Efficient Alkaline-Free Electrooxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid using Electrochemically-Charged NixCo1-x(OH)2 as a Redox Mediator

Converting biomass-derived molecules like 5-hydroxymethylfurfural (HMF) into value-added products alongside hydrogen production using renewable energy offers significant opportunities for sustainable chemical and energy production. Yet, HMF electrooxidation requires strong alkaline conditions and membranes for efficient conversion. These harsh conditions destabilize HMF, leading to humin formation and reduced product purity, meanwhile membranes increase costs. Addressing these challenges, we introduce a two-step, decoupling system that operates without strong alkaline conditions and eliminates the need of membranes. In this system, nickel-cobalt hydroxides serve as effective redox mediators, driving HMF oxidation in pure water. The experimental results showed that Ni0.85Co0.15OOH effectively promotes the dehydrogenation of substrate and achieves a highly efficient oxidation of HMF in pure water, with the selectivity of product 2,5-furandicarboxylic acid (FDCA) approaching 100%. This system has been expanded to oxidize various substrates, achieving yields exceeding 92% for the corresponding acids of functionalized compounds such as furfuryl alcohol, furfural, benzyl alcohol, and benzaldehyde. By replacing fixed electrodes with flow electrodes, the scalability of decoupling strategy was evaluated for the harvesting of pure solid FDCA, highlighting the broad prospects in practical applications.