A Study On Power Generation From Nanofluidic Device With Salt Gradient

Since single nanopores were firstly proposed as a potential rapid and low-cost tool for DNA sequencing in 1990s(PNAS,1996,93,13770),extensive studies on nanofluidic devices such as both biological and synthetic nanopores and nanochannels have been reported.However,there are the coupling of various physical mechanisms in the nanofluidic devices,such as hydrodynamic equation,the electrostatic equation caused by the charge on the channel wall,and the ion transport equation describing the motion of ions.And the multi-physical field coupling makes it very complicated to analyze the physical properties of nanofluidic devices.Based on the approximation of decoupling the channel axial and radial transport,we establish the Space-Charge Model of the nanofluidic system with salt concentration bias..Not only has the existence of exclusion and diff usion potentials been outlined from the expressions of self-built voltage,but also the competing roles of the two mechanisms in determining the ion transport.The electrokinetic model provides the physical explanation for various experimental phenomena based on the two competitive mechanisms.We then discuss two key performance indexes of the power generation of the nanofluidic system with salt concentration bias,which are the output power density and the energy converting efficiency,and their dependence on the nanochannel parameters such as channel length and salt bias.In order to yield maximized output electrical power,we propose a device design by stepwise usage of the saline bias between river and sea,and the lengths of the nanochannels are optimized to achieve the best trade-off between the input thermal power and the energy converting efficiency.Finally,the weak electrolyte transport in nanochannels or nanopores has been actively explored in recent experiments.So we establish a new electrokinetic model where the ionization balance effect of weak electrolytes is outlined,and the transports of ion and fluid are described by the Poisson-Nernst-Plank(PNP)equation and Navier-Stokes equation,respectively.The simulation results of the model show quantitative agreement with experimental observations.Based on the model,we predict that enhanced energy harvesting capacity could be accomplished by utilizing weak electrolytes compared to the conventional strong electrolyte approaches in a concentration gradient-based power-generating system.