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

Abstract

High-performance osmotic energy conversion (OEC) with a perm-selective porous membrane requires both high ionic selectivity and permeability simultaneously. Here hydrodynamic slip is considered on the surfaces of nanopores to break the trade-off 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. 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.