Surface Interrogation of Electrodeposited MnOx and CaMnO3 Perovskites by Scanning Electrochemical Microscopy: Probing Active Sites and Kinetics for the Oxygen Evolution Reaction.

Surface interrogation scanning electrochemical microscopy (SI-SECM) of two electrodeposited manganese-based electrocatalysts, amorphous MnOx and perovskite CaMnO3 , was used to investigate the manganese oxidation state relating to the oxygen evolution reaction (OER) under neutral conditions. The results indicate the amounts of MnIII and MnIV species in MnOx and CaMnO3 depend on potential. A MnV species was identified in both structures during the OER. Time-delay titration of MnV further revealed that MnOx produced two types of active sites with different OER reaction rates: k'fast (MnOx )=1.21 s-1 and k'slow (MnOx )=0.24 s-1 . In contrast, CaMnO3 perovskites in which the MnV species formed at a less positive potential than that in MnOx , displayed only one kinetic behavior with a faster reaction rate of 1.72 s-1 .