A step potential electrochemical spectroscopy (SPECS) investigation of anodically electrodeposited thin films of manganese dioxide

Herein the utility of step potential electrochemical spectroscopy for determining the mechanisms by which capacitance changes as a function of film parameters such as fractional material content and film thickness in thin film capacitors is demonstrated. The change in the capacitive behaviour of anodically electrodeposited thin films of MnO2 is investigated as a function of deposition time. With increasing film deposition time, the gravimetric double layer capacitance associated with small pores in the material increases. Thus, it is inferred that the number of small pores in the material, with respect to mass, increases in thicker films. This is due to a transition between MnOOH to MnO2 as deposition proceeds, with a subsequent contraction of the structure. It is also shown that the pseudocapacitive behaviour of the thin film electrode decreases with increasing film thickness, which has been attributed to a change in the cation diffusion characteristics of the material as it transitions from the Mn(III) to Mn(IV) states. Further, it is shown that a large portion of the pseudo-capacitive behaviour of MnO2 arises from a very thin surface coating of MnOOH.