Electrochemically active surface area effects on the performance of manganese dioxide for electrochemical capacitor applications

The specific surface area, morphology and electrochemical performance of thin films of electrodeposited manganese dioxide have been examined. Electrodeposition of these films was carried out using chronoamperometry, using times ranging from 10 to 120 s in order to obtain deposits with different masses. Using a novel approach to analysing the chronoamperometric i-t data, the specific surface area of the electrodeposited material was found to range from 13 to 67 m2/g across the range of deposition times, with short deposition times leading to higher specific surface areas. This has implications on the electrodeposition mechanism of manganese dioxide, which favours crystallite nucleation initially, leading to a high surface area material, followed by growth of these crystallites leading to a denser, lower surface area electrode material. This is the first time that the electrochemically active surface area of porous electrode materials has been determined. This decrease in surface area with deposition time was also reflected in the specific capacitance values of the material, which decreased slightly with increased deposition time, and hence lower surface area.