Design Strategies and Advanced Research Methodologies of Iron-Group Transition Metal Electrocatalysts Toward Efficient Hydrogen Evolution in Water Splitting.

The electrochemical hydrogen evolution reaction (HER) in overall water splitting is one of the core technological pathways for green hydrogen production. Developing nonprecious metal electrocatalysts with high activity, low cost, and earth abundance is critical for promoting their large-scale practical application. Transition metal materials, especially Fe, Co, and Ni, have attracted extensive research interest due to their unique electron configurations, abundant tunable active sites, and excellent economic feasibility. This study focuses on Fe-group transition metal electrocatalysts toward the HER, systematically elaborating on the fundamental reaction mechanisms and intrinsic catalytic properties of such materials. On this basis, we summarize key performance-enhancing strategies, including composition engineering, morphology engineering, interface engineering, defect and coordination engineering, external field-assisted strategies, and other strategies. Furthermore, this article outlines the vital roles of advanced multiscale characterization techniques and multiparadigm research methods including artificial intelligence, in the study of Fe-group electrocatalysts, and summarizes the latest advances in their applications for overall water-splitting devices. Finally, the key challenges regarding catalytic activity, structural stability, and mechanistic cognition of Fe-group electrocatalysts are discussed, and future research directions are proposed. This work aims to provide systematic theoretical guidance and reliable references for the rational design and practical development of high-efficiency Fe-group electrocatalysts.