Analysis of Galvanostatic Data from Electrochemical Capacitors

The ability to deconvolute charge storage mechanisms in electrochemical capacitor materials and systems is essential for understanding and improving behaviour. From an electrochemical perspective, this deconvolution can be achieved through an understanding of the expected response of a particular contribution. Voltametric measurements can be deconvoluted through the current response relative to the applied sweep rate. Herein we describe an analogous approach for galvanostatic data in which the charge or discharge time is related to the applied current (I). Specifically, capacitive charge storage is shown proportional to I −1 , while diffusional processes are proportional to I 2 . Coupling this with a constant contribution from ohmic and residual charge storage processes allows for an effective approach to deconvolution for galvanostatic data. This is demonstrated with data from a glassy carbon electrode in non-aqueous electrolyte (an expected electrical double layer system) and from a manganese dioxide electrode in aqueous electrolyte (an expected pseudo-capacitive system).