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

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.