High-Rate, Tunable Syngas Production with Artificial Photosynthetic Cells

An artificial photosynthetic (APS) system consisting of a photoanodic semiconductor that harvests solar photons to split H₂ O, a Ni-SNG cathodic catalyst for the dark reaction of CO₂ reduction in a CO₂ -saturated NaHCO₃ solution, and a proton-conducting membrane enabled syngas production from CO₂ and H₂ O with solar-to-syngas energy-conversion efficiency of up to 13.6 %. The syngas CO/H₂ ratio was tunable between 1:2 and 5:1. Integration of the APS system with photovoltaic cells led to an impressive overall quantum efficiency of 6.29 % for syngas production. The largest turnover frequency of 529.5 h^-1 was recorded with a photoanodic N-TiO₂ nanorod array for highly stable CO production. The CO-evolution rate reached a maximum of 154.9 mmol g^-1  h^-1 in the dark compartment of the APS cell. Scanning electrochemical-atomic force microscopy showed the localization of electrons on the single-nickel-atom sites of the Ni-SNG catalyst, thus confirming that the multielectron reduction of CO₂ to CO was kinetically favored.