Study on the treatment of carbon black for slurry electrodes of all-iron redox flow batteries

All-iron redox flow batteries (IRFBs) are considered as potential energy storage devices due to the abundance of iron and durability. During the charging process, metallic iron is formed from Fe²⁺ and may block electrolyte paths in the negative porous electrode, decreasing reaction kinetics. Therefore, a slurry electrode using conductive particles in the electrolyte can be the solution to the problem. To study the effect of carbon black on the performance of slurry electrode, various surface modifications of carbon black are carried out to further enhance electrode performance. The surface morphology, X-ray diffraction, and electrochemical properties are investigated. The performance of the IRFB with various types of carbon black is evaluated at different operating conditions. Both acid and heat treatments of Ketjen black (H-KB) show higher performance than pristine Ketjen black. Thermally treated Ketjen black exhibits voltage efficiency, coulombic efficiency, and energy efficiency of 69%, 95%, and 65%, respectively, at 20 mA cm⁻². The durability of the IRFB using the H-KB slurry electrode shows an EE decreasing rate of around 1% after 100 cycles at 20 mA cm⁻².