Electrochemical Analysis of the Electrocatalytic Reduction of 5-Hydroxymethylfurfural in Cu Electrodes

The electroreduction of 5-hydroxymethylfurfural (HMF) offers promising opportunities for the synthesis of valuable chemical precursors. However, achieving high selectivity in this process remains challenging due to the complexity of the reaction mechanisms involved. Here, this study employs different electrochemical techniques to analyze each of the HMF electroreduction pathways. These findings demonstrate that the primary products of HMF electroreduction are 2,5-bis(hydroxymethyl)furan (BHMF) and 5-methylfurfural alcohol (MFA), with lower formation of 5-methylfurfural (5-MF) and 2,5-dimethylfuran. This study identifies a significant competition between hydrogen evolution reaction and the reduction of HMF and 5-MF that affect the faradaic efficiencies of the organic transformation. In contrast, BHMF and MFA display a reduced reactivity, behaving as terminal molecules. Through impedance analysis, it is possible to follow the reaction pathways by associating each reaction step with the changes observed in charge transfer and accumulation phenomena. These are key parameters for understanding the reaction mechanisms in the system as they allow to distinguish between adsorption, absorption and reaction of the organic molecules onto the electrode surface. This approach helps to accurately select the optimal potential for the reduction reactions. The results obtained in this study facilitate the design of efficient and selective electrocatalytic systems for biomass conversion.