Effects of current scan rate on the polarization curve of vanadium redox flow batteries

Polarization curve is one of the commonly used methods to evaluate the performance of electrochemical devices such as proton exchange membrane (PEM) fuel cells and vanadium redox flow batteries (VRFB). For an optimized PEM fuel cell system, the performance of the fuel cell is steady as long as the fuels are supplied. Long duration of measurement points will have minimum effects on the polarization curves. On the other hand, electrolytes used in vanadium redox flow batteries are circulated through the cell and returned to the reservoirs after the electrochemical reactions. The oxidation state of the vanadium ions in the reservoirs will no longer be the same after the oxidized or reduced vanadium ions pass through the cell. For this reason, the duration between each measurement point is critical to the polarization curves, particularly for laboratory scale research where the volume of electrolytes is relatively small. Long duration of measurement points could result in misleading polarization curves due to the contaminated electrolytes. In this work, a single vanadium redox flow battery cell with 50 cm² active area was fabricated and the electrolytic solution was prepared. The objective of this work is to investigate the effects of current scan rate on the polarization curve of the single VRFB cell.