Nanofluidic Energy Research Articles

Experimental Study on the Effects of Applied Electric Field on Liquid Infiltration into Hydrophobic Zeolite

A nanofluidic energy absorption system (NEAS) is composed of nanoporous material and functional liquid with high energy absorption density. Applying an electric field to adjust the energy absorption characteristics of a nanofluidic system will open broader prospects for its application. In the current work, ZSM-5 zeolite was adopted as the nanoporous material and water, a 25% KCl solution, and a saturated KCl solution were adopted as functional liquids to configure NEASs. Pressure-induced infiltration experiments were carried out to study the infiltration and defiltration characteristics of the NEASs under the action of an applied electric field. The results show that the introduction of an applied electric field can weaken the hydrogen bonds between molecules, thus reducing the equivalent surface tension and contact angle, changing the infiltrability of liquid molecules into the nanopores, and reducing the infiltration pressure of the system. In an electrolyte solution/zeolite system, the anions and cations move close to the two plate electrodes under the action of an external electric field, and the fluid properties in the central zone of the pressure chamber are close to the water/zeolite system. For both an ultra-low conductivity liquid and an electrolyte solution/zeolite system, applying an electric field can effectively improve the relative outflow rate of liquid, thus improving the reusability of the system.

Electrokinetic ion rectification in the coupling asymmetric charged nanochannel

Ion transport in nanochannels attracts increasing attention with the advance of nanotechnology, where ion rectification has been intensively studied due to its diode-like electrokinetic behavior. However, the electrochemical interface in most ion rectification is not uniform but involves asymmetric-charged characteristics that offer new degrees of electrical double layer (EDL) confinement. Herein, we investigate the ion transport in coupling asymmetric charged nanochannel to evaluate how the asymmetric geometry and surface charge influences the ion rectification performance. The results show that at low surface charge gradient, the coupling effect enhances ion rectification performance. While at high surface charge gradient, an anomalous electrokinetic behavior is observed that coupling effect deteriorates ion rectification performance. Further analysis discloses that the enhancement-deterioration transition threshold depends on the coordination mechanism of asymmetric geometry and surface charge. It is found that the asymmetric geometry shaped nanochannel with low surface charge gradient and homogeneous geometry shaped nanochannel with high surface charge gradient have the better ion rectification performance. This work fills the gap in understanding the coupling asymmetry effect on ion rectification, providing the useful guidance to design nanofluidic energy devices.

In Situ Growth of Imine‐Bridged Anion‐Selective COF/AAO Membrane for Ion Current Rectification and Nanofluidic Osmotic Energy Conversion

AbstractFacing the energy crisis, using the salinity gradient between seawater and freshwater for osmotic energy conversion is a direct way to obtain energy. So far, most nanofluidic membranes utilized for osmotic energy generation are cation‐selective. Given that both anion‐ and cation‐selective membranes have the identical importance for energy conversion devices, it is of great significance to develop anion‐selective membranes. Herein, an anion‐selective membrane is synthesized by in situ growth of imine‐bridged covalent organic framework (COF) on ordered anodic aluminum oxide (AAO) at room temperature. The imine groups and residual amino groups of COF can combine with protons in neutral solution, enabling the COF positively charged and efficiently transport of anions. Particularly, due to the asymmetry in the charge and structure of COF/AAO, the as‐prepared membrane exhibits excellent ionic current rectification property, which can inhibit ion concentration polarization effectively and possess high ion selectivity and permeability. Using the present COF/AAO membrane, salinity gradient energy can be successfully harvested from solutions with high salt content, and the output power density reached 17.95W m−2 under a 500‐fold salinity gradient. The study provides a new avenue for construction and application of anion‐selective membranes in the smart ion transport and efficient energy conversion.

PH-depended behaviors of electrolytes in nanofluidic salinity gradient energy harvesting

Transmembrane ion transportation in the nanofluidic salinity gradient energy conversion process is significantly regulated by the ion characteristics and concentration-depended physical and chemical properties of the electrolyte solution. In this paper, considering the Born and dielectrophoretic forces and nonhomogeneous electrolyte solution, impacts of various electrolytes on the nanofluidic energy conversion performance are systematically investigated under various solution pHs. When the solution pH is less than the isoelectric point (IEP), with BeCl2 solution employed, where the anion diffusion and concentration coefficient are much larger than those of the anion, significant transmembrane anion diffusion exists, leading to the highest osmotic current and maximum power output, even when the solution pH > IEP where the nanochannel is negatively charged, the ion selectivity is still not altered. At pH < IEP, 2:1 electrolytes, where the cation has small ion diffusion coefficient and the anion has larger diffusion coefficient and hydrated radius could result in upgraded energy conversion performance; At pH > IEP, 1:1 electrolytes where the cation has large ion diffusion coefficient and the anion has small diffusion coefficient and large hydrated radius are more appealing. In addition, the relationships between ion characteristics, power extracted, and energy conversion efficiency are further obtained via machine learning.

Confined Ionic-Liquid-Mediated Cation Diffusion through Layered Membranes for High-Performance Osmotic Energy Conversion.

Ion-selective membranes act as the core components in osmotic energy harvesting, but remain with deficiencies such as low ion selectivity and a tendency to swell. 2D nanofluidic membranes as competitive candidates are still subjected to limited mass transport brought by insufficient wetting and poor stability in water. Here, an ionic-liquid-infused graphene oxide (GO@IL) membrane with ultrafast ion transport ability is reported, and how the confined ionic liquid mediates selective cation diffusion is revealed. The infusion of ionic liquids endows the 2D membrane with excellent mechanical strength, anti-swelling properties, and good stability in aqueous electrolytes. Importantly, immiscible ionic liquids also provide a medium, allowing partial dehydration for ultrafast ion transport. Through molecular dynamics simulation and finite element modeling, that GO nanosheets induce ionic liquids to rearrange, bringing in additional space charges, which can be coupled with GO synergistically, is proved. By mixing 0.5/0.01m NaCl solution, the power density can achieve a record value of ≈6.7W m-2 , outperforming state-of-art GO-based membranes. This work opens up a new route for boosting nanofluidic energy conversion because of the diversity of the ILs and 2D materials.

Vacancy Engineering for High-Efficiency Nanofluidic Osmotic Energy Generation.

Two-dimensional (2D) nanofluidic membranes have shown great promise in harvesting osmotic energy from the salinity difference between seawater and fresh water. However, the output power densities are strongly hampered by insufficient membrane permselectivity. Herein, we demonstrate that vacancy engineering is an effective strategy to enhance the permselectivity of 2D nanofluidic membranes to achieve high-efficiency osmotic energy generation. Phosphorus vacancies were facilely created on NbOPO4 (NbP) nanosheets, which remarkably enlarged their negative surface charge. As verified by both experimental and theoretical investigations, the vacancy-introduced NbP (V-NbP) exhibited fast transmembrane ion migration and high ionic selectivity originating from the improved electrostatic affinity of cations. When applied in a natural river water|seawater osmotic power generator, the macroscopic-scale V-NbP membrane delivered a record-high power density of 10.7 W m-2, far exceeding the commercial benchmark of 5.0 W m-2. This work endows the remarkable potential of vacancy engineering for 2D materials in nanofluidic energy devices.

Heterogeneous Electrospinning Nanofiber Membranes with pH‐regulated Ion Gating for Tunable Osmotic Power Harvesting

AbstractBiological ion channels existing in organisms are critical for many biological processes. Inspired by biological ion channels, the heterogeneous electrospinning nanofiber membranes (HENM) with functional ion channels are constructed by electrospinning technology. The HENM successfully realizes ion‐gating effects, which can be used for tunable energy conversions. Introduction of pyridine and carboxylic acid groups into the HENM plays an important role in generating unique and stable ion transport behaviors, in which gates become alternative states of open and close, responding to symmetric/asymmetric pH stimulations. Then we used the HENM to convert osmotic energy into electric energy which reach a maximum value up to 12.34 W m−2 and the output power density of HENM‐based system could be regulated by ion‐gating effects. The properties of the HENM provide widespread potentials in application of smart nanofluidic devices, energy conversion, and water treatment.

Heterogeneous Electrospinning Nanofiber Membranes with pH-regulated Ion Gating for Tunable Osmotic Power Harvesting.

Biological ion channels existing in organisms are critical for many biological processes. Inspired by biological ion channels, the heterogeneous electrospinning nanofiber membranes (HENM) with functional ion channels are constructed by electrospinning technology. The HENM successfully realizes ion-gating effects, which can be used for tunable energy conversions. Introduction of pyridine and carboxylic acid groups into the HENM plays an important role in generating unique and stable ion transport behaviors, in which gates become alternative states of open and close, responding to symmetric/asymmetric pH stimulations. Then we used the HENM to convert osmotic energy into electric energy which reach a maximum value up to 12.34 W m-2 and the output power density of HENM-based system could be regulated by ion-gating effects. The properties of the HENM provide widespread potentials in application of smart nanofluidic devices, energy conversion, and water treatment.

Multi‐Control of Ion Transport in a Field‐Effect Iontronic Device based on Sandwich‐Structured Nanochannels

AbstractBiomimetic smart nanochannels can regulate ion transport behavior responsive to the external stimuli, having huge potential in nanofluidic devices, sensors and energy conversion. Field‐effect nanofluidic diodes or transistors based on electric‐responsive nanochannels are emerging owing to their advantages such as non‐invasiveness, in situ, real time, and high efficiency. However, simultaneously realizing the voltage‐control of the ion conductance and ion current rectification (ICR) properties is still a big challenge. Here, a field‐effect iontronic device is developed based on ionomer/anodic aluminum oxide/conducting polymer sandwich‐structured nanochannel to realize the multi‐control of ion transport behaviors including ion conductance, ICR magnitude, and ICR direction by modulating the surface charge, wettability, and morphology of the nanochannel. The electroactive conducting polymer carries tunable surface charges responsive to the electric stimuli, leading to the regulation of ICR values. The complex three‐segment structures lead to the reverse of ICR direction by reconfiguring the charge distribution along with the whole channel. The switching wettability between hydrophilic and hydrophobic results in the regulation of ion conductance. Furthermore, the field‐effect iontronic device functions in a wide salinity range especially in hypersaline environment, due to the salinity‐adaptive properties of the membrane. A new route is provided for designing more functional field‐effect nanofluidic devices.

Investigation on performance of square pyramid solar still using nanofluid and thermal energy storage material: An experimental and theoretical study

The rapid growth in population and industrialization are exacerbating the global water crisis, which is pressurizing investigators to quest for an alternative solution. Solar still is an ingenious solar thermal energy-based device facing the issue of less distillate yield. The aim of the current work is to examine the influence of the use of thermal energy storage material and nanoparticles on the distillate yield and to enhance the performance of square pyramid solar still. In the first set of experiments, the comparative performance of the square pyramid solar still was investigated using thermal energy storage material (sodium nitrate (NaNO3)) and aluminium oxide (Al2O3) nanofluid. The total distillate yield and daily average efficiency of the solar still with thermal energy storage material (NaNO3) was higher by 5.50% and 5.58% than the use of Al2O3 nanofluid. Based on the outcomes of the first set of experiments, the comparative performance of square pyramid solar still was investigated with and without thermal energy storage material (NaNO3) in the second set of experiments. The total distillate yield and daily average efficiency of the solar still with thermal energy storage material (NaNO3) was higher by 2.15% and 3.20% than the solar still without NaNO3. The theoretical models were developed for the square pyramid solar still with thermal energy storage material (NaNO3), Al2O3 nanofluid, and without augmentation. The results of the developed theoretical models were compared with the experimental outcomes. The cost of distillate water per liter for the most productive square pyramid solar still with thermal energy storage material (NaNO3) was nearly 3.82 ₹/L.

Geometry design and mechanism analysis of artificial nanoroughness for enhanced osmotic energy conversion

Nanofluidic osmotic energy conversion is widely regarded as a promising technology for the conversion of clean salinity-gradient energy into electricity. Surface roughness can increase the surface charge of nanochannels, but its effect on the ion flux and osmotic energy generation has rarely been investigated. In this study, we propose artificial nanoroughness with rectangular units in nanochannels to enhance ion selectivity and osmotic energy conversion of nanochannels without obvious influence on the ion flux. The osmotic energy conversion performance is separated into an ion selectivity-sufficient zone, a driving force-sufficient zone, and a transition region called balanced zone according to the ion concentration ratio. The artificial nanoroughness significantly increases the ion selectivity in the balanced zone and the driving force-sufficient zone by improving the space charge density in the concave region. The artificial nanoroughness distributed in the rear region of the nanochannel can generate higher osmotic power than that in the frontal region. Moreover, either the maximum osmotic power or energy conversion efficiency can be realized by manipulating the height of artificial nanoroughness under a concentration ratio less than 100, whereas both of them can be achieved simultaneously by reducing the width or pitch of the artificial nanoroughness under all concentration ratios. The current work paves a promising path to consolidate ion selectivity and osmotic power generation through the interfacial design of nanochannels.

Thermal-enhanced nanofluidic osmotic energy conversion with the interfacial photothermal method

Nanofluidic osmotic energy conversion is widely considered a promising technology that converts sustainable salinity-gradient energy. Current studies on temperature regulation require extra electrical consumption to raise the solution temperature, causing the deterioration of the net power generation. In this study, a thermal-enhanced nanofluidic osmotic energy conversion with photothermal conversion structure (PCS-TOEC) integrated device is proposed to utilize sustainable solar energy as the heat source. This device is a reformation by adding photothermal conversion structure (PCS) into a salinity gradient utilization component. PCS is composed of a high solar-absorption cupric oxide film and a high thermal-conductive silicon carbide porous foam, and it can efficiently convert solar energy into solution heat. In addition, PCS can promote bulk heating at a high rate. The experiment shows that the solution temperature is raised from 25 ℃ to 68 ℃ after 240 min under one sun illumination, and the output power density achieves 8.6 W/m2 with 0.5 M/0.01 M NaCl solution, exhibiting a 188 % increase compared to that at room temperature. The increased bulk solution temperature under the photothermal effect can improve the ion diffusion coefficient and electrolyte convection, as well as reduce the electrolyte viscosity, resulting in the enhancement of the associated ion flux. The underlying mechanism of thermally enhanced osmotic power is primarily attributed to the elevated ion flux at increased bulk solution temperatures. Finally, the environmental adaptability of this device is verified over a wide range of concentration gradients (from 10-fold to 100-fold) and pH (from 4 to 10) conditions. In this work, a sustainable solution that enhances osmotic power generation is provided, and a novel method that achieves hybrid renewable energy cooperative utilization is developed.

Heat transfer attributes of Al2O3-Fe3O4/H2O hybrid nanofluid flow over a yawed cylinder

Flow over yawed and unyawed blunt bodies often occurs in various engineering applications. The fluid flow over a yawed cylinder explains the practical significance of subsea applications such as transference control, separating the boundary layer above submerged blocks, and suppressing recirculating bubbles. The current study uses viscous dissipation to analyze the mixed convective hybrid nanofluid flow around a yawed cylinder. Unlike the standard nanofluid model, which only considers one type of nanoparticle, this work considers the hybridization of two types of nanoparticles: alumina (Al2O3) and magnetite (Fe3O4). A model was developed to investigate the heat transport behaviour of a hybrid nanofluid while accounting for the solid volume fraction. The flow problem is modelled in terms of highly nonlinear partial differential equations (NPDEs) subject to the appropriate boundary conditions. Then appropriate non-similar transformations were used to non-dimensionalize the governing equations. Furthermore, the non-dimensional governing equations were solved using the finite difference method (FDM) and the quasilinearisation technique. The effects of water and nanoparticle concentrations on the velocity and the temperature patterns were illustrated graphically. The hybrid nanofluid reduces the velocity distribution in the spanwise and chordwise directions while increasing the surface drag coefficient. The hybrid nanofluid's fluid temperature and energy transport strength was higher than the base fluid and nanofluid. Also, the temperature of the fluid rises as the energy transfer strength diminishes due to an increase in the Eckert number, which characterizes viscous dissipation. However, when the yaw angle increases in the chordwise and spanwise directions, so does the fluid's velocity. The new outcomes were compared to previously published research and were in good agreement.

Magneto-thermogravitational convection for hybrid nanofluid in a novel shaped enclosure

The proposed work exhibits a numerical simulation of steady thermogravitational convection of Cu–Al2O3(50%−50%) water hybrid magneto-nanofluid in a novel shaped enclosure regulated by magnetic field dependent (MFD) viscosity in presence of flush mounted variable heaters. Various cases (Case-I to Case-IV) have been considered depending on the location of the heaters on the bottom and left boundaries. Pertaining to this analysis, the streamfunction (ψ)- vorticity (ζ) form including the energy transport equation of coupled partial differential equations are evaluated with the help of an efficient higher order compact finite difference scheme. Results are exhibited in terms of streamlines, isotherms and Nusselt numbers to describe the transport phenomena obtained for different physical parametric values to this simulation. The influence of the physical parameters such as, Rayleigh number (104≤Ra≤106), Hartmann number (0≤Ha≤60), hybrid nanoparticles volume fraction (0≤ϕhnp≤0.04), orientation of magnetic field (00≤γ≤600) and magnetic number (0≤δ0≤1) on the hybrid nanofluid flow and energy transfer are analyzed. Obtained results indicate that the combinations of the heaters location and the shaped of the geometry have major impact on all the transport phenomena. Moreover, Cu–Al2O3 hybrid nanoparticles play an essential role to levitate the thermal transmission compared to other physical parameters. An addition of hybrid nanoparticles leads to an increase in the average Nusselt number up to 10.8% in Case-I, 12% in Case-II, 11.66% in Case-III and 11.65% in Case-IV. The novelty of the present work is to examine the rheological properties of hybrid nanoliquid in a novel shaped cavity subjected to magnetic field dependent viscosity (MFDV) along with flush mounted variable heaters.

Cation-Selective Oxide Semiconductor Mesoporous Membranes for Biomimetic Ion Rectification and Light-Powered Ion Pumping.

Artificial membranes precisely imitating the biological functions of ion channels and ion pumps have attracted significant attention to explore nanofluidic energy conversion. Herein, inspired by the cyclic ion transport for the photosynthesis in purple bacteria, a bilayer inorganic membrane (TiO2 /AAO) composed of oxide semiconductor (TiO2 ) mesopores on anodic alumina (AAO) macropores is wedeveloped. This inorganic membrane achieves the functions of ion channels and ion pumps, including the ion rectification and light-powered ion pumping. The asymmetric charge distribution across the bilayer membrane contributes to the cationic selectivity and ion rectification characteristics. The electrons induced by ultraviolet irradiation introduce a built-in electric field across TiO2 /AAO membrane, which pumps the active ion transport from a low to a high concentration. This work integrates the functions of biological ion channels and ion pumps within an artificial membrane for the first time, which paves the way to explore multifunctional membranes analogous to its biological counterpart.

Silicone oil nanofluids dispersed with mesoporous crumpled graphene for medium-temperature direct absorption solar-thermal energy harvesting

Direct absorption and conversion of sunlight by optical nanofluids into storable heat is an efficient and facile way to harness abundant clean solar energy, but achieving long-term stable dispersion of the nanofluids is challenging under elevated temperatures. Herein, we report the preparation of mesoporous crumpled graphene particles as self-dispersible solar absorbers that can achieve homogenous dispersion within medium-temperature silicone oil. The mesoporous crumpled graphene particles were synthesized by using an aerosol-assisted capillary compression process and a subsequent oxidative-etching reaction. By controlling the etching time, the introduced mesopores can tune the apparent density of the crumpled particles into a value comparable with the dispersing base fluid. The crumpled surface structure, small particle size and compatible density weaken the inter-particle van der Waals attraction and gravitational sedimentation tendency. The resultant silicone oil nanofluids have maintained their uniform dispersion under a heating temperature of 200 °C for 50 h. The stable uniform dispersion together with the high solar absorptance, the large specific heat capacity and the proper viscosity enabled the application of prepared nanofluids for consistent high-performance medium-temperature solar-thermal energy harvesting under concentrated solar irradiation. • Mesopores are introduced to crumpled graphene particles to tailor the density. • Stable dispersion of mesoporous crumpled graphene particles in silicone oil is achieved. • The nanofluids have high solar absorptance, large heat capacity and suitable viscosity. • Medium-temperature nanofluidic solar-thermal energy harvesting is demonstrated.

Ultrathin Self‐Standing Covalent Organic Frameworks toward Highly‐Efficient Nanofluidic Osmotic Energy Generator

AbstractNanofluidics is promising in the construction of highly‐efficient osmotic energy generator, but it is still a challenge to develop large‐scale and high‐performance nanofluidic membranes. The emerging covalent organic frameworks (COFs) provide a desirable platform to create nanofluidic membranes with high ion selectivity and permeability towards effective osmotic energy conversion. Herein, an ultrathin self‐standing COF nanofluidic membranes based on terephthalaldehyde‐tetrakis(4‐aminophenyl)methane is developed to construct high‐efficiency nanofluidic osmotic energy generator. Benefiting from the nano‐confined channels (1.4 nm) and negative surface charges, the COF based nanofluidic membrane demonstrates both excellent cation selectivity and high ion conductance. Moreover, an ultrathin thickness of ≈1.5 µm significantly reduces the membrane resistance. Consequently, the nanofluidic osmotic energy generator based on COF membrane can deliver a high output power of 5.31 W m−2 under a 50‐fold salinity gradient simulating natural river/sea junction, which is superior to most reported systems and reaches the industrial level. More importantly, such a COF nanofluidic membrane exhibits excellent stability in response to various environmental factors, including wide saline solution concentration, temperature and pH ranges. This work is anticipated to highlight the great potential of 1D COF nanofluidic membranes toward highly‐efficient osmotic energy generators.

Experimental analysis of novel ionic liquid-MXene hybrid nanofluid's energy storage properties: Model-prediction using modern ensemble machine learning methods

The current work employs two modern ensemble machine learning algorithms, Matern 5/2 Gaussian process regression (GPR) and quadratic support vector regression (SVR), to model-predict the thermal conductivity, specific heat, and viscosity of novel Ionic liquid-MXene hybrid nanofluids. The data for model development was obtained in the lab at various temperatures and mass concentrations. The obtained thermal conductivity value for the pure aqueous Ionic liquid (IL) solution at 20 °C was 0.443 W/m·K which rose to 0.82 W/m·K due to the inclusion of 0.5 wt% MXene nanomaterial. The achieved result for the specific heat capacity of the pure aqueous IL solution is 1.985 J/g·K, while this value enhances up to 2.374 J/g·K due to the inclusion of the highest loading concentration (0.5 wt%) of MXene nanomaterial. The acquired data was divided into two portions, with 70% of the data utilized for model training and 30% (hold-out) data used for model testing. Several statistical indicators were used to evaluate the GPR and SVR-based prognostic models created for specific heat, viscosity, and thermal conductivity. For SVM models, the correlation coefficient (R) ranged from 0.9741 to 0.9958, while for GPR-based models, it ranged from 0.9942 to 0.9998. The inaccuracy in the prediction model was quantified using root mean squared error, which ranged from 0.0129 to 0.0398 for SVM-based models and 0.004 to 0.105 for GPR-based models. The predictive effectiveness of the models was tested using Willmott's Index of Agreement, which was 0.9833 to 0.999 for SVM-based models and 0.9834 to 0.9999 for GPR-based models, respectively. The close to unity regression coefficient, low model error, and good prediction effectiveness illustrate the robustness of both SVM and GPR prognostic models. However, the GPR outperformed the SVM on all the statistical indices. The experiment results were also used to compute the Mouromtseff number (<4) and Figure of merit (>1). The results showed that the studied nanofluids can successfully substitute water in specified applications for solar energy. • Thermophysical properties of novel Ionic liquid-MXene hybrid nanofluids are investigated. • Thermal conductivity of 0.82 W/m·K with 0.5 wt% MXene nanomaterial was obtained. • GPR and SVR-based prognostic models were created for specific heat, thermal conductivity, and viscosity. • For SVM models, the correlation coefficient (R) ranged from 0.9741 to 0.9958. • GPR-based models, the correlation coefficient (R) ranged from 0.9942 to 0.9998. • Mouromtseff number (<4) and figure of merit (>1) were achieved.

Nanoengineered nanochannels for thermally ionic nanofluidic energy harvesting

This work demonstrates thermal-to-electric energy conversion based on ionic nanofluidic transport in nanochannels inducted by a temperature gradient. Two types of highly periodic and high aspect ratio nanochannels have been fabricated in a silicon (Si) substrate and in an aluminium oxide (Al2O3) membrane. Silicon nanochannels with diameter of 100 nm and height of 300 μm have been produced by metal-assisted chemical etching process (MACE), while nanochannels with the dimensions of the 10 nm and 3 μm respectively, were fabricated in a Al2O3 membrane by the anodic aluminum oxidation (AAO) process. Moreover, a novel approach of thermally nanofluidic energy harvesting was proposed and conducted. The performance of the thermally ionic nanofluidic energy harvesting system in cases with and without nanochannels has been evaluated and compared. The advantage of the presence nanochannels on energy conversion has been confirmed. The electrolyte concentration dependence on the output power has been determined. Also, the effect of nanochannel materials, including alumina and silicon materials, on the power density has been verified. The ionic Seebeck coefficient was enhanced by 7.3 times when the nanochannels were present. The silicon substrate with nanochannels demonstrated the highest performance for energy harvesting. Its power density reaches approximately 1.47 mW/m2, which was 13.3 times larger than the case without nanochannels. This investigation may open new opportunities for the future thermoelectric generators based on ionic transport in nanochannels.

Simultaneous electrokinetic energy conversion and organic molecular sieving by two-dimensional confined nanochannels

With the development of nanofabrication and nanomaterials, electrokinetic nanofluidic energy conversion has been studied in nanometre-scale, even sub-1-nm channels, which can sieve organic molecules. However, achieving simultaneous nanofluidic energy conversion and organic molecular sieving still remains a challenge. In this work, functional MXene-based membranes were prepared for simultaneous electrokinetic energy conversion and organic molecular sieving. The surface charges of MXene-based membranes were successfully transferred from negative to positive by functionalizing poly (diallyldimethylammonium chloride) (PDDA) polycation chain. The positively charged PDDA-MXene (PMXene) composite membranes displayed good rejection (greater than 99 %) for positively charged methylene blue (MB) molecules. The streaming currents through PMXene and MXene membranes were opposite, indicating the successful modification of the surface charge in the nanochannels of the membranes. In addition, the output current improved around four times from ∼ 95 nA (50 kPa) to ∼ 380 nA (150 kPa) through the PMXene membranes. The flux and rejection of the membranes can also be enhanced by tuning the applied pressure and the thickness of the membranes. Given the superior selective transport of ions and molecules, functional MXene-based membranes can offer many exciting opportunities for self-powered and energy recovery systems during the separation process.