Design and operando/in situ characterization of precious-metal-free electrocatalysts for alkaline water splitting

Electrochemical water splitting has attracted considerable attention for the production of hydrogen fuel by using renewable energy resources. However, the sluggish reaction kinetics make it essential to explore precious-metal-free electrocatalysts with superior activity and long-term stability. Tremendous efforts have been made in exploring electrocatalysts to reduce the energy barriers and improve catalytic efficiency. This review summarizes different categories of precious-metal-free electrocatalysts developed in the past 5 years for alkaline water splitting. The design strategies for optimizing the electronic and geometric structures of electrocatalysts with enhanced catalytic performance are discussed, including composition modulation, defect engineering, and structural engineering. Particularly, the advancement of operando/in situ characterization techniques toward the understanding of structural evolution, reaction intermediates, and active sites during the water splitting process are summarized. Finally, current challenges and future perspectives toward achieving efficient catalyst systems for industrial applications are proposed. This review will provide insights and strategies to the design of precious-metal-free electrocatalysts and inspire future research in alkaline water splitting.