Collaborative photocatalytic C–C coupling with Cu and P dual sites to produce C2H4 over CuxP/g-C3N4 heterojunction

Abstract

Light-driven CO₂ reduction reaction (CO₂RR) to value-added ethylene (C₂H₄) holds significant promise for addressing energy and environmental challenges. While the high energy barriers for *CO intermediates hydrogenation and C–C coupling limit the C₂H₄ generation. Herein, Cu_xP/g-C₃N₄ heterojunction prepared by an in-situ phosphating technique, achieved collaborative photocatalytic CO₂ and H₂O, producing CO and C₂H₄ as the main products. Notably, the selectivity of C₂H₄ produced by Cu_xP/g-C₃N₄ attained to 64.25%, which was 9.85 times that of Cu_xP (6.52%). Detailed time-resolution photoluminescence spectra, femtosecond transient absorption spectroscopy tests and density functional theory (DFT) calculation validate the ultra-fast interfacial electron transfer mechanism in Cu_xP/g-C₃N₄ heterojunction. Successive *H on P sites caused by adsorbed H₂O splitting with moderate hydrogenation ability enables the multi-step hydrogenation during CO₂RR process over Cu_xP/g-C₃N₄. With the aid of mediated asymmetric Cu and P dual sites by g-C₃N₄ nanosheet, the produced *CHO shows an energetically favorable for C–C coupling. The coupling formed *CHOCHO further accepts photoexcited efficient e^– and *H to deeply produce C₂H₄ according to the C2+ intermediates, which has been detected by in-situ diffuse reflectance infrared Fourier transform spectroscopy and interpreted by DFT calculation. The novel insight mechanism offers an essential understanding for the development of Cu_xP-based heterojunctions for photocatalytic CO₂ to C2+ value-added fuels.