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Although the electronic state of catalysts is strongly corrected with their oxygen evolution reaction (OER) performances, understanding the role of spin state in dynamic electronic structure evolution during OER process is still challenging. Herein, we developed a spin state regulation strategy to boost the OER performance of CoOOH through elemental doping (CoMOOH, M=V, Cr, Mn, Co and Cu). Experimental results including magnetic characterization, in situ X‐ray absorption spectroscopy, in situ Raman and density functional theory calculations unveil that Mn doping could successfully increase the Co sites from low spin state to intermediate spin state, leading to the largest lattice distortion and smallest energy gap between dxy and dz2 orbitals among the obtained CoMOOH electrocatalysts. Benefiting from the promoted electron transfer from dxy to dz2 orbital, facilitated formation of active high‐valent *O−Co(IV) species at applied potential, and reduced energy barrier of rate‐determining step, the CoMnOOH exhibits the highest OER performance. Our work provides significant insight into the correction between dynamic electronic structure evolution and OER performance by understanding the role of spin state regulation in metal oxyhydroxides, paving a new avenue for rational design of high‐activity electrocatalysts. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Developing highly efficient and low‐cost electrocatalysts towards oxygen evolution reaction (OER) is essential for practical application in water electrolyzers and rechargeable metal‐air batteries. Although Fe‐based oxyhydroxides are regarded as state‐of‐the‐art non‐noble OER electrocatalysts, the origin of performance enhancement derived from Fe doping remains a hot topic of considerable discussion. Herein, we demonstrate that in situ generated Fe vacancies in the pristine CoFeOOH catalyst through a pre‐conversion process during alkaline OER result from dynamic Fe dissolution, identifying the origin of Fe‐vacancy‐induced enhanced OER kinetics. Density functional theory (DFT) calculations and experimental results including X‐ray absorption fine‐structure spectroscopy, in situ UV‐Vis spectroscopy, and in situ Raman spectroscopy reveal that the Fe vacancies could significantly promote the d‐band center and valence states of adjacent Co sites, alter the active site from Fe atom to Co atom, accelerate the formation of high‐valent active Co4+ species, and reduce the energy barrier of the potential‐determining step, thereby contribute to the significantly enhanced OER performance. [ABSTRACT FROM AUTHOR]

The electrolyte cations‐dependent kinetics have been widely observed in many fields of electrocatalysis, however, the exact mechanism of the influence on catalytic performance is still a controversial topic of considerable discussion. Herein, combined with operando X‐ray diffraction (XRD) and high‐resolution transmission electron microscopy (HRTEM), we verify that the electrolyte cations could intercalate into the layer of pristine CoOOH catalyst during the oxygen evolution reaction (OER) process, while the bigger cations lead to enlarged interlayer spacing and increased OER activity, following the order Cs+>K+>Na+>Li+. X‐ray absorption spectroscopy (XAS), in situ Raman, in situ Ultraviolet‐visible (UV/Vis) spectroscopy, in situ XAS spectroscopy, cyclic voltammetry (CV), and theoretical calculations reveal that the intercalation of electrolyte cations efficiently modify the oxidation states of Co by enlarging the Co−O bonds, which in turn enhance the d‐band center of Co, optimize the adsorption strength of oxygen intermediates, facilitate the formation of OER active Co(IV) species, and reduce the energy barrier of the rate‐determing step (RDS), thereby enhancing the OER activity. This work not only provides an informative picture to understand the complicated dependence of OER kinetics on electrolyte cations, but also sheds light on understanding the mechanism of other electrolyte cation‐targeted electrocatalysis. [ABSTRACT FROM AUTHOR]

Developing highly efficient and cost effective electrocatalysts towards hydrogen oxidation reaction under alkaline electrolyte is essential for the commercial application of anion exchange membrane fuel cells (AEMFCs). Nickel‐based materials showed great performance for alkaline HOR which have been regarded as promising alternatives for Pt‐group metals. In this review, several effective strategies which can successfully optimize the interaction with intermediates and promote the HOR kinetics of Ni under alkaline medium are discussed, including heteroatom doping, forming alloys and compounds, decorating with supports and constructing heterointerfaces. Meanwhile, based on the structural adjustment, the durabilities of Ni‐based materials are enhanced significantly. We believe this paper might provide guidance for future catalysts design and mechanism investigation for alkaline HOR. [ABSTRACT FROM AUTHOR]

The development of electrocatalysts with high‐efficiency and clear structure‐activity relationship towards the sluggish oxygen evolution reaction (OER) is essential for the wide application of water electrolyzers. Recently, the dynamic reconstruction phenomenon of the catalysts' surface structures during the OER process has been discovered. With the help of various advanced ex situ and in situ characterization, it is demonstrated that such surface reconstruction could yield actual active species to catalyze the water oxidation process. However, the attention and studies of potential interaction between reconstructed species and substrate are lacking. This review summarizes the recent development of typical reconstructed electrocatalysts and the substrate effect. First, the advanced characterization for electrocatalytic reconstruction is briefly discussed. Then, typical reconstructed electrocatalysts are comprehensively summarized and the key role of substrate effects during the OER process is emphasized. Finally, the future challenges and perspectives of surface reconstructed catalysts for water electrolysis are discussed. [ABSTRACT FROM AUTHOR]

Transition metal‐based electrocatalysts will undergo surface reconstruction to form active oxyhydroxide‐based hybrids, which are regarded as the "true‐catalysts" for the oxygen evolution reaction (OER). Much effort has been devoted to understanding the surface reconstruction, but little on identifying the origin of the enhanced performance derived from the substrate effect. Herein, we report the electrochemical synthesis of amorphous CoOOH layers on the surface of various cobalt sulfides (CoSα), and identify that the reduced intermolecular energy gap (Δinter) between the valence band maximum (VBM) of CoOOH and the conduction band minimum (CBM) of CoSα can accelerate the formation of OER‐active high‐valent Co4+ species. The combination of electrochemical and in situ spectroscopic approaches, including cyclic voltammetry (CV), operando electron paramagnetic resonance (EPR) and Raman, reveals that Co species in the CoOOH/Co9S8 are more readily oxidized to CoO2/Co9S8 than in CoOOH and other CoOOH/CoSα. This work provides a new design principle for transition metal‐based OER electrocatalysts. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Developing highly efficient and low‐cost electrocatalysts towards oxygen evolution reaction (OER) is essential for practical application in water electrolyzers and rechargeable metal‐air batteries. Although Fe‐based oxyhydroxides are regarded as state‐of‐the‐art non‐noble OER electrocatalysts, the origin of performance enhancement derived from Fe doping remains a hot topic of considerable discussion. Herein, we demonstrate that in situ generated Fe vacancies in the pristine CoFeOOH catalyst through a pre‐conversion process during alkaline OER result from dynamic Fe dissolution, identifying the origin of Fe‐vacancy‐induced enhanced OER kinetics. Density functional theory (DFT) calculations and experimental results including X‐ray absorption fine‐structure spectroscopy, in situ UV‐Vis spectroscopy, and in situ Raman spectroscopy reveal that the Fe vacancies could significantly promote the d‐band center and valence states of adjacent Co sites, alter the active site from Fe atom to Co atom, accelerate the formation of high‐valent active Co4+ species, and reduce the energy barrier of the potential‐determining step, thereby contribute to the significantly enhanced OER performance. [ABSTRACT FROM AUTHOR]

Keywords: alkaline electrolyte; oxygen evolution reaction; reconstruction phenomenon; substrate effect; water electrolysis EN alkaline electrolyte oxygen evolution reaction reconstruction phenomenon substrate effect water electrolysis 1 1 1 03/03/23 20230301 NES 230301 This short review summarizes the reconstruction phenomena in different types of electrocatalysts, and then concludes the potential substrate effects, offering insights into both the fundamental of the reconstruction chemistry and the design of reconstructed electrocatalysts with the guideline of substrate effect. Alkaline electrolyte, oxygen evolution reaction, reconstruction phenomenon, substrate effect, water electrolysis. [Extracted from the article]

Understanding the structure and dynamic process of interfacial water molecules at the catalyst‐electrolyte interface on acidic oxygen evolution reaction (OER) kinetics is highly desirable for the development of proton exchange membrane water electrolyzers. Herein, we construct a series of p‐block metal elements (Ga, In, Sn) doped RuO2 catalysts with manipulated electronic structure and Ru−O covalency to investigate the effect of electrochemical interfacial engineering on the improvement of acidic OER activity. Associated with operando attenuated total reflectance surface‐enhanced infrared absorption spectroscopy measurements and theoretical analysis, we uncover the free‐H2O enriched local environment and dynamic evolution from 4‐coordinated hydrogen‐bonded water and 2‐coordinated hydrogen‐bonded water to free‐H2O on the surface of Ga−RuO2, are responsible for the optimized connectivity of hydrogen bonding network in the electrical double layer by promoting solvent reorganization. In addition, the structurally ordered interfacial water molecules facilitate high‐efficiency proton‐coupled electron transfer across the interface, leading to reduced energy barrier of the follow‐up dissociation process and enhanced acidic OER performance. This work highlights the key role of structure and dynamic process of interfacial water for acidic OER, and demonstrates the electrochemical interfacial engineering as an efficient strategy to design high‐performance electrocatalysts. [ABSTRACT FROM AUTHOR]