Abstract
Ample studies have shown the use of nanofluidics in the ionic diode and osmotic power generation, but similar ionic devices performed with large-sized mesopores are still poorly understood. In this study, we model and realize the mesoscale ionic diode and osmotic power generator, composed of an asymmetric cone-shaped mesopore with its narrow opening filled with a polyelectrolyte (PE) layer with high space charges. We show that, only when the space charge density of a PE layer is sufficiently large (>), the considered mesopore system is able to create an asymmetric ionic distributions in the pore and then rectify ionic current. As a result, the output osmotic power performance can be improved when the filled PE carries sufficiently high space charges. For example, the considered PE-filled mesopore system can show an amplification of the osmotic power of up to 35.1-fold, compared to the bare solid-state mesopore. The findings provide necessary information for the development of large-sized ionic diode and osmotic power harvesting device.
Highlights
IntroductionNanofluidics, such as nanopores and nanochannels [1,2,3], has been extensively studied, because unique ion transport properties are expected to emerge from the overlapping effect of electric double layers (EDLs) in confined nanospaces, making it with diverse applications from energy, to environment, to biosensors [4,5,6,7,8,9,10,11,12,13,14,15,16,17]
Considerable experimental [20,21,22] and theoretical [23,24,25,26,27,28,29,30,31,32] efforts have been made on ion current rectification (ICR) in nanofluidics and all these studies concluded that the ICR property only can emerge in case the pore size is comparable to the electric double layers (EDLs) thickness
The ion transport in the mesopore system considered can be described by the coupled Poisson–Nernst–Planck and Stokes–Brinkman equations, taking account of the space charge density stemming from the PE layer, which have been validated for the nanopore systems [48,49,50,51]:
Summary
Nanofluidics, such as nanopores and nanochannels [1,2,3], has been extensively studied, because unique ion transport properties are expected to emerge from the overlapping effect of electric double layers (EDLs) in confined nanospaces, making it with diverse applications from energy, to environment, to biosensors [4,5,6,7,8,9,10,11,12,13,14,15,16,17]. It was experimentally shown that a significant ICR effect can be found in neutral and high saline solutions, capable of achieving an osmotic power of ~120 pW under a 500-fold salinity gradient This opens a pathway towards high-performance osmotic power harvesting, and it is highly necessary to simulate the ion transport and osmotic power conversion in the relevant mesopore system, which is able to improve the understanding of underlying mechanisms behind the mesoscale transport. The finding provides significant information for exploration of novel relevant mesoscale devices in the future
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