Synergy Effect between Facet and Zero-Valent Copper for Selectivity Photocatalytic Methane Formation from CO2

The application of Cu2O catalysts in CO2 photocatalytic reduction has attracted much attention due to the capacity to generate high-calorific-value hydrocarbon fuels with pre-eminent selectivity. However, the origin of the high selectivity remains unclear. In this study, the (111) facet of Cu2O was verified as the origin of selectivity for CH4 (the simplest hydrocarbon) formation by comparing the photocatalytic CO2 reduction behaviors of Cu2O catalysts with varied active facets. Results showed that Cu2O-100 produced negligible CH4 (selectivity = 0%), whereas the yield of CH4 on Cu2O-111 was 12.24 μmol·g–1·h–1 with a substantially high selectivity of 91.4%. After decoration with zero-valent copper on the surface of Cu2O-111 (Cu2O-111-Cu0), the yield of CH4 reached 78.4 μmol·g–1·h–1, affording a selectivity of CH4 as high as 97%. In situ FT-IR and theoretical calculations showed that the (111) facet has stronger CO absorption capacity and electron reduction capacity for highly selective photocatalytic CO2 conversion. Moreover, the presence of Cu0 on the (111) facet could accelerate the carrier separation efficiency, thus providing more electrons for efficient hydrocarbon formation. This work provides a promising idea to design Cu2O catalysts for the conversion of CO2 into high value-added hydrocarbon products with high activity and selectivity.