Electrocatalytic Oxygen Evolution Research Articles

Ligand-Induced Electronic Structure Modulation of Self-Evolved Ni3S2 Nanosheets for the Electrocatalytic Oxygen Evolution Reaction.

Modulating the electronic structure of the electrocatalyst plays a vital role in boosting the electrocatalytic performance of the oxygen evolution reaction (OER). In this work, we introduced a one-step solvothermal method to fabricate 1,1-ferrocene dicarboxylic acid (FcDA)-decorated self-evolved nickel sulfide (Ni3S2) nanosheet arrays on a nickel foam (NF) framework (denoted as FcDA-Ni3S2/NF). Benefiting from the interconnected ultrathin nanosheet architecture, ligand dopants induced and facilitated in situ structural reconstruction, and the FcDA-decorated Ni3S2 (FcDA-Ni3S2/NF) outperformed its singly doped and undoped counterparts in terms of OER activity. The optimized FcDA-Ni3S2/NF self-supported electrode presents a remarkably low overpotential of 268 mV to achieve a current density of 10 mA cm-2 for the OER and demonstrates robust electrochemical stability for 48 h in a 1.0 M KOH electrolyte. More importantly, in situ electrochemical Raman spectroscopy reveals the generation of catalytically active oxyhydroxide species (NiOOH) derived from the surface construction during the OER of pristine FcDA-Ni3S2/NF, contributing significantly to its superior electrocatalytic performance. This study concerns the modulation of electronic structure through ligand engineering and may provide profound insight into the design of cost-efficient OER electrocatalysts.

Constructing a potential electrocatalyst: highly multi-porous Co3O4 nanostructures to enhance electrocatalytic oxygen evolution reactions

Constructing a potential electrocatalyst: highly multi-porous Co3O4 nanostructures to enhance electrocatalytic oxygen evolution reactions

Self-Assembled Conjugated Coordination Polymer Nanorings: Role of Morphology and Redox Sites for the Alkaline Electrocatalytic Oxygen Evolution Reaction.

Electrocatalytic water splitting provides a sustainable method for storing intermittent energies, such as solar energy and wind, in the form of hydrogen fuel. However, the oxygen evolution reaction (OER), constituting the other half-cell reaction, is often considered the bottleneck in overall water splitting due to its slow kinetics. Therefore, it is crucial to develop efficient, cost-effective, and robust OER catalysts to enhance the water-splitting process. Transition-metal-based coordination polymers (CPs) serve as promising electrocatalysts due to their diverse chemical architectures paired with redox-active metal centers. Despite their potential, the rational use of CPs has faced obstacles including a lack of insights into their catalytic mechanisms, low conductivity, and morphology issues. Consequently, achieving success in this field requires the rational design of ligands and topological networks with the desired electronic structure. This study delves into the design and synthesis of three novel conjugated coordination polymers (CCPs) by leveraging the full conjugation of terpyridine-attached flexible tetraphenylethylene units as electron-rich linkers with various redox-active metal centers [Co(II), Ni(II), and Zn(II)]. The self-assembly process is tuned for each CCP, resulting in two distinct morphologies: nanosheets and nanorings. The electrocatalytic OER performance efficiency is then correlated with factors such as the nanostructure morphology and redox-active metal centers in alkaline electrolytes. Notably, among the three morphologies studied, nanorings for each CCP exhibit a superior OER activity. Co(II)-integrated CCPs demonstrate a higher activity between the redox-active metal centers. Specifically, the Co(II) nanoring morphology displays exceptional catalytic activity for OER, with a lower overpotential of 347 mV at a current density of 10 mA cm-2 and small Tafel slopes of 115 mV dec-1. The long-term durability is demonstrated for at least 24 h at 1.57 V vs RHE during water splitting. This is presumably the first proof that links the importance of nanostructure morphologies to redox-active metal centers in improving the OER activity, and it may have implications for other transdisciplinary energy-related applications.

Preparation and electrocatalytic oxygen evolution of bimetallic phosphates (NiFe)2P/NF

Abstract The energy and environmental crisis pose a great challenge to human development in the 21st century. The design and development of clean and renewable energy and the solution for environmental pollution have become a hotspot in the current research. Based on the preparation of transition metal phosphates, transition metals were used as raw materials, Prussian blue-like NiFe(CN)6 as a precursor, which was in situ grown on nickel foam (NF) substrate. After low temperature phosphating treatment, a bimetallic phosphide electrocatalyst (NiFe)2P/NF was prepared on NF substrate. Using 1 mol·L−1 KOH solution as a basic electrolyte, based on the electrochemical workstation of a three-electrode system, the electrochemical catalytic oxygen evolution performance of the material was tested and evaluated. Experiments show that (NiFe)2P/NF catalyst has excellent oxygen evolution performance. In an alkaline medium, the overpotential required to obtain the catalytic current density of 10 mA·cm−2 is only 220 mV, and the Tafel slope is 67 mV·dec−1. This is largely due to: (1) (NiFe)2p/NF nanocatalysts were well dispersed on NF substrates, which increased the number of active sites exposed; (2) the hollow heterostructure of bimetallic phosphates promotes the electron interaction between (NiFe)2P and NF, increased the rate of charge transfer, and the electrical conductivity of the material is improved; and (3) theoretical calculations show that (NiFe)2P/NF hollow heterostructure can effectively reduce the dissociation barrier of water, promote the dissociation of water; furthermore, the kinetic reaction rate of electrocatalytic oxygen evolution is accelerated. Meanwhile, the catalyst still has high activity and high stability in 30 wt% concentrated alkali solution. Therefore, the construction of (NiFe)2P/NF electrocatalysts enriches the application of non-noble metal nanomaterials in the field of oxygen production from electrolytic water.

Substantial Electrocatalytic Oxygen Evolution Performances of Activated Carbon-Decorated Vanadium Pentoxide Nanocomposites

Developing the ecofriendly and high-fidelity electrocatalysts for the oxygen evolution reaction (OER) is essential to foster effective production of environmentally friendly hydrogen. Herein, we fabricated the highly efficient OER electrocatalysts of the activated carbon-decorated vanadium pentoxide (AC-V2O5) nanocomposites using a facile hydrothermal technique. The AC-V2O5 nanocomposites displayed an aggregated structure of the AC nano-sheet-anchored orthorhombic V2O5 nanorods. When performing the OER process in an alkaline electrolyte at 10 mA/cm2, AC-V2O5 exhibited the low overpotential (~230 mV), small Tafel slope (~54 mV/dec), and excellent stability. These substantial OER performances of AC-V2O5 could be ascribed to the synergistic effects from both the electrochemically active V2O5 nanorods and the highly conductive AC nanosheets. The results infer that the AC-V2O5 nanocomposites possess a substantial aptitude as a high-performance OER electrocatalyst for production of the future green energy source—hydrogen.

Neighbouring Synergy in High-Density Single Ir Atoms on CoGaOOH for Efficient Alkaline Electrocatalytic Oxygen Evolution.

The catalytic performance of single-atom catalysts was strictly limited by isolated single-atom sites. Fabricating high-density single atoms to realize the synergetic interaction in neighbouring single atoms could optimize the adsorption behaviors of reaction intermediates, which exhibited great potential to break performance limitations and deepen mechanistic understanding of electrocatalysis. However, the catalytic behavior governed by neighbouring single atoms is particularly elusive and has yet to be understood. Herein, we revealed that the synergetic interaction in neighbouring single atoms contributes to superior performance for oxygen evolution relative to isolated Ir single atoms. Neighbouring single atoms was achieved by fabricating high-density single atoms to narrow the distance between single atoms. Electrochemical measurements demonstrated that the Nei-Ir1/CoGaOOH with neighbouring Ir single atoms exhibited a low overpotential of 170 mV at a current density of 10 mA cm-2, and long-durable stability over 2000 h for oxygen evolution. Mechanistic studies revealed that neighbouring single atoms synergetic stabilized the *OOH intermediates via extra hydrogen bonding interactions, thus significantly reducing the reaction energy barriers, as compared to isolated Ir single atoms. The discovery of the synergetic interaction in neighbouring single atoms could offer guidance for the development of efficient electrocatalysts, thus accelerating the world's transition to sustainable energy.

Neighbouring Synergy in High‐Density Single Ir Atoms on CoGaOOH for Efficient Alkaline Electrocatalytic Oxygen Evolution

AbstractThe catalytic performance of single‐atom catalysts was strictly limited by isolated single‐atom sites. Fabricating high‐density single atoms to realize the synergetic interaction in neighbouring single atoms could optimize the adsorption behaviors of reaction intermediates, which exhibited great potential to break performance limitations and deepen mechanistic understanding of electrocatalysis. However, the catalytic behavior governed by neighbouring single atoms is particularly elusive and has yet to be understood. Herein, we revealed that the synergetic interaction in neighbouring single atoms contributes to superior performance for oxygen evolution relative to isolated Ir single atoms. Neighbouring single atoms was achieved by fabricating high‐density single atoms to narrow the distance between single atoms. Electrochemical measurements demonstrated that the Nei‐Ir1/CoGaOOH with neighbouring Ir single atoms exhibited a low overpotential of 170 mV at a current density of 10 mA cm−2, and long‐durable stability over 2000 h for oxygen evolution. Mechanistic studies revealed that neighbouring single atoms synergetic stabilized the *OOH intermediates via extra hydrogen bonding interactions, thus significantly reducing the reaction energy barriers, as compared to isolated Ir single atoms. The discovery of the synergetic interaction in neighbouring single atoms could offer guidance for the development of efficient electrocatalysts, thus accelerating the world‘s transition to sustainable energy.

Viologen-Cucurbit[7]uril Based Polyrotaxanated Covalent Organic Networks: A Metal Free Electrocatalyst for Oxygen Evolution Reaction.

Viologen-based covalent organic networks represent a burgeoning class of materials distinguished by their captivating properties. Here, supramolecular chemistry is harnessed to fabricate polyrotaxanated ionic covalent organic polymers (iCOP) through a Schiff-base condensation reaction under solvothermal conditions. The reaction between 1,1'-bis(4-aminophenyl)-[4,4'-bipyridine]-1,1'-diium dichloride (DPV-NH2) and 1,3,5-triformylphloroglucinol (TPG) in various solvents yields an iCOP-1 and iCOP-2. Likewise, employing cucurbit[7]uril (CB[7]) in the reaction yielded polyrotaxanated iCOPs, denoted as iCOP-CB[7]-1 and iCOP-CB[7]-2. All four iCOPs exhibit exceptional stability under the acidic and basic conditions. iCOP-CB[7]-2 displays outstanding electrocatalytic Oxygen Evolution Reaction (OER) performance, demanding an overpotential of 296 and 332mV at 10 and 20mA cm-2, respectively. Moreover, the CB[7] integrated iCOP-2 exhibits a long-term stable nature for 30h in 1m KOH environment. Further, intrinsic activity studies like TOF show a 4.2-fold increase in generation of oxygen (O2) molecules than the bare iCOP-2. Also, it is found that iCOP-CB[7]-2 exhibits a high specific (19.48mA cm-2) and mass activity (76.74mAmg-1) at 1.59V versus RHE. Operando-EIS study evident that iCOP-CB[7]-2 commences OER at a relatively low applied potential of 1.5V versus RHE. These findings pave the way for a novel approach to synthesizing various mechanically interlocked molecules through straightforward solvothermal conditions.

Self-supported low-crystallinity CoFe layered double hydroxide nanospheres on monolayer Ti3C2 electrode for oxygen evolution reaction

The electrocatalytic oxygen evolution reaction is a crucial means to support the conversion and storage of the sustainable renewable energy. Low-crystallinity can offer short-range structural ordering and high active site density. In this work, an efficient self-supported oxygen evolution reaction (OER) electrocatalyst, cobalt iron layered double hydroxide (LDH) grown on Ti3C2 modified nickel foam (NF) heterostructure anode (CoFe-LDH/Ti3C2/NF) was prepared using electrodeposition. The exceptional electrocatalytic OER performance is ensured by in situ decorating monolayer Ti3C2/NF (s-Ti3C2/NF) with low-crystallinity CoFe nanospheres. By harnessing the low crystallinity, well-chosen composition and reasonable heterostructure, the overpotential of CoFe-LDH/Ti3C2/NF decreases to 246 mV at a current density of 10 mA·cm−2 in alkaline media. After 3000 cyclic voltammograms cycles, the ignorable increase in overpotential of 14 mV suggest the excellent long circular stability. Moreover, an accelerated reaction kinetics is implied by the smaller Tafel slope (28.76 mV·dec−1) and higher double-layer specific capacitance (2.33 mF·cm−2), which surpassed the counterparts CoFe-LDH grown on NF (CoFe-LDH/NF) and s-Ti3C2/NF. This work paves a new way to fabricate the low-crystallinity materials for electrocatalysis and energy storage.

Rapid electronic transport channel of Co‐P with Mo in a heterostructure embedded with P, N dual doped porous carbon for electrocatalytic oxygen and hydrogen evolution

We developed a molybdenum (Mo)‐doped cobalt (Co)‐heterostructure embedded on a phosphorous (P) and nitrogen (N) dual‐doped porous carbon which exhibits an intrinsic electronic transport channel of Co to Mo and P. The P,Mo,O‐Co/PNC/NF (NF = Nickel foam) electrode offers 335 mV overpotential at 10 mA cm‐2 in OER as compared with PMA‐ZIF67‐NC/NF and ZIF67‐NC/NF electrode with an overpotential of 357 and 373 mV respectively. Linear sweep voltammetry (LSV) of overall water splitting (OWS) supports that the current density gradually increased at a cell potential of 1.6 V with a maximum of 40 mA with a corresponding cell potential of 1.79 V at a current density of 10 mA cm−2. Density functional theory (DFT) calculations for water adsorption on optimized [111] surface of Co, CoMo, and CoMoP2 with adsorbed H2O and corresponding lattice determine the electron density difference of [111] surface with adsorbed H2O for Eads (eV) 4.23 corresponds to adsorption energy for CoMoP2. XANE‐EXAFS spectroscopy of P,Mo,O‐Co/PNC at Co K edge and Mo K edge suggests the presence of higher valence of both Cox+ and Mox+ without metallic Co and Mo and Co‐P and Mo‐P bonds as major structural units due to phosphidation as determined by R‐space FT‐EXAFS spectra.

Highly efficient anion exchange membrane water electrolyzers via chromium-doped amorphous electrocatalysts

In-depth comprehension and modulation of the electronic structure of the active metal sites is crucial to enhance their intrinsic activity of electrocatalytic oxygen evolution reaction (OER) toward anion exchange membrane water electrolyzers (AEMWEs). Here, we elaborate a series of amorphous metal oxide catalysts (FeCrOx, CoCrOx and NiCrOx) with high performance AEMWEs by high-valent chromium dopant. We discover that the positive effect of the transition from low to high valence of the Co site on the adsorption energy of the intermediate and the lower oxidation barrier is the key factor for its increased activity by synchrotron radiation in-situ techniques. Particularly, the CoCrOx anode catalyst achieves the high current density of 1.5 A cm−2 at 2.1 V and maintains for over 120 h with attenuation less than 4.9 mV h−1 in AEMWE testing. Such exceptional performance demonstrates a promising prospect for industrial application and providing general guidelines for the design of high-efficiency AEMWEs systems.

Electron regulation of CeO2 on CoP multi-shell hetero-junction micro-sphere towards highly efficient water oxidation

CeO2 has been identified as a significant cocatalyst to enhance the electrocatalytic activity of transition metal phosphides (TMPs). However, the electrocatalytic mechanism by which CeO2 enhances the catalytic activity of TMP remains unclear. In this study, we have successfully developed a unique CeO2-CoP-1–4 multishell microsphere heterostructure catalyst through a simple hydrothermal and calcination process. CeO2-CoP-1–4 exhibits great potential for electrocatalytic oxygen evolution reaction (OER), requiring only an overpotential of 254 mV to achieve a current density of 10 mA cm−2. Moreover, CeO2-CoP-1–4 demonstrates excellent operating durability lasting for 55 h. The presence of CeO2 as a cocatalyst can regulate the microsphere structure of CoP, the resulting multishell microsphere structure can shorten the mass transfer distance, and improve the utilization rate of the active site. Furthermore, in situ Raman and ex situ characterizations, and DFT theoretical calculation results reveal that CeO2 can effectively regulates the electronic structure of Co species, reduces the reaction free energy of rate-limiting step, thus increase the reaction kinetic. Overall, this study provides experimental and theoretical evidence to better comprehend the mechanism and structure evolution of CeO2 in enhancing the OER performance of CoP, offering a unique design inspiration for the development of efficient hollow heterojunction electrocatalysts.

Crystal Structure Regulation of CoSe2 Induced by Fe Dopant for Promoted Surface Reconstitution toward Energetic Oxygen Evolution Reaction.

Most nonoxide catalysts based on transition metal elements will inevitably change their primitive phases under anodic oxidation conditions in alkaline media. Establishing a relationship between the bulk phase and surface evolution is imperative to reveal the intrinsic catalytic active sites. In this work, it is demonstrated that the introduction of Fe facilitates the phase transition of orthorhombic CoSe2 into its cubic counterpart and then accelerates the Co-Fe hydroxide layer generation on the surface during electrocatalytic oxygen evolution reaction (OER). As a result, the Fe-doped cubic CoSe2 catalyst exhibits a significantly enhanced activity with a considerable overpotential decrease of 79.9 and 66.9 mV to deliver 10 mA·cm-2 accompanied by a Tafel slope of 48.0 mV·dec-1 toward OER when compared to orthorhombic CoSe2 and Fe-doped orthorhombic CoSe2, respectively. Density functional theory (DFT) calculations reveal that the introduction of Fe on the surface hydroxide layers will tune electron density around Co atoms and raise the d-band center. These findings will provide deep insights into the surface reconstitution of the OER electrocatalysts based on transition metal elements.

Perovskite for Electrocatalytic Oxygen Evolution at Elevated Temperatures.

The development of advanced electrolysis technologies such as anion exchange membrane water electrolyzer (AEMWE) is central to the vision of a sustainable energy future. Key to the realization of such AEMWE technology lies in the exploration of low-cost and high-efficient catalysts for facilitating the anodic oxygen evolution reaction (OER). Despite tremendous efforts in the fundamental research, most of today's OER works are conducted under room temperature, which deviates significantly with AEMWE's operating temperature (50-80 °C). To bridge this gap, it is highly desirable to obtain insights into the OER catalytic behavior at elevated temperatures. Herein, using the well-known perovskite catalyst Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) as a proof of concept, the effect of temperature on the variation in OER catalytic activity and stability is evaluated. It is found that the BSCF's activity increases with increasing temperature due to enhanced lattice oxygen participation promoting the lattice oxygen-mediated OER process. Further, surface amorphization and cation leaching of BSCF become more pronounced as temperature increases, causing a somewhat attenuated OER stability. These new understandings of the fundamental OER catalysis over perovskite materials at industrial-relevant temperature conditions are expected to have strong implications for the research of OER catalysts to be deployed in practical water electrolyzers.

Ultrasound-Assisted Synthesis of High-Entropy Materials for Enhanced Oxygen Evolution Electrocatalysis

High-entropy materials (HEMs) play a significant role in the electrocatalytic oxygen evolution reaction (OER) due to their unique properties. However, there are still challenges in the preparation of HEMs for OER catalysts. In this study, the FeCoNiMnCr catalyst is synthesized for the first time using the ultrasonic hydrothermal-sintering technique and exhibits excellent performance for OER electrocatalysis. There is an optimal ultrasonic hydrothermal time and power for achieving the best OER performance. The results demonstrate that the performance of FeCoNiMnCr catalysts prepared through ultrasonic hydrothermal sintering (US-FeCoNiMnCr) is significantly improved compared with the traditional hydrothermal-sintering method. The US-FeCoNiMnCr catalyst exhibits an overpotential of 228 mV at the current density of 10 mA cm−2 and a Tafel slope as low as 45.39 mV dec−1 in an alkaline medium. Moreover, the US-FeCoNiMnCr catalyst demonstrates remarkable stability in electrocatalytic OER with a minimal potential increase observed even after 48 h. This work not only provides valuable insights into high-entropy material synthesis, but also presents a powerful electrocatalyst for water electrolysis.

Tuning Electrocatalytic Water Oxidation Activity: Insights from the Active-Site Distance in LnCu6 Clusters.

Atomically precise metal clusters serve as a unique model for unraveling the intricate mechanism of the catalytic reaction and exploring the complex relationship between structure and activity. Herein, three series of water-soluble heterometallic clusters LnCu6, abbreviated as LnCu6-AC (Ln = La, Nd, Gd, Er, Yb; HAC = acetic acid), LnCu6-IM (Ln = La and Nd; IM = Imidazole), and LnCu6-IDA (Ln = Nd; H2IDA = Iminodiacetic acid) are presented, each featuring a uniform metallic core stabilized by distinct protected ligands. Crystal structure analysis reveals a triangular prism topology formed by six Cu2+ ions around one Ln3+ ion in LnCu6, with variations in Cu···Cu distances attributed to different ligands. Electrocatalytic oxygen evolution reaction (OER) shows that these different LnCu6 clusters exhibit different OER activities with remarkable turnover frequency of 135s-1 for NdCu6-AC, 79s-1 for NdCu6-IM and 32s-1 for NdCu6-IDA. Structural analysis and Density Functional Theory (DFT) calculations underscore the correlation between shorter Cu···Cu distances and improves OER catalytic activity, emphasizing the pivotal role of active-site distance in regulating electrocatalytic OER activities. These results provide valuable insights into the OER mechanism and contribute to the design of efficient homogeneous OER electrocatalysts.

Synergistic RB5 dye degradation and oxygen evolution reaction (OER) catalysis by WO3 nano-pellets: mechanistic insights and water remediation applications

Transition metal oxides (TMO), a non-noble element based oxides, establish remarkable potential in the realm of textile wastewater remediation and water splitting due to their sustainable catalytic performance. Highly functional TMO materials, in form of nanostrcutures, are of great interest owing to their robust photo and electro-catalytic activities for instituting sustainable development for the water and energy resource management framework. In the present article, we have reported catalytically active WO3 nano-pellets (NP) synthesized using microwave-assisted for photocatalytic wastewater remediation and electrocatalytic oxygen evolution reaction (OER). Promisingly, WO3 NP abetted degradation of the reactive black 5 (RB5) dye by almost 95 % in short time interval of 60 min in exposer of sun light. Present work includes the strategies to remove and observe the progression of reaction kinetics of dye degradation in neutral and alkaline media. By varying concentration of the catalyst (ranging from 250 mg/L to 1000 mg/L, in the step of 250 mg/L), we have prolifically verified that 750 mg/L turn out optimal dosage for 100% degradation in time interval of 120 min. Besides, WO3 NP has shown highest photocatalytic behaviour at 9 pH. The WO3 NP shows the electrocatalytic OER performance in an alkaline condition (1M KOH) with an overpotential of 418 mV to generate the geometric current density of 10 mA/cm² and Tafel slope of 178 mV dec⁻¹. Owing to robust nature, WO3 NP shows the almost similar photocatalytic response for ten cycles dye degradation and demonstrates the stable electrochemical charge transport for OER at 10 mA/cm2 for 50 hours.

Tuning the Electronic Property of Reconstructed Atomic Ni-CuO Cluster Supported on N/O-C for Electrocatalytic Oxygen Evolution.

Electrochemical activation usually accompanies in situ atom rearrangement forming new catalytic sites with higher activity due to reconstructed atomic clusters or amorphous phases with abundant dangling bonds, vacancies, and defects. By harnessing the pre-catalytic process of reconstruction, a multilevel structure of CuNi alloy nanoparticles encapsulated in N-doped carbon (CuNi nanoalloy@N/C) transforms into a highly active compound of Ni-doped CuO nanocluster supported on (N/O-C) co-doped C. Both the exposure of accessible active sites and the activity of individual active sites are greatly improved after the pre-catalytic reconstruction. Manipulating the Cu/Ni ratios of CuNi nanoalloy@N/C can tailor the electronic property and d-band center of the high-active compound, which greatly optimizes the energetics of oxygen evolution reaction (OER) intermediates. This interplay among Cu, Ni, C, N, and O modifies the interface, triggers the active sites, and regulates the work functions, thereby realizing a synergistic boost in OER.

Enhanced Electrocatalytic Oxygen Evolution by In Situ Growth of Tetrametallic Metal-Organic Framework Electrocatalyst FeCoNiMn-MOF on Nickel Foam.

Developing highly efficient, cost-effective, non-noble-metal-based electrocatalysts with superior performance and stability for oxygen evolution reactions is of immense challenge as well as great importance for the upcoming sustainable and green energy conversion technologies. The multivariate metal-organic frameworks with hierarchical porous structures and unsaturated coordination modes are considered to be promising emerging energy materials. In this work, a series of multimetallic MOFs were directly grown on nickel foam (NF) through the solvothermal method. Notably, the optimized tetrametallic FeCoNiMn-MOF/NF shows a low overpotential of 239 mV to achieve a current density of 50 mA cm-2 with a Tafel slope of 62.05 mV dec-1 for OER in 1 M KOH. It also exhibits excellent stability and durability over 100 h in chronoamperometric studies. The enhanced performance is closely tied to the high activity of iron and nickel ions and the decomposed and reconstructed Ni/Fe-OOH intermediates of the FeCoNiMn-MOF/NF during the OER process, which are revealed by XPS analysis and in situ Raman spectroscopy. This present work demonstrates the feasibility and advantage of utilizing highly efficient and durable multimetallic MOFs for electrocatalytic oxygen evolution.

In Situ X-ray Absorption Spectroscopy of LaFeO3 and LaFeO3/LaNiO3 Thin Films in the Electrocatalytic Oxygen Evolution Reaction.

We study the electrocatalytic oxygen evolution reaction using in situ X-ray absorption spectroscopy (XAS) to track the dynamics of the valence state and the covalence of the metal ions of LaFeO3 and LaFeO3/LaNiO3 thin films. The active materials are 8 unit cells grown epitaxially on 100 nm conductive La0.67Sr0.33MnO3 layers using pulsed laser deposition (PLD). The perovskite layers are supported on monolayer Ca2Nb3O10 nanosheet-buffered 100 nm SiNx membranes. The in situ Fe and Ni K-edges XAS spectra were measured from the backside of the SiNx membrane using fluorescence yield detection under electrocatalytic reaction conditions. The XAS spectra show significant spectral changes, which indicate that (1) the metal (co)valencies increase, and (2) the number of 3d electrons remains constant with applied potential. We find that the whole 8 unit cells react to the potential changes, including the buried LaNiO3 film.