Co-Determination of the Kinetics and Stoichiometry of Electrochemical Ion Transfer at the Liquid-Liquid Interface

Abstract

The desolvation of ions at electrochemical interfaces is widely accepted as being the rate limiting step to charge transfer in devices such as ion-intercalation batteries and electrolyzers. While activation energies can be obtained for processes like ion intercalation, the kinetics and mechanism of desolvation remain elusive because they are often convoluted with resistances arising from complex interfacial chemistries. Here I present the use of a biphasic microfluidic electrochemical cell to simultaneously study the kinetics and stoichiometry of tetrabutylammonium (TBA) ion transfer at the interface between two immiscible electrolyte solutions (ITIES). Ion transfer at the ITIES allows one to mostly eliminate the variable of complex interfacial chemistry in the process of desolvation, and with our flow cell geometry we can separate the two phases after ion transfer to measure reaction products via quantitative nuclear magnetic resonance spectroscopy (qNMR). Thus, our novel microfluidic platform for studying electrochemical ion transfer allows us to correlate desolvation kinetics with ion-solvent shell identity, and eventually inform the design of ion transfer mediators/catalysts for the improvement of energy storage technology. Figure 1