus promoting water oxidation and improving OER performance. This research provides crucial insights into high-performance OER catalyst design, informing future developments in efficient renewable energy devices.

Outstanding oxygen evolution reaction properties released at the interface of NiMoO4 and FeNi layer double hydroxide heterostructures

For the alkaline oxygen evolution reaction (OER), FeNi layered double hydroxide (FeNi LDH) exhibits good activity and stability. For the sake of saving freshwater, the use of abundant seawater as an electrolyte poses new requirements for its OER performance. A novel method was designed based on a corrosion reaction to convert commercial Fe foam into a high-performance OER catalyst (FeNiM), which consisted of FeNi LDH layers and NiMoO4 nanoparticles modified on its surface. FeNiM exhibited excellent OER activity, only requiring an overpotential of 250 mV to achieve a current density of 100 mA cm−2. Experimental results indicated that the heterostructures formed by NiMoO4 and FeNi LDH was conducive to exposing active sites, promoting the adsorption of active intermediates, and generating highly active oxyhydroxides. In addition, the heterostructure was beneficial to stabilizing the electrode surface structure and inhibiting seawater corrosion. Therefore, FeNiM could maintain high current density activity in both alkaline freshwater and alkaline seawater, which only required low overpotentials of 326 mV and 304 mV to achieve a high current density of 1500 mA cm−2, respectively. This catalyst preparation method has the advantages of economic efficiency, industrial compatibility, and significantly promoting the development of green hydrogen economy and industrial seawater desalination.