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.