Green copper oxide photocathodes using plant extracts for an efficient photoelectrochemical CO2 conversion to alcohols

Abstract

In this study, green home-made synthesized copper oxide (CuO) nanoparticles are employed as photocathodes in the form of gas diffusion electrodes (GDEs) for the continuous photoelectrochemical (PEC) conversion of CO2 into valuable products, including methanol and ethanol. CuO nanoparticles synthesized using plant extracts from Salvia rosmarinus (CuO-R), Laurus nobilis (CuO-L), and Origanum vulgare (CuO-O) are prepared in a green, sustainable manner, leveraging the phytochemicals in these plants for nanoparticle formation and stabilization. The eco-friendly synthesized CuO-based photocathodes are then prepared by an automated spray pyrolysis deposition technique and comprehensively physico-chemically, optically, and photoelectrochemically characterized, revealing enhanced photocurrent densities and promising product selectivity for CO2 reduction to alcohols under visible light irradiation. Among the eco-synthesized photocathodes, CuO-R exhibited the highest PEC activity, achieving a Faradaic efficiency exceeding 66 % for methanol, with an energy efficiency of 39.2 %, while requiring a minimized external potential of −0.37 V (vs. RHE), lower than that for the chemically synthesized catalyst (CuO-P). Post-reaction analysis further confirmed that CuO-R maintained its structural integrity after continuous operation, reinforcing its superior stability and PEC efficiency. These results demonstrate that green synthesis pathways provide a sustainable and efficient approach to developing high-performance photocathodes for PEC CO2 reduction, offering promising potential for scalable solar-driven carbon conversion technologies.