Electrocatalytic reduction of CO2 occurred efficiently using a glassy carbon electrode modified with a cobalt(II) chlorin complex adsorbed on multi-walled carbon nanotubes at an applied potential of -1.1 V vs. NHE to yield CO with a Faradaic efficiency of 89% with hydrogen production accounting for the remaining 11% at pH 4.6.

Photoelectrochemical reduction of CO 2 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 BiVO 4 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)/BiVO 4 /FTO photoanode under visible light irradiation in a CO 2 -saturated aqueous solution (pH 4.6). The difference in the oxidation potential of the FeO(OH)/BiVO 4 /FTO electrode under dark and that under light illumination was ∼1.5 V, which was smaller than the band gap of BiVO 4 (band gap energy ≈ 2.4 eV), indicating that the FeO(OH)/ BiVO 4 /FTO photoanode lowered the total bias that enabled simultaneous water oxidation and CO 2 reduction.