Factors affecting the performance of the Zn-Ce redox flow battery

The Hull Cell was used to investigate the impact of current density j on the morphology and uniformity of zinc electrodeposited from a 2.5 mol dm−3 Zn2+ solution in 1.5 mol dm−3 methanesulfonic acid at 40◦C onto carbon-composite surfaces. The range of the applied deposition current density used was between1 mA cm−2 and 100 mA cm−2. Good, robust deposits were obtained when j ≥ 10 mA cm2 whereas at j’s lower than this, patchy films formed due to the competing hydrogen evolution reaction (HER) on the bare carbon-composite surface. An understanding of these effects and its application in the redox flow battery enabled both the coulombic and cell potential efficiencies to be maintained at relatively high values, 90% and 69% respectively, indicating a successful inhibition of the HER on the fully formed Zn layer. Flow velocity at the low Reynolds number in the cell (Re <200) had little impact on the electrochemical cell performance. Depletion of the cerium species became an issue for long charge times.