Selective CO Production in Photoelectrochemical Reduction of CO2 with a Cobalt Chlorin Complex Adsorbed on Multiwalled Carbon Nanotubes in Water

Photoelectrochemical reduction of CO2 occurred using cobalt(II) chlorin (Co-II(Ch)) as a cathode active material adsorbed on multiwalled carbon nanotubes as a current collector in combination with a surface-modified BiVO4 photoanode with iron(III) oxide(hydroxide), FeO(OH), to produce CO with 83% Faradaic efficiency at an applied bias voltage of -1.3 V at the Co-II(Ch)-modified cathode vs the FeO(OH)/BiVO4/FTO photo anode under visible light irradiation in a CO2-saturated aqueous solution (pH 4.6). The difference in the oxidation potential of the FeO(OH)/BiVO4/FTO electrode under dark and that under light illumination was similar to 1.5 V, which was smaller than the band gap of BiVO4 (band gap energy approximate to 2.4 eV), indicating that the FeO(OH)/ BiVO4/FTO photoanode lowered the total bias that enabled simultaneous water oxidation and CO2 reduction.