Electrolyte dependence for the electrochemical decarboxylation of medium-chain fatty acids (n-octanoic acid) into fuel on Pt electrode

The deoxygenation of organic acids, important biomass feedstocks and derivatives, to synthesize hydrocarbon products under mild electrochemical conditions, holds significant importance for the production of carbon-neutral biofuels. There is still limited research on the influential factors of the electrochemical decarboxylation reaction of medium-chain fatty acids. In this study, n-octanoic acid (OA) was chosen as the research subject to investigate the electrochemical decarboxylation behavior of OA on a platinum electrode, focusing on the influence of different alkali metal cations (Li⁺, Na⁺, K⁺), common anions (SO₄²⁻, Cl⁻), and electrolyte pH. It was found that KOH as an electrolyte exhibited the best performance for OA. Possibly, the larger size of K⁺ increased the alkalinity of the electrode surface, facilitating OA deprotonation. LiOH electrolyte reduced the solubility of OA, thereby inhibiting the decarboxylation reaction. SO₄²⁻ exhibited a weak promoting effect on the decarboxylation reaction of OA, while Cl⁻ showed no adverse effect although Cl⁻ may adsorb on the electrode surface. Furthermore, unlike short-chain fatty acids, medium-chain OA can only achieve efficient decarboxylation under alkaline conditions due to its solubility properties. This study provides references and foundations for future efforts to enhance the efficiency of electrochemical decarboxylation synthesis of hydrocarbon biofuels from medium-chain fatty acids.