CO2 Photoelectrochemical Reduction Catalyzed by a GaP(001) Photoelectrode

Several types of metal electrodes (especially copper) can catalyze electrochemical CO2 reduction. Among semiconductor electrodes for CO2 photoelectroreduction, GaP electrodes exposing (111) and (110) facets were observed to be the most promising for methanol production. Inspired by the good catalytic properties of metal surfaces for CO2 electroreduction, here we examine CO2 photoelectroreduction on the known Ga-metal-rich GaP(001) δ(2 × 4) mixed-dimer surface. We employ density functional theory-based atomic-scale models to explore reaction paths for two possible mechanisms: proton-coupled electron transfer (PCET) and hydride transfer (HT). Our simulations reveal that both mechanisms are favorable thermodynamically. However, PCET is kinetically sluggish and therefore unlikely to contribute to CO2 reduction. By contrast, we predict that HT is kinetically feasible, producing CH2(OH)2 (the dominant product) and CH3OH. However, HT may induce a moderate amount of hydrogen evolution as a side reaction, thus lowering the overall selectivity of this photoelectrode. We conclude that HT could enable a facile CO2 photoelectroreduction to CH2(OH)2 on a Ga-rich GaP(001) photoelectrode.