Operando monitoring of activated carbon electrodes operating with aqueous electrolytes

Remarkable changes in the volume of activated carbon electrodes operating with aqueous electrolytes were measured with scanning electrochemical microscopy (SECM) and electrochemical dilatometry (ECD) techniques. It appears that the electrolyte volume absorbed by the carbon electrode strongly depends on the polarization direction and the electrode potential. It is assumed that these changes result from different ion adsorption properties and the volume of the electrolyte. Furthermore, the electrode surface functionalities appear to change. This has been confirmed by operando contact angle measurements. In addition to the observations of volume changes, the method of preconditioning electrochemical capacitors is proposed, which is an outcome of the observed electrode dilatations and modulated wettability. The conditioning method promotes deep electrochemical impregnation of the electrodes by an electrolyte. In fact, remarkably better wetting of the electrodes is reflected in significant changes in the potential distribution between electrodes. Moreover, the internal pressure build-up during the potentiostatic hold test is reduced. Finally, in situ observations of the electrodes with X-ray tomography suggest the precipitation of insoluble deposits at the surface of the positive electrode near the separator.