Investigation of the Electrochemical Oxygen Reduction Reaction in Non-Aqueous, Magnesium-Ion-Containing Electrolytes for Magnesium Air Batteries

Secondary magnesium-air batteries (MAB) hold great promise for cheap and highly dense energy storage as needed in automobiles and portable devices. While magnesium-ion-batteries1 and primary magnesium-air-batteries (magnesium air fuel cells, aqueous electrolyte)2 do already exist, there are difficulties in the development of the secondary magnesium air battery. In principal, the work which was done on the Lithium-air-batteries (LAB) should also be usable in MABs. Therefore, in this work the system Mg(ClO4)2 + DMSO, first proposed by Shiga et al.3, was investigated. The equivalent electrolyte for LABs (LiClO4 + DMSO) is proven to work4. It is shown that the oxygen reduction reaction (ORR) takes place (see Figure 1) within the stability window of the electrolyte and the electrochemical behavior of the system is discussed when using gold, platinum and glassy carbon as electrodes. It is shown that the ORR is not reversible and that passivating films are formed. By using a change-disk-RRDE-setup, we could investigate those films with IR, Raman, XPS, SEM and EDX. It was possible to trace the electrolyte components (S-O-groups and Cl-O groups) on the surface and a quantitative analysis proves that oxygen is mainly contributing to the composition and structure of the surface film. The resulting decomposition products on the respective electrodes and a probable pathway of reaction are presented. Acknowledgments This work has been funded by the German Federal Ministry of Education and Research (BMBF) under the project “Mg-Air”, under the reference 03EK3027C. References 1. H. D. Yoo et al., Energy Environ. Sci., 6, 2265 (2013) 2. I. C. Blake, J. Electrochem. Soc., 99, 202C–203C (1952) 3. T. Shiga, Y. Hase, Y. Kato, M. Inoue, and K. Takechi, Chem. Commun. (Camb)., 49, 9152–4 (2013) 4. M. M. Ottakam Thotiyl et al., Nat. Mater., 12, 1050–6 (2013) Figures Figure 1 Cyclic voltammograms of a 5mm diameter platinum disk (mirror polished) in 0.5 M Mg(ClO4)2 / DMSO electrolyte solution, argon saturated (red) and oxygen saturated (blue). Scan speed: 10 mV s-1 Figure 1