Modulating surface chemistry of copper oxides through annealing environment for enhanced selective HMF oxidation: A DFT-electrochemical approach

A comprehensive study was reported to address the effects of both copper (I) and copper (II) oxides on the electrocatalytic 5-hydroxymethylfurfural (HMF) oxidation reaction. Cu₂O (1 1 1) demonstrated an outstanding selectivity (80 %) and product yield in the oxidation process towards 2,5-diformylfuran (DFF). The recorded current density of 0.12 mA/cm² for Cu₂O-dominated sample was doubled comparing to its counterpart electrocatalyst, CuO, under mild pH 9.6 condition. Periodic density functional theory calculations show that the higher DFF selectivity for the Cu₂O dominant catalyst can be explained by the Cu₂O (1 1 1) surface being more oxyphilic while being less carbophilic than the CuO (1 1 1) surface. As a result, all the reaction intermediates that lead to DFF are stabilized significantly more than those that lead to other products. This work deepens the understanding of copper-based oxide material for the HMF electrooxidation and provides a new window for designing electrocatalyst.