Seven steps to reliable cyclic voltammetry measurements for the determination of double layer capacitance

Discovery of electrocatalytic materials for high-performance energy conversion and storage applications relies on the adequate characterization of their intrinsic activity, which is currently hindered by the dearth of a protocol for consistent and precise determination of double layer capacitance (C (DL)). Herein, we propose a seven-step method that aims to determine C (DL) reliably by scan rate-dependent cyclic voltammetry considering aspects that strongly influence the outcome of the analysis, including (a) selection of a suitable measuring window, (b) the uncompensated resistance, (c) optimization of measuring settings, (d) data acquisition, (e) selection of data suitable for analysis, (f) extraction of the desired information, and (g) validation of the results. To illustrate the proposed method, two systems were studied: a resistor-capacitor electric circuit, and a glassy carbon disk in an electrochemical cell. With these studies, it is demonstrated that when any of the mentioned steps of the procedure are neglected, substantial deviations of the results are observed with misestimations as large as 61% in the case of the investigated electrochemical system. Moreover, we propose allometric regression as a more suitable model than linear regression for the determination of C (DL) for both the ideal and the non-ideal systems investigated. We stress the importance of assessing the accuracy of not only highly specialized electrochemical methods, but also of those that are well-known and commonly used as it is the case of the voltammetric methods. The procedure proposed herein is not limited to the determination of C (DL), but can be effectively applied to any other analysis that aims to deliver quantitative results via voltammetric methods, which is crucial for the study of kinetic and diffusion phenomena in electrochemical systems.