Manganese dioxide electrode. Part 2.—Hydrogen ion response in the presence of manganese(II) ions

Abstract

Potential-pH and proton release-pH measurements were made in manganese(II) chloride solutions for a “hydrogen form” electrodeposited γ-manganese dioxide and for a “hydrogen form”β-manganese dioxide. The slope of all potential against pH plots was –0.118 V/pH. Proton release data showed that at least the surface of the manganese dioxide varied throughout these potential against pH plots due to reaction with the solution. When the extent of this reaction was kept constant or made zero by an extrapolation procedure, slopes were –0.059 V/pH. No direct response to manganese(II) ions was observed.

It is concluded that the potential determining reaction in all solution is MnO₂+ H⁺+ e ⇌ MnOOH and that the –0.118 V/pH slopes are the result of the chemical potential of MnOOH being controlled by the equilibrium MnO₂+ Mn²⁺+ 2H₂O ⇌ 2MnOOH + 2H⁺.