Effective charge separation in rGO/NiWO4@Au photocatalyst for efficient CO2 reduction under visible light

Abstract Catalyst performance can be improved by introducing an electron donor into both the valence band (VB) and conduction band (CB) to facilitate charge separation and suppress electron-hole recombination. Herein, Au nanoparticles served as CB electron donors in NiWO4 core particles which were evenly dispersed on a reduced graphene oxide (rGO) sheet that served as a VB electron donor. The resulting rGO/NiWO4@Au photocatalyst was applied to reducing CO2. The particles exhibited broadband absorbance from the ultraviolet to near-infrared, with a specific Au surface plasmon resonance (SPR) absorption peak at 600 nm. Moreover, the catalyst exhibited low photoluminescence (PL) and a high photocurrent density, indicating that photo-excited electron-hole recombination was suppressed and the charges effectively separated. Photocatalytic reduction of CO2 on rGO/NiWO4@Au was significantly enhanced as evidenced by the total amounts of reduction products (CO and CH4), which were 15 times those for NiWO4 and six times those for rGO/NiWO4 and NiWO4@Au. The expected electron-transfer mechanism on rGO/NiWO4@Au involves electron donation into the VB from the π-electron rich rGO, combined with photo-excited electrons from the NiWO4 and Au particles where electrons on the Au surfaces were amplified by the SPR and then moved to the CB of NiWO4. Intensity-modulated photovoltage spectroscopy of rGO/NiWO4@Au indicated a significantly reduced electron-hole recombination rate.