Substrate specificity in decarboxylation of mixtures of acetate and propionate using oxidized Pt electrodes and galvanic square-wave pulsed electrolysis†

Abstract

The decarboxylation (of mixtures) of short-chain carboxylic acids (C₂ and C₃) on oxidized platinum anodes was investigated using constant current and galvanic square-wave pulse electrolysis. At constant current, a high ethylene to ethane product ratio indicates that propionate is the substrate of preferential decarboxylation in propionate/acetate mixtures, depending on the feed ratio. The specificity of (oxidized) Pt electrodes towards C₃ decarboxylation can be further enhanced by the application of cathodic and anodic pulses. The application of relatively long cathodic pulses and very short anodic pulses has been demonstrated to facilitate the formation of high ethylene to ethane ratio product mixtures, which are higher than those obtained under constant current conditions. In particular, extended cathodic pulses have been observed to enhance the faradaic efficiency towards oxygen and to reduce carboxylate conversion. Based on isotherm and RRDE data, we propose that the selectivity for propionate is attributable to a higher affinity for the oxidized Pt electrode, which is further enhanced by cathodic and anodic pulses. The use of galvanic square wave-pulse electrolysis thus offers a promising pathway for the efficient conversion of bio-derived acids into fuels and chemicals.