Saturated Alcohols Electrocatalytic Oxidations on Ni-Co Bimetal Oxide Featuring Balanced B- and L-Acidic Active Sites.

Investigating structural and hydroxyl group effects in electrooxidation of alcohols to value-added products by solid-acid electrocatalysts is essential for upgrading biomass alcohols. Herein, we report efficient electrocatalytic oxidations of saturated alcohols (C1-C6) to selectively form formate using NiCo hydroxide (NiCo-OH) derived NiCo2O4 solid-acid electrocatalysts with balanced Lewis acid (LASs) and Brønsted acid sites (BASs). Thermal treatment transforms BASs-rich (89.6%) NiCo-OH into NiCo2O4 with nearly equal distribution of LASs (53.1%) and BASs (46.9%) which synergistically promote adsorption and activation of OH- and alcohol molecules for enhanced oxidation activity. In contrast, BASs-enriched NiCo-OH facilitates formation of higher valence metal sites, beneficial for water oxidation. The combined experimental studies and theoretical calculation imply the oxidation ability of C1-C6 alcohols increases as increased number of hydroxyl groups and decreased HOMO-LUMO gaps: methanol (C1) < ethylene glycol (C2) < glycerol (C3) < meso-erythritol (C4) < xylitol (C5) < sorbitol (C6), while the formate selectivity shows the opposite trend from 100 to 80%. This study unveils synergistic roles of LASs and BASs, as well as hydroxyl group effect in electro-upgrading of alcohols using solid-acid electrocatalysts.