Highly Efficient Photoelectrocatalytic Reduction of CO₂ to Methanol by a p-n Heterojunction CeO₂/CuO/Cu Catalyst

Photoelectrocatalytic reduction of CO₂ to fuels has great potential for reducing anthropogenic CO₂ emissions and also lessening our dependence on fossil fuel energy. Herein, we report the successful development of a novel photoelectrocatalytic catalyst for the selective reduction of CO₂ to methanol, comprising a copper catalyst modified with flower-like cerium oxide nanoparticles (CeO₂ NPs) (a n-type semiconductor) and copper oxide nanoparticles (CuO NPs) (a p-type semiconductor). At an applied potential of - 1.0 V (vs SCE) under visible light irradiation, the CeO₂ NPs/CuO NPs/Cu catalyst yielded methanol at a rate of 3.44 μmol cm^-2 h^-1, which was approximately five times higher than that of a CuO NPs/Cu catalyst (0.67 μmol cm^-2 h^-1). The carrier concentration increased by ~ 10⁸ times when the flower-like CeO₂ NPs were deposited on the CuO NPs/Cu catalyst, due to synergistic transfer of photoexcited electrons from the conduction band of CuO to that of CeO₂, which enhanced both photocatalytic and photoelectrocatalytic CO₂ reduction on the CeO₂ NPs. The facile migration of photoexcited electrons and holes across the p-n heterojunction that formed between the CeO₂ and CuO components was thus critical to excellent light-induced CO₂ reduction properties of the CeO₂ NPs/CuO NPs/Cu catalyst. Results encourage the wider application of composite semiconductor electrodes in carbon dioxide reduction.