Activated carbon as a pseudo-reference electrode for electrochemical measurement inside concrete

The application of Kynol based activated carbon (KAC) as a pseudo-reference electrode for potentiometric measurement inside concrete is presented. Due to its high surface area the activated carbons has a large electrical double layer capacitance (EDLC > 50 F g(-1)) and are used as electrode material for super capacitors. The change in potential of an electrical double layer capacitor is given by Delta E = dQ/C-DL, where E (V) is the potential, Q(C) is the charge and C-DL (F) is the EDLC. Therefore any small amount of oxidation/reduction reaction as well as adsorption/desorption of charge (dQ) at the KAC will be neutralized by its large capacitance Cm, and its potential will not change significantly. The open circuit potential (OCP) of the KAC with an EDLC of 90-110 F g(-1), shows a stable potential (drift <0.2 mV/day over two weeks) when immersed in the concrete pore solution. The OCP is stable w.r.t. pH changes up to pH 12. The nature of the ions does affect the OCP in the pore solution only at higher concentrations. The AC electrode is proposed as a feasible alternative for a pseudo-reference electrode in concrete