Electrochemical Generation of Single Emulsion Droplets and In Situ Observation of Collisions on an Ultramicroelectrode

Abstract

The Br-/Br-2 redox couple in aqueous solution has been often employed for redox flow batteries along with N-methyl-N-ethyl pyrrolidinium bromide (MEPBr) as a bromine-complexing agent, which forms insoluble organic droplets of MEPBr3 complexes during electro-oxidation of Br-. We, for the first time, report the electrochemistry of Br-. electro-oxidation in electrochemically generated single droplets of MEPBr3 using the current transient method on an ultramicroelectrode (UME). Current spikes were observed in the chronoamperogram of the aqueous solutions containing more than 32 mM of MEPBr, and they correspond to electro-oxidation of Br- in MEPBr3. The voltammetric behavior of Br- electro-oxidation in single droplets of MEPBr3 was similar to that in the aqueous phase. The maximum concentration of Br in the MEPBr3 droplets was estimated to be similar to 7.5 M by fitting the observed current transient curves to the simulation using a bulk electrolysis model. Our study reveals that MEPBr3 also plays a vital role as an electrochemical reaction medium for Br- electro-oxidation in the Br-/Br-2 redox system.