The electrochemical characterisation of graphite felts

Abstract

With the increasing demand for advanced energy storage, redox flow batteries (RFBs) are a rapidly growing market and research area. Carbon fibre based materials like graphite felts (GFs) are commonly used in RFBs as electrodes due to their electrochemical activity, high permeability for liquids, high surface area and relatively low cost. Previous characterisation of GFs has involved flow systems, which can be complicated to replicate and expensive. Using pre-treatment techniques to ensure sufficient wetting, GFs can be used effectively in quiescent electrochemistry. By combining the experimental voltammograms with digital simulations, key properties such as capacitance, electrode kinetics, average pore size and electrochemical surface area can be determined. This allows for the rapid and low cost examination of multiple GFs and pre-treatment methods, providing a useful tool for RFB development. In addition, the GF electrodes used in the study show promising limit of detection values, with initial experiments suggesting these electrodes may have applications in electroanalysis.

Anodic stripping voltammetry with graphite felt electrodes for the trace analysis of silver

“…This is expected given the porous nature of GF electrodes, which results in low current densities compared to conventional disc electrodes. 6 Second, the stripping signal at the GF electrode appears to be sharper than that for the PFC electrode at the same Ag + concentration. Finally, the limit of detection (LoD) appears to be significantly lower for the GF electrode, with a signal still observed at 25 nM Ag + , which was the lowest concentration to produce a recognizable signal for the given experimental conditions.…”

“…A 0.5 mm (diameter) platinum wire was then passed through the felt to secure it and provide a good electrical connection to the whole of the felt piece, as described previously. 6 The size of the voltammetric signal from the platinum wire was negligible compared to the signal from the GF electrode.…”

“…The GF wetting procedure used was similar to that previously reported. 6 The GF electrode was initially washed in ethanol then rinsed with ultrapure water via a wash-bottle. The water-wet GF electrode was then sonicated for 1 minute in a sacrificial sample of the test electrolyte before being transferred to the electrochemical cell.…”

“…Previous work suggested GF electrodes may have beneficial properties for electroanalysis, capable of producing good signals at low levels of analyte. 6 This is surprising given that GF electrodes are "mega-macro" electrodes and the perceived trend in electroanalysis is towards smaller electrodes with increased current densities. This work builds from the recent study of solution phase redox systems to investigate the use of graphite felt electrodes for stripping voltammetry in quiescent solution.…”

The influence of lateral flake size in graphene/graphite paste electrodes: an electroanalytical investigation

“…44 In terms of the electrochemical properties of carbon materials, it should be noted that there is a reported distinction between basal and edge planes in graphitic materials, 45 where basal planes are considered almost "electrochemically inert", [46][47][48][49] and edge plane like-sites/defects are considered to have "anomalously fast" heterogeneous electron transfer (HET) kinetics. 46,[49][50][51][52][53] Regarding the electrochemical capabilities of edge plane like-sites/defects in graphitic materials, recent work involving the HET kinetics of graphitic paste electrodes has shown a trend demonstrating that as lateral ake size (L a ) decreases, the edge plane to basal plane ratio shis, increasing the electrochemical activity of such electrodes. 54 However, there is an ongoing debate regarding the true contributions of edge and basal plane likesites/defects at the macroscopic scale 49,[55][56][57][58][59][60] with respect to their observed HET kinetics.…”