Insights into the surface and stress behavior of manganese-oxide catalyst during oxygen reduction reaction

Abstract

The electro-catalysts for oxygen reduction reaction (ORR) on air-cathodes have a decisive impact on metal-air batteries and fuel cells performance. Manganese-oxides (MnOx) are particularly interesting as non-precious electro-catalysts candidates. In order to broaden our understanding on the surface chemistry of manganese-oxide, we performed in-situ electrochemical surface stress (ESS) measurements. The in-situ ESS response was measured on an Au/MnOx electrode in both de-oxygenated and O2 saturated electrolytes. A complex stress response was measured during the electrochemical scan, caused by various crystal structure transitions and surface reconstruction processes. It was found that the presence of oxygen resulted in a less compressive stress response during the ORR. In addition, an overall tensile trend was recorded during multiple cycling, explaining the poor mechanical stability of the MnOx film. These findings have major implications on the applicability of MnOx as catalyst.