OH− dependence for the electrocatalytic decarboxylation of a medium-chain fatty acid into hydrocarbons using Pt and carbon electrodes

Abstract

Electrolysis of fatty acids in aqueous systems typically exhibits a high conversion rate of fatty acids but a low selectivity for the resulting hydrocarbon products. This characteristic significantly hinders the industrialization of the electrochemical decarboxylation method for the synthesis of hydrocarbon biofuels. Herein, we investigated the electrolysis of a medium-chain fatty acid (octanoic acid, OA) by monitoring the electrolysis process, examining the oxidation of OA by the oxygen evolution reaction (OER), and controlling the pH of the alkaline electrolyte. Our findings revealed that at high OH⁻ concentrations (pH ≥ 11), OA was more susceptible to be over-oxidized by the reactive oxygen species (ROS) generated during the electrolysis process, leading to decreased selectivity and FE for the hydrocarbon products. Under weakly alkaline conditions (pH ≤ 8), owing to low OH⁻ concentration, in situ generated CO₂ easily caused a decrease in the electrolyte pH, leading to the precipitation of OA at the electrode interface, which was unfavorable for the decarboxylation reaction. When the OH⁻ concentration was at around pH 10, overoxidation of OA was partially prevented, thereby enhancing the selectivity and FE of the hydrocarbon products. This work aids in understanding the conversion behavior of medium-chain fatty acids and provides new insights into improving the selectivity of decarboxylation of carboxylic acids.