A study of Kolbe electrolysis using High-Energy Facet Pt electrode

Abstract

Kolbe electrolysis is a renewable and sustainable method capable of generating energy to replace fossil fuels. This electrochemical process involves the decomposition of carboxylic acids derived from biomass, synthesizing hydrocarbons through C-C dimerization. Kolbe electrolysis is the only approach to increase the carbon count under mild conditions of room temperature and atmospheric pressure. The number of carbons of the starting material, carboxylic acid, dictates the hydrocarbon produced, and in this thesis, hexane, which has six carbon atoms, was synthesized using butyric acid, which has four carbon atoms. However, the use of short-chain carboxylic acids (C2~C5) results in ineffective Kolbe production, leading to the formation of byproducts such as alcohols or esters. To produce the desired Kolbe product, hexane, the OH group of butyric acid must be effectively adsorbed on the catalyst, facilitating the formation of stable propyl radicals, the crucial intermediates in the reaction. Herein, we implemented the electrodeposition method and a low- temperature system to enhance the improved production of hexane from the short-chain carboxylic acid, butyric acid. We synthesized a electrocatalyst having high-energy facets using square wave potential. These high-energy facets facilitated the efficient adsorption of the OH group of butyric acid, inducing the production of stable propyl radicals by promoting the formation of intermediates. Moreover, the low temperature system at 0°C decreases the Gibbs free energy for the spontaneous dimerization of the produced propyl radicals, leading to the synthesis of hexane. This study suggests that the simultaneous development of electrocatalyst with high-energy facet and operating temperature control is the key to improving the performance of Kolbe electrolysis for short-chain carboxylic acid, providing valuable insights into the potential for efficient Kolbe production.