Ex-situ Spectroscopy Study of Manganese Oxide Catalytic Surfaces under Reaction Conditions Relevant to Oxygen Reduction and Oxygen Evolution

In our previous work, we developed a promising non-precious metal catalyst with bifunctional activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). We identified the catalyst as manganese (III) oxide with some alpha-Mn2O3 crystallinity in its initial state, but needed to further characterize the catalyst to understand its properties under reaction conditions. In this work, we performed cyclic voltammetry in an inert gas environment to identify electrochemical features of the catalyst and used ex-situ x-ray photoelectron spectroscopy (XPS) to probe the surface oxidation state of manganese after exposing the catalyst to ORR or OER potentials. XPS did not detect a surface oxidation state difference between samples tested at ORR and OER potentials, while electrochemical methods could discern a difference in the oxidation state upon re-insertion of the samples into an electrochemical cell. This result suggested an extremely shallow depth of electrochemical oxidation.