Mastering vacancy engineering for electrocatalysis: Insights into classification, synthesis, and characterization

Electrocatalysis is essential in energy conversion, but the lack of efficient electrocatalysts limits its large-scale application. Vacancy engineering has a significant impact in increasing the active sites of catalysts, improving the conductivity, and enhancing the stability, and is widely used to improve the activity of electrocatalysts. In this review, we first classify vacancies, including anionic and cationic vacancies, and emphasize the effects of vacancies on the electronic structure, conductivity, and stability of catalysts. Secondly, some representative methods for introducing vacancies into materials, such as hydrothermal, electrochemical and plasma treatments are summarized. In addition, advanced characterization techniques used for vacancy identification, such as HRTEM, STM, XPS and EPR, are systematically discussed. The experiments and theoretical calculations have proved the positive effect of vacancy engineering in improving electrocatalytic performance. However, there are still some challenges, such as the variety of vacancies is not rich enough, the specific relationship between vacancy and electrocatalytic performance is not clear, and the number of vacancies needs to be rationally designed. In addition, by integrating DFT, artificial intelligence technology and in-situ characterization techniques can deepen the understanding of catalytic mechanisms by monitoring the dynamic changes of vacancy defects during electrocatalytic reactions. Despite there are many difficulties and challenges, designing and fabricating efficient electrocatalysts containing vacancies has a promising research prospect.