Electrokinetic flows and energy conversion in nanofluidic channels: Assessing continuum predictions via molecular dynamics

The flow of electrolyte solutions in nanoscale channels can convert mechanical forces into electrical power. High efficiencies (> 50%) are predicted by the classical Poisson-Boltzmann and Navier-Stokes equations. Employing molecular dynamics (MD) we assess the accuracy of such continuum-level descriptions for slit channels with small nanoscale heights (h ∼ 10 nm) where there is significant overlap of the electric double layers at the wall-fluid interface. We study nanochannels with atomically smooth surfaces and periodic geometric features. The hydrodynamic slip length and ion solvation energy are varied over a moderate range, which is found to significantly affect the nanochannel hydrodynamic and electrical resistance, and thus the conversion efficiency. Despite steric effects, nanoscale hydration layers, and localized charge heterogeneities, the employed continuum model predicts with reasonable accuracy electrokinetic coupling coefficients and conversion efficiencies from MD simulations. Our results support the application of conventional continuum descriptions with minor modifications to design nanofluidic devices for electrokinetic energy conversion with high efficiencies.