Analysis of the electrochemical performance of carbon felt electrodes for vanadium redox flow batteries
J. E. Barranco, A. Cherkaoui, M. Montiel, A. González-Espinosa, A. Lozano, F. Barreras. Analysis of the electrochemical performance of carbon felt electrodes for vanadium redox flow batteries. Electrochimica Acta, 470 (2023) 143281.
In the present research, the performance of three commercial graphite felts (a 6 mm thick Rayon-based Sigracell®, a 4.6 mm thick PAN-based Sigracell®, and a 6 mm thick PAN-based AvCarb®) used as electrodes in vanadium redox flow batteries (VRFBs) is analyzed before and after thermal activation. The thermal treatment of the electrodes at 500 °C for 1 h in a self-designed industrial furnace under a synthetic air atmosphere. XPS confirms that thermal activation provides with different C=O/Csingle bondO and sp2/sp3 ratios to the graphite electrodes depending on their carbon precursors, providing different catalitic behavior. T-GFD4.6-EA felt electrode was also oxidized by cycling in H2SO4 and in 0.4 M VOSO4 + 2 M H2SO4 solution. In the first case, the graphite electrode increased the current density 24.27 mA cm−2 for the VO2+ electrooxidation, however the cathodic current density (VO2+ reduction reaction) was decreased 36 mA cm−2. In the second case, the increase was of 21.27 mA cm−2, whereas the current density for the VO2+ reduction hardly changed. Thermally treated GFD4.6-EA graphite felt chemical composition also changed differently when exposed to different laboratory experiments which mimic the electrode behavior in a VRFB. XPS analysis confirmed that the chemical modification of the graphite surfaces can either improve or decrease the electrocatalytic activity of the electrodes depending on their carbon precursors.
In the present research, the performance of three commercial graphite felts (a 6 mm thick Rayon-based Sigracell®, a 4.6 mm thick PAN-based Sigracell®, and a 6 mm thick PAN-based AvCarb®) used as electrodes in vanadium redox flow batteries (VRFBs) is analyzed before and after thermal activation. The thermal treatment of the electrodes at 500 °C for 1 h in a self-designed industrial furnace under a synthetic air atmosphere. XPS confirms that thermal activation provides with different C=O/Csingle bondO and sp2/sp3 ratios to the graphite electrodes depending on their carbon precursors, providing different catalitic behavior. T-GFD4.6-EA felt electrode was also oxidized by cycling in H2SO4 and in 0.4 M VOSO4 + 2 M H2SO4 solution. In the first case, the graphite electrode increased the current density 24.27 mA cm−2 for the VO2+ electrooxidation, however the cathodic current density (VO2+ reduction reaction) was decreased 36 mA cm−2. In the second case, the increase was of 21.27 mA cm−2, whereas the current density for the VO2+ reduction hardly changed. Thermally treated GFD4.6-EA graphite felt chemical composition also changed differently when exposed to different laboratory experiments which mimic the electrode behavior in a VRFB. XPS analysis confirmed that the chemical modification of the graphite surfaces can either improve or decrease the electrocatalytic activity of the electrodes depending on their carbon precursors.