Modulating Cobalt Valence Cycle Energetics for Selective Biomass Polyol Oxidation

Biomass-derived intermediates often contain multiple alcohol groups, and their selective oxidation is crucial for effective valorization. CoOOH is a promising electrocatalyst for polyol upgrading, converting alcohols into valuable products, such as carboxylic acids. However, the Co³⁺/Co⁴⁺ transition limits its performance in dehydrogenation and C─C bond cleavage, requiring high overpotentials. Using glycerol as a model polyol, this study demonstrates that heteroatom co-doping of CoOOH with Cu and Fe enhances the energetics of Co oxidation cycle, improving glycerol oxidation reaction (GOR) efficiency at lower overpotentials. The Cu-Fe co-doped CoOOH exhibits a favorable synergy between efficiency and selectivity, exhibiting 95.5% formic acid selectivity, a productivity of 1.55 mmol cm^-2 h^-1, and a Faradaic efficiency of 84.7%. Mechanical analyses reveal the complementary roles of Cu and Fe doping: Cu facilitates glycerol adsorption and supports the Co²⁺/Co³⁺/Co⁴⁺ redox cycle, while Fe enhances catalytic activity through the Co³⁺/Co⁴⁺ transition, and aids in OH^- replenishment during catalyst regeneration. The heteroatom Cu-Fe co-doping strategy optimizes glycerol oxidation by improving glycerol adsorption, promoting dehydrogenation, facilitating C─C bond cleavage, mitigating over-oxidation, and enhancing active site regeneration. The findings gained from this study provide a valuable framework for the rational design of more efficient, non-precious metal-based catalysts for biomass valorization.