Accelerated Testing of Vanadium Catholyte Stability

Using our standard methodology, we have examined the stability of electrolytes with compositions close to those used in actual flow batteries over a range of temperature from 70 to 30°C. Measurements at higher temperatures (45-70°C) showed excellent reproducibility but measurements at lower temperatures (30-45°C) showed some scatter. Furthermore, the measurements at higher temperatures are in good agreement with our (single-slope) model which is based on earlier data but there is some divergence from the model at lower temperatures. Arrhenius plots of the data show two linear regimes: one in the range 45-70°C and another in the range 30-45°C, the latter having a higher Arrhenius slope. Based on linear least-squares best fits in these two regimes, we have formulated an improved stability model (two-slope model). For each of the two models, we derive expressions for acceleration factors for temperature testing of catholyte stability and estimate values over a range of test and use temperatures. Acceleration factors based on the two-slope model are higher than those for the single slope model by a factor of 3-6 depending on the temperatures. Thus, predictions based on the single-slope model are more conservative.