Multidimensional Nonstoichiometric Electrode Materials for Electrochemical Energy Conversion and Storage

Abstract Nonstoichiometry plays an important role in determining physicochemical properties such as conductivity, activity, and stability due to the composition‐induced change in phase, local atomic environment, and electronic structure. A variety of materials with nonstoichiometry have emerged in electrochemical energy conversion and storage, which necessitates a solid understanding of their formation mechanism and structure–function relationship. This review presents a summary of the progress made in this emerging field, starting from the introduction of the multiscale top‐down and bottom‐up strategies for generating nonstoichiometry and the related characterization methodologies. Then, representative nonstoichiometric materials (NMs) are discussed in properties and merits, with selected examples of each material category. A special focus is placed on the dimensionality from atomic sites to surface/interfaces, grains, microstructure, and hierarchical macroscale. After that, recent advances are overviewed for the use of exemplified NMs in electrocatalysis (i.e., oxygen reduction/evolution, hydrogen evolution, and nitrogen reduction) and batteries (i.e., Li/Na/Zn batteries). The review is concluded with a summary highlighting the beneficial effects of NMs and a perspective on further research to address remaining issues.