Characterization and Modeling of the Nonfaradaic Response of Ultrahigh Surface Area Carbon Fibers by Electrochemical Flow Injection Analysis

The ion partitioning properties of ultrahigh surface area carbon fibers (UHSACF's) have been studied using electrochemical flow injection analysis. Previous work has shown ion partitioning depends on the extent of fracture of the fiber and the charge and size of the analyte ion. We now show the polarizability of the partitioning species also plays an important role by comparing the response of electrochemically fractured fibers to monovalent inorganic cations, divalant inorganic cations, and a series of quaternary ammonium salts. Highly fractured fibers with capacitances >4000 μF/cm2 show a reduced selectivity but an order of magnitude enhanced sensitivity to positively charged ions. This is consistent with increased surface area and increased pore size as a result of the fracture process. Previously, a simultaneous faradaic and nonfaradaic response from K3Fe(CN)6 at a UHSACF was reported. Here we apply a simple Gaussian model that provides a qualitative basis for understanding the ion flow into and out o...