Ag─S Sites Steer Furfural Electroreduction to Furfuryl Alcohol

The electrochemical upgrading of furfural (FF), a biomass-derived platform molecule, using renewable electricity offers a promising route toward green and sustainable chemical synthesis. However, achieving high selectivity toward hydrogenated products, such as furfuryl alcohol (FA), remains challenging as hydrogenation competes with C─C coupling reactions that generate undesired dimers. In this study, we show that trace sulfide species introduced into the electrolyte dynamically generate Ag─S sites on Ag surfaces during electrolysis, thereby steering the FF reduction reaction toward FA formation. Using Ag disk electrodes, the introduction of 0.5 mM sulfide ions (S^2-) into the electrolyte increases the Faradaic efficiency (FE) for FA formation from 59% to 88% and enhances its partial current density (j_FA) from 5.4 to 12.5 mA cm^-2. X-ray photoelectron spectroscopy, in situ Raman spectroscopy, and density functional theory simulations collectively reveal that the low-coverage sulfide species on Ag regulate FF adsorption and facilitate proton transfer to the carbonyl oxygen, steering FA formation, while suppressing hydrofuroin (HF) formation by disrupting the Ag ensembles required for C─C coupling. Overall, our findings establish the deliberate introduction of trace sulfide into the electrolyte as a simple and potentially broadly applicable strategy to steer selectivity in the electrochemical hydrogenation of biomass-derived furanic aldehydes.