Solar-driven reduction of aqueous CO2 with a cobalt bis(terpyridine)-based photocathode

The selective reduction of CO2 with inexpensive solar-driven photoelectrochemical devices is a contemporary challenge in the quest for renewable fuel production. Here, we report a molecular catalyst-based photocathode assembled from precious-metal-free components that is active towards aqueous CO2 reduction. The reported photocathode is based on a phosphonated cobalt bis(terpyridine) catalyst that is interfaced via a mesoporous TiO2 scaffold with a light-harvesting p-type silicon electrode. The hybrid photoelectrode reduces CO2 to CO in both organic-water and purely aqueous conditions, achieving a turnover number of ~330 and maintaining stable activity for more than one day. Critically, in-depth electrochemical as well as in situ resonance Raman and infrared spectroelectrochemical investigations alluded to a catalytic mechanism that differs to that reported for the soluble metal bis(terpyridine) catalyst as the consequence of the immobilization. In addition, it further unlocks an earlier catalytic onset and better electrocatalytic performance while enabling aqueous CO2 reduction with the reported photocathode. Immobilized molecular catalysts can be efficient for the electroreduction of CO2, but their practical applicability is hampered by the continued use of rare metals. Here, a photoelectrode based on an earth-abundant molecular catalyst with high CO2 reduction performance is introduced.