Visible-Light Photocatalytic CO2-to-CO and H2O-to-H2O2 by g-C3N4/Cu2O–Pd S-Scheme Heterojunctions

Visible-light photocatalytic conversion of CO₂-to-fuels for green electricity is sustainably attractive for alleviating carbon emissions. Photocatalytic CO₂-to-CO frequently suffered from relatively low yields, mainly due to ineffective charge transfer rates. A new approach for photocatalytic CO₂-to-CO enhanced with effective H⁺ from H₂O-to-H₂O₂ through the water oxidation reaction (WOR) has been studied in the present work. Here, the nano palladium (9 wt %), serving as a cocatalyst, dispersed on the g-C₃N₄/Cu₂O heterojunctions (i.e., g-C₃N₄/Cu₂O-Pd) has been prepared to facilitate charge separation for the two-electron reduction of CO₂ to CO. Experimentally, the g-C₃N₄/Cu₂O-Pd heterojunctions have a higher photocatalytic H₂O-to-H₂O₂ yield than the g-C₃N₄/Cu₂O heterojunction by 5.3 times. The photocatalytic WOR provides sufficient electrons (e^-) and H⁺ (2H₂O → H₂O₂ + 2H⁺) for CO₂-to-CO (CO_2(aq) + 2H⁺ + 2e^- → CO_(g) + H₂O_(l)). Relatively high photocatalytic yields of H₂O₂ (34.0 μmol/mg) and CO (14.6 μmol/mg) affected by the heterojunctions can be achieved. Also, the heterojunctions have a high photostability with a photocatalytic generated CO/H₂ ratio of 1.75 approximately. This visible-light photocatalytic CO₂-to-CO and H₂O-to-H₂O₂ by the new g-C₃N₄/Cu₂O-Pd S-scheme heterojunctions demonstrates the feasibility of the zero carbon emission approach with additional green oxidant (H₂O₂) generation.