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The rational design and development of highly efficient oxygen evolution reaction (OER) electrocatalysts is vital for the application of renewable energy devices. Recently, the strategy of defect engineering draws much attention due to its positive effect on regulating the electronic structure, and thus, promoting the electrocatalytic performance of various materials. In this review, the main focus is on the cation vacancy defects of transition metal‐based electrocatalysts; the latest progress in cation vacancy defect engineering for the electrocatalytic OER is summarized. The different effects of cation vacancy defects on OER are well discussed together with the reaction mechanism, mainly including improving the conductivity, optimizing the adsorption of key intermediates, guiding the surface reconstruction to form active species, and enhancing the long‐term stability. Then, methods to construct cation vacancy defects on different electrocatalysts and the characterization of cation vacancies are systematically introduced. Finally, the remaining challenges and future prospects of cation vacancy defect engineering for promoting OER performance are further proposed. [ABSTRACT FROM AUTHOR]

Exploring advanced technologies to efficiently produce green hydrogen energy is imperative to alleviate the energy crisis and environmental pollution. Conventional overall water electrolysis (OWE) has been regarded as a promising approach for effective H2 production, however, it is largely restricted by the sluggish kinetics of the anodic oxygen evolution reaction (OER). Coupling kinetically favorable anodic reactions, such as biomass‐derived compound oxidation and pollutant degradation, with the hydrogen evolution reaction (HER) in hybrid water electrolysis (HWE), can not only solve the biomass recycling and pollutant emission problems but also save the energy cost for clean H2 generation. Hence, various advanced earth‐abundant electrocatalysts have been developed to catalyze those promising anodic reactions, yet some problems such as tedious preparation and unsatisfactory performance still exist. Given the gap between research and practical applications, this review summarizes the recent progress in electrocatalysts for diverse alternative anodic oxidation reactions over the last five years together with their application in HWE systems. An in‐depth understanding of different reaction mechanisms and assessments toward electrocatalysts is discussed to further enhance anodic efficiency. The advantages, differences, and critical issues of different HWE systems are thoroughly discussed as well, providing a new avenue for low‐voltage H2 production from renewable resources and waste products. [ABSTRACT FROM AUTHOR]

The electronic band structure of MoS2 exerts far‐ranging effects on the applications of these materials, ranging from chemical catalysis, electronic, and magnetic behaviors. However, the underlying relationship between the electronic band structure and activity is largely unknown in heterogeneous catalysis including the hydrogen evolution reaction, partly due to the lack of a controllable methodology to achieve desirable electronic band structures in the 2H‐phase MoS2. Herein it is demonstrated that dual dopants can engineer the band structure of MoS2 by substituting into the adjacent Mo sites. Specifically, these constructed PdRe dimers bridged by sulfur (PdSRe sites) introduce conducting electronic states around the Fermi level to increase the metallic characteristics of MoS2, resulting in metallic‐like behavior, which is initially semiconducting. Furthermore, the efficacy of inducing a phase conversion from 2H to metallic 1T is higher for codoping with dual dopants as compared to that for the use of a single dopant, thereby generating more intrinsically active PdS*Mo sites to further increase active sites density. Ultimately, this leads to the MoS2 catalyst showing a low overpotential of 46 mV at a current density of 10 mA cm−2 and a high exchange current density of 1.524 mA cm−2, along with superior operating durability. [ABSTRACT FROM AUTHOR]

Ultrathin nanomeshes perfectly inherit the integrated advantages of ultrathin 2D materials and porous nanostructures, which have shown their great application potential in catalysis and electronic devices. Here, the general synthesis of ultrathin metal borate (i.e., Co‐Bi, Ni‐Bi, and Fe‐Bi) nanomeshes is reported by capitalizing on 3D bark‐like N‐doped carbon (denoted BNC) as nanoreactors. Indeed, this strategy is straightforward, only comprising a one‐step reaction between metal cations and sodium borohydride without using templates. As nanoreactors, the BNC derived from biomass waste of lychee exocarp possesses distinctive advantages of low cost, fractured textures, porous nanostructures (surface area: 1915.5 m2 g−1), electronegative surface (zeta potential: −43.4 mV), and superhydrophilicity for greatly facilitating the adsorption of metal cations with strong strength to effectively control the growth of 2D nanomeshes. The as‐synthesized Co‐Bi and Ru‐doped Co‐Bi (Ru‐Co‐Bi) nanomeshes exhibit excellent performance for the oxygen evolution reaction and hydrogen evolution reaction, respectively. Impressively, the water splitting device based on the Co‐Bi and Ru‐Co‐Bi nanomeshes can enable a current density of 10 mA cm−2 at a small cell voltage of 1.53 V. Therefore, this work paves new avenues for the facile synthesis of ultrathin metal nanomeshes. [ABSTRACT FROM AUTHOR]

Despite the exciting achievements made in synthesis of monofunctional electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), or hydrogen evolution reaction (HER), it is challenging to develop trifunctional electrocatalysts for both ORR/OER/HER. Herein, N, O‐codoped graphene nanorings‐integrated boxes (denoted NOGB) are crafted via high‐temperature pyrolysis and following acid etching of hybrid precursors containing polymers and Prussian blue analogue cubes. The electrochemical results signified that the resulting NOGB‐800 (800 refers to pyrolysis temperature) is highly active for trifunctional electrocatalysis of ORR/OER/HER. This can be reasonably attributed to the advanced nanostructures (i.e., the hierarchically porous nanostructures on the hollow nanorings) and unique chemical compositions (i.e., N, O‐codoped graphene). More attractively, the rechargeable Zn–air battery based on NOGB‐800 displays maximum power density of 111.9 mW cm−2 with small charge–discharge potential of 0.72 V and excellent stability of 30 h, comparable with the Pt/C+Ir/C counterpart. The NOGB‐800 could also be utilized as bifunctional electrocatalysts for overall water splitting to yield current density of 10 mA cm−2 at a voltage of 1.65 V, surpassing most reported electrocatalysts. Therefore, the NOGB‐800 is a promising candidate instead of precious metal–based electrocatalysts for the efficient Zn–air battery and water splitting. An easy yet robust route, for the first time, is developed to craft N, O‐codoped graphene‐integrated boxes by employing hybrids containing polymers and Prussian blue analogue cubes as precursors. Benefiting from the hierarchically porous nanostructures and highly active N, O‐codoped graphene, the resulting electrocatalysts display excellent performance on the overall water splitting and Zn–air battery. [ABSTRACT FROM AUTHOR]