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

Visible-light photocatalytic conversion of CO 2 -to-fuels for green electricity is sustainably attractive for alleviating carbon emissions. Photocatalytic CO 2 -to-CO frequently suffered from relatively low yields, mainly due to ineffective charge transfer rates. A new approach for photocatalytic CO 2 -to-CO enhanced with effective H + from H 2 O-to-H 2 O 2 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-C 3 N 4 /Cu 2 O heterojunctions (i.e., g-C 3 N 4 /Cu 2 O–Pd) has been prepared to facilitate charge separation for the two-electron reduction of CO 2 to CO. Experimentally, the g-C 3 N 4 /Cu 2 O–Pd heterojunctions have a higher photocatalytic H 2 O-to-H 2 O 2 yield than the g-C 3 N 4 /Cu 2 O heterojunction by 5.3 times. The photocatalytic WOR provides sufficient electrons (e – ) and H + (2H 2 O → H 2 O 2 + 2H + ) for CO 2 -to-CO (CO 2(aq) + 2H + + 2e – → CO (g) + H 2 O (l) ). Relatively high photocatalytic yields of H 2 O 2 (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/H 2 ratio of 1.75 approximately. This visible-light photocatalytic CO 2 -to-CO and H 2 O-to-H 2 O 2 by the new g-C 3 N 4 /Cu 2 O–Pd S-scheme heterojunctions demonstrates the feasibility of the zero carbon emission approach with additional green oxidant (H 2 O 2 ) generation.