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 (CoII(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 photoanode 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 ∼1.5 V, which was smaller than the band gap of BiVO4 (band gap energy ≈ 2.4 eV), indicating that the FeO(OH)/BiVO4/FTO photoanode lowered the total bias that enabled simultaneous water oxidation and CO₂ reduction.