title: A mean-field theory on the differential capacitance of asymmetric ionic liquid electrolytes.
abstract: The size of ions significantly influences the electric double layer structure of room temperature ionic liquid (IL) electrolytes and their differential capacitance (Cd). In this study, we extended the mean-field theory (MFT) developed independently by Kornyshev (2007J. Phys. Chem. B 111 5545-57) and Kilic, Bazant, and Ajdari (2007 Phys. Rev. E 75 021502) (the KKBA MFT) to take into account the asymmetric 1:1 IL electrolytes by introducing an additional parameter ξ for the anion/cation volume ratio, besides the ionic compressibility γ in the KKBA MFT. The MFT of asymmetric ions becomes KKBA MFT upon ξ = 1, and further reduces to Gouy-Chapman theory in the γ → 0 limit. The result of the extended MFT demonstrates that the asymmetric ILs give rise to an asymmetric Cd, with the higher peak in Cd occurring at positive polarization for the smaller anionic size. At high potential, Cd decays asymptotically toward KKBA MFT characterized by γ for the negative polarization, and characterized by ξγ for the positive polarization, with inverse-square-root behavior. At low potential, around the potential of zero charge, the asymmetric ions cause a higher Cd, which exceeds that of Gouy-Chapman theory.
authors.affiliation: Tianjin Key Laboratory of Metal- and Molecule-Based Material Chemistry, Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Institute of New Energy Material Chemistry, College of Chemistry, Nankai University, Tianjin 300071, People's Republic of China.
authors.forename: Yining
authors.initials: Y
authors.lastname: Han
authors.forename: Shanghui
authors.initials: S
authors.lastname: Huang
authors.forename: Tianying
authors.initials: T
authors.lastname: Yan
mesh_terms: D003198:Computer Simulation; D025802:Electric Capacitance; D004573:Electrolytes / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D008956:Models, Chemical; D055672:Static Electricity
chemical_list: D004573:Electrolytes; D052578:Ionic Liquids; D007477:Ions