Reduction of CO2 to C2 products by tandem actives sites of a novel 2D/3D structured photoelectrocatalyst Ag/Cu2O/g-C3N4

Photoelectrocatalytic (PEC) CO2 reduction integrates the benefits of both photocatalysis and electrocatalysis, emerging as a promising approach to address the energy crisis and mitigate global warming. While the photocatalytic properties of g-C3N4 have been extensively investigated, there are relatively few studies exploring its modification for PEC applications. Herein, a ternary heterojunction composite of Ag/Cu2O/g-C3N4 with twodimensional (2D) /three-dimensional (3D) structure was prepared using a deposition method and employed as the photocathode for PEC CO2 reduction. The spatial structure of g-C3N4 restricted the growth of doped nanoparticles, exposing additional active sites on the surface of the composite. Compared to binary materials, Ag/ Cu2O/g-C3N4 exhibited superior PEC performance, achieving a CO2 reduction current density of -30.46 mA/cm2 at -1.2 V vs. reversible hydrogen electrode (RHE), attributed to the formation of the ternary heterojunction. The serial catalysis of various active sites enhanced the C2 product selectivity in the PEC CO2 reduction with Ag/ Cu2O/g-C3N4, achieving a Faradaic efficiency for ethanol of up to 44.0 % at -1.0 V vs. RHE. Furthermore, this study explored the heterojunction type of Ag/Cu2O/g-C3N4 and the associated reduction mechanisms.