Silicon photocathode functionalized with osmium complex catalyst for selective catalytic conversion of CO₂ to methane

Solar-driven CO₂ reduction to yield high-value chemicals presents an appealing avenue for combating climate change, yet achieving selective production of specific products remains a significant challenge. We showcase two osmium complexes, przpOs, and trzpOs, as CO₂ reduction catalysts for selective CO₂-to-methane conversion. Kinetically, the przpOs and trzpOs exhibit high CO₂ reduction catalytic rate constants of 0.544 and 6.41 s^-1, respectively. Under AM1.5 G irradiation, the optimal Si/TiO₂/trzpOs have CH₄ as the main product and >90% Faradaic efficiency, reaching -14.11 mA cm^-2 photocurrent density at 0.0 V_RHE. Density functional theory calculations reveal that the N atoms on the bipyrazole and triazole ligands effectively stabilize the CO₂-adduct intermediates, which tend to be further hydrogenated to produce CH₄, leading to their ultrahigh CO₂-to-CH₄ selectivity. These results are comparable to cutting-edge Si-based photocathodes for CO₂ reduction, revealing a vast research potential in employing molecular catalysts for the photoelectrochemical conversion of CO₂ to methane.