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Water electrolysis is a promising method for efficiently producing hydrogen and oxygen, crucial for renewable energy conversion and fuel cell technologies. The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are two key electrocatalytic reactions occurring during water splitting, necessitating the development of active, stable, and low-cost electrocatalysts. Transition metal (TM)-based electrocatalysts, spanning noble metals and TM oxides, phosphides, nitrides, carbides, borides, chalcogenides, and dichalcogenides, have garnered significant attention due to their outstanding characteristics, including high electronic conductivity, tunable valence electron configuration, high stability, and cost-effectiveness. This timely review discusses developments in TM-based electrocatalysts for the HER and OER in alkaline media in the last 10 years, revealing that the exposure of more accessible surface-active sites, specific electronic effects, and string effects are essential for the development of efficient electrocatalysts towards electrochemical water splitting application. This comprehensive review serves as a guide for designing and constructing state-of-the-art, high-performance bifunctional electrocatalysts based on TMs, particularly for applications in water splitting. [ABSTRACT FROM AUTHOR]

Perovskite oxides are regarded as promising electrocatalysts for water splitting due to their cost‐effectiveness, high efficiency and durability in the oxygen evolution reaction (OER). Despite these advantages, a fundamental understanding of how critical structural parameters of perovskite electrocatalysts influence their activity and stability is lacking. Here, we investigate the impact of structural defects on OER performance for representative LaNiO3 perovskite electrocatalysts. Hydrogen reduction of 700 °C calcined LaNiO3 induces a high density of surface oxygen vacancies, and confers significantly enhanced OER activity and stability compared to unreduced LaNiO3; the former exhibit a low onset overpotential of 380 mV at 10 mA cm−2 and a small Tafel slope of 70.8 mV dec−1. Oxygen vacancy formation is accompanied by mixed Ni2+/Ni3+ valence states, which quantum‐chemical DFT calculations reveal modify the perovskite electronic structure. Further, it reveals that the formation of oxygen vacancies is thermodynamically more favourable on the surface than in the bulk; it increases the electronic conductivity of reduced LaNiO3 in accordance with the enhanced OER activity that is observed. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) are considered to be promising candidates for electrochemical water splitting. However, most MOFs are characterized by low electronic conductivity limiting their use as bulk materials for anodes and cathodes. Furthermore, the understanding of the critical parameters controlling the activity and stability of MOF electrocatalysts is still insufficient. Herein, a systematic analysis is presented of the key structural parameters controlling the oxygen evolution reaction (OER) performance and stability of a representative family of bimetallic NiFe‐MOFs, where the role of the metal cations on the accessible active sites and intrinsic activity can be investigated independently from the crystal structure. The models and in‐depth structural and morphological characterizations reveal a hierarchy of properties affecting the OER activity with accessible sites and intrinsic activity playing a major role in the charge transfer efficiency. Optimization of these properties and addition of a conductive support substrate leads to efficient MOF‐nanocomposite electrocatalysts achieving a low overpotential of 258 mV at a current density of 10 mA cm−2 with a small Tafel slope of 49 mV dec−1 and excellent stability for more than 32 h of continuous OER in alkaline medium. [ABSTRACT FROM AUTHOR]

Keywords: graphene; MOF grains; nanocomposites; ultrafine structure; water oxidation EN graphene MOF grains nanocomposites ultrafine structure water oxidation 1 1 1 04/29/21 20210428 NES 210428 In article number 2003759, Antonio Tricoli, Chuan Zhao and co-workers design well-dispersed bimetallic NiFe-MOF nanograins homogeneously grafted on graphene for use in the oxygen evolution reaction (OER). Oxygen Evolution Reaction: Engineering the Activity and Stability of MOF-Nanocomposites for Efficient Water Oxidation (Adv. Graphene, MOF grains, nanocomposites, nanocomposites, ultrafine structure, water oxidation. [Extracted from the article]

Tailoring the surface structure of Earth-abundant perovskite oxides can provide cost-effective, high-efficient, and durable electrocatalysts for oxygen evolution reaction (OER). However, the structural origin leading to high OER performance of perovskite is not fully understood. Here, we present a strategy of tuning the surface energy density of non-stoichiometric perovskite by creating surface defects in the 3D inverse opal LaCoO 3-x (3DIO-LaCoO 3-x) through a colloidal template strategy. The defective 3DIO-LaCoO 3-x , which has an enhanced surface energy density and a shift in the d-band centre of Co relative to the Fermi level, demonstrates significantly improved intrinsic OER activity, with a TOF (0.21 s−1) ten-folder larger than that of conventional LaCoO 3 nanoparticles (0.02 s−1). The defective surfaces of 3DIO-LaCoO 3-x are theoretically proven to alter the rate determining step of OER and significantly reduce the adsorption energies of the intermediate species, resulting in dramatically enhanced OER activity. Moreover, rich surface defects with high electrical conductivity can mitigate structural corrosion by fast transfer of charge through defective conductive channels, and thus enables long-term stability for the defective 3DIO-LaCoO 3-x. These results provide an effective approach for enhancing the intrinsic activity of perovskite for water oxidation towards understanding the surface structure engineering for perovskite-based materials. Image 1 • A surface defective 3D inverse opal LaCoO 3-x perovskite was synthesized. • Rich surface defects modified surface energy density and d-band centre of Co. • Intrinsic activity and stability against OER were significantly increased. • Defective sites reduced the energy barrier of the rate determining step of OER. [ABSTRACT FROM AUTHOR]