(Invited) Influencing the Catalytic Activity for Oxygen Reduction and Evolution in Aqueous and Non-Aqueous Electrolytes: Support and Cations

The idea of a battery employing a lightweight metal anode and an oxygen cathode has inspired many electrochemists during the last decades. This is mainly due to the theoretically high specific energies, which would allow for surpassing some of the shortcomings of conventional lithium–ion batteries. However, one of the main issues to address is the stability of the metal anode in contact with the electrolyte and possibly oxygen. This is why the oxygen reduction in organic electrolytes has recently attracted much attention [1]. Organic electrolytes, unlike aqueous electrolytes, generally exhibit an increased compatibility with metal anodes like lithium or sodium, which are unstable in aqueous electrolytes due to their low redox potential. Although lithium is the most promising metal energy-wise, other alkaline and earth alkaline metals would still yield superior specific energies in comparison with lithium-ion batteries. This is why this work aims at elucidating the role of the metal cation on the ORR and OER in organic solvents. Previous DEMS (differential electrochemical mass spectrometry)-studies imply that there might be a charge-density related effect within the alkaline metals: Monovalent Cations with high charge densities seem to foster the formation of the corresponding peroxide [2]. However, recent observations using Ca 2+ as a cation show that the picture is obviously more complicated when using the earth alkaline metals. Despite its low charge density, Ca 2+ fosters the peroxide at gold electrodes [3]. Within the earth alkaline series, the (average) number of electrons transferred per oxygen molecule increased in the order: z(Ca 2+ )