(Keynote) Oxygen Reduction and Evolution in Ca²⁺ Containing DMSO on Atomically Smooth and Rough Pt and Au – Towards a Generalized ORR Mechanism in M²⁺ Containing DMSO

We demonstrate via cyclic voltammetry, differential electrochemical mass spectrometry (DEMS) and rotating ring disk electrode (RRDE) investigations with variation of the electrode surface roughness and atomically surface structure, that the CaO/CaO2 adsorbate layer formation determines the ORR product distribution. We found that on Pt electrodes peroxide is formed on the clean electrode, whereas superoxide is formed at the adsorbate covered electrode. We furthermore identified four key parameters, which strongly affect the ORR product distribution. The electrode oxide interaction: A strong interaction shifts the product distribution to larger superoxide contribution. The alkaline earth metal oxide interaction: A strong interaction shifts the product distribution to larger peroxide contribution. The electrode surface area: A large electrode surface area delays the completion of the adsorbate layer and increases the peroxide contribution. Electrode surface defects: Defects allow for faster nucleation and thus foster the adsorbate formation, which finally leads to a larger superoxide contribution. Finally, reviewing earlier results of our group we provide a more general mechanism for the oxygen reduction alkaline earth metal cation containing DMSO, for a variety of electrode materials. [1] A. Koellisch-Mirbach, I. Park, M. Hegemann, E. Thome and H. Baltruschat, ChemSusChem, (2021). [2] P.P. Bawol, A. Koellisch-Mirbach, C.J. Bondue, H. Baltruschat and P.H. Reinsberg, ChemSusChem, 14 (2021) 428.