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 Mn-III and Mn-IV species in MnOx and CaMnO3 depend on potential. A Mn-V species was identified in both structures during the OER. Time-delay titration of Mn-V 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 Mn-V 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).

Automated summary

Surface interrogation scanning electrochemical microscopy (SI-SECM) was used to investigate the manganese oxidation state in two electrodeposited manganese-based electrocatalysts, revealing differences in Mn-III and Mn-IV species quantities in MnOx and CaMnO3 under different potentials, as well as the presence of a Mn-V species during the oxygen evolution reaction (OER). Time-delay titration of Mn-V showed that MnOx exhibited two types of active sites with different OER reaction rates, while CaMnO3 only displayed one kinetic behavior with a faster reaction rate.