Engineering of Electronic States on Co₃O₄ Ultrathin Nanosheets by Cation Substitution and Anion Vacancies for Oxygen Evolution Reaction

Abstract

Due to the earth abundance and tunable electronic properties, etc., transition metal oxides (TMOs) show attractive attention in oxygen evolution reaction. O‐vacancies (Vo) play important roles in tailoring the local surface and electronic environment to lower the activation barriers. Herein, an effective strategy is shown to enhance the oxygen evolution reduction (OER) performance on Co3O4 ultrathin nanosheets via combined cation substitution and anion vacancies. The oxygen‐deficient Fe‐Co‐O nanosheets (3–4 nm thickness) display an overpotential of 260 mV@10 mA cm−2 and a Tafel slope of 53 mV dec−1, outperforming those of the benchmark RuO2 in 1.0 m KOH. Further calculations demonstrate that the combined introduction of Fe cation and Vo with appropriate location and content finely tune the intermediate absorption, consequently lowering the rate‐limiting activation energy from 0.82 to as low as 0.15 eV. The feasibility is also proved by oxygen‐deficient Ni‐Co‐O nanosheets. This work not only establishes a clear atomic‐level correlation between cation substitution, anion vacancies, and OER performance, but also provides valuable insights for the rational design of highly efficient catalysts for OER.

Recent advances in vacancy engineering of metal‐organic frameworks and their derivatives for electrocatalysis

“…Wang et al. presented an effective strategy to introduce oxygen vacancies on Co 3 O 4 ultrathin NSs to enhance OER performance 149 . The Fe‐Co‐O NSs with oxygen vacancies exhibited a low overpotential of 260 mV@10 mA/cm 2 and a Tafel slope of 53 mV/dec.…”

“…Copyright 2019, The Royal Society of Chemistry F I G U R E 1 1 Scheme of the synthetic route to Fe-Co-O ultrathin NSs. Reproduced with permission from Ref [149]…”

Modulation of Disordered Coordination Degree Based on Surface Defective Metal–Organic Framework Derivatives toward Boosting Oxygen Evolution Electrocatalysis

“…Such defects would lead to plentiful high-energy dangling bonds and coordinative unsaturated metal sites, which modulated the local surface electronic environment of catalysts. [33] To evaluate the water oxidation abilities of electrocatalysts with different degrees of disordered coordination and the influences of defects on electrochemical performances, we obtained linear sweep voltammetry (LSV) curves by using rotating disk electrode. Based on Figure 3a, we found that pristine Co-MOF displayed an onset potential at 1.53 V versus RHE (reversible hydrogen electrode) while Co-MOF-3h required the lowest onset potential at 1.49 V versus RHE.…”

Borate Anion Dopant Inducing Oxygen Vacancies over Co3O4 Nanocages for Enhanced Oxygen Evolution

“…Nevertheless, the poor electronic conductivity of Co 3 O 4 is the main bottleneck hindering the improvement of its OER activity [23,24]. In this regard, the regulation in morphologic and electronic structure has been reported as an effective way to improve the electrochemical performances of Co 3 O 4 -based materials [25][26][27]. On one hand, the unique nanostructures, such as nanosheets and nanocages, usually possess large specific surface area, which are beneficial to the mass transport and exposure of catalytically active sites, and the release of the generated gas during the water splitting process [24,[27][28][29][30].…”

“…In this regard, the regulation in morphologic and electronic structure has been reported as an effective way to improve the electrochemical performances of Co 3 O 4 -based materials [25][26][27]. On one hand, the unique nanostructures, such as nanosheets and nanocages, usually possess large specific surface area, which are beneficial to the mass transport and exposure of catalytically active sites, and the release of the generated gas during the water splitting process [24,[27][28][29][30]. On the other hand, recent studies have shown that the introduction of dopants can induce the formation of a large number of oxygen vacancy defects, increasing electronic conductivity and promoting the improvement of electrochemical OER performance [31,32].…”