Effective Charged Exterior Surfaces for Enhanced Ionic Diffusion through Nanopores under Salt Gradients

TL;DR

This study investigates how charged exterior surfaces of nanopores enhance ionic diffusion under salt gradients, providing insights for designing efficient osmotic energy harvesting membranes.

Contribution

It introduces a detailed analysis of how exterior surface charges influence ionic diffusion, highlighting the effects of pore dimensions and salt gradients, which is novel for nanopore design optimization.

Findings

Ionic diffusion is significantly enhanced by exterior surface charges in shorter, wider nanopores.

Effective charged areas depend inversely on pore length and directly on diameter, salt gradient, and surface charge density.

Results guide the design of porous membranes for improved osmotic energy conversion.

Abstract

High-performance osmotic energy conversion requires both large ionic throughput and high ionic selectivity, which can be significantly promoted by exterior surface charges simultaneously, especially for short nanopores. Here, we investigate the enhancement of ionic diffusion by charged exterior surfaces under various conditions and explore corresponding effective charged areas. From simulations, ionic diffusion is promoted more significantly by exterior surface charges through nanopores with a shorter length, wider diameter, and larger surface charge density, or under higher salt gradients. Effective widths of the charged ring regions near nanopores are reversely proportional to the pore length and linearly dependent on the pore diameter, salt gradient, and surface charge density. Due to the important role of effective charged areas in the propagation of ionic diffusion through single nanopores to cases with porous membranes, our results may provide useful guidance to the design and fabrication of porous membranes for practical high-performance osmotic energy harvesting.