The effect of activation on the electrochemical behaviour of graphite felt towards the Fe3+/Fe2+ redox electrode reaction

This paper is dedicated to the study of the effect of graphite felt activation by thermal oxidation in air on its electrocatalytic activity towards Fe3+/Fe2+ redox electrode reaction. For the first time, the exchange current densities and electron transfer coefficients determined from the Tafel equation were obtained within the wide range of burn-off levels (0–50%). The maximal catalytic activity was obtained at the burn-off of 17%. The cathode having this burn-off level expressed almost three-fold enhancement in the galvanic cell performance (criterion for the performance evaluation in our case was a cell voltage at the current density of 300 mA cm−2) as compared to that with the non-activated graphite felt, and allowed to obtain current densities up to 670 mA cm−2 at the cathode polarization as low as 150 mV. The correlation between electrocatalytic activity and a surface oxide chemistry of graphite felt was established. The cell performance was found to be the best when the pH at a point of zero charge and the amount of surface quinoid groups per unit area were minimal. The results obtained are of significant importance for practical applications, including the development of electrodes in redox flow batteries.