Insights into the electrochemical oxidation selectivity of hydroxymethylfurfural over humin-layered Au nanoparticles

Au nanoparticle catalysts are promising electrocatalysts for biomass upgrading. Starting from a pristine Au electrode, herein we demonstrate a simple route for the electrochemical preparation of Au NPs supported on thin layers of humin (Au/H). Utilizing an oxidized Au surface as a precursor, these electrocatalytic structures are formed upon reduction of 5-hydroxymethylfurfural (HMF) in alkaline media while performing a potential sweep. We subsequently utilize this Au/H structure for the electrochemical oxidation of ethanol and HMF in a rotating disk electrode (RDE) configuration and perform additional analysis via electrochemical surface-enhanced Raman Scattering (SERS). The RDE test reveals Au/H has different reaction kinetics towards alcohol and aldehyde functional groups, enabling a mechanistic understanding of the reaction pathway for HMF oxidation. The SERS experiment identifies the favorable reduction pathway from Au₂O₃ to gold, suggesting the possible active site on this catalyst for HMF oxidation.