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

Abstract

Measured apparent activation energies, EA, 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). EA 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 EA under accumulation mode conditions (at applied negative voltages versus an external ground) and a large increase in EA under depletion mode conditions (at positive voltages). Finite element simulations based on the Poisson–Nernst–Planck model semiquantitatively predict the measured temperature-dependent conductivity and dependence of EA on applied voltage. The results highlight the relationships between the distribution of ions with the nanopore, ionic current, and EA and their dependenc...