ORR electrocatalysis on Cr3+, Fe2+, Co2+-doped manganese(IV) oxides

Abstract

The ionic dopant additives have di erent mechanisms of their influence upon MnO2 electrocrystallisation process and depending on dopants added the following polymorphs are stabilised: α-MnO2 (hollandite, I4/m) — NH+4 ; 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 di raction 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.