Noble-metal-free heterojunction photocatalyst for selective CO₂ reduction to methane upon induced strain relaxation

Abstract

Sunlight-driven CO₂ hydrogenation has drawn tremendous attention. However, selective CH₄ formation via CO₂ photoreduction is very challenging. Herein, we report a metal oxide semiconductor heterojunction consisting of BiVO₄ and WO₃ as a photocatalyst for the efficient conversion of carbon dioxide (CO₂) selectively to methane (105 μmol g^–1h^–1) under visible light in the absence of a sacrificial agent. Wise selection of the reaction medium and the strategically tuned heterojunction upon strain relaxation suppresses the competitive hydrogen generation reaction. The detailed photophysical, photoelectrochemical, and X-ray absorption spectroscopy studies pointed to the Z-scheme mechanism of electron transfer, which favors superior electron and hole separation compared to the individual components of the composite catalyst and other well-known photocatalysts reported for CO₂ reduction. The observations are further corroborated by experimental diffuse reflectance infrared Fourier transform spectroscopy and theoretical density-functional theory calculations, which reveal that the heterojunction has a lower free-energy barrier for CO₂ conversion to CH₄ due to the larger stabilization of the *CH₂O intermediate on the strain-relaxed heterojunction surface, in comparison to the pristine BiVO₄ surface. The present work provides fundamental insights for constructing high-performance heterojunction photocatalysts for the selective conversion of CO₂ to desired chemicals and fuels.