Theory for anomalous electric double-layer dynamics in ionic liquids

Abstract

Anomalous slow dynamics with impedance phase modulation and two capacitive arcs are seen in the recent experiments with room-temperature ionic liquid (RTIL) on gold single-crystal electrodes. Single-crystal electrodes have low surface atomic heterogeneity and can show crystal face dependent multiorientation adsorbing states. We have extended our recently developed model of electric double-layer (EDL) impedance of a heterogeneous electrode with single state compact layer (see J. Electroanal. Chem. 2013, 704, 197–207) to a multistate compact layer for accounting ion shape asymmetry in RTILs. The modified multistate model incorporates ion shape asymmetry dependent molecular properties and related relaxation dynamics in the compact layer. Our model with two or three ion orientation states in the compact layer for systems with shape asymmetric cations explains such anomalous dynamics. Comparisons of the theoretical impedance and capacitance responses with recent experiments on electrode/IL systems are in good agreement.