*2.7. The Construction of the Single Cell of VRFB*

Figure 1B depicts the construction of the single cell of VRFB. The single cell comprises two plastic plates with a 3 mm depth of flow field, two copper plates with 3 mm thickness, two embedded graphite plates of 6 mm thickness, and two stainless steel plates, which served as the endplates. There are also two gaskets that are 1 mm in thickness, two 25 cm<sup>2</sup> treated or pristine carbon felt electrodes with a thickness of 6.5 mm, and an N212 Nafion® membrane (purchased form Chemours, Taipei, Taiwan) for electrolyte separation.
