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

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 degrees C. Thus, we conclude that the optimum activation temperature for this type of carbon felt concerning the investigated properties is around 400 degrees 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.

Automated summary

Thermal activation at different temperatures was investigated for its impact on the structure, surface composition, wettability, and electrochemical activity of rayon-based carbon felt electrodes for VRFBs. Novel techniques including AFM, DVS, EIS, and DRT analysis were used to study these properties. The results showed that higher activation temperatures improved the wettability and reduced process impedances, but also caused severe carbon decomposition. The optimum electrochemical performance was observed at an activation temperature of 400 degrees C.