ORR Electrocatalysis on Cr³⁺, Fe²⁺, Co²⁺-Doped Manganese(IV) Oxides

The ionic dopant additives have different mechanisms of their influence upon MnO₂ electrocrystallisation process and depending on dopants added the following polymorphs are stabilised: α -MnO₂ (hollandite, I4/m) - NH₄⁺; γ -MnO₂ (ramsdellite, Pbnm) - Co²⁺, Fe²⁺; layered polymorph δ -MnO₂ (birnessite, C2/m) - Cr³⁺. The defect states of intergrowth method in ramsdellite matrix and twinning, OH groups studied by X-ray diffraction and the Fourier transform infrared mtehod, respectively, indicate their high content in case of Fe²⁺ and Co²⁺-doped manganese dioxide. CVA oxygen reduction reaction peaks were established after experiments in alkaline electrolytes and dioxygen (argon, air) atmosphere. Activity of doped samples studied is comparable with other published data. Both doped with Co²⁺ and Fe²⁺ samples display maximal currents and some distinctive features in oxygen reduction reaction.