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

Solar-driven CO 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 CO reduction catalysts for selective CO-to-methane conversion. Kinetically, the przpOs and trzpOs exhibit high CO reduction catalytic rate constants of 0.544 and 6.41 s, respectively. Under AM1.5 G irradiation, the optimal Si/TiO/trzpOs have CH as the main product and >90% Faradaic efficiency, reaching -14.11 mA cm photocurrent density at 0.0 V. Density functional theory calculations reveal that the N atoms on the bipyrazole and triazole ligands effectively stabilize the CO-adduct intermediates, which tend to be further hydrogenated to produce CH, leading to their ultrahigh CO-to-CH selectivity. These results are comparable to cutting-edge Si-based photocathodes for CO reduction, revealing a vast research potential in employing molecular catalysts for the photoelectrochemical conversion of CO to methane.