Abstract
AbstractWe report on a comprehensive structural and electrocatalytic reactivity study of a diverse set of non‐noble monometallic and bimetallic Fe, Mn, Co, and Ni ‐based oxide bifunctional ORR and OER electrocatalysts. To assess their catalytic activity and suitability for bifunctional operation in a consistent manner, we introduce and apply a standardized successive electrochemical testing protocol. Correlations are established between bifunctional activity and structure, by which the materials are classified. The large set of tested catalyst materials in this study enabled us to unravel entire reactivity trends across material groups and to make conclusions as to their suitability for reversible operating oxygen electrode applications. Our analysis reveals both beneficial synergistic effects of MnFe and MnCo based catalysts towards the oxygen reduction reaction (ORR) as well as favorable trends of NiFe based materials towards the oxygen evolution reaction (OER). We visualize synoptic activity trends in so‐called “double overpotential” diagrams to elucidate easily the underlying activity trends. The highest bifunctional activity was found for a novel mixed spinel phase of Co and Mn and the highest OER performance was demonstrated for a mixed metal NiFe layered double hydroxide catalysts, from which practical guidance for the design of bifunctional fuel cell or metal‐air battery electrodes ensues.
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