Photoelectrochemical C–H activation of methane to methyl radical at room temperature

Abstract

Herein, we report a continuous gas-fed photoelectrochemical (PEC) system with a proton exchange membrane for CH₄ activation at ambient temperature and pressure. We found that both water splitting and steam reforming of CH₄ were induced over oxide photoanodes. When the CH₄ concentration was low, O₂ and CO₂ were formed on titanium oxide (TiO₂) and tungsten trioxide (WO₃) photoanodes under ultraviolet light irradiation. We also found that visible light enhanced CH₄ activation and ethane (C₂H₆) formation over the WO₃ photoanode. When the CH₄ concentration increased, O₂ formation was suppressed, with increasing production rates of CO₂, C₂H₆, and CO. Under optimised conditions, the selectivity of C₂H₆ reached 57% on a carbon basis over the WO₃ photoanode under visible-light irradiation. The production of C₂H₆ implies the formation of methyl radicals during the CH₄ gas-fed PEC process. We also demonstrated the PEC coupling of ethane to n-butane and the visible-light-induced oxidation of CH₄ without external bias.