Utilizing nature's endowment: artificial leaf concept for methane activation to C–C coupled ethanol or ethylene

Abstract

Methane activation (MA) to platform chemicals under ambient conditions still remains an open challenge to be fully realised. The present work shows the fabrication of CeVO₄ quantum dots (CV-QDs) by a bottom-up approach; they are assembled from Ce³⁺ and metavanadate ions, and structurally and electronically integrated into the micro-/meso-pores of TiO₂ (CV-QD-TiO₂ (CVT)), demonstrating the conversion of MA to ethanol/ethylene by visible light-driven photocatalysis. CV-QDs in confined pores modify the quantum confinement effects and are characterized by physicochemical methods. The current synthetic strategy is potentially scalable and results in sub-quadrillion heterojunctions in a 1 mg CVT photoanode spread over 1 cm². MA with CVT under one-sun conditions demonstrates ∼100% selectivity to ethanol, yielding 4.36 μmol h⁻¹ cm⁻², with a solar-to-fuel efficiency (STFE) of 0.56. Further, by employing a co-catalyst, significant STFE (5.08) and yield (39.5 μmol h⁻¹ cm⁻²) are achieved selectively towards ethylene. A deliberate addition of methanol increases the rate of ethanol production by 17.2 times, indicating that the methyl-methoxy interaction is the origin of C–C coupling. Weight is normalized to a gram of CV-QDs in a large area CVT photoanode to yield 109 mmol h⁻¹ g_CV-QD⁻¹ of ethanol and 988 mmol h⁻¹ g_CV-QD⁻¹ of ethylene. Enhanced activity and selectivity towards the C₂-product is attributed to band-edge modulation and trillions of heterojunctions, which in turn facilitate charge separation and charge transfer for effective charge utilisation at redox sites.