Influence of electrode design parameters on the performance of vanadium redox flow battery cells at low temperatures

Performance of electrochemical batteries suffers at cold temperatures. In this paper, we report on an 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 426 cm(2) at cell temperatures of 25, +10 and -10 degrees C. Measured parameters include cycle efficiency and discharge capacity at three current densities and two flow rates, peak power and cell impedance obtained through electrochemical impedance spectroscopy (EIS) studies. The influence of electrode compression and electrode thickness has also been studied through comparative experimental protocols. Results indicate significant loss of discharge capacity and cell efficiency at low temperatures; this can be attributed to substantial increase in ohmic resistance and even higher increase in charge transfer resistance of the cell. Two methods known to reduce cell resistance, namely, increasing compression ratio of the electrode and using thinner electrode, have led to restoring much of the lost discharge capacity and energy efficiency. Optimizing the electrode parameters such as its compression, permeability and thickness for industrial scale cells, together with possible use of electrocatalysts, seems to be a promising way of improving low temperature performance of VRFB cells.