Investigation of the complex influence of divalent cations on the oxygen reduction reaction in aprotic solvents

The resurgence of interest in oxygen reduction in non-aqueous electrolytes makes it necessary to develop a fundamental understanding of the factors influencing its kinetics and reversibility. One of these key factors is the cation of the conducting salt. This study focuses on the influence of the cation by extending research to the field of the alkaline earth cations. At gold electrodes, the main formation of the peroxides is observed for all the different cations. However, the peroxides do not lead to a deactivation of the electrode as opposed to the observations in the presence of lithium ions. Interestingly, at platinum and glassy carbon the cation exerts a more complex influence on the product distribution: The number of electrons transferred per oxygen molecule (z) increases in the order z(Ca2+)<z(Sr2+)<z(Ba2+) approximate to z(Mg2+). This is in good agreement with the acceptor numbers of the cations, with high acceptor numbers fostering the formation of peroxides. These results add an important aspect in understanding the oxygen reduction in non-aqueous solvents. (c) 2018 Elsevier Ltd. All rights reserved.