Electrodeposition and Ageing of Mn‐Based Binary Composite Oxygen Reduction Reaction Electrocatalysts

Electrodeposition and ageing under oxygen reduction reaction (ORR) of Mn‐X/PPy (X=Co, Mg, Ni; PPy=polypyrrole) and Mn‐Ag/G (G=graphene) composite electrocatalysts have been studied by quasi‐in‐situ soft X‐ray absorption and fluorescence microspectroscopy. The fabricated materials exhibit micro‐grained morphologies in which Mn is present mainly as Mn 2+ , accompanied by combinations of Co 0 /Co 2+ and Ni 0 /Ni 2+ . Ageing leads to the formation of progressively larger mesoscopic aggregates. Initial ageing yields more active Mn 3+ and Mn 4+ , in agreement with an improved ORR behaviour. Prolonged ageing causes the loss of Mn 3+ and Mn 4+ from the surface, in correlation with a degradation of the ORR response. In the investigated ageing period, Mn‐Mg/PPy exhibits the best durability, with about half of the catalyst grains still showing the presence of Mn 3+ /Mn 4+ , while the others consist mainly of Mn 2+ . In Mn‐Ni/PPy, the Ni 2+ content tends to increase with ageing whereas Co 3+ forms in the Mn‐Co/PPy composites.