Purification of Copper-Contaminated Vanadium Electrolytes Using Vanadium Redox Flow Batteries

Abstract

Corrosion of carbon-based electrodes and bipolar plates is a major challenge and a common cause of failure in commercial vanadium redox flow batteries (VRFB). Herein, we describe a typical carbon corrosion that occurred on several stacks of a 10kW/40kWh and a 200kW/400kWh commercial vanadium redox flow batteries (VRFB) installed in the framework of a demonstrator. Cracks through graphite bipolar plates enabled the electrolyte to leach the copper current collectors and contaminated the entire electrolyte solution with copper.In this work, we first highlighted the deleterious effects of copper contaminants on the operation of a VRFB. It was observed that metallic copper enhanced the parasitic hydrogen evolution reaction (HER) on the negative side and accelerated the oxidation state imbalance between the two redox electrolytes. To tackle the problems related to copper pollution, a simple, eco-friendly and cost-effective procedure to identify copper contamination on-site and to purify the electrolyte was developed.A classical VRFB stack was used to plate out the copper ions contaminants. The optimal cathode potential for copper deposition onto carbon felt electrode was determined to be −100 mV vs. SHE. The process described was successfully used to purify on-site 6000 L of vanadium electrolyte (V+3/V+4 mixture) to levels below 1 ppm. At the end of the purification, the stack was regenerated by flashing 20-30 L of electrolyte that represents only a fraction of what would have been necessary to dispose the contaminated electrolyte. This work has been accepted as a full paper in ChemSusChem. [1][1] D. Reynard, H. Vrubel, C. R. Dennison, A. Battistel, H. Girault, ChemSusChem 2019, 12, 1222.Figure 2 A. Schematic illustration of the purification process developed to remove copper contaminants from the vanadium electrolytes B. SEM images of fresh carbon felt (a), carbon felt sample close to the inlet (b) and the outlet of the single-cell (c), and carbon felt sample after re-generation (d) C. Evolution of copper concentration (ICP-MS) at the negative-side outlet and the container electrolyte with time of purification Figure 1