Display omitted •Adsorbed OH– ions on the Au surface behave as active sites for HMF oxidation.•Aldehyde oxidation on Au catalysts is favorable at high OH– ions surface coverage.•Alcohol oxidation is kinetically slow on Au catalysts.•Au catalysts become inactive for aldehyde and alcohol oxidation when oxidized. 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.