The selective reduction of CO 2 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 CO 2 reduction. The reported photocathode is based on a phosphonated cobalt bis(terpyridine) catalyst that is interfaced via a mesoporous TiO 2 scaffold with a light-harvesting p-type silicon electrode. The hybrid photoelectrode reduces CO 2 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 CO 2 reduction with the reported photocathode.