Cation Vacancy Engineering in Transition Metal Catalysts for Hydrogen Evolution, Oxygen Evolution and Oxygen Reduction Reactions

Developing highly efficient electrocatalysts through rational design is of vital importance for advancing renewable energy technologies. Rapidly growing research interests are focused on cation vacancy engineering for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which are critical for energy technologies including water electrolyzers, fuel cells and metal-air batteries. Several papers have been published in this field. However, a systematic review concerning cation vacancy engineering for HER, OER, and ORR, along with a summary of the most recent advancements, is still lacking. To fill this gap, this work presents a timely and comprehensive review of this rapidly expanding and highly significant research field. This review begins with a brief introduction to the fundamentals of electrocatalysts for HER, OER and ORR. It then summarizes various strategies for introducing cation vacancies. Subsequently, detailed methods for characterizing these defects are discussed. The review further explores the diverse effects of cation vacancy defects on catalytic activity, including their roles in enhancing catalyst stability, exposing more active sites, improving electrical conductivity, facilitating the spillover effect, promoting structural reconstruction, and optimizing the adsorption of key intermediates. Finally, the review outlines the remaining challenges and future directions for enhancing catalytic performance through cation vacancy defect engineering.