Imidazolium Triflate Ionic Liquids' Capacitance-Potential Relationships and Transport Properties Affected by Cation Chain Lengths

In this paper wereport the effects of five imidazolium cationswith varying alkyl chain lengths to study the effects of cation sizeon capacitance versus voltage behavior. The cations include ethyl-,butyl-, hexyl-, octyl-, and decyl-3-methylimidazolium, all pairedwith a triflate anion. We analyze the capacitance with respect tothe cation alkyl chain length qualitatively and quantitatively byanalyzing changes in the capacitance-potential curvature shapeand magnitude across several standard scanning protocols and electrochemicaltechniques. Further, three transport properties (viscosity, diffusioncoefficient, and electrical conductivity) are experimentally determinedand integrated into the outcomes. Ultimately, we find higher viscosities,lower diffusion coefficients, and lower electrical conductivitieswhen the alkyl chain length is increased. Also, capacitance valuesincrease with cation size, except 1-octyl-3-methylimidazolium, whichdoes not follow an otherwise linear trend. This capacitive increaseis most pronounced when sweeping the potential in the cathodic direction.These findings challenge the conventional hypothesis that increasingthe length of the alkyl chain of imidazolium cations diminishes thecapacitance and ionic liquid performance in charge storage.

Automated summary

This study investigates the effects of five imidazolium cations with different alkyl chain lengths on capacitance versus voltage behavior. The results show that increasing alkyl chain length leads to higher viscosity, lower diffusion coefficients, and lower electrical conductivities, except for one specific cation. Capacitance values generally increase with cation size, challenging the conventional hypothesis that longer alkyl chains diminish capacitance and ionic liquid performance in charge storage.