Multistep Proton‐Coupled Electron Transfer for C─C Coupling in CO 2 Reduction

ABSTRACT Kinetically demanding multi‐step proton‐coupled electron transfer (PCET) and the high energy barrier associated with C─C coupling are the primary reasons for the low selectivity toward multi‐carbon products. Numerous interconnected parameters like catalyst composition, surface structure, doping, morphology, reaction medium, pH, and photocatalytic cell design influence both PCET and C─C coupling. Although these processes are fundamentally independent, they are indirectly affected by the structural and catalytic environmental factors, which often promote one pathway. This interdependence complicates rational catalyst discovery. A critical understanding and careful deconvolution of these parameters are essential for identifying the conditions that synergistically enhance both PCET and C─C coupling for selective product formation. In this review, we present a historical perspective on key catalyst design strategies and mechanistic insights, and highlight the intricate interplay among different catalytic systems, and summarize the latest advancements in CO 2 to C2+ products. Subtle variations in catalyst structure that alter reaction pathways or electron‐transfer dynamics are discussed in detail, as these insights provide powerful guidelines for designing next‐generation C2+ selective photocatalysts. We also emphasize in situ/operando characterization of intermediates, and their energetics relevant to C─C coupling. Finally, we outline current challenges and propose future research directions for advancing the field.