Electrochemical Double Layer Behavior on Vertically Oriented Cnt Electrodes

Electrochemical double layer behavior of carbon materials is important in several applications such as super-capacitors, ionic separations and in responsive surfaces.

We have investigated the interfacial double layer behavior of vertically-oriented CNT electrodes encapsulated in a polymer matrix. These electrodes have been used as mass transport channels through the hollow interiors of the CNTs; however, they provide a interesting electrode materials with the edge-planes of the CNTs being exposed to the electrolytic solution.

Capacitance estimation, interpreted from electrochemical impedance spectroscopy measurements, indicated almost 4-5 times increase in functional density of carboxylic acid groups after electrochemical diazonium grafting chemistry. Potential of zero charge (PZC) measurements of these electrodes failed to provide a sharp transition associated with other atomically smooth surfaces, however, electrolyte screening effects were observed. Non-faradic impedance spectroscopy measurements of large macro-molecular tethers covalently attached to the electrodes indicated a potential dependent switching behavior. This switching behavior has been attributed to potential-dependent conformational change based on complementary faradaic impedance spectroscopy and equivalent circuit analysis. A similar potential-induced conformational change has been utilized for making voltage-gated CNT membranes.