Density functional theory-guided C–C coupling pathways in photocatalytic CO2 reduction to C2–C3 products

Photocatalytic CO 2 reduction offers a promising route to fuels and value-added chemicals, with density functional theory (DFT) providing mechanistic insights into the reaction pathways, active sites, and product selectivity. Beyond classical formaldehyde and carbene pathways to CH 4 and CH 3 OH, recent studies increasingly target C 2 –C 3 products, where C–C bond formation is a critical mechanistic step. This review evaluates proposed C–C coupling pathways, including CO–CO, CO 2 –CO 2 , CO–CHO, CH 3 –CH 3 , CO–CHOH, CO–COH, and CHO–CHO coupling, and identifies photocatalyst site characteristics governing multicarbon product formation. Particular emphasis is placed on reaction-pathway calculations using the climbing-image nudged elastic band rather than relying solely on reaction Gibbs energies. Comparisons between DFT predictions and experiments are used to assess plausible active sites and mechanisms. Effects of pH, solvent, and competing H 2 evolution are also discussed, alongside complementary dimer, activation-relaxation technique nouveau (ARTn), and metadynamics approaches.