Asymmetric Electrokinetic Energy Conversion in Slip Conical Nanopores

Abstract

Ion current rectification (ICR) phenomena in asymmetric nanofluidic structures, such as conical-shaped nanopores and funnel-shaped nanochannels, have been widely investigated in recent decades. To date, the effect of asymmetric nanofluidic structures on electrokinetic power generation driven by the streaming current/potential has not been explored. Accordingly, this study employed a numerical model based on the Poisson equation, Nernst–Planck equation, and Navier–Stokes equation to investigate the electrokinetic energy conversion (EKEC) in a conical nanopore while considering hydrodynamic slippage. The results indicated that the asymmetric characteristics of streaming current (short-circuit current), streaming potential (open-circuit voltage), maximum power generation, maximum conversion efficiency, and flow rate were observed in conical nanopores under the forward pressure bias (tip-to-base direction) and reverse pressure bias (base-to-tip direction) once the nonequilibrium ion concentration polarization (ICP) became considerable. The rectification behaviors in the streaming current, maximum power, and maximum conversion efficiency were all shown to be opposite to those of the well-known ICR in conical nanopores. In other words, the reverse pressure bias revealed a higher EKEC performance than the forward pressure bias. It was concluded that the asymmetric behavior in EKEC is attributed to the asymmetric electrical resistance resulting from asymmetric ion depletion and ion enrichment. Particularly, it was found that the decrease in electrical resistance (i.e., the change in electrical resistance dominated by the ion enrichment) observed in the reverse pressure bias enhanced the maximum power and maximum conversion efficiency. The asymmetric EKEC characteristics became more significant with increasing slip length, surface charge density, cone angle, and pressure bias, especially at lower salt concentrations. The present findings provide useful information for the future development of EKEC in engineered membranes with asymmetric nanopores.

Chemiosomotic flow in a soft conical nanopore: harvesting enhanced blue energy

“…We have presented the maximum power density (= P max /π a m 2 , a m is the radius in the middle of the nanopore 43 ) and corresponding maximum efficiency η max as a function of pH T and pH B for c B / c T = 10 and 10 3 in Fig. 7(a–d), respectively.…”

“…Noteworthily, this observation is in agreement with the observation of other researchers as well. 10,20 We have presented the maximum power density P Ã max (=P max / pa m 2 , a m is the radius in the middle of the nanopore 43 ) and corresponding maximum efficiency Z max as a function of pH T and pH B for c B /c T = 10 and 10 3 in Fig. 7(a-d), respectively.…”

Slip Flow Analysis in an Experimental Chamber Simulating Differential Pumping in an Environmental Scanning Electron Microscope

“…With significantly reduced shear stress on the nozzle wall, the increased gas expansion results in a shorter distance. This fact will be tested together with the following methods using the Schlieren method of optical refraction [ 23 ].…”

Carbonized Cotton Fibers for Ultrahigh Power-Density Electrokinetic Energy Harvesting

“…Electric eels, for example, demonstrate unique nervous systems having the capacity to synchronize their electricity-producing cells in a way that sodium ions may be driven into them by an external stimulus, resulting in a temporary discharge of electricity of hundreds of volts . Analogously, natural or engineered systems having mobile ions of a net charge may drive their separation by an external stimulus (such as pressure-driven − or evaporation-induced − fluid flow) and thus set up an electrical potential, also known as the streaming potential. The resulting voltage can be tapped to induce a current in an external circuit, thereby converting hydraulic energy to electrical power. − Coined as electrokinetic energy conversion, the underlying science has continued to offer great promises in deriving clean energy from naturally abundant water, − but compelling technological bottlenecks have restrained extensive adaptation of the same in real-life practice.…”