Engineering a Cu Cluster Supported on 1T-Rich MoS2 for the Efficient Electrocatalytic Hydrogenation of Furfural to Furfuryl Alcohol in a Neutral Aqueous Solution

The electrochemical selective reductive transformation of biomass-derived furanic compounds into valuable oxygenated arometrics is important to establish a sustainable biorefinery. Yet, the recent electrocatalytic hydrogenation (ECH) of furfural to furfuryl alcohol still suffers from harsh pH conditions and low selectivity. In this study, a single subnanometric Cu cluster decorated 1T-rich MoS2 (noted as Cu-MoS2) electrocatalyst was proposed to realize the ECH of furfural into furfuryl alcohol in a neutral environment (pH = 7), with a Faraday efficiency (FE%) of 58.75% and over 94.53% selectivity at 71.54% conversion of furfural. The Cu-MoS2 electrode was fabricated on a carbon cloth support via a novel amorphous MoSx-based Cu electrodeposition followed by an annealing treatment. The resulting Cu-MoS2 catalyst demonstrated great stability without deactivation after 14 times of repeated applications in bulk electrolysis. Mechanistic investigation via underpotential hydrogen desorption (HUPD) studies revealed that the integrated single subnanometric Cu clusters may function as additional electrotransfer (ET) sites to raise the relative coverage ratio of the furfuryl radicals on the MoS2 surface, thereby promoting the surface hydrogenation step and, consequently, improving the efficiencies of the ECH reaction even after the pH was lowered to neutral. This study experimentally narrowed down that adequate provision of ET sites, where the charges transfer from the electrode to the furfural, in an HER-friendly catalyst could be a considerable strategy to improve the catalysts' ECH activity. Overall, the mechanistic insights obtained herein highlighted the importance of active site engineering in the electrocatalysis process.