Multimodal characterization of carbon electrodes' thermal activation for vanadium redox flow batteries

• Published in: Journal of power sources 2023-06, Vol.569, p.233010, Article 233010
• Main Authors: Köble, K., Jaugstetter, M., Schilling, M., Braig, M., Diemant, T., Tschulik, K., Zeis, R.
• Format: Article
• Language: English
• Subjects: Atomic force microscopy (AFM); Carbon felt; Distribution of relaxation times (DRT); Dynamic vapor sorption (DVS); Electrochemical impedance spectroscopy (EIS); Vanadium redox flow battery
• ISSN: 0378-7753
• DOI: 10.1016/j.jpowsour.2023.233010

Thermal activation has proven to be a valuable procedure to improve the performance of carbon electrodes in vanadium redox flow batteries (VRFBs). This work investigates how different activation temperatures impact the rayon-based carbon felt's structure, surface composition, wettability, and electrochemical activity. A unique combination of non-standard techniques, including atomic force microscopy (AFM), dynamic vapor sorption (DVS), and electrochemical impedance spectroscopy (EIS) combined with the distribution of relaxation times (DRT) analysis, was used for the first time in the context of VRFB electrodes. The wettability of the carbon felts improved, and the process impedances decreased with higher activation temperatures. However, severe carbon decomposition occurs at high activation temperatures. The optimum electrochemical performance of the carbon felts in the vanadium(IV)/vanadium(V) redox reaction was observed after activation at 400 °C. Thus, we conclude that the optimum activation temperature for this type of carbon felt concerning the investigated properties is around 400 °C. Furthermore, we want to highlight the successful approach of using AFM, DVS, and EIS combined with DRT analysis for an integral investigation of key properties such as structure, wettability, and performance of VRFB electrodes. [Display omitted] •Carbon felts are characterized by several novel techniques.•Complementary information on structure, composition, wettability, and performance.•Probing the wettability of carbon felts employing EIS and DVS.•Quantifying the wettability of carbon electrodes.•Determining optimized activation temperature and time.