Photoelectrochemical CO₂ reduction by Cu₂O/Cu₂S hybrid catalyst immobilized in TiO₂ nanocavity arrays

Photoelectrocatalytic CO₂ reduction to CO was achieved on Cu₂O/Cu₂S nanoparticles which are immobilized in TiO₂ nanocavity array. The Cu₂S shell was obtained by ions exchange reaction of O²⁻ and S²⁻ on the surface of Cu₂O by a chemical vapor deposition with Na₂S precursor. This coating can protect the Cu₂O nanoparticle from photocorrosion during photocatalysis. The lower resistance and plasmonic absorbance endow a superior activity of the Cu₂O/Cu₂S heterostructures toward photoelectrochemical reduction of CO₂. It exhibits a current density of 10.7 mA cm⁻² at the overpotential of − 0.26 V with a CO faradaic efficiency (FE) higher than 81%. The excellent photo-assisted catalytic performance (photo-induced current increment is more than 50%) is attributed to the localized surface plasmonic resonance of Cu₂S coatings and highly ordered hierarchical structure of the Cu₂O/Cu₂S nanoparticles, which facilitate charge carrier separation and mass transfer. These hybrid electrodes demonstrate a long-term stability by resisting photocorrosion within 5 h with a higher FE of CO₂ to CO conversion.