Surface Interrogation of Electrodeposited MnO<sub>x</sub> and CaMnO<sub>3</sub> Perovskites by Scanning Electrochemical Microscopy: Probing Active Sites and Kinetics for the Oxygen Evolution Reaction
Zhaoyu Jin, Allen J. Bard
Abstract
Abstract Surface interrogation scanning electrochemical microscopy (SI‐SECM) of two electrodeposited manganese‐based electrocatalysts, amorphous MnO x and perovskite CaMnO 3 , was used to investigate the manganese oxidation state relating to the oxygen evolution reaction (OER) under neutral conditions. The results indicate the amounts of Mn III and Mn IV species in MnO x and CaMnO 3 depend on potential. A Mn V species was identified in both structures during the OER. Time‐delay titration of Mn V further revealed that MnO x produced two types of active sites with different OER reaction rates: k ′ fast (MnO x )=1.21 s −1 and k ’ slow (MnO x )=0.24 s −1 . In contrast, CaMnO 3 perovskites in which the Mn V species formed at a less positive potential than that in MnO x , displayed only one kinetic behavior with a faster reaction rate of 1.72 s −1 .