The influence of operational parameters on the performance of an undivided zinc-cerium flow battery

An undivided zinc-cerium redox flow battery was studied under a wide range of operational conditions, including: (i) electrolyte composition; the concentrations of ([Zn2+], [Ce3+] and [H+]), (ii) current density (0-80 mA cm(-2)), (iii) electrolyte flow linear velocity (0.64-7.0 cm s(-1)) and (iv) temperature (20-60 degrees C). The charge efficiency increased at higher current densities and at higher electrolyte flow velocities. Unlike the divided zinc-cerium system, the charge-discharge performance decreased at higher temperature, since oxygen evolution became increasingly favored at the positive electrode. The use of a low acid concentration led to a poor conversion of Ce(III) to Ce(IV) ions during the discharge cycle. Mixed electrolytes containing methanesulfonate and sulfate anions have been evaluated at a high Ce(III) ion concentration, e.g. 0.4 mol dm(-3). After charging the battery for 4 h, the conversion of Ce(III) to Ce(IV) ions became less efficient over time due to a greater fraction of the current being used in oxygen evolution. Critical aspects for improvements in the battery performance are considered. (C) 2012 Elsevier Ltd. All rights reserved