Examining the Electrodeposition Mechanism of Manganese Dioxide Using In-Situ Small Angle X-ray Scattering

Manganese dioxide thin films, produced by anodic electrodeposition, have been found to exhibit extremely high specific capacitance. However, their capacitive performance decreases markedly as the film thickness increases, so despite exhibiting specific capacitance values of up to 2000 F/g (for extremely thin films), their applications are limited due to their low volumetric capacitance.

The enhanced performance of thin films is largely due to their high specific surface area and conductivity, both of which decrease as the film thickness increases. Improving the performance of thicker films requires synthesis methods in which the morphology of the films can be tailored to optimise surface area and conductivity. To achieve this, the mechanism by which manganese dioxide is electrodeposited must be fully understood.

In this work, manganese dioxide was deposited onto a platinum electrode from a solution of MnSO₄ in H₂SO₄. The deposition process was examined in-situ­ using small angle x-ray scattering (SAXS) using a synchrotron x-ray beam.

SAXS analysis was used characterise the material at different stages throughout the deposition. Features such as the pore size and particle size and shape were obtained from the data, showing how the morphology of the film changes as deposition is occurring. The deposition solution and deposition potential were varied in order to find the optimum deposition conditions required to create high performance thin film capacitors.

The performance of the thin films was analysed using standard electrochemical techniques including cyclic voltammetry and constant current charge discharge.