Electrooxidation and reduction of propylenecarbonate, ethylene carbonate and 1,2-propanediol in aqueous acid solution—A comparative study using on-line MS and isotope labelled electrolytes

Abstract

The electrooxidation and reduction of propylenecarbonate, ethylenecarbonate and 1,2-propanediol is investigated at porous platinum electrodes in aqueous acid electrolytes by a combination of potentiodynamic and potential step techniques with on-line MS (DEMS) for detection of volatile products. Propylenecarbonate forms (oxidatively) only CO 2 above 0.5 V vs. rhe, without the contribution of a bulk reaction being evidenced by transient experiments. In addition, CO 2 is also produced around 0.3 V vs. rhe during anodic and cathodic scans of cyclic voltammograms. In order to investigate the origin of these signals, a H 2O 18 containing electrolyte was used. The electrooxidation of ethylenecarbonate to CO 2 also starts at 0.5 V vs. rhe, showing a small contribution of a bulk reaction in addition to the oxidation of the adsorbate. At 0.3 V vs. rhe, CO 2 production is significantly decreased in comparison to propylenecarbonate. In contrast to the behaviour of the carbonates, the electrooxidation of 1,2-propanediol is dominated by two independent bulk reactions. One reaction pathway forms CO 2, while the other produces aldehydes. The three compounds studied show fewer differences during electroreduction, forming hydrocarbons via adsorbates below 0.15 V vs. rhe. Hydrocarbons are produced having the same as or a smaller number of carbon atoms than the original compounds with the exception of 1,2-propanediol, which additionally forms butane. Ethanes and propanes with a high number of deuterium atoms are formed during electroreduction of propylenecarbonate as well as 1,2-propanediol in D 2SO 4/D 2O containing solutions. Under these conditions, 1,2-propanediol produces butanes with only a small number of deuterium atoms.