Mechanistic Insights Evaluating Ag, Pb, and Ni as Electrocatalysts for Furfural Reduction from First-Principles Methods

Electrochemical reduction of furfural (ECRFF) emerges as an efficient and sustainable means to obtain high-value chemicals and biofuels with the activity and product selectivity being sensitive to cathode materials. In this work, elementary steps describing furfuryl alcohol (FA) and 2-methylfuran (MF) production routes in ECRFF are studied by using periodic density functional theory on Ag, Pb, and Ni, as alternative cathode materials. The established Bronsted-Evans-Polanyi (BEP) relationship has been proven to be reliable to estimate energy barriers of C-O bond cleavage. The intrinsic characters of Ag, Pb, and Ni are then summarized in free energy diagrams to reflect the FA and MF production trends as future guidelines to evaluate ECRFF activity and selectivity on these metals. On all metal surfaces, at both terrace and stepped sites, the first C-H or O-H hydrogenation step, producing respective mh6 or mh7 intermediates, influences overall FA production. On Ag and Pb, pathways involving the mh6 intermediate are thermodynamically and kinetically favored, whereas on Ni, both mh6 and mh7 routes are competitive due to strong interactions between the furan ring and the substrate. In addition, these partially hydrogenated intermediates can also undergo C-O bond cleavage with reduced energy barriers (compared to direct C-O bond cleavage in furfural), which opens potential paths for parallel MF production. Conversion of FA into MF catalyzed by these metallic cathodes was considered as well, although the high C-O bond cleavage energy barrier is likely to hinder this process.