Electroneutrality Breakdown in Nanoporous Membranes

The transport of ions in charged membranes underlies a number of important technologies in separations, electrochemistry, and energy harvesting. In general, the charge selectivity and conductivity performance characteristics of the membranes arise from the fixed charge on the membrane, the concentrations of salt, and the size of the pores. Here, we identify unique characteristics of electrostatic screening in 1D nanopores, and demonstrate how these screening properties can affect conductivity and selectivity of membrane systems. In particular, we show that in extreme 1D confinement, the screening length in a nanopore is exponentially long, approaching macroscopic length scales, and can eclipse even the length of extremely long nanotubes. The long-range 1D screening results in the phenomenon of electroneutrality breakdown, where the number of charges within the pore does not match the number of charges on the pore walls, since a significant fraction of the electric field can escape through the pore walls into the membrane matrix. Electroneutrality breakdown has strong consequences on selectivity and conductivity, because the number of mobile charges inside the pore determines these parameters.