Electrochemical Flow Injection Analysis Study of Ion Partitioning at High Surface Area Carbon Fiber Electrodes

Abstract

Charge-selective electrochemistry was previously shown to occur at high surface area carbon fibers that were produced by fracturing the outer periphery with anodic current or positive potential. The cyclic voltammetric behavior of electroactive species observed at these fibers exhibited a distinct pH dependence related to the protonation/deprotonation of oxygen-containing functional groups at the surface of the carbon fiber. In this paper, electrochemical flow injection analysis (EC-FIA) is used to probe ion partitioning in to and out of the interior microstructure of the treated carbon fiber, for both electroactive and electroinactive species. It was found that the extent of partitioning was the result of both ion charge and hydrated ionic radius, in addition to the level of fracture. It was further observed that the direction of movement for an injected ionic species could be controlled relative to the ion concentration, the pH of the carrier solution, or both. EC-FIA allowed the simultaneous observation of current due to ion movement and that due to electron transfer to a redox-active species. The results presented are consistent with a model in which fixed negatively charged sites in the interior of fractured fibers govern ion partitioning with positively charged ions in the carrier solution, with counterions located in the interior "free" volume.

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

“…As the pH of the injected sample was varied to more acidic values, larger and larger cathodic currents were measured. This is consistent with the flow of protons into the fractured carbon fiber purely on the basis of the concentration gradient . Likewise, as the pH was adjusted to more basic values an anodic current was observed due to protons now moving out from the carbon fiber due to a reversal in the proton concentration gradient.…”

“…Computer modeling of the faradaic current response indicates these electrodes behave like thin-layer electrochemical cells where the internal thin-layer volume depends on ion charge and pH . Additional measurements of the faradaic and nonfaradaic response of these electrodes have further elucidated a size dependence associated with the cationic partitioning under “low fracture” (750−1500 μF/cm 2 ) conditions …”

Highly sensitive determination of chlorpromazine by electrochemically treated pencil graphite fiber as both solid-phase microextraction fiber and working electrode for use in voltammetry method

“…[23][24][25] Formation of carbonyl, phenolic groups, lactone, ether, quinine, hydroxyl and carboxyl as a graphite oxide lm has been previously reported. [23][24][25] Formation of carbonyl, phenolic groups, lactone, ether, quinine, hydroxyl and carboxyl as a graphite oxide lm has been previously reported.…”

“…Electrochemical oxidation is one of the procedures for creating oxygen-containing functional groups on the surface of graphite. [23][24][25] Formation of carbonyl, phenolic groups, lactone, ether, quinine, hydroxyl and carboxyl as a graphite oxide lm has been previously reported. 26,27 Depending on the type of anodization, the carbon surface can be disrupted signicantly, to the point of forming a surface lm of "electrogenerated graphitic oxide".…”

Galvanically Stimulated Degradation of Carbon-Fiber Reinforced Polymer Composites: A Critical Review

“…Though the presence of these surface oxides are almost inevitable and undesirable, it is possible in some situations to manipulate them for beneficial electrochemical performance [315]. The application of a high current density through carbon fibers in an electrolyte solution is reported to have extraordinary effects on the fiber morphology, by the generation of a very high surface area with an apparent capacitance up to 4000 µF cm −2 , which is more than two orders of magnitude higher than the typical values for glassy carbon and carbon fibers [315,316,317,318,319]. Generally the double layer capacitance of carbon materials is reported to be about 20 μF cm −2 or less [320].…”