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AMn2O4 spinels (A - Li, Mg, Mn, Cd) as ORR catalysts: The role of Mn coordination and oxidation state in the catalytic activity and their propensity to degradation
Using the rotating disk electrode (RDE) and cyclic voltammetry (CV) techniques, we studied electrochemical behavior, including activity in the oxygen reduction reaction (ORR) in an alkaline solution, of different AMn2O4 (A=Mn(II), Mg(II), Li(I) and Cd(II)) oxides with the spinel structure. With the help of postmortem XPScharacterization we demonstrate that the surface of the studied spinels (except for MgMn2O4) undergoes essential modification not only under potential cycling but also after contacting alkaline solution under open circuit conditions, and even during the electrode preparation. The widely studied Mn3O4 spinel demonstrates the strongest surface modifications due to the presence of easily oxidizable and unstable Mn(II). The results of this work are of importance for the field of electrocatalysis and emphasize significant influence of degradation processes occurring at the surface and in the near-surface layers of materials on their electrochemical characteristics.