Mechanistic Insights Into H₂O Dissociation in Overall Photo-/Electro-Catalytic CO₂ Reduction

Photo-/electro-catalytic CO₂ reduction with H₂O to produce fuels and chemicals offers a dual solution to address both environmental and energy challenges. For a long time, catalyst design in this reaction system has primarily focused on optimizing reduction sites to improve the efficiency or guide the reaction pathway of the CO₂ reduction half-reaction. However, less attention has been paid to designing activation sites for H₂O to modulate the H₂O dissociation half-reaction. Impressively, the rate-determining step in overall CO₂ reduction is the latter, and it influences the evolution direction and formation energy of carbon-containing intermediates through the proton-coupled electron transfer process. Herein, we summarize the mechanism of the H₂O dissociation half-reaction in modulating CO₂ reduction performance based on cutting-edge research. These analyses aim to uncover the potential regulatory mechanisms by which H₂O activation influences CO₂ reduction pathways and conversion efficiency, and to establish a mechanism-structure-performance relationship that can guide the design and development of high-efficiency catalytic materials. A summary of advanced characterization techniques for investigating the dissociation mechanism of H₂O is presented. We also discuss the challenges and offer perspectives on the future design of activation sites to improve the performance of photo-/electro-catalytic CO₂ reduction.