The title of the thesis: Modification of graphite felt electrode with cobalt oxide agent for vanadium redox flow battery application
Nowadays, developing renewable energy sources requires large-scale energy storage systems to utilize these energy sources effectively. Among the available large-scale energy storage solutions, the Vanadium Redox Flow Battery (VRFB) is being actively developed. The VRFB offers advantages such as large storage capacity, high power (>1000 W), low self-discharge, and long lifespan (20-30 years). Among the structural components of VRFBs, the electrode is one of the most crucial. It significantly impacts the electrochemical reaction rate, performance, and life cycle of VRFB. Therefore, research on electrode materials or modifications is increasingly gaining interest to improve the performance of VRFB. In this thesis, the graphite felt electrode is modified by changing the morphology and attaching Co3O4 to the surface, using Co(NO3)2 as the precursor through a two-step thermal treatment combined (calcination in Agron at 500 oC and calcination in air at 400 oC) with immersing the graphite felt in the precursor solution. Different concentrations of Co(NO3)2 (1, 2, 3, 4, and 5 mM) and various calcination times in air (0.5, 1.0, and 2.0 hours) were investigated.
After modification, the etching process created nanorod structures, which significantly increased the surface area and improved wettability. A Co(NO3)2 concentration of 4 mM (GF4) demonstrated optimal electrochemical activity compared to pristine graphite felt. Following modification, the electrochemically active surface area (ECSA) reached a high value of 131.71 cm2, the charge transfer resistance decreased to 12.27 Ω, and the exchange current density increased to 25.02 mA/cm2. Cyclic voltammetry measurements revealed that GF4 exhibited reversible redox activity across various scan rates and maintained stability over 50 cycles at a scan rate of 1.0 mV/s, with Ipa/Ipc = 1.18 and ∆Ep = 220 mV. Additionally, the discharge capacity in the first cycle of the GF4 is higher than that of the pristine electrode (258.3 > 130.5 mAh), and higher Coulombic efficiency over 50 cycles. These findings indicate that the modification improves the performance of graphite felt as electrodes in vanadium redox flow batteries (VRFB), emphasizing its potential for energy storage applications.
