Photoelectrochemical hybrid cell for unbiased CO 2 reduction coupled to alcohol oxidation

The reduction of CO 2 to renewable fuels must be coupled to a sustainable oxidation process to devise a viable device that produces solar fuels. In photoelectrochemical cells, water oxidation to O 2 is the predominant oxidation reaction and typically requires a pair of light absorbers or an applied bias voltage when coupled to CO 2 reduction. Here, we report a bias-free photoelectrochemical device for simultaneous CO 2 reduction to formate and alcohol oxidation to aldehyde in aqueous conditions. The photoanode is constructed by co-immobilization of a diketopyrrolopyrrole-based chromophore and a nitroxyl-based alcohol oxidation catalyst on a mesoporous TiO 2 scaffold, which provides a precious-metal-free dye-sensitized photoanode. The photoanode is wired to a biohybrid cathode that consists of the CO 2 reduction enzyme formate dehydrogenase integrated into a mesoporous indium tin oxide electrode. The bias-free cell delivers sustained photocurrents of up to 30 µA cm −2 under visible-light irradiation, which results in simultaneous aldehyde and formate production. Our results show that in the absence of an external bias, single light absorber photoelectrochemical cells can be used for parallel fuel production and chemical synthesis from CO 2 and alcohol substrates.