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

Abstract In this study, the charge/discharge cycling behaviour of the Ce 3+ /Ce 4+ redox couple in methanesulfonic acid medium on various Pt and Pt-Ir coated titania based substrates was investigated as a function of solution flow rate, temperature and charge/discharge current density using a rotating disk electrode. Although superior performances (in terms of the voltage efficiency, η V ) were obtained from the electrodes containing higher amounts of platinum, a deterioration of these electrodes with cycling was evident (after 150 cycles). At rotation rates between 600 rpm and 1200 rpm, high η V (>90%) could be obtained as long as the current density j applied was below the mass transport limiting current density, j L . For j 's above this value, the oxygen evolution reaction occurred with Ce 3+ oxidation whereas the Ce 4+ reduction was accompanied by oxygen reduction, resulting in lowered η V 's. Better stability towards cycling and higher η V 's were observed at 60 °C compared to 25 °C, especially for the etched Pt electrodes. The optimum loading for the Pt substrates was 3 g m −2 while for the case of the heat treated samples 10 g m −2 of Pt.