Boosting 5-hydroxymethylfurfural electrooxidation in neutral electrolytes via TEMPO-enhanced dehydrogenation and OH adsorption

5-Hydroxymethylfurfural (HMF) electrooxidation in neutral conditions is a promising strategy to suppress the formation of humins and corrosive effects on electrochemical devices. However, scarce studies have been reported in neutral media due to the deficiency in electrophilic oxygen (eg OH–) required for the activation of HMF. Herein, 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO)/Co3O4 was utilized to co-catalyze HMF in neutral media, successfully achieving 2,5-furandicarboxylic acid (FDCA) with yield > 99%. It was found that TEMPO could promote HMF dehydrogenation to 2,5-diformylfuran (DFF) and simultaneously activated water via hydrogen-bonding interactions. As a result, the formation of OH* in neutral electrolytes was favored, which was absorbed by electrogenerated active Co species to facilitate subsequent conversion of formyl-group-involved intermediates to FDCA. This work provides a current understanding of the catalytic mechanism for HMFOR in neutral media and guides the design of highly efficient electrocatalysts for biomass upgrading.