Function-orchestrated CaO/BiVO4/rGO interfaces for efficient CO2 methanation via coupled charge separation and adsorptive activation

Abstract

The photocatalytic conversion of CO₂ into methane (CH₄) under mild conditions offers a promising route for renewable fuel production, yet it remains hindered by poor CO₂ adsorption, fast electron–hole recombination, and limited redox efficiency. Herein, we report a ternary heterostructured photocatalyst composed of CaO, BiVO₄, and reduced graphene oxide (rGO), designed to synergistically integrate CO₂ activation, visible-light harvesting, and interfacial charge transfer. The CaO/BiVO₄/rGO composite exhibited a remarkable CH₄ evolution rate of 2.89 μmol g⁻¹ h⁻¹ under visible light (λ > 420 nm), outperforming BiVO₄ and binary systems by a factor of 3.6. This enhancement is attributed to the basicity-driven CO₂ chemisorption of CaO, the charge migration pathway enabled by rGO, and the visible-light absorption of BiVO₄. Time-resolved photoluminescence and electrochemical impedance spectroscopy confirmed prolonged carrier lifetimes and reduced recombination losses. In situ FTIR and mass spectrometry analyses revealed that the photocatalytic process proceeded via a direct CO*–CH_x intermediate pathway, excluding formate or methanol routes. The catalyst retained its structural integrity and activity over five cycles, demonstrating excellent photostability and recyclability. This work offers a robust design strategy for integrating multifunctional interfaces to unlock low-temperature photocatalytic CO₂ methanation, with potential for application in solar-to-methane fuel systems.