Hydrogen evolution mitigation in iron-chromium redox flow batteries via electrochemical purification of the electrolyte

Top: Schema illustrating the electrochemical purification method in Fe-Cr RFBs. Bottom: Discharge capacity as a function of cycle number for purified and unpurified electrolytes.

Scientific Achievement

An electrochemical purification method is used to mitigate the hydrogen evolution reaction (HER) in iron-chromium (Fe-Cr) redox flow batteries (RFBs), resulting in reduced capacity fade rates.

Significance and Impact

Fe-Cr RFBs hold promise due to their use of low-cost, abundant chemicals, but reductions in HER rates are needed to improve performance (efficiency, capacity fade). This work describes a purification method, electroplating of soluble impurities into a sacrificial electrode, that enables decay rates comparable to those obtained in cells with expensive catalysts or electrolyte additives.

Research Details

  • The electrolyte-soluble impurities hypothesized to promote HER are removed via electrodeposition onto a sacrificial cathode in a temperature-controlled flow cell testbed (electrolytic process).
  • The cell was dissembled after the purification step, the sacrificial electrodes were replaced, and the cell was re-assembled for cycling analysis.
  • The protocol enables reduced capacity fade (ca. 5× slower) during galvanostatic cycling.
  • A meta-analysis of cycling data in Fe-Cr RFB literature reveals a statistically significant association between coulombic efficiency and discharge capacity decay rate.

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DOI: 10.1016/j.jpowsour.2022.232248

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