Coupling of glycerol indirect oxidation and hydrogen evolution via Cu2+/Cu+ redox mediation: Reducing electricity consumption through spontaneous Cu2+ reduction in alkaline glycerol medium

The core innovation of this study lies in the construction of an indirect glycerol oxidation coupled with hydrogen (H 2 ) evolution system mediated by the Cu 2+ /Cu + redox pathway. By leveraging the spontaneous reduction of the Cu(OH) 2 pre-catalyst with glycerol, the latter is converted into high-value products such as glycerate and formate. The resulting Cu + species are subsequently electrooxidized back to Cu 2+ , establishing a continuous Cu 2+ /Cu + redox cycle that effectively bypasses the high overpotential limitations of traditional direct oxidation pathways. X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and operando Raman spectroscopy confirm that, under alkaline conditions, glycerol efficiently reduces Cu(OH) 2 to Cu 2 O, ensuring the sustainability of the Cu + electrooxidation process. This mechanism lowers the anodic onset potential to 0.65 V RHE (versus reversible hydrogen electrode), approximately 1 V below that required for OER, achieving a "low-potential-driven" reaction. A coupled Cu(OH) 2 /CF || Pt/C cell delivers 100 mA cm⁻ 2 at a H 2 production energy demand of only 2.7 kWh m⁻ 3 H 2 , exceeding 50% reduction than that required in the conventional water electrolysis (5.6 kWh m⁻ 3 H 2 ). In alkaline media, glycerol spontaneously and rapidly reduces the pre-catalyst Cu(OH) 2 to Cu 2 O (Cu + ), while it is itself oxidized to the valuable products, formate and glycerate. These Cu + species is then electro-oxidized back to Cu 2+ , establishing a continuous Cu 2+ /Cu + redox cycle that enables the indirect upgrading oxidation of glycerol at a low potential and effectively bypasses the high overpotential limitation of the conventional direct oxidation route. • Glycerol spontaneously reduces Cu(OH) 2 to Cu 2 O in alkaline medium. • Indirect glycerol oxidation via Cu 2+ /Cu + redox shuttle is achieved. • This system lowers the anodic onset potential to 0.65 V RHE , ~1 V below than that of OER. • Low-voltage H 2 production and glycerol valorization are simultaneously achieved.