Abstract
This paper introduces the method which allows determining the accurate electrode contributions during cyclic voltammetry (CV) scan of electrochemical capacitor. As a result of theoretical considerations, a calculation method which reveals voltammetry response of both electrodes during CV of two-electrode cell with reference is developed. The technique is based on the preservation of charge neutrality where the accurate potential sweep rate of individual electrode is dynamically assigned based on its total contribution to the total two-electrode cell voltage ramp. This practice should be used in the research with CV scans of energy storage devices in order to improve their precision. The technique is not an alternative to real three-electrode measurements, where constant sweep rate of working electrode is applied and an oversized auxiliary electrode is used, but it is rather a supplement, which allows observing the true electrode behavior during operation of the capacitor. The paper provides comparison of CV scans obtained with fixed scan rates of both electrodes with dynamic CV scan for electrochemical capacitors operating in aqueous media of 1 mol L−1 Li2SO4 and 7 mol L−1 KSCN. For the first time, the simple procedure is proposed to visualize the real qualitative electrode responses.
Highlights
Developing area in electrochemical storage devices includes electrochemical capacitors (EDLC) [1]
The cell voltage is governed by electrical double-layer (EDL) polarizable electrode, while the redox one is responsible for the increased cell capacitance as it can be found in hybrid capacitors [5,6,7]
Observing electrode potential profiles for the cell operating in KSCN, it is possible to see that the positive electrode is responsible for providing redox contribution, whereas the negative one has essentially EDL character
Summary
Developing area in electrochemical storage devices includes electrochemical capacitors (EDLC) [1]. In order to achieve high double-layer capacitance values (Eq (1)), the electrodes are made of porous material with developed surface area, e.g., activated carbon, which are connected to the external circuit via metallic current collectors [4]. During ideal EDLC capacitor operation, the polarizable electrodes change their potential, meaning that the charges of opposite signs are attracted to the designated surfaces. The cell voltage is governed by electrical double-layer (EDL) polarizable electrode, while the redox one is responsible for the increased cell capacitance as it can be found in hybrid capacitors [5,6,7]. In real capacitors utilizing electrode materials of high surface area, these two limiting conditions occur simultaneously and the final cell voltage is an outcome of partial chemical and electrical potential changes of the electrodes
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