Mechanistic Insights Into H 2 O Dissociation in Overall Photo‐/Electro‐Catalytic CO 2 Reduction

Abstract Photo‐/electro‐catalytic CO 2 reduction with H 2 O 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 CO 2 reduction half‐reaction. However, less attention has been paid to designing activation sites for H 2 O to modulate the H 2 O dissociation half‐reaction. Impressively, the rate‐determining step in overall CO 2 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 H 2 O dissociation half‐reaction in modulating CO 2 reduction performance based on cutting‐edge research. These analyses aim to uncover the potential regulatory mechanisms by which H 2 O activation influences CO 2 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 H 2 O 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 CO 2 reduction.