Long-Term Structural And Chemical Stability Of Carbon Electrodes In Vanadium Redox Flow Battery

Predicting the performance decay in carbon electrodes is critical to maximizing the longevity of redox flow battery (RFB) systems. This study investigates the effect of long-term cycling (over 8000 cycles) on the structural and chemical evolution of carbon electrodes. We find that the microstructural aspects such as graphitic stacking order and interlayer spacing along with overall morphological construct remain largely unchanged even after the prolonged cycling process. Conversely, significant changes in surface chemistry such as the evolution of functional groups and point defects are evident from our combined multimodal spectroscopic and computational analysis. The X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis reveal chemical absorption of chloride counter anions at point defects within the graphitic surface. Additionally, our results suggest that vanadium cation plays an important role in counter anion-carbon surface interaction and subsequently the surface chemistry evolutions. Our findings provide insights about surface chemical evolution that is critical for predicting electrode performance and longevity of RFB.