Browsing by Author "Caudle, James"

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    Manganese Dioxide Electrode: Part 1.—Hydrogen Ion Response in the Absence of other Cations
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (5), 1973) Caudle, James; Summer, Keith G.; Tye, Frank L.
    Potential against pH plots have been obtained for a “hydrogen form” electrodeposited γ-manganese dioxide and for a “hydrogen form”β-manganese dioxide ore. The electrolyte solution was hydrochloric acid; no cations other than hydrogen ions were present. The plots were straight lines with a slope of –0.059 V/pH and changes of pH caused no hysteresis. Changing the electrolyte to sulphuric acid did not affect the potential against pH relationship. When other cations are present, the effects on the potential against pH plot caused by ion exchange between the manganese dioxide and these cations, can be minimised by an extrapolation procedure. The potential determining reaction for manganese dioxide is most probably MnO2+ H++ e ⇌ MnOOH.
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    Manganese Dioxide Electrode: Part 2.—Hydrogen Ion Response in the Presence of Manganese(II) Ions
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (5), 1973) Caudle, James; Summer, Keith G.; Tye, Frank L.
    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+.