Vanadium redox flow batteries are well suited for large scale energy storage applications. Like many other electrochemical devices, flow batteries too give poor performance when operated at low temperatures. In this work, we report on experimental investigation of sensitivity of the vanadium redox flow battery (VRFB) to the cell operating temperature. Experiments have been carried out on a VRFB cell with an active area of 400 cm2 at cell temperatures of 25, 10 and -10oC. The influence of cell design parameters such as electrode compression, electrode thickness and channel width of flow field has been studied through comparative experimental protocols. Results indicate significant loss of discharge capacity and cell efficiency at low temperatures; this is attributed to substantial increase in ohmic resistance and even higher increase in charge transfer resistance of the cell. Pressure drop data show a substantial increase (by 100 to 150%) in the pressure drop across the cell at - 10oC compared to that at 25oC.


Reducing sulphuric acid concentration and using thermally activated electrode felts, have been investigated thoroughly at cell level for their effect on improving the performance. The first one addresses the issue of increased viscosity and reduced diffusivity of vanadium ions at low temperatures, and the second one is aimed at decreasing the overpotential at high current densities. Based on the observed beneficial effects of these measures, an 8-cell stack of
412 cm2 active area for each cell has been constructed with optimized cell design parameters. This modified stack has delivered the good discharge energy of 87.6 Wh for 6 liters of electrolyte even at -10oC and current density of 60 mA/cm2 . A physics-based model has been
developed to model the electrochemical performance of the VRFB cell. It shows good agreement with the experimental data over a range of circulation rates and operating temperatures.