Електрохімічно NH4+-допований манган (IV) оксид з α-MnO2 фазовою компонентою як перспективний електрод електровідновлення кисню

Abstract

α-MnO2 with hollandite structure type is considered to be the most effective oxygen electrocatalyst. It has been demonstrated that manganese dioxide samples doped with ammonium cations possess promising properties for different types of lithium-air batteries. The measured earlier high catalytic activity of H2O2 decomposition on NH4+-doped manganese dioxide [1] caused our interest to further in-depth research. Thin films were electrodeposited using the following electrolyte composition: 1M MnSO4; 0,1 HF; 0,75M (NH4)2SO4 with current density3-4 мA/cm2 and temperature was 15-20°C or 90-95°C. The current density100 мA/cm2 was applied to obtain powders. NH4+-Doping or (NH4)2SO4 additive to a fluorine containing electrolyte of manganese dioxide in electrocrystallisation acts as a template of hollandite-structure channels in samples. There is a template effect of other indifferent ions (alkali, alkaline earth metals) on the structure ordering in the electrocrystallisation process, which was demonstrated in our earlier publications. An increase in the content of α-MnO2 phase component and the crystallite size of this phase is shown in this work as a result of increasing the temperature of electrodeposition up to 90-95°C. To prove this hypothesis, the simulations of XRD patterns by the Rietveld refinement method using PowderCell v. 2.3 package were realized. XRD patterns were registered on MoKα-irradiation to improve signal/noise ratio. Diffuse peaks of XRD patterns were successfully interpreted by the Rietveld refinement as a set of phase components detected in samples with sizes of crystallites lower than XRD detection limit (about 5 nm).