Communication—A new additive for increased stabilization of catholytes in vanadium flow batteries (VFBs)

We report a new additive, monobasic potassium arsenate (KH₂AsO₄), for improving the thermal stability of VFB catholytes. Using our standard accelerated testing methodology at 30–70°C, we showed that the effect increases continuously with increasing concentration of arsenate over the range investigated (0 – 0.10 mol dm−³). In comparison to similar experiments with phosphate (H₃PO₄), the magnitude of the effect was greater for arsenate. A combination of arsenate and phosphate was also effective. Based on these results, we speculate that other Group-V elements in the +5 oxidation state may also stabilize VFB catholytes.