Aqueous Electrolyte Electrical Double Layer Nanocapacitors via Molecular Dynamics Simulations
Date Issued
2010
Date
2010
Author(s)
Tseng, Kuo-Yuan
Abstract
Electrochemical double layer capacitors(ECs), also known as the super-capacitor, is an electrical energy storage device whose capacitance can be tens or hundreds times higher than that of the conventional ones. The electric double layer (EDL) structure and capacitance have been studied using flat electrodes with different aqueous electrolytes via classical molecular dynamics simulation. The change in molecular structure and the electrical properties of the electrolyte solutions are investigated by applying different charges to the electrodes. The dielectric constant of water decrease with applied electric field. At high applied electric fields, the water molecules may even align into highly ordered layer structure. At low applied electric fields, the differential capacitance were calculated by numerical differentiation of the obtained surface charge density vs. double layer potential curve. The value of differential capacitance for water is about
8 microF/cm2 and for 4M NaCl solution is 15 microF/cm2.The maximum of differential capacitance increase with concentration and size of ion, which is in qualitatively good agreement with experimental observations. The structure of water layer near the flat electrode surface is affected by the sign of charge of the electrode. The structure of water has a great influence on its screening capability, leading to the asymmetry behavior in the differential capacitance curve.
Subjects
Molecular Dynamics Simulation
Differential capacitance.
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