An EQCM investigation of capacitance of MnO₂ in electrolytes containing multivalent cations

MnO₂ is electrochemically deposited on Au coated quartz crystal to study the electrochemical capacitance properties and to monitor the mass variations that accompany reversible adsorption/desorption of Na⁺, Mg²⁺ and La³⁺ ions during discharge/charge cycling. There is an increase in the values of specific capacitance of MnO₂ with increase in charge of the cation in the electrolyte. Also, there is an increase in mass during discharge due to adsorption of cations from the electrolyte resulting from reduction of MnO₂. Mass decreases during charging process due to desorption of cations. The magnitude of mass variation is approximately proportional to the atomic weight of the cationic element.