In-situ Raman investigation for porous carbon electrodes operating in neutral aqueous media indicated that there is mild oxidation of positive electrode during cycling (vibration modes from oxygen-based functionalities found) whereas the surface chemistry of negative electrode appears to be stable. EQCM study confirmed significant frequency/mass variation on the positive side, whereas the negative electrode remained stable. However, SECM demonstrated that during positive and negative polarization, the thickness (and volume) of the electrode changed remarkably. Additionally, it has been found that charge/discharge process, even at the cell voltages well below the electrolyte decomposition values, induces quasi-reversible changes of the cell pressure and kind of the gas evolved (on-line GC-MS study).

Interesting results were obtained for carbon electrodes operating in KI, KBr and KSCN solutions. It has been confirmed that halide anions undergo several redox processes and actively interacts with activated carbon surface. Oxidation of carbon surface has been identified near the redox activity potentials. EQCM study confirmed the presence of various species in the electrolyte. Carbon ‘corrosion' has been observed especially for more concentrated solutions. However, we proved that highly oxidized anions do not contribute significantly to this process.

Operando results will be supported by conventional post-mortem studies (XPS, N2 adsorption/desorption, elemental analysis).