Charge/discharge cycles on Pt and Pt-Ir based electrodes for the positive side of the Zinc-Cerium hybrid redox flow battery

tIn this study, the charge/discharge cycling behaviour of the Ce3+/Ce4+redox couple in methanesulfonicacid medium on various Pt and Pt-Ir coated titania based substrates was investigated as a function ofsolution flow rate, temperature and charge/discharge current density using a rotating disk electrode.Although superior performances (in terms of the voltage efficiency, V) were obtained from the electrodescontaining higher amounts of platinum, a deterioration of these electrodes with cycling was evident (after150 cycles). At rotation rates between 600 rpm and 1200 rpm, high V(>90%) could be obtained as longas the current density j applied was below the mass transport limiting current density, jL. For j’s abovethis value, the oxygen evolution reaction occurred with Ce3+oxidation whereas the Ce4+reduction wasaccompanied by oxygen reduction, resulting in lowered V’s. Better stability towards cycling and higherV’s were observed at 60◦C compared to 25◦C, especially for the etched Pt electrodes. The optimumloading for the Pt substrates was 3 g m−2while for the case of the heat treated samples 10 g m−2of Pt.