Measurement of competition between oxygen evolution and chlorine evolution using rotating ring-disk electrode voltammetry

Selectivity between chlorine evolution and oxygen evolution in aqueous media is a phenomenon of central importance in the chlor-alkali process, water treatment, and saline water splitting, which is an emerging technology for sustainable energy conversion. An apparent scaling between oxygen vs. chlorine evolution has been established, making it challenging to carry the two reactions out individually with 100% faradaic efficiency. To aid selectivity determination, we developed a new method to quickly measure chlorine evolution rates using a conventional RRDE setup. We showed that a Pt ring fixed at 0.95 V vs. RHE in pH 0.88 can selectively reduce the Cl2 formed on the disk and this allows precise and flexible data acquisition. Using this method, we demonstrate that oxygen evolution and chlorine evolution on a glassy carbon supported IrOx catalyst proceed independently, and that the selectivity towards chlorine evolution (εCER) rapidly approaches 100% as [Cl−] increases from 0 to 100 mM. Our results suggest that on IrOx, oxygen evolution is not suppressed or influenced by the presence of Cl− or by the chlorine evolution reaction taking place simultaneously on the surface.