Abstract
The point of zero charge (PZC) is a crucial parameter for investigating the charge storage mechanisms in energy storage systems at the molecular level. This paper presents findings from three different electrochemical techniques, compared for the first time: cyclic voltammetry (CV), staircase potentio electrochemical impedance spectroscopy (SPEIS), and step potential electrochemical spectroscopy (SPECS), for two activated carbons (ACs) with 0.1 mol L(-1) aqueous solution of LiNO(3), Li(2)SO(4), and KI. The charging process of AC operating in aqueous electrolytes appears as a complex phenomenon - all ionic species take an active part in electric double-layer formation and the ion-mixing zone covers a wide potential region. Therefore, the so-called PZC should not be considered as an absolute one-point potential value, but rather as a range of zero charge (RZC). SPECS technique is found to be a universal and fast method for determining RZC, as applied here together with the EQCM. In most cases, the RZC covers a potential range from ≈100 to ≈200 mV and the correlation of the range with the carbon microtexture is clear, highlighting the role of the ion-sieving effect. It is postulated that PZC for porous materials in aqueous electrolytic solutions should be considered instead as RZC.