Degradation of all-vanadium redox flow batteries (VRFB) investigated by electrochemical impedance and X-ray photoelectron spectroscopy: Part 2 electrochemical degradation
Abstract
Electrochemical degradation (ED) of carbon felt electrodes was investigated by cycling of a flow through all-vanadium redox flow battery (VRFB) and conducting half-cell measurements with two reference electrodes inside the test bench. ED was detected using half-cell and full-cell electrochemical impedance spectroscopy (EIS) at different states of charge (SOC). Reversing the polarity of the battery to recover cell performance was performed with little success. Renewing the electrolyte after a certain amount of cycles restored the capacity of the battery. X-ray photoelectron spectroscopy (XPS) reveals that the amount of surface functional increases by more than a factor of 3 for the negative side as well as for the positive side. Scanning electron microscope (SEM) images show a peeling of the fiber surface after cycling the felts, which leads to a loss of electrochemically active surface area (ECSA). Long term cycling shows that ED has a stronger impact on the negative half-cell [V(II)/V(III)] than the positive half-cell [V(IV)/V(V)] and that the negative half-cell is the rate-determining half-cell for the VRFB.
- Publication:
-
Journal of Power Sources
- Pub Date:
- September 2016
- DOI:
- 10.1016/j.jpowsour.2016.06.040
- Bibcode:
- 2016JPS...325..351D
- Keywords:
-
- Vanadium;
- Redox flow battery;
- Degradation;
- EIS;
- Carbon felts;
- XPS