Abstracts Category : Other

Variations in the electrodeposition of manganese dioxide for enhanced thin-film capacitor performance

by Andrew J Gibson

Research Doctorate - Doctor of Philosophy (PhD) In this thesis, the relationship between the preparation conditions of electrodeposited manganese dioxide thin films and their resultant physico-chemical properties has been investigated. Specific attention has been paid to the morphology of the resultant film along with its capacitive behaviour. Preparation conditions investigated include the time for which electrodeposition was allowed to proceed, the electrodeposition mechanism, the starting reagent and electrolyte additives. The impact these preparation conditions have on both the electrodeposition mechanism, resulting film morphology and structure of the prepared manganese dioxide film is discussed in depth. Additionally, the effect of these variations in morphology and structure on the capacitive behaviour of the film is discussed. The project work encompasses two broad areas, the first of which comprises an investigation into how the electrodeposition mechanism informs the morphology and capacitance of manganese dioxide. In the second, the effects of film thickness and the genesis of layered films are investigated with respect to morphology and capacitance. In the first section this thesis presents, for the first time, a comprehensive investigation of the electrodeposition mechanism of manganese dioxide (Mn(IV)) when prepared from permanaganate (Mn(VII)) in an aqueous electrolyte. Additionally, this thesis presents significant refinements to the currently accepted mechanism for depositing manganese dioxide from a precursor of aqueous Mn(II). Variation in both electrodeposition mechanism and the rate of individual steps have been linked to significant changes in eventual film morphology. Additionally included in this thesis is the effect of film thickness on capacitive performance of anodic manganese dioxide, along with a novel method for preparing multi-layered films with tuneable individual layer thickness by changing the electrolyte composition. The change in capacitive performance of single layer manganese oxide films with respect to thickness has been investigated to inform decisions regarding layer thickness in the multilayered material. Previously capacitance has been understood to decrease with increasing film thickness, however the answer presented in this thesis has been found to be more nuanced. The pseudo-capacitive behaviour decreases with increasing mass loading, however the mass-specific double layer capacitance increases. This has been related to the temporal variation in the electrodeposition mechanism leading to more small pores per unit mass in the deposited material, but an overall decrease in material pseudo-capacitive activity.Advisors/Committee Members: University of Newcastle. Faculty of Science, School of Environmental and Life Sciences.