Concentration Polarization Research Articles

Mo doping V0.76Mn0.032Ni0.029O2 vanadium based ternary metal oxides as cathode active materials for lithium-ion hybrid supercapacitor with high lithium storage performance

Lithium-ion hybrid supercapacitors as high-performance energy storage devices are proposed to bridge the electrochemical performances between lithium-ion batteries and supercapacitors. In this paper a novel Mo doping V0.76Mn0.032Ni0.029O2 vanadium based ternary metal oxide is constructed as cathode active material for lithium-ion hybrid supercapacitor. Structural analysis demonstrates Mo doping as interlayer support can ameliorate the V0.76Mn0.032Ni0.029O2 crystal structure and raise the lattice size thus providing more adequate mass transfer channels for lithium-ion storage. In addition, 5 % Mo doping V0.76Mn0.032Ni0.029O2 represents relatively regular crystal particle arrangement with some integrated crystalline form and closely packing together. These structural features enable them to exhibit higher lithium storage performance and when as cathode active material for lithium-ion hybrid supercapacitor, it exhibits the lowest electrochemical and concentration polarization and the highest discharge specific capacities of 150.7, 140.2, 125.4 and 102.5 mAh.g−1 at different current densities along with a high capacity retention rate of 77.3 % at 1000 mA g−1 current density after 2000 cycles.

Piezoelectric reverse osmosis (RO) membrane: Fabrication and anti-fouling effect

In this study, a novel piezoelectric RO membrane with vibrating mechanism when exposed to an electric field was developed. The vibration due to the piezoelectric effect can disturb the concentration polarization layer on the membrane surface and minimize membrane fouling. Polyvinylidene fluoride (PVDF) which has piezoelectric properties was selected as the porous substrate for a thin film composite (TFC) polyamide RO membrane in this study. Electrical poling was performed to enhance the piezoelectric properties of the PVDF substrate. RO membranes fabricated via interfacial polymerization using different PVDF substrates (i.e., with and without pre-wetting the PVDF substrate, with and without polyethylene terephthalate (PET) non-woven fabric support (denoted as NWF and no-NWF, respectively), with and without electrical poling) were systematically investigated. The results indicated that RO membrane fabricated on poled PVDF-NWF substrate shows reasonable pure water permeability of ∼2 LMH/bar and sodium chloride (NaCl, 2000 ppm) rejection of ∼98.9 % when tested at 15 bar. In the accelerated fouling study using colloidal silica particles (∼20 nm in diameter, 200 ppm with background of 2000 mg/L NaCl), when the RO membrane fabricated using both unpoled and poled PVDF-NWF substrates were excited with AC signal, membrane fouling was significantly reduced. These findings suggested that electrical poling may not be necessary for such piezoelectric RO membrane.

Modeling of an all-solid-state battery with a composite positive electrode

All solid-state batteries are considered as the most promising battery technology due to their safety and high energy density. This study presents an advanced mathematical model that accurately simulates the complex behavior of all-solid-state lithium-ion batteries with composite positive electrodes. The partial differential equations of ionic transport and potential dynamics in the electrode and electrolyte are solved and reduced to a low-order system with Padé approximation. Moreover, the imperfect contact and the electrical double layers at the solid-solid interface are also taken into consideration. Subsequent experiments are conducted for the blocked cell and half-cells to extract parameters. Next, the parameterized model is validated with extensive experimental data from NCM811/LPSC/Li4.4Si batteries, illustrating the superior capability of predicting cell voltage with an average RMSE of 19.5 mV for the discharging/charging phases and 2.8 mV for the end of relaxation under a total of 15 conditions. From the simulations, it can be concluded that the limiting factors for battery performance are overpotentials caused by concentration polarization within positive particles and interface reactions. Finally, through a parameter sensitivity analysis, we offer strategic guidelines for optimizing battery performance, thus enhancing the development efficiency of ASSBs.

Borate-containing triblock copolymer electrolytes for improved lithium-ion transference number and interface stability

The electrolytes with high lithium-ion transference number (tLi+) can reduce the formation of concentration polarization during charge/discharge process and improve the electrochemical performance of lithium-ion batteries (LIBs). Herein, we report triblock copolymer electrolytes (PBOEE) containing borate. The sp2 hybridized boron atoms acting as Lewis acids can anchor the anions of lithium salts, enabling PBOEE to achieve high tLi+ of up to 0.53. Also, the borate groups can promote the formation of stable organic-rich solid electrolyte interphase (SEI) film, which enables the Li symmetric cell to cycle stably at 0.1 mA cm−2/0.1 mAh cm−2 for more than 3100 h with a low overpotential of 0.08 V under 50 °C. The optimized PBOEE_24 has an ionic conductivity of 1.41 × 10−4 S cm−1 and electrochemical stability window of 4.8 V vs. Li+/Li at 50 °C. Combining these advantages, the LiFePO4/PBOEE_24/Li cell exhibits an initial discharge specific capacity of 157.3 mA h g−1 at 0.5C with a capacity retention of 85 % after 600 cycles under 50 °C. At a higher current density of 1C, the discharge capacity maintains at 128.0 mA h g−1 after 400 cycles with a capacity retention of 84.88 %. These results suggest that block copolymer containing sp2 hybridized boron atoms is a promising all-solid-state polymer electrolyte.

An Ion Concentration Polarization Microplatform for Efficient Enrichment and Analysis of ctDNA.

Strategies for rapid, effective nucleic acid processing hold tremendous significance to the clinical analysis of circulating tumor DNA (ctDNA), a family of important markers indicating tumorigenesis and metastasis. However, traditional techniques remain challenging to achieve efficient DNA enrichment, further bringing about complicated operation and limited detection sensitivity. Here, we developed an ion concentration polarization microplatform that enabled highly rapid, efficient enrichment and purification of ctDNA from a variety of clinical samples, including serum, urine, and feces. The platform demonstrated efficiently separating and enriching ctDNA within 30 s, with a 100-fold improvement over traditional methods. Integrating an on-chip isothermal amplification module, the platform further achieved 100-fold enhanced sensitivity in ctDNA detection, which significantly eliminated false-negative results in the serum or urine samples due to the low abundance of ctDNA. Such a simple-designed platform offers a user-friendly yet powerful diagnosis technique with a wide applicability, ranging from early tumor diagnosis to infection screening.

Review of Hybrid Membrane Distillation Systems.

Membrane distillation (MD) is an attractive separation process that can work with heat sources with low temperature differences and is less sensitive to concentration polarization and membrane fouling than other pressure-driven membrane separation processes, thus allowing it to use low-grade thermal energy, which is helpful to decrease the consumption of energy, treat concentrated solutions, and improve water recovery rate. This paper provides a review of the integration of MD with waste heat and renewable energy, such as solar radiation, salt-gradient solar ponds, and geothermal energy, for desalination. In addition, MD hybrids with pressure-retarded osmosis (PRO), multi-effect distillation (MED), reverse osmosis (RO), crystallization, forward osmosis (FO), and bioreactors to dispose of concentrated solutions are also comprehensively summarized. A critical analysis of the hybrid MD systems will be helpful for the research and development of MD technology and will promote its application. Eventually, a possible research direction for MD is suggested.

Self‐Regulating Interfacial Space Charge through Polyanion Repulsion Effect towards Dendrite‐Free Polymer Lithium‐Metal Batteries

AbstractUncontrolled transport of anions leads to many issues, including concentration polarization, excessive interface side reactions, and space charge‐induced lithium dendrites at the anode/electrolyte interface, which severely deteriorates the cycling stability of lithium metal batteries. Herein, an asymmetrical polymer electrolyte modified by a boron‐containing single‐ion conductor (LiPVAOB), is designed to inhibit the nonuniform aggregation of free anions in the vicinity of the lithium anode through the repulsion effect improving the lithium‐ion transference number to 0.63. This LiPVAOB exerts a repulsion interaction with free anions even at a long distance and a selective effect for free anions transport, which diminishes uneven aggregation of free anions at the interface and suppresses space charges‐induced lithium dendrites growth. Consequently, the assembled Li||Li cell delivers an ultra‐long cycle for over 5400 h. The Li||LiFePO4 cell exhibits outstanding cycle performance with a capacity retention of 93% over 4500 cycles. In particular, the assembled high‐voltage Li||Li1.2Ni0.2Mn0.6O2 cell (charged to 4.8 V) exhibits good cycle stability with a high specific capacity of 245 mAh g−1. This designed polymer electrolyte provides a promising strategy for regulating ion transport to inhibit space charge‐induced lithium dendrite growth for high‐performance lithium metal batteries.

Inducing Deep Sweeps and Vortex Ejections on Patterned Membrane Surfaces to Mitigate Surface Fouling.

Patterned membrane surfaces offer a hydrodynamic approach to mitigating concentration polarization and subsequent surface fouling. However, when subjected to steady crossflow conditions, surface patterns promote particle accumulation in the recirculation zones of cavity-like spaces. In order to resolve this issue, we numerically subject a two-dimensional, patterned membrane surface to a rapidly pulsed crossflow. When combined with cavity-like spaces, such as the valleys of membrane surface patterns, a rapidly pulsed flow generates mixing mechanisms (i.e., the deep sweep and the vortex ejection) and disrupts recirculation zones. In only four pulses, we demonstrate the ability of these mechanisms to remove over half of the particles trapped in recirculation zones via massless particle tracking studies (i.e., numerical integration of the simulated velocity field). The results of this work suggest that when combined with a rapidly pulsed inlet flow, patterned membrane surfaces can not only alleviate concentration polarization and the surface fouling that follows but also reduce the need for traditional cleaning methods that require operational downtime and often involve the use of abrasive chemical agents.

Theoretical Analysis of the Influence of Spacers on Salt Ion Transport in Electromembrane Systems Considering the Main Coupled Effects.

This article considers a theoretical analysis of the influence of the main coupled effects and spacers on the transfer of salt ions in electromembrane systems (EMS) using a 2D mathematical model of the transfer process in a desalting channel with spacers based on boundary value problems for the coupled system of Nernst-Planck-Poisson and Navier-Stokes equations. The basic patterns of salt ion transport have been established, taking into account diffusion, electromigration, forced convection, electroconvection, dissociation/recombination reactions of water molecules, as well as spacers located inside the desalting channel. It has been shown that spacers and taking into account the dissociation/recombination reaction of water molecules significantly change both the formation and development of electroconvection. This article confirms the fact of the exaltation of the limiting current studied by Harkatz, where it is shown that the current (flux) of salt ions increases when the dissociation reaction begins by a certain value called the exaltation current, which is proportional to the flow of water dissociation products. A significant combined effect of electroconvection and dissociation/recombination reactions as well as the spacer system in the desalting channel on the transport of salt ions are shown. The complex, nonlinear, and non-stationary interaction of all the main effects of concentration polarization and spacers in the desalting channel are also considered in the work.

A finite element model for concentration polarization and osmotic effects in a membrane channel

AbstractIn this article, we study a mathematical model that represents the concentration polarization and osmosis effects in a reverse osmosis cross‐flow channel with dense membranes at some of its boundaries. The fluid is modeled using the Navier–Stokes equations and the solution‐diffusion is used to impose the momentum balance on the membrane. The scheme consist of a conforming finite element method with the velocity–pressure formulation for the Navier–Stokes equations, together with a primal scheme for the convection–diffusion equations. The Nitsche's method is used to impose the permeability condition across the membrane. Several numerical experiments are performed to show the robustness of the method. The resulting model accurately replicates the analytical models and predicts similar results to previous works. It is found that the submerged configuration has the highest permeate production, but also has the greatest pressure loss of all three configurations studied.

On the behavior of sub-micrometer polystyrene particles subjected to AC insulator-based dielectrophoresis.

Polymer beads, especially polystyrene particles, have been extensively used as model species in insulator-based dielectrophoresis (iDEP) studies. Their use in alternating current iDEP (AC-iDEP) is less explored; however, an assessment in the low-frequency regime (≤10kHz) allows to link surface conduction effects with the surface properties of polymer particles. Here, we provide a case study for various experimental conditions assessing sub-micrometer polystyrene particles with AC-iDEP and link to accepted surface conduction theory to predict and experimentally verify the observed AC-iDEP trapping behavior based on apparent zeta potential and solution conductivity. We find excellent agreement with the theoretical predictions, but also the occurrence of concentration polarization electroosmotic flow under the studied conditions, which have the potential to confound acting dielectrophoresis conditions. Furthermore, we study a case relevant to the assessment of microplastics in human and animal body fluids by mimicking the protein adsorption of high abundant proteins in blood by coating polystyrene beads with bovine serum albumin, a highly abundant protein in blood. Theoretical predictions and experimental observations confirm a difference in observed AC-iDEP behavior between coated and non-coated particles, which might be exploited for future studies of microplastics in blood to assess their exposure to humans and animals.

Ion Concentration Polarization Tunes Interpore Interactions and Transport Properties of Nanopore Arrays

AbstractBiological processes require concerted function of many channels embedded in the cell membrane. While single solid‐state nanopores are already designed to mimic properties of individual biological channels, it is not yet known how to connect the pores to achieve biomimetic ionic circuits with interacting components. To identify fundamental processes that control interactions between nanopores embedded in the same membrane, a model system of minimal arrays consisting of two and three nanopores in silicon nitride films is designed. The constituent nanopores have an opening diameter <10 nm, and the interpore spacing is tuned between 15 and 200 nm. The experimental and modeling results reveal that nanopores in an array interact with each other via overlapping depletion zones created by the process of concentration polarization. The interactions can be further controlled by salt concentration and voltage. These results showcase a possibility of tuning interactions between nanopores and transport properties of arrays by chemical modification of the pore walls. Arrays consisting of nanoporous ionic diodes feature depletion zones with higher concentrations, and lower current suppression than homogeneously charged pores. These experiments and modeling provide the first steps to leave the constraints of single nanopores and to design biomimetic ionic circuits.

Controlling the Supramolecular Architecture Enables High Lithium Cationic Conductivity and High Electrochemical Stability for Solid Polymer Electrolytes

AbstractSolid polymer electrolytes (SPEs) are long sought after for versatile applications due to their low cost, light weight, flexibility, ease of scale‐up, and low interfacial impedance. However, obtaining SPEs with high Li+ conductivity (σ+) and high voltage stability to avoid concentrated polarization and premature capacity loss has proven challenging. Here a stretchable dry‐SPE is reported with a semi‐interpenetrating, supermolecular architecture consisting of a cross‐linked polyethylene oxide (PEO) tetra‐network and an alternating copolymer poly(ethylene oxide‐alt‐butylene terephthalate). Such a unique supermolecular architecture suppresses the formation of Li+/PEO intermolecular complex and enhances the oxidation stability of PEO‐based electrolyte, thus maintaining high chain segmental motion even with high salt loading (up to 50 wt%) and achieving a wide electrochemical stability window of 5.3 V. These merits enable the simultaneous accomplishment of high ionic conductivity and high Li+ transference number (t+) to enhance the energy efficiency of energy storage device, and electrochemical stability.

A numerical study on applying ion concentration polarization in micropump design

This work focuses on applying the phenomenon of ion concentration polarization to design and investigate a micropump model that is a kind of electroosmotic micropump. Numerical study is conducted for ion concentration polarization in the manner that generates electro-osmosis flow and pumping effect. The formation of the extended space charge layer and the actions of the electric field upon this layer is applied to generate electro-osmosis flow to drive flow in the system. It is clarified that pumping effect can be enhanced by improving the geometry configurations. Multiple simulations are conducted to obtain an optimal micropump design.

Synergistic improvements on capacity and Coulombic efficiency of lithium-sulfur batteries with NiSe-Ni2P/C modification on PP separators

Lithium-sulfur batteries (LSBs) emerge as promising energy storage devices due to their high theoretical energy density. So far, there are constrained issues that need to be urgently addressed, such as the shuttle effect of lithium polysulfides (LiPS) and the sluggish kinetics of redox reactions. Herein, NiSe-Ni2P/C composite was synthesized and casted on the cathode side of polypropylene (PP) separator. This investigation reveals that the adsorption-catalysis synergistic effect of NiSe-Ni2P/C composite, accelerates the reduction of LiPS to lithium sulfide (Li2S) as well as the oxidation of Li2S. The synergistic effect effectively mitigates the shuttle effect of LiPS, reduces concentration polarization, and improves Coulombic efficiency (CE) throughout the entire lifespan. At a current density of 0.05 C, LSBs with NiSe-Ni2P/C modified PP separators exhibit a remarkable high initial CE of 97.0% and a substantial discharge specific capacity of 1205.4 mAh gs−1. Even under conditions of a high sulfur loading (4.3 mg cm−2) and a limited electrolyte dosage (10 μL mgs−1), the LSBs maintained a reversible specific capacity of 804 mAh gs−1, a CE of 94%, and an energy density of 1232.1 Wh kgs−1 after 720 h of continuous cycling at 0.05 C. This work provides a solution for achieving long-time, high-capacity, and high-CE electrochemical performance in LSBs with a high sulfur loading and a limited electrolyte dosage.

Corrosion behavior of riveted joints with electrophoretic treatment in neutral salt spray environment

AbstractThis study delves into the corrosion behavior of riveted joints with electrophoretic treatment in a neutral salt spray environment using tensile test and surface analysis. The results showed that the open‐circuit potentials of the dual‐phase steels (590DP and 780DP) exceeded those of the AlSi10MnMg‐T7 and JDA1b die‐casting aluminum alloys by 100 mV, and exceeded that of the AA6063‐T6 extruded aluminum alloy by 50 mV. AlSi10MnMg‐T7 and JDA1b die‐casting aluminum alloys were more susceptible to corrosion in contrast to the AA6063‐T6 extruded aluminum alloy. The corrosion mechanism of the steel/aluminum riveted joints was not only galvanic corrosion but also oxygen concentration polarization. Over the 720‐h corrosion period, the failure loads of the riveted joints were not reduced at all. On the contrary, they increased at least 17% for the two‐sheet self‐piercing riveting (SPR) joints, 6% for the three‐sheet SPR joints, and 4% for the flow drill screw joints.

Process optimization of osmotic membrane distillation for the extraction of valuable resources from water streams

The rising demand for sustainable wastewater management and high-value resource recovery is pressing industries involved in, e.g., textiles, metals, and food production, to adopt energy-efficient and flexible liquid separation methods. The current techniques often fall short in achieving zero liquid discharge and enhancing socio-economic growth sustainably. Osmotic membrane distillation (OMD) has emerged as a low-temperature separation process designed to concentrate valuable elements and substances in dilute feed streams. The efficacy of OMD hinges on the solvent’s migration from the feed to the draw stream through a hydrophobic membrane, driven by the vapor pressure difference induced by both temperature and concentration gradients. However, the intricate interplay of heat and mass processes steering this mechanism is not yet fully comprehended or accurately modeled. In this research, we conducted a combined theoretical and experimental study to explore the capabilities and thermodynamic limitations of OMD. Under diverse operating conditions, the experimental campaign aimed to corroborate our theoretical assertions. We derived a novel equation to govern water flux based on foundational principles and introduced a streamlined version for more straightforward application. Our findings spotlight complex transport-limiting and self-adjusting mechanisms linked with temperature and concentration polarization phenomena. Compared with traditional methods like membrane distillation and osmotic dilution, which are driven by solely temperature or concentration gradients, OMD may provide improved and flexible performance in target applications. For instance, we show that OMD—if properly optimized—can achieve water vapor fluxes 50% higher than osmotic dilution. Notably, OMD operation at reduced feed temperatures can lead to energy savings ranging between 5 and 95%, owing to the use of highly concentrated draw solutions. This study underscores the potential of OMD in real-world applications, such as concentrating lithium in wastewater streams. By enhancing our fundamental understanding of OMD’s potential and constraints, we aim to broaden its adoption as a pivotal liquid separation tool, with focus on sustainable resource recovery.

Fast-charging aqueous batteries enabled by a three-dimensional ordered Zn anode at deliberate concentration polarization.

A finely controlled concentration polarization environment was deliberately created to fabricate a three-dimensional ordered Zn metal anode with (002)-dominated planes, which enabled a high-rate aqueous Ni-Zn pouch cell with a high discharge capacity of 187.3 mA h g-1 at 50 C, and a capacity retention of 94.7% and an average Coulombic efficiency of 99.8% for 500 charge/discharge cycles.

Industrial-scale 61-channel monolithic silicalite-1 membranes for butane isomer separation

Developing energy-saving membrane and technology is important for the separation of hydrocarbon isomers to replace the energy-intensive distillation. Silicalite-1 membrane is a promising membrane material but difficult to be scaled up. In this work, separation performance of industrial-scale monolithic silicalite-1 membranes in term of actual butane mixtures has been reported for the first time. Each 61-channel monolithic membrane has effective area and surface-to-volume ratio of 0.2 ​m2 and 400 ​m2/m3, which are about 20 and 5.6 times higher than that of the common tubular one with the same length, respectively. Average n-butane/i-butane separation factor (34) of the industrial-scale membranes was even higher than or comparable to that of the reported small-area zeolite membranes. The influences of test parameters on permeances and separation factors of the membranes and the long-term stability were examined. Reynold numbers was used to correlate the concentration polarization (CP) with the reduction of separation performance. A solution was proposed to reduce the effect of CP. It suggests that the industrial-scale and high-performance monolithic silicalite-1 membranes are suitable for actual applications of butane separation.

Multiscale study of the chiral self-assembly of cellulose nanocrystals during the frontal ultrafiltration process.

The structural organization of cellulose nanocrystal (CNC) suspensions at the membrane surface during frontal ultrafiltration has been characterized, for the first time, at the nano- and microscale by in situ small-angle X-ray and light scattering (SAXS and SALS, respectively). During filtration, the particles assembled at the membrane surface and formed the so-called concentration polarization layer (CPL), which contains CNCs arranged in a chiral nematic (cholesteric) helicoidal structure, with the long axis of the CNCs oriented parallel to the membrane surface, and the helical axis of the cholesteric structure oriented perpendicular to the membrane surface. The self-organization of CNCs in the form of oriented cholesteric structures was further characterized by a pitch gradient in the CPL. The structure of the CPL was also investigated upon release of the transmembrane pressure. SAXS data revealed a relaxation process associated with a diffusion of the CNCs from the membrane surface towards the bulk, while SALS measurements revealed a re-organization of the cholesteric phase that was preserved all along the deposit. The preservation of the observed structure after 14 days of continuous filtration followed by air-drying was confirmed using scanning electron microscopy and wide-angle X-ray diffraction, demonstrating the feasibility of the process scale-up.