Enhancement of ionic conductivity in electrically conductive membranes by polarization effect

• Published in: Electrochimica acta Vol. 506; p. 144994
• Main Authors: Kharchenko, Ivan A., Vaulin, Nikita V., Simunin, Mikhail M., Mareev, Semen A., Nemtsev, Ivan V., Goltaev, Alexandr S., Lebedev, Denis V., Ryzhkov, Ilya I.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2024
• Subjects: Carbon nanotubes; Ionic conductivity; Modeling; Nanopore; Polarization; Porous anodic alumina membrane; Porous anodic alumina membrane; Carbon nanotubes; Polarization; Nanopore; Modeling; Ionic conductivity
• ISSN: 0013-4686
• DOI: 10.1016/j.electacta.2024.144994

Electrically conductive nanoporous membranes represent a class of stimuli–responsive materials, which selectivity/permeability characteristics can be adjusted by varying the surface potential. In this work, we perform a comprehensive theoretical and experimental study of ionic conductivity of such membranes. The 2D Space charge and 1D Uniform potential models are used to describe the ion transport through a cylindrical nanopore. The calculations show that the imposed electric field polarizes the conductive surface, which results in the continuous variation of electronic surface charge from positive to negative along the nanopore. A higher concentration of cations (anions) is observed at negatively (positively) charged part of the nanopore. The increase of charge carries concentration due to polarization effect results in the enhancement of ionic conductivity with increasing the voltage difference. The corresponding current–voltage curves are non-linear. The enhancement can reach a few orders of magnitude at low salt concentrations, but becomes much smaller at high concentrations. The presence of chemical charge has a screening effect on the interaction of electric field with the electronic charge on the nanopore surface, and reduces the conductivity enhancement. A novel analytical solution is derived for the dependence of ionic current on the Stern layer capacitance, salt concentration, and the applied potential difference. The theoretical predictions are first confirmed by the ionic conductivity measurements in porous anodic alumina membranes with carbon nanotubes inside the pores. The experimental data are approximated by the 1D Uniform potential model curves using chemical charge as a fitting parameter. Strong enhancement of ionic conductivity (more than 6 times) and the corresponding non-linear dependence of current on the applied voltage is experimentally registered at low KCl concentrations (0.1 – 10 mM) with increasing the voltage difference. [Display omitted]