  Bipolar nanochannels comprising two domains of positively and negatively
charged walls along the pore axis are known to rectify current when exposed to
an electric potential bias. We find that addition of charged nanoparticles can
increase rectification considerably, by approximately one order of magnitude.
Two bipolar channel geometries are considered here; their behavior is examined
at rest and under the influence of a negative bias and a positive bias,
respectively. We do so by relying on a molecular-level model of the electrolyte
solution in the channels. The large increase in current rectification can be
explained by the inherent electric field that charged nanoparticles generate
within the channel. This effect is found to be largely dependent on the pore's
geometry, its charge distribution, and the sign of the nanoparticles' charge,
thereby offering new opportunities for design of engineered nanopore
membrane-nanoparticle systems for energy storage.
