Ionic Liquid/Non-Ionic Surfactant Mixtures as Versatile, Non-Volatile Electrolytes: Double-Layer Capacitance and Conductivity

Abstract

Ionic liquids (ILs) are being increasingly used as processing aids to formulate electrode/electrolyte composites where the electrolyte acts as a template, defining the effective electrolyte-filled pore space between 2D materials such as graphene and MXenes. This is often facilitated with non-ionic surfactants. However, little is currently known about how these surfactants impact double-layer formation and ionic conductivity. Herein, we measure these properties for two commonly used non-ionic surfactants, P123 and Triton X-100 (TX-100) mixed with the IL, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI). A significant increase in the minimum capacitance is observed at 40 wt% surfactant by up to 88% and 102% for P123 and TX-100, respectively. On the other hand, the higher viscosity of the mixtures, lowers the ionic conductivity from 8.5 mS cm−1 (neat IL) to 1 mS cm−1 (40 wt% surfactant). Despite the significantly higher viscosity of P123/IL mixtures compared to TX-100/IL, both electrolyte series show the same reduction in ionic conductivity with respect to concentration. Pulse field gradient nuclear magnetic resonance was also used to show that for both electrolyte series, the diffusion coefficients follow a similar trend.