Significantly Enhanced Performance of Nanofluidic Osmotic Power Generation by Slipping Surfaces of Nanopores

TL;DR

This study demonstrates that hydrodynamic slip on specific nanopore surfaces can significantly improve osmotic energy conversion efficiency by increasing ionic permeability and selectivity, guiding better membrane design.

Contribution

It reveals the crucial role of slipping surfaces, especially surfaceL, in enhancing nanopore performance for osmotic power generation, a novel insight for membrane engineering.

Findings

Slipping surfaceL boosts ionic permeability and selectivity.

Hydrodynamic slip increases electric power and efficiency.

SurfaceL modification is more feasible than surfaceinner modification.

Abstract

High-performance osmotic energy conversion (OEC) with perm-selective porous membrane requires both high ionic selectivity and permeability simultaneously. Here, hydrodynamic slip is considered on surfaces of nanopores to break the tradeoff between ionic selectivity and permeability, because it decreases the viscous friction at solid-liquid interfaces which can promote ionic diffusion during OEC. Taking advantage of simulations, influences from individual slipping surfaces on the OEC performance have been investigated, i.e. the slipping inner surface (surfaceinner) and exterior surfaces on the low- and high-concentration sides (surfaceL and surfaceH). Results show that the slipping surfaceL is crucial for high-performance OEC. For nanopores with various lengths, the slipping surfaceL simultaneously increases both ionic permeability and selectivity of nanopores, which results in both significantly enhanced electric power and energy conversion efficiency. While for nanopores longer than 30 nm, the slipping surfaceinner plays a dominant role in the increase of electric power, which induces a considerable decrease in energy conversion efficiency due to enhanced transport of both cations and anions. Considering the difficulty in hydrodynamic slip modification to the surfaceinner of nanopores, the surface modification to the surfaceL may be a better choice to achieve high-performance OEC. Our results provide feasible guidance to the design of porous membranes for high-performance osmotic energy harvesting.