posted on 2015-12-17, 07:09authored byVaibhav Thakore, James J. Hickman
Understanding ion relaxation dynamics
in overlapping electric double
layers (EDLs) is critical for the development of efficient nanotechnology-based electrochemical energy
storage, electrochemomechanical energy conversion, and bioelectrochemical
sensing devices as well as the controlled synthesis of nanostructured
materials. Here, a lattice Boltzmann (LB) method is employed to simulate
an electrolytic nanocapacitor subjected to a step potential at t = 0 for various degrees of EDL overlap, solvent viscosities,
ratios of cation-to-anion diffusivity, and electrode separations.
The use of a novel continuously varying and Galilean-invariant molecular-speed-dependent
relaxation time (MSDRT) with the LB equation recovers a correct microscopic
description of the molecular-collision phenomena and enhances the
stability of the LB algorithm. Results for large EDL overlaps indicated
oscillatory behavior for the ionic current density, in contrast to
monotonic relaxation to equilibrium for low EDL overlaps. Further,
at low solvent viscosities and large EDL overlaps, anomalous plasmalike
spatial oscillations of the electric field were observed that appeared
to be purely an effect of nanoscale confinement. Employing MSDRT in
our simulations enabled modeling of the fundamental physics of the
transient charge relaxation dynamics in electrochemical systems operating
away from equilibrium wherein Nernst–Einstein relation is known
to be violated.