Effect of the Electric Double Layer on the Activation Energy of Ion Transport in Conical Nanopores

Measured apparent activation energies, E-A, of ion transport (K+ and Cl-) in conical glass nanopores are reported as a function of applied voltage (-0.5 to 0.5 V), pore size (20-2000 nm), and electrolyte concentration (0.1-50 mM). E-A values for transport within an electrically charged conical glass nanopore differ from the bulk values due to the voltage and temperature-dependent distribution of the ions within the double layer. Remarkably, nanopores that display ion current rectification also display a large decrease in E-A under accumulation mode conditions (at applied negative voltages versus an external ground) and a large increase in E-A under depletion mode conditions (at positive voltages). Finite element simulations based on the Poisson-Nernst-Planck model semiquantitatively predict the measured temperaturedependent conductivity and dependence of E-A on applied voltage. The results highlight the relationships between the distribution of ions with the nanopore, ionic current, and E-A and their dependencies on pore size, temperature, ion concentration, and applied voltage.