A hybrid method composed of the classical density functional theory (cDFT) and molecular dynamics (MD) simulation is applied to predict the current and thermodynamic efficiency of electrokinetic energy conversion in slit nanochannels. By introducing velocity distribution from MD simulations with surfaces of different wettability, significant difference in electrokinetic current is revealed compared with that from traditional Navier-Stokes equation, which indicates the influence of water flow in nanochannels on the current. Different from the net charge profiles derived from mean-field theory and velocity distribution from Navier-Stokes equation, cDFT combined with the MD simulation indicates that the predicted electrokinetic current and thermodynamic efficiency is much larger in small slit nanochannels than those from Navier-Stokes equation as the result of fast water transport. This is in good agreement with recent experiments. Novel phenomena like non-monotonic relation between current per height versus height are also discovered because of the water structure in nanochannels and the specific ion distribution in slit nanochannels as the result of excluded-volume effects and the long-ranged interactions. For given nanochannels, optimal conditions are sensitive to many aspects of electrolyte properties including concentrations, ion diameters, valences and asymmetry of oppositely charged ions in valence and size. The results of MD simulation-assisted cDFT give new insights into pressure-driven current process and provide helpful guidelines for related facility design in electrokinetic energy conversion.

Hybrid method composed of cDFT and MD simulation for predicting electrokinetic energy conversion in slit nanochannels

2019 Spring National Meeting

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