Time-dependent density functional theory for ion diffusion in electrochemical systems

被引:68
作者
Jiang, Jian [1 ,2 ]
Cao, Dapeng [2 ]
Jiang, De-en [3 ]
Wu, Jianzhong [1 ]
机构
[1] Univ Calif Riverside, Dept Chem & Environm Engn & Math, Riverside, CA 92521 USA
[2] Beijing Univ Chem Technol, Dept Chem Engn, Beijing 100029, Peoples R China
[3] Oak Ridge Natl Lab, Div Chem Sci, Oak Ridge, TN 37831 USA
关键词
time-dependent density functional theory; Poisson-Nernst-Planck equations; electric double layers; electro-osmotic flows; ion transport; MESOPOROUS MATERIALS; TRANSPORT; NANOFLUIDICS; CAPACITANCE; NANOPORES; CHANNELS; WATER;
D O I
10.1088/0953-8984/26/28/284102
中图分类号
O469 [凝聚态物理学];
学科分类号
070205 ;
摘要
We introduce a generic form of time-dependent density functional theory (TDDFT) to describe ion diffusion in electrochemical systems to account for steric effects and electrostatic correlations neglected in the Poisson-Nernst-Planck equations. An efficient numerical algorithm is proposed to analyze the charging kinetics of electric double layers in model electrochemical systems that consist of spherical ions in a dielectric continuum confined between two planar electrodes. By comparing the theoretical predictions from TDDFT and conventional electrokinetic methods for constant-voltage charging of the model electrochemical cells, we demonstrate that thermodynamic non-ideality plays a pivotal role in electrodiffusion even at relatively low electrolyte concentrations, and this effect cannot be captured by the lattice-gas model for the excluded volume effects. In particular, TDDFT predicts 'wave-like' variation of the ionic density profiles that has not been identified in previous investigations. At conditions where there are no significant correlations between electric double layers from opposite electrodes, the charging kinetics follows an exponential behavior with a linear dependence of the relaxation time on the cell thickness in excellent agreement with the equivalent circuit model. However, the conventional electrokinetic model breaks down when the electrodes are at small separation, in particular for systems with low ionic strength or high charging voltage. We also find that ionic screening retards the charging kinetics at low salt concentrations, but has the opposite effect at large salt concentrations.
引用
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页数:13
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