Quantitative Study for Oxygen Reduction and Evolution in Aprotic Organic Electrolytes at Gas Diffusion Electrodes by DEMS

Abstract

Cyclic voltammetry and differential electrochemical mass spectrometry (DEMS) have been combined to study the cycling performance of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) at a gold electrode in non-aqueous dimethyl sulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP) based LiClO4 and N(Bu)4ClO4 containing electrolytes. An Au-sputtered Teflon membrane (with a thickness of Au of only 50 nm resulting in an extremely short pore length on the electrolyte side) has been used as a model for a gas diffusion electrode (GDE) in this study: The oxygen molecules diffuse through a membrane from the gas side and are reduced at Au on the electrolyte side. The redox couple O2−•/O2 is the predominant reaction during ORR in N(Bu)4ClO4 based electrolytes whereas the calculated number of electron transferred is one. In presence of Li-ions, the average number of electrons transferred is 2 during oxygen reduction, which indicates the formation and oxidation of peroxide during ORR and OER respectively. The mass spectrometric cyclic voltammograms (MSCVs) data show that the maximum true coulombic efficiency of OER/ORR in DMSO and NMP is about 60% and 25%, respectively, with the evolution of CO2 in NMP at 0.1 V (vs. Ag+/Ag) due to the decomposition of the electrolyte.