An ever increasing number of electrode materials are nowadays presented as potential candidates for electrochemical capacitor. This includes different forms of carbons (carbon nanotubes, graphene, activated carbon, ...), conducting polymers (PEDOT, PANI, PPy, ...), metal oxides (RuO₂, MnO₂, FeWO₄, ...), or other inorganic materials such as metal nitrides, phosphates, etc... However, most of the reported performance of related electrodes are based on only few mg of active material and/or few mm² surface area. Such low values definitely do not enable to upscale the performance using simple multiplying factor. Indeed, several studies have shown that experimental up-scaling of electrodes and devices often leads to quite different values, usually much lower than those reported for small scale electrodes.[1-3]

In this manuscript, we will illustrate such discrepancy between small cell and larger cell performance by using commercially available activated carbon in different configurations, including coin-type cells (< 1F) and pouch cells (up to 25 F). The different parameters influencing the electrode preparation (binder, additives, porosity, ...) as well as those related with cell assembly (current collectors, separators, ...) will be detailed as well as their influence on the cell performance. Finally, a practical illustration of symmetrical carbon based EDLC in neutral aqueous electrolyte will be given, namely the internal hybridization of such cell in a PEMFC. Its influence on power capability will be reported and compared with external hybridization using a commercial cylindrical EDLC.

[1] True performance metrics in electrochemical energy storage, Y. Gogotsi and P. Simon, Science, 334, 917 (2011).

[2] Improving the volumetric energy density of supercapacitors, N. Goubard-Bretesché, O. Crosnier, F. Favier, T. Brousse, Electrochimica Acta 206 (2016) 458–463.

[3] A Guideline for Reporting Performance Metrics with Electrochemical Capacitors: From Electrode Materials to Full Devices, A. Balducci, D. Belanger, T. Brousse, J.W. Long, W. Sugimoto, Journal of The Electrochemical Society (2017) 164 (7), A1487-A1488.