(532aw) Unraveling the Mechanisms of Electrocatalytical Reduction of Furfural Via Tailoring Interfacial Environments

Electrochemical conversion of biorenewable feedstocks holds great promise to produce higher-valued chemicals and fuels powered by renewable electricity. Despire great progress has been made, mechanistic understanding of the electro-reduction of aldehydes toward valuable products at the molecular level within the interfacial regions is still lacking. Herein, we studied the furfural reduction on Pb electrodes in acid conditions and elucidated the detailed pathways toward three key products: furfuryl alcohol (FA), 2-methylfuran (MF), and hydrofuroin, through tailoring the local environments, including H/D composition and local H₃O⁺ and H₂O content. By combining isotopic labeling and incorporation and electrokinetic studies, we revealed the source of protons (H₂O and H₃O⁺) plays a critical role in the hydrogenation and hydrogenolysis pathways toward FA and MF, respectively. In particular, the product-selective kinetic isotopic effect of H/D and the surface property-dependent hydrogenation/deuteration pathway strongly impacted the generation of FA but not MF, owing to their different formation pathways: Langmuir-Hinshelwood and Eley-Rideal pathways, respectively. Through modifying the double layer by cations with large radii, we further correlated the product selectivity (FA and MF) qualitatively and quantitively with interfacial environments (local H₃O⁺ and H₂O content, interfacial electric field, and differential capacitances). Experimental and DFT computation investigations further suggested competitive pathways toward hydrofuroin and FA: hydrofuroin is favorably produced through the self-coupling of ketyl radicals in the electrolyte, which are formed from outer-sphere, single-electron transfers, while FA is generated from hydrogenation of the adsorbed furfural/ketyl radical on the electrode surface.