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. Yet, the rate‐determining step in overall CO2 reduction is the latter, as 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.