Bromide-Borate Coupling Enables Selective Electrochemical Oxidation of Glycerol to Dihydroxyacetone

Selective electrochemical valorization of biodiesel-derived glycerol is challenged by competing oxidation pathways that generate complex product mixtures. Here, we report a bromide-borate-mediated indirect glycerol electrooxidation for selective dihydroxyacetone (DHA) production on carbon electrodes. Bromide is electrochemically converted into soluble oxidized bromine species that mediate homogeneous glycerol oxidation, whereas borate provides a weakly alkaline bromine-speciation window and coordinates glycerol to bias C3-product formation toward DHA. At identical pH, borate favored DHA formation, whereas phosphate shifted selectivity toward glyceric acid. Under optimized conditions using 100 mM glycerol and 100 mM KBr in 1 M borate buffer solution (pH 8.2), divided H-cell electrolysis afforded DHA with 75% relative selectivity and high overall Faradaic efficiency (FE). Recirculating flow-cell operation increased DHA selectivity to 80% while maintaining high overall FE, and one-way flow-cell achieved a DHA production rate of 1205 mmol m^-2 h^-1.