Oxygen Reduction in Mixed Calcium‐Based Electrolytes

Dimethyl sulfoxide is a suitable solvent for reversible oxygen reduction in the presence of Ca 2+ , but not sufficiently stable towards the anode. Solvents suitable as anolytes tend to underperform in the context of oxygen reduction. Thus, a combined approach using different electrolytes at the cathode and anode promises superior performance. However, due to the electroosmotic drag, a cross‐contamination of both electrolytes is expected. In this work, the influence of solvent mixtures of dimehtyl sulfoxide as an excellent electrolyte is investigated for the cathode with tetraglymeor tetrahydrofuran for oxygen reduction in the presence of Ca 2+ at gold and glassy carbon electrodes using the rotating ring disc electrode assembly and oxygen solubilities and diffusivities are determined. While a high share of tetraglyme and tetrahydrofuran leads to a quick deactivation of the electrodes products, intermediate shares (1:1 mixture by volume), are beneficial for the oxygen reduction. This is due to the increased solubility of oxygen in those solvent. Even more interesting is the fact that the re‐oxidizability of soluble peroxide species is eased by the addition of the ethers. While the reasons for this behavior remain elusive, the beneficial effect of other solvents is an encouraging starting point for a dual electrolyte Ca 2+ ‐battery.