Bermuda grass derived nitrogen-doped carbon as electrocatalyst in graphite felt electrode to increase the efficiency of all‑iron redox flow batteries

Abstract

For large-scale energy storage, iron-based flow batteries (IRFBs) have been considered as a better choice because of their low-cost and use of environmentally friendly iron-based salts. The development of a IRFBs has been limited by the sluggish kinetics of the reaction, especially at the positive electrode during charging. Therefore, it is very important to look for stable electrolytes and superior electrode materials along with their modifications. Carbon-based electrodes are majorly used in IRFBs and these electrodes are feasible to modify using electrocatalysts. In the current study, nitrogen-doped carbon particles (NICaps) derived from Bermuda grass were used to modify graphite felt electrode. SEM, EDAX, Raman, and XPS analysis were used to characterize the modified graphite felt (MGF) electrode. It was observed that the NICaps MGF electrode had a significant improvement in electrochemical properties. The cathodic and anodic peak currents for the MGF electrode (1.55 and 1.63 mA/cm2 respectively) had a remarkable increase in comparison with the untreated graphite felt electrode (UGF) (0.48 and 0.88 mA/cm2 respectively). The Nyquist plot and the data derived from the equivalent circuit indicated lower charge transfer resistance for MGF. The charge-discharge studies carried out using 132 cm2 cell reveals that the modified electrodes result in higher current uptake of 50 mA/cm2 whereas the current uptake from the UGF electrode was limited to 20 mA/cm2. The battery resulted in an average coulombic efficiency of 95%, the peak power density of 60 mW/cm2, and better stability during multiple cycling.