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Heteroatom doping has emerged as a highly effective strategy to enhance the activity of metal‐based electrocatalysts toward the oxygen evolution reaction (OER). It is widely accepted that the doping does not switch the OER mechanism from the adsorbate evolution mechanism (AEM) to the lattice‐oxygen‐mediated mechanism (LOM), and the enhanced activity is attributed to the optimized binding energies toward oxygen intermediates. However, this seems inconsistent with the fact that the overpotential of doped OER electrocatalysts (<300 mV) is considerably smaller than the limit of AEM (>370 mV). To determine the origin of this inconsistency, we select phosphorus (P)‐doped nickel‐iron mixed oxides as the model electrocatalysts and observe that the doping enhances the covalency of the metal‐oxygen bonds to drive the OER pathway transition from the AEM to the LOM, thereby breaking the adsorption linear relation between *OH and *OOH in the AEM. Consequently, the obtained P‐doped oxides display a small overpotential of 237 mV at 10 mA cm−2. Beyond P, the similar pathway transition is also observed on the sulfur doping. These findings offer new insights into the substantially enhanced OER activity originating from heteroatom doping. [ABSTRACT FROM AUTHOR]

Heteroatom doping has emerged as a highly effective strategy to enhance the activity of metal‐based electrocatalysts toward the oxygen evolution reaction (OER). It is widely accepted that the doping does not switch the OER mechanism from the adsorbate evolution mechanism (AEM) to the lattice‐oxygen‐mediated mechanism (LOM), and the enhanced activity is attributed to the optimized binding energies toward oxygen intermediates. However, this seems inconsistent with the fact that the overpotential of doped OER electrocatalysts (<300 mV) is considerably smaller than the limit of AEM (>370 mV). To determine the origin of this inconsistency, we select phosphorus (P)‐doped nickel‐iron mixed oxides as the model electrocatalysts and observe that the doping enhances the covalency of the metal‐oxygen bonds to drive the OER pathway transition from the AEM to the LOM, thereby breaking the adsorption linear relation between *OH and *OOH in the AEM. Consequently, the obtained P‐doped oxides display a small overpotential of 237 mV at 10 mA cm−2. Beyond P, the similar pathway transition is also observed on the sulfur doping. These findings offer new insights into the substantially enhanced OER activity originating from heteroatom doping. [ABSTRACT FROM AUTHOR]

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 ability to develop bifunctional electrocatalysts for concurrent CO2 reduction reaction (CO2RR) and oxygen evolution reaction (OER) is the key to the practical application of CO2 splitting to produce CO. However, this remains a grand challenge. Herein, a robust strategy to rationally craft hierarchical structured bifunctional electrocatalysts composed of 3D CoS2 nanocages interconnected on 2D CoS2 nanosheet arrays (denoted hierarchical CoS2 nanocages) for high‐performance CO2 splitting is developed. The subsequent calcination removes the partial S edges of CoS2, thereby strongly suppressing the hydrogen evolution reaction (HER) of CoS2. By combining theoretic and experimental results, for the first time, it is discovered that the plane S of CoS2, instead of S edges, are highly active for CO2RR but inactive for HER, rendering the plane S as ideal active sites for CO2RR. Intriguingly, the composition tuning via calcination and the presence of a hierarchical architecture confer hierarchical CoS2 nanocages respective outstanding CO2RR and OER performance. Notably, the hierarchical CoS2 nanocages can be exploited as bifunctional electrocatalysts for overall CO2 splitting to yield the current density of 1 mA cm−2 at a small cell voltage of 1.92 V, much lower than the widely reported values (>2.5 V). [ABSTRACT FROM AUTHOR]

• Facile synthesis of amorphous VO 2 –crystalline NiS 2 heterostructures. • Identifying the different co-catalytic function of VO 2 for boosting the HER and OER. • VO 2 tunes the binding energy of NiS 2 with hydrogen intermediates to enhance the HER activity. • VO 2 alters the electrochemical reconstruction behavior of NiS 2 during the process of OER. • The obtained VO 2 / NiS 2 requires a low voltage of 1.53 V at10 mA cm−2 for overall water splitting. The rational design of bifunctional electrocatalysts is essential to achieve efficient hydrogen production from water splitting. Here, inspired by cocatalysts widely utilized in photocatalysis, we designed a heterostructure comprising amorphous VO 2 and crystalline NiS 2 , aiming at using VO 2 cocatalyst to boost activity of NiS 2 for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Intriguingly, we found that VO 2 displayed different co-catalytic function in boosting the OER and HER. Specifically, the VO 2 optimized the binding energy of hydrogen intermediate on NiS 2 and thus improved the HER activity. As for the OER, the amorphous VO 2 was easily dissolved in the KOH electrolyte, resulting in the generation of abundant oxygen vacancies in the in-situ generated active phase of NiOOH from NiS 2 , thereby drastically enhancing the OER activity. Consequently, the obtained VO 2 –NiS 2 @CC displayed excellent performance for overall water splitting, with a low voltage of 1.53 V at 10 mA cm−2. [ABSTRACT FROM AUTHOR]

Recently, metal‐free, heteroatom‐doped carbon nanomaterials have emerged as promising electrocatalysts for the oxygen evolution reaction (OER), but their synthesis is a tedious process involving energy‐wasting calcination. Molecular electrocatalysts offer attractive catalysts for the OER. Here, phytic acid (PA) was selected to investigate the OER activity of carbons in organic molecules by DFT calculations and experiments. Positively charged carbons on PA were very active towards the OER. The PA molecules were fixed into a porous, conductive hydrogel with a superhydrophilic surface. This outperformed most metal‐free electrocatalysts. Besides the active sites on PA, the high OER activity was also related to the porous and conductive networks on the hydrogel, which allowed fast charge and mass transport during the OER. Therefore, this work provides a metal‐free, organic‐molecule‐based electrocatalyst to replace carbon nanomaterials for efficient OER. Positively charged carbons on organic molecules (i.e. phytic acid, denoted PA) can participate in the oxygen evolution reaction (OER), as shown by DFT calculations and experiments. Moreover, doping of PA into a porous and conductive hydrogel is a robust strategy for stabilizing PA, as well as boosting the charge and mass transport of PA during the OER. [ABSTRACT FROM AUTHOR]

Recently, metal‐free, heteroatom‐doped carbon nanomaterials have emerged as promising electrocatalysts for the oxygen evolution reaction (OER), but their synthesis is a tedious process involving energy‐wasting calcination. Molecular electrocatalysts offer attractive catalysts for the OER. Here, phytic acid (PA) was selected to investigate the OER activity of carbons in organic molecules by DFT calculations and experiments. Positively charged carbons on PA were very active towards the OER. The PA molecules were fixed into a porous, conductive hydrogel with a superhydrophilic surface. This outperformed most metal‐free electrocatalysts. Besides the active sites on PA, the high OER activity was also related to the porous and conductive networks on the hydrogel, which allowed fast charge and mass transport during the OER. Therefore, this work provides a metal‐free, organic‐molecule‐based electrocatalyst to replace carbon nanomaterials for efficient OER. [ABSTRACT FROM AUTHOR]

The ability to develop low-cost highly efficient electrocatalyst for oxygen evolution reaction (OER) is key to the overall water splitting device that represents a viable and promising source of alternative energy. Herein, we crafted three-dimensional (3D) network comprising nitrogen-doped graphitic carbon-coated heterojunctions (denoted NC-Ni 0.36 Fe 0.64 /MnO x ) via one-step calcination of hybrid precursors containing ternary Prussian blue analogues and polymers. The NC-Ni 0.36 Fe 0.64 /MnO x nanocomposites were then exploited as catalysts for OER, displaying exceptional performance with a small overpotential of 300 mV to reach 10 mA cm −2 , a low Tafel slope of 43 mV/dec and an outstanding stability without deactivation over a 10-h OER. Notably, compared to commercial RuO 2 catalysts, NC Ni 0.36 Fe 0.64 /MnO x catalysts demonstrated much lower overpotential and Tafel slope. The excellent OER performance can be attributed to the presence of high-valence oxidized metal species (Ni 2+ , Fe 2+ and Mn 2+ ) at the heterostructured interface as well as pyridinic N-doped carbon species on highly conductive graphitic carbon network, thus greatly facilitating the electron-withdrawing from OH − and thus charge transfer during OER. This simple yet effective strategy may open new possibilities for creating a wide range of low-cost, high-efficiency, non-precious transition metal OER catalysts for the overall water splitting. [ABSTRACT FROM AUTHOR]

Rational designing of efficient bifunctional oxygen electrocatalysts is significantly important but rather challenging for rechargeable zinc-air batteries. Herein, a novel high-performance bifunctional oxygen electrocatalyst for rechargeable zinc–air batteries are constructed based on bimetal Mn@Co-N-C encapsulated in in situ grown N,S-doped graphitic carbon framework with within a porous three-dimensional (3D) structure. The final catalyst shows a high half-wave potential of 0.89 V for oxygen reduction reaction, and a low operating overpotential of 0.38 V to achieve a 10 mA cm−2 current density for oxygen evolution reaction. The physical characterizations reveal that a strong synergetic coupling between bimetal Mn@Co-N-C and S dopant can effectively increase the active sites, meanwhile achieve a rational manipulation of the active site configuration toward a favorable electronic structure. Impressively, the assembled zinc–air batteries using liquid electrolytes and the all-solid-state batteries with this catalyst exhibit excellent charging–discharging performance, long lifetime, and high flexibility. [Display omitted] • The second metal source is Mn, which utilizes a controlled self-assembly method to orient on N, S-doped carbon-based materials generated from MOFs. • The synthesized Mn@Co-NS catalyst exhibits excellent bifunctional electrocatalytic activity. • The reasons for the superior performance of Mn@CO-NS catalysts are revealed. • Mn@Co-NS has good performance and long-term stability in the field of zinc-air batteries. • It provides direction guidance for the qualitative landing of various metals on carbon substrates, bringing the application of zinc-air batteries to a new level. [ABSTRACT FROM AUTHOR]

A facile construction of Ru/RuO 2 composite with porous reticular structure (denoted as Ru/RuO 2 -PRS) by controllable pyrolysis of Ru3+ coordinated cyanoguanidine was presented for oxygen evolution reaction (OER). The Ru/RuO 2 heterostructure was identified in Ru/RuO 2 -PRS. Taking the advantages of the Ru/RuO 2 heterostructure and large specific surface area, Ru/RuO 2 -PRS exhibits much more improved OER activity with much lower onset potential and overpotential to reach the current density of 10 mA cm−2 compared with RuO 2 porous powder and RuO 2 nano-particles counterparts in both acidic and alkaline solution. Specifically, Ru/RuO 2 -PRS exhibits much improved durability because the unique Ru/RuO 2 heterostructure relieves the dissolution of RuO 2 at high anodic potential that has been the bottleneck of Ru-based catalysts for OER, especially in acidic electrolyte. This study provides a new strategy to promote the OER application in acidic solution. • We present a facile one-step calcination method to synthesize 3D porous reticular structure of Ru/RuO 2 (Ru/RuO 2 -PRS). • The as prepared Ru/RuO 2 -PRS presents abundant Ru/RuO 2 heterostructure, which benefits to the electrocatalytic process. • Ru/RuO 2 -PRS exhibits excellent OER activity and stability in both acid and alkaline electrolyte. [ABSTRACT FROM AUTHOR]

• A nature-inspired etching strategy is developed for the construction of karst topography (KT)-featured electrode. • The KT architecture offers a "superaerophobic" surface for rapidly releasing O 2 bubbles during electrocatalysis. • Experimentally identifying that the core-shell structure optimizes the adsorption strength of *OH intermediates. • The obtained electrocatalysts achieve the large current densities of 1500 mA cm−2 at an overpotential of 380 mV. Exploring of electrocatalysts for high-output oxygen evolution reaction (OER) is key to practical applications, but still remains challenging. Here, we developed a nature-inspired etching strategy for the construction of karst topography (KT)-featured electrode comprising core-shell structured Ni(0)@Ni(II) towards efficient OER. Intriguingly, the KT architecture confers a "superaerophobic" surface to render the large amount of generated O 2 bubbles release rapidly and timely from the electrode surface at the high current density of OER (i.e., 1500 mA cm−2). Moreover, this strategy allows good control over the generated core-shell structure for promoting the heterointerface synergetic effect of Ni(0)@Ni(II). By adding probing molecules to react with OER intermediates under operation conditions, we obtain first direct experimental evidence that the core-shell structure can optimize the adsorption strength of *OH for significantly boosting the OER kinetics. Notably, the obtained electrode has excellent performance for OER with a small overpotenital of 380 mV at 1500 mA cm−2. [ABSTRACT FROM AUTHOR]

A novel structure of Fe-doped NiO coupled Ni cluster hollow nanotube arrays (Fe-NiO-Ni CHNAs) composed of defect-rich NiO phase and Ni clusters anchored on outside of nanotubes is presented. The d-band downshifted by Fe-doping, coupled of Ni clusters and defect-rich nature greatly improve electrocatalytic performances of Fe-NiO-Ni CHNAs toward oxygen evolution reaction. • A multi-level structure of Fe-doped NiO coupled Ni cluster hollow nanotube arrays (Fe-NiO-Ni CHNAs) was synthesized as a catalyst for OER. • Fe-NiO-Ni CHNAs exhibits overpotential of 245 mV at 10 mA cm−2 and outstanding durability that surpasses most of transition metal oxides. • The improved OER activity is mainly because Fe doping downshifts the d-band of metal sites. • Fe-NiO-Ni CHNAs obeyed the adsorbate evolution mechanism with a nonconcerted proton-electron transfer pathway. Herein we present a novel multi-level structure of Fe-doped NiO coupled Ni cluster hollow nanotube arrays (Fe-NiO-Ni CHNAs) grown on carbon fiber cloth as an efficient catalyst for oxygen evolution reaction. In this multi-level structure, rocksalt-type Fe-doped NiO phase hybrids with Ni clusters coupled into the nanospheres anchored to the outside of nanotube, forming a unique 3D corn-like structure. This novel multi-level structure represents a large specific area for catalytic reaction. X-ray absorption fine structure indicates that the defect-rich Fe-doped NiO phase has abundant coordinative unsaturated sites as active sites, and Fe doping downshifts the d-band of metal sites, which is the main contribution to the improved oxygen evolution reaction catalytic activity. The OER of Fe-NiO-Ni CHNAs obeys the adsorbate evolution mechanism with the nonconcerted proton-electron transfer pathway as a rate-determining step. Thus Fe-doped NiO CHNAs exhibits excellent OER performance and outstanding durability that surpasses most of transition metal oxides. [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]