Manganese oxides (MnO₂, MnOOH) are promising materials for electrochemical capacitors due to their low cost and toxicity, coupled with their attractive energy storage properties, and as such are well represented in the literature [1]. Thin films of MnO₂ prepared by electrodeposition are capable of achieving high values for gravimetric specific capacitance (>2000 F/g) [2], however this rapidly decreases with increasing film thickness. Material activity, as well as material morphology play an important role in determining the capacitive behaviour of a material [3]. Recently, a new method for using step potential electrochemical spectroscopy to separate double layer and faradaic capacitance has been developed [4].

In this presentation, the change in both the double layer and faradaic capacitance with increasing film thickness of anodically prepared deposits will be discussed. With increasing film thickness the gravimetric double layer capacitance increases; however, this is significantly offset by a degradation in material activity, leading to an overall decay in material capacitance. The proposed structural and morphological reasons for these changes will be discussed.

1. Wei, W., et al., Manganese oxide-based materials as electrochemical supercapacitor electrodes. Chemical Society Reviews, 2011(40): p. 1697 - 1721.

2. Cross, A., et al., Enhanced Manganese Dioxide Supercapacitor Electrodes Produced by Electrodeposition. Journal of Power Sources, 2011. 196: p. 7847 - 7853.

3. Conway, B.E., Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications. 1999, New York: Springer.

4. Dupont, M.F. and S.W. Donne, A Step Potential Electrochemical Spectroscopy Analysis of Electrochemical Capacitor Electrode Performance. Electrochimica Acta, 2015. 167: p. 268 -277.