Optimizing the thermal treatment procedure using electrochemical methods to improve the performance of vanadium redox flow batteries

Abstract

In this article, different thermal treatment procedures were carefully investigated by electrochemical methods to find the optimized time and temperature for enhancing the electrochemical performance and activity of the graphite felt electrodes within the vanadium redox flow battery. Two prestigious and commercially used graphite felts of SGL GFD 4.65 EA and AvCarb G150 were used for this purpose. Cyclic voltammetry results initially were used to recognize the procedures with the most improved kinetics. This demonstrated the influences of treatment procedures on electrode kinetics by showing an improved electrode rate constant. In the following, area-specific resistance obtained by the polarization curves technique was used to examine the role of the thermal treatment procedure on improvement of the mass-transfer effect and, consequently, explore a treatment procedure to maximize the electrode activity. Both obtained CV and ASR data showed a better performance for thermally treated SGL 4.65 EA compared to that of AvCarb G150. Enhancing the electrode kinetics due to thermal treatment showed the largest contribution to reducing the ASR indicated by electrochemical impedance spectroscopy of the SGL 4.65 EA. The best electrode performance and activity was observed using the thermal treatment of the SGL 4.65 EA at 500/550 °C for 3/3.5 h with an ASR of 0.63/0.64 Ωcm², respectively, lower than prior works with almost the same membrane properties. An interesting conclusion is that thermal treatment with an optimized procedure can sufficiently catalyze vanadium redox reactions on graphite felts better than those treated with electro-catalysts impressing no need for further electrode modification.