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Anionic redox allows the direct formation of O─O bonds from lattice oxygens and provides higher catalytic in the oxygen evolution reaction (OER) than does the conventional metal ion mechanism. While previous theories have predicted and experiments have suggested the possible O─O bond, it has not yet been directly observed in the OER process. In this study, operando soft X‐ray absorption spectroscopy (sXAS) at the O K‐edge and the operando Raman spectra is performed on layered double CoFe hydroxides (LDHs) after intercalation with [Cr(C2O4)3]3−, and revealed a three‐step oxidation process, staring from Co2+ to Co3+, further to Co4+ (3d6L), and ultimately leading to the formation of O─O bonds and O2 evolution above a threshold voltage (1.4 V). In contrast, a gradual oxidation of Fe is observed in CoFe LDHs. The OER activity exhibits a significant enhancement, with the overpotential decreasing from 300 to 248 mV at 10 mA cm−2, following the intercalation of [Cr(C2O4)3]3− into CoFe LDHs, underscoring a crucial role of anionic redox in facilitating water splitting. [ABSTRACT FROM AUTHOR]

Identifying real active sites and understanding the mechanism of oxygen evolution reaction (OER) are still a big challenge today for developing efficient electrochemical catalysts in renewable energy technologies. Here, using a combined in situ/operando experiments and theory, the catalytic mechanism of the ordered OER active Co and Ir ions in Sr2CoIrO6−δ is studied, which exhibits an unprecedented low overpotential 210 mV to achieve 10 mA cm–2, ranking the highest performance among perovskite‐based solid‐state catalysts. Operando X‐ray absorption spectroscopies as a function of applied voltage indicates that Ir4+ ion is gradually converted into extremely high‐valence Ir5+/6+, while the part of Co3+ ion is transferred into Co4+ under OER process. Density functional theory calculations explicitly reveal the order Co‐O‐Ir network as an origin of ultrahigh OER activity. The work opens a promising path to overcome the sluggish kinetics of OER bottleneck for water splitting via proper arrangements of the multi‐active sites in catalyst. [ABSTRACT FROM AUTHOR]

The structural diversity and tunable functionality of the amorphous metal‐organic frameworks (aMOFs) highlights this class of materials as a promising candidate for the development of sustainable energy technologies. The electrocatalytic performance in oxygen evolution reaction (OER) can be greatly improved by incorporating the hetero‐metallics into MOFs. Herein, the OER performance was significantly improved by the incorporation of Fe3+ ions into the crystalline cobalt‐based MOF, leading to amorphous structure. Benefiting from the optimized surface morphology and electrochemical surface area, charge transport, was greatly facilitated. The Fe/Co aMOF with 1/4 ratio (labeled as AFC‐MOFs (1 : 4)) exhibited an excellent and stable OER activity, with an ultralow overpotential (256 mV at 10 mA cm−2) and Tafel slope of 42.7 mV dec−1. XAS found that the majority of Co2+ in AFC‐MOFs (1 : 4) is converted to low‐spin Co3+ upon OER, while Fe3+ is maintained during the OER process, supporting the synergistic catalytic mechanism between Fe and Co. This material outperforms benchmark IrO2, which could be attributed to the hollow amorphous structure and the optimized electronic properties. [ABSTRACT FROM AUTHOR]

The development of an efficient and low-cost electrocatalyst for the oxygen evolution reaction (OER) via an eco-efficient route is a desirable, although challenging, outcome for overall water splitting. Herein, an iron-rich La0.6Sr0.4Co0.2Fe0.8O2.9 (LSCF28) perovskite with an open porous topographic structure was developed as an electrocatalyst by a straightforward molten-salt synthesis approach. It was found that porosity correlates with both the iron content and the molten-salt approach. Benefiting from the large surface area, high activity of the porous internal surface, and the optimal electronic configuration of redox sites, this inexpensive material exhibits high performance with a large mass activity of 40.8 A·g-1 at a low overpotential of 0.345 V in 0.1 M KOH, surpassing the state-of-the-art precious metal IrO2 catalyst and other well-known perovskites, such as Ba0.5Sr0.5Co0.8Fe0.2O3 and SrCoO2.7. Our work illustrates that the molten-salt method is an effective route to generate porous structures in perovskite oxides, which is important for energy conversion and storage devices. [ABSTRACT FROM AUTHOR]

Keywords: Amorphous materials; Bimetallic MOFs; Electrocatalysts; Oxygen evolution reaction EN Amorphous materials Bimetallic MOFs Electrocatalysts Oxygen evolution reaction 688 688 1 03/02/21 20210225 NES 210225 B The Front Cover b shows how the cobalt-based MOF is transformed from a crystalline structure to an amorphous structure by incorporation of optimal Fe SP 3+ sp ions. Front Cover: A Tunable Amorphous Heteronuclear Iron and Cobalt Imidazolate Framework Analogue for Efficient Oxygen Evolution Reactions (Eur. J. Inorg. Amorphous materials, Bimetallic MOFs, Electrocatalysts, Oxygen evolution reaction. [Extracted from the article]

The oxygen evolution reaction's (OER) poor kinetics is a considerable obstacle to overcome in the development of water‐derived hydrogen fuel. Research into OER catalysts using earth abundant elements is required to achieve desirable catalytic efficiency. Herein, a selection of misfit‐layered calcium cobaltite and transition metal (Mn, Fe, and Cu)‐doped compounds are synthesized and investigated in order to evaluate their potential as OER catalysts in an alkaline environment. It is discovered that Ca3Co4O9 OER activity may be substantially improved through incorporation of Fe, exhibiting low overpotential (331 mV) at 10 mA cm−2 current density, small Tafel slope of 52 mV dec−1, and an exceptional long‐term stability of electrolysis in 1 m KOH alkaline solution >100 h. Moreover, all materials used are systematically studied using a variety of characterization techniques, resulting in enhanced activity, which is attributed to the enhanced electrical conductivity, and optimized proportion of Co (III) and Co (IV), as well as the synergistic effect between Fe with Co. A collection of misfit‐layered calcium cobaltite and transition metal (Mn, Fe, and Cu)‐doped are investigated for their potential as catalysts for the oxygen evolution reaction (OER). OER activity for Ca3Co4O9 is improved by different valence of transition metal doping, not only by a synergistic effect, but also by the optimized proportion of Co (III) and Co (IV). [ABSTRACT FROM AUTHOR]

Developing efficient electrocatalyst at large current densities to meet the requirement of industrial water splitting is a big challenge today. Herein, we report a class of catalyst, BiCoO 3 with pyramidally coordinated Co3+. BiCoO 3 exhibits a large current density of 1000 mA cm−2 at a low overpotential of 402 mV and the overpotential even reduces to only 303 mV to achieve 1000 mA cm−2 by replacing Co with Fe, which belongs to the first-class level among large-current-densities electrocatalysts reported so far. Different from artificially created oxygen vacancies to optimize the bonding strength of the intermediate for enhancement of OER activity, BiCoO 3 has the rich active sites and the shortest reaction pathway leading to a large current density, as structurally every Co-O cluster has one oxygen vacancy. This work opens a new avenue for enhanced OER activity at high current densities via optimizing the arrangement of ligand vacancies. [Display omitted] • The first in-depth study of BiCoO 3 perovskite with pyramidally coordinated Co3+ in the water oxidation reaction. • The OER performance of BCFO belongs to the first-class level among large-current-densities electrocatalysts reported so far. • BiCoO 3 has the rich active sites and the shortest reaction pathway leading to an extraordinary large current density. [ABSTRACT FROM AUTHOR]

• Mo-doping is responsible for an enhanced OER activity of the exsoluted catalyst Co 0.76 Fe 0.18 Mo 0.06 O 1.35. • Mo-doping enhanced the oxidation state of the exsolved Co 0.76 Fe 0.18 Mo 0.06 O 1.35 before and after OER. • The O-K SXAS spectra revealed no La ions at the surface layers, and confirmed the formation of oxyhydroxide. Developing and understanding efficient catalysts for anodic oxygen evolution reaction (OER) is critical for the electrochemical production of H 2 for energy storage and transformation. Herein, a Co 0.76 Fe 0.18 Mo 0.06 O 1.35 catalyst with a spinel structure (CFMO-800) was prepared from Mo-doped LaCo 0.8 Fe 0.2 O 3 perovskites (LCF) by a simple exsolution method. The CFMO-800 catalyst exhibited a low potential of 1.48 V (vs. RHE) at a current density of 10 mA cm−2 in 1 M KOH surpassing all spinel and perovskite Co/Fe oxide catalysts reported. The surface-sensitive soft X-ray absorption spectroscopies (SXAS) at the Co-L 2,3 and the O-K edges revealed an unexpected increase in the Co valence state of CFMO-800 upon doped with the high-valence Mo and the clear formation of Co/Fe (oxyhydr)oxides on the surface layers of the exsolved catalyst. This study presents a strategy for the surface reconstruction by combining the exsolution and the high-valence ion doping to develop highly active electrochemical catalysts. [ABSTRACT FROM AUTHOR]