EQUILIBRIUM POTENTIALS OF SPINEL-TYPE MANGANESE OXIDE IN AQUEOUS-SOLUTIONS

Equilibrium potentials of spinel-type manganese oxide, lambda-MnO2, were measured in various aqueous solutions. The Pt/lambda-MnO2 electrode showed a near-Nernstian response to lithium ions and not to other alkali metal and alkaline earth metal ions in the concentration range between 3 x 10(-6) and 0.5 mol/dm3. The selectivity coefficents for lithium ions against sodium, and potassium ions and protons were found to be: log k(LiNa)pot = -4.8, log k(LiK)pot = -4.6, and log k(LiH)pot = +1.9. The equilibrium potential was stable and pH-independent over a wide pH range (pH 4 to 9.5) in a solution with a lithium ion concentration above 5 mmol/dm3. The thermodynamic parameters for Li+insertion/extraction with lambda-MnO2 were evaluated from the temperature dependence of the equilibrium potentials in the temperature range between 298.15 and 318.15 K.