Evaluation of graphite felt activation and aging by electroanalysis at microfiber electrodes

Microfiber electrodes, derived from graphite felt, were used for the evaluation of charge transfer kinetic constants in a ferrocyanide-based electrolyte, which is a model system for redox flow batteries. Cyclic voltammetry experiments were performed in the presence of 10−2 M or 0.5 M Fe(CN)64−. Within this framework, microfiber electroanalysis allowed for the quantitative assessment of four distinct activation protocols for graphite felt: thermal treatment under CO2 at 850°C, nitric acid immersion at 70°C, exposure to Fenton's reagent at ambient temperature, and treatment with urea under atmospheric conditions at 550°C. This analytical method enabled a hierarchical categorization of the various activation techniques, aiding in the identification of optimal conditions that yield the highest charge transfer kinetics for the ferrocyanide electrolyte. Additionally, the methodology provided insights into the temporal degradation or aging of these activated materials. These empirical observations are discussed alongside characterization data obtained from X-ray Photoelectron Spectroscopy (XPS), Raman spectrometry, and capacitive current measurements.