Research In Nanofluidic Reverse Electrodialysis For Salinity Gradient Energy Harvesting

As one of new kind of renewable clean energy,salinity gradient energy is widely contained in the estuary of rivers.With the development of diversified energy sources and prominent environmental problems worldwide,the utilization of salinity gradient energy has attracted extensive attention.Nanofluidic reverse electrodialysis is one of the technologies that convert the salinity gradient energy into electrical energy.Its basic principle is to generate net current through the selective nano channels,and form power generation circuit after adding loads.Based on the subject of"Analysis of an alternative thermodynamic system based on membrane distillation and reverse electrodialysis for low-temperature waste heat utilization",in order to improve the power generation performance of nanofluidic reverse electrodialysis system,this paper systematically studied the influence of geometry,multi ion,asymmetric temperature and hydrodynamic slip on the system through numerical simulation.To evaluate the geometry impact on reverse electrodialysis system,we proposed bilayer and fractal nanopore.For bilayer nanochannels,at low concentration ratio,the osmotic current and maximum power have a maximum value,while the maximum power efficiency decreases continuously.The fractal nanochannel can significantly improve the power generation performance of the system.When the concentration ratio is 1000,compared to the common straight nanochannel,the output power density of the bifurcated and trifurcated structure are increased by 123%and 357%,and the energy conversion efficiency are increased by 147%and 336%,respectively.In the simulation of multi ion system,this paper studied the power generation under different ion proportion,and finded that the power generation performance of K~+is better than that of Na~+.In the same case,the higher the proportion of K~+,the higher the power generation.Previous researches on the temperature for nanofluidic reverse electrodialysis system only focus on the isothermal condition.In this paper,we further study the performance of the system with the external asymmetric temperature.Under the condition of asymmetric temperature,when the concentration gradient is low,due to the enhancement of ion transmembrane migration,the power generation is augmented with the higher average temperature.Compared to the isothermal condition,energy efficiency in the negative temperature gradient is decreased while which in the positive temperature gradient is augmented.In addition,we have proposed a simple and efficient way to fabricate tunable ionic voltage sources by adjusting the transmembrane temperature difference.The ion transport behavior in nanochannel can be significantly improved by surface hydrodynamic slip modification.At low concentration ratio,a larger modification factor can significantly contribute to the maximum power generation,while it also goes against the energy conversion efficiency.For example,when the concentration ratio is 100-fold,if half of the nanopore is modified into slip surface,the power generation of the system can be increased by 60.7%,while the energy conversion efficiency is only reduced by 6.41%.