Concentration Polarization Research Articles

Effects of porous supports and binary gases on hydrogen permeation in Pd–Ag–Y alloy membrane

This study investigates the effects of various porous supports and the presence of additional gases in the feed on hydrogen permeation using an unsupported Pd82–Ag15–Y3 membrane. The pore sizes and thicknesses of metallic supports varied from 1 to 270 μm and 50–3000 μm, respectively. The membrane was unsupported, synthesized by cold-rolling, and characterized by a thickness of 38 μm. The tests were performed at 400 °C with pressures ranging from 1.4 to 3 bar. Results showed that the unsupported Pd82–Ag15–Y3 membrane reached 12 % and 267 % higher hydrogen permeation than the supported membrane by 1 μm pore size and 50 μm thick woven mesh, and 1 μm pore size and 3 mm thick of porous stainless steel (PSS), respectively. The unsupported Pd82–Ag15–Y3 membrane showed one of the highest hydrogen permeability in the literature (7.5 × 10−8 mol m−1 s−1.Pa−0.5 at 400 °C). However, the presence of porous supports used to enhance the mechanical stability of the membrane negatively affected the hydrogen permeation due to mass transfer limitation. In addition, the presence of supports induced an unreal ‘n’ value for the Pd-based membrane, where the ‘n’ value is the exponent of the driving force in the equation of hydrogen transport, varying between 0.5 and 1. In particular, for the unsupported membrane, the ‘n’ value was 0.6, but it increased to 0.7 and 0.8 when supports with 1 μm pore size and 50 μm thick and 5 μm and 80 μm thick were utilized. Binary hydrogen permeation tests were also performed in the presence of N2, CH4, CO2, and CO at 400 °C by using unsupported and supported membranes to investigate the reduction in hydrogen permeation flux due to the effect of the supports plus the effect of the presence of other gas. The results revealed that CO had the highest inhibition effect for all the unsupported and supported membranes tested due to competitive adsorption on the surface. No superficial adsorption on the membrane was observed for N2, CH4, and CO2 during permeation, and they inhibited hydrogen permeation mainly due to depletion, dilution, and concentration polarization. The PSS_1–3000 indicated the lowest hydrogen permeation between the gas mixture and the porous support, whereas the presence of 40 % of the binary gas mixture had lower hydrogen permeation than porous support except for the PSS.

Population Distribution in Guizhou’s Mountainous Cities: Evolution of Spatial Pattern and Driving Factors

Guizhou is a typical mountainous province and is also one of the lowland regions in China that has attracted a population influx. Here, using population density data from 2000 to 2020 as the basic dataset and the coefficient of variation method and standard deviation ellipse analysis, we investigated the spatial characteristics across different years. The results show: Firstly, Guizhou’s population has a distinct spatial distribution, characterized by a lower population density in the southeast and a higher density in the northwest as well as an increasing polarization of population concentration toward the centers of prefecture-level cities and provincial capitals. Fluctuations in population density resemble a central siphon effect, which is particularly pronounced in the provincial capital and show a significant gravitational pull. Secondly, the coefficient of variation in population density across Guizhou’s counties is spatially divided by Guiyang, showing higher values in the east and lower values in the west. Furthermore, the ellipse of the standard deviation of population density is gradually shrinking, indicating an increasingly concentrated population distribution. Thirdly, the explanatory power of the population and socio-economic systems on the population distribution in Guizhou is significantly greater than that of the natural systems. Population distribution and migration patterns have shifted from purely “economic driven” to coexisting with “economic and comfort-oriented” trends, and there is an urgent need to improve the comfort level of public services as a typical supply, in order to boost Guizhou’s population attraction.

Optimising the effectiveness of osmotic desalination process by using graphene-based nanomaterials

This work examines how graphene-based nanoparticles can be integrated into membranes to improve the effectiveness of water treatment in osmotic desalination processes. This is important since sustainable practices can help address the world's water scarcity. Water treatment, desalination, and resource recovery are areas where osmotic desalination shows great potential. However, membrane performance constraints frequently impede its efficacy. High mechanical strength, superior hydrophilicity, and the ability to lessen internal concentration polarisation are just a few of the remarkable qualities that make graphene-based nanoparticles stand out. In order to increase the membranes' overall functionality, these nanoparticles were created and added to them. Comparing the study to conventional membranes, the main goals were to increase water flux rates and salt ion rejection capacities. It was shown by experimental results that the membranes strengthened with graphene-based nanoparticles performed better. They outperformed conventional membranes in terms of water flow growth and salt ion rejection rates improvement. In order to advance osmotic desalination technologies towards more effective and sustainable water treatment options, this study highlights the revolutionary potential of graphene-based nanoparticles. Graphene-based nanoparticles provide an attractive option for tackling major water issues worldwide by improving membrane characteristics that are essential for osmotic desalination, such as permeability and selectivity. Water management techniques that are environmentally sustainable are supported by their integration into membranes, which also enhances performance metrics. This study opens the door for creative approaches to resource recovery and water treatment by providing important insights into the creation of cutting-edge materials specifically designed for osmotic desalination applications.

A comprehensive analysis of the advantages and disadvantages of pulsed electric fields during soil electrokinetic remediation

AbstractSoil electrokinetic remediation (SEKR) is considered an effective method for removing pollutants by integrating chemical, physical, and biological treatments. It has multiple applications in fields such as dewatering, consolidation, sedimentation, seed germination, etc. This work builds upon a series of recent publications on SEKR, covering topics like electrode approaches, reverse polarity-based SEK, SEK design modifications, installation of perforated materials, and chemical-based SEK. This review focuses on the role of pulsed electric field (PEF) in enhancing the performance of SEKR. There are several other names for the PEF, including periodic, interval, “ON” and “OFF”, intermittent, and breaking electric fields. PEF is proposed as a solution to overcome certain obstacles in SEKR. The review evaluates PEF's impact on (a) remediating organic and inorganic hazards, anions, and salt, (b) integrating with other processes (reverse polarity, phytoremediation, and bioremediation), and (c) electro-dewatering and consolidation. PEF offers several advantages, such as reducing energy consumption, converting the residual fractions into weakly bound fractions, achieving satisfactory remediation, avoiding the voltage drop in the area across the cation exchange membrane, enhancing desorption and/or migration of charged species, permits the exchange of contaminant from solid to the liquid phase (interstitial fluid), allows contaminant diffusion through the soil pores during the off time, generate high electroosmotic flow, avoiding electrode corrosion, decreasing concentration polarization, etc. However, it may also prolong the remediation period and cause contaminant diffusion through the soil pores, which are considered obstacles for SEKR. This review also describe different techniques related to PEF and highlights the potential use of solar cells as a renewable energy source for SEKR. Graphic abstract

In Situ Synthesized HOF Ion Rectification Membrane with Ultrahigh Permselectivity for Nanofluidic Osmotic Energy Harvesting

AbstractThe utilization of salt concentration gradients as a renewable energy source represents a pivotal solution to the energy crisis. However, it is a persistent challenge to fabricate high‐performance ion permeable membranes with excellent ion permselectivity. In this work, hydrogen‐bonded organic framework (HOF) is in situ growth on anodic aluminum oxide (AAO) via chemical‐binding and solution‐processing strategy. The hydrogen bonding and π–π interactions forming the porous structure and the internal unprotonated carboxyl groups endow the HOF with superior cation selectivity and ion permeability. Furthermore, benefiting from the remarkable asymmetry of the prepared nanofluidic membrane arising from structure and charge of AAO and HOF, the HOF/AAO presents outstanding ion current rectification (ICR) characteristic, which can eliminate the ion concentration polarization (ICP) and power loss. Therefore, an impressive output power density with 500‐fold NaCl gradient is achieved as 75.2 W m−2 using the as‐prepared HOF/AAO, which is superior to most of reported membranes (7.0–40.0 W m−2). To show the critical role of HOF, 2D and 3D MOF with the same monomers are also synthesized, achieving decreased power densities of 36.2 and 58.3 W m−2 respectively. The present work provides a novel strategy to develop high‐performance nanofluidic ICR membranes for osmotic energy harvesting.

Study on the impact of active intake air fluctuation on the performance and mass transfer of PEM Fuel Cell

Enhancing mass transfer is imperative for mitigating concentration polarization and thereby optimizing fuel cell performance. This study presents numerical investigation to explore the performance of a proton exchange membrane fuel cell, which involves implementation of actively controlled fluctuating mass fluxes at cathode inlet in order to achieve desirable mass transfer enhancement. The trajectories of liquid droplets within channel were predicted by employing volume of fluid method. The results revealed that the current density exhibits frequency-dependent fluctuations, aligning with input oscillations. A marginal increase in mean current density was observed with frequency amplified and the maximum power density with fluctuated flow increased by 3.9 % compared to that with steady flow inlet. A noteworthy and linear augmentation was evident with amplitude escalation. The mean current density surpassed 34.7 % of the steady current at the amplitude of 10. Beyond a frequency threshold of 1000 Hz, the fluctuating current density surpassed that of steady flow throughout the entire period, attributed to the time constant of gas transport within the gas diffusion layer. Moreover, fluctuation phenomenon of the pressure field within the fuel cell channel, which contributed to reinforced mass transfer and accelerated product alleviation in the region facing bipolar rib was identified during gas transport in the gas diffusion layer. Numerical simulations adopting the volume of fluid method revealed a heightened tendency for the disintegration and expulsion of liquid droplets in the channel attributable to fluctuating flow.

Development of charged membranes for the ultrafiltration of siRNA

RNA interference (RNAi) is an exciting new therapeutic approach, using small interfering RNA (siRNA) to silence specific genes for treating various diseases. Ultrafiltration has been widely used for the concentration and purification of monoclonal antibodies and other biotherapeutics; however, its application in the downstream processing of double-stranded oligonucleotides remains underexplored. This study investigates the use of ultrafiltration in the final formulation for concentrating a siRNA drug substance. Initial experiments were conducted with Ultracel™ composite regenerated cellulose membranes over a range of molecular weight cutoffs (MWCO) at different siRNA feed concentrations. Results demonstrated significant effects of both fouling and concentration polarization, with the maximum achievable concentration falling well below the target required for subcutaneous injection. Novel surface-modified ultrafiltration membranes were made by reaction of the cellulose with bromopropanesulfonic acid. These negatively charged membranes showed improved siRNA retention, reduced fouling, and a large increase in the maximum achievable siRNA concentration (from 52 to >180 mg/mL). These findings offer critical insights into novel approaches for developing high performance ultrafiltration processes for siRNA concentration.

Development of a local wall concentration model for the design of single pass tangential flow filtration (SPTFF) systems with viral vector surrogates

Recent advances in the use of viral vectors for gene therapy has created a need for efficient downstream processing of these novel therapeutics. Single-pass tangential flow filtration (SPTFF) can potentially improve final product quality via reductions in shear, and it can increase manufacturing productivity via simple implementation into continuous/intensified processes. This study investigated the impact of variations in pressure and flow rate along the length of the membrane on overall SPTFF performance. Constant-flux filtration experiments at feed fluxes from 14 to 420 L/m2/h (Reynolds numbers <20) were performed using Pellicon® 3 TFF cassettes with fluorescent nanoparticles as model viral vectors. The location of nanoparticle accumulation shifted towards the filter outlet at high conversion and was also a function of the permeate flow configuration. These phenomena were explained using a newly developed concentration polarization model that predicts the distribution in local wall concentration over the length of the membrane. The model accurately captured the observed nanoparticle accumulation trends, including the effects of the permeate flow profile (co-current, divergent, or convergent flow) on nanoparticle accumulation within the SPTFF module. Nanoparticle accumulation at moderate conversion was more uniform using convergent flow, but nanoparticle accumulation at 80 % conversion (5x concentration factor) can be minimized using a divergent flow configuration. The local wall concentration model was also used to evaluate the critical flux by assuming that fouling occurs when the nanoparticle concentration at any point along the membrane surface exceeds 15 % by volume. These results provide important insights for the design and operation of SPTFF technology for inline concentration of viral vectors.

An innovative 3D wave channel design for boosting the dynamic response of proton exchange membrane fuel cell stack

The dynamic response of proton exchange membrane fuel cell (PEMFC) is a crucial metric for evaluating these systems in vehicular applications. The forced convection effect can significantly enhance the dynamic response capabilities of proton exchange membrane fuel cells. In this study, we propose the application of the forced convection effect within a parallel flow field. This approach retains the advantages of low pressure drop at the inlets and outlets of the parallel flow field and facilitates rapid distribution of reaction gases, while simultaneously enhancing the dynamic response of actual PEMFC stacks without compromising drainage efficiency. we propose an innovative 3D wave channel design for PEMFC. Specifically, we design and assemble a stack optimized for performance. The proposed design is tested against the traditional 2D straight channel stack, with the 3D wave channel stack demonstrating an increase in peak power density by 8.05% to 33.92% across a relative humidity range of 20% to 100%. This novel design outperforms the 2D straight channel design in terms of gas distribution uniformity, and enhancedmass transfer to the diffusion layer, as well as reduction of concentration polarization in the PEMFC. It also enhances self-humidification under low humidity conditions. Most importantly, the 3D wave channel stack exhibits a superior dynamic response, with voltage fluctuations after current loading being 74.36% to 91.15% lower than those of the 2D straight channel stack. Furthermore, the 3D wave channel stack maintains superior voltage stability under starvation conditions. The findings from this study contribute significantly to optimizing the dynamic response capability of PEMFC systems, highlighting the potential of the 3D wave channel design in enhancing PEMFC performance.

Study of interfacial competitive distribution and synergistic permeation in nanofiltration separation of Salvia divinorum acids from the aqueous extract

The contact between solution and membrane during nanofiltration separation produces the interfacial layer fluid, and the competitive distribution laws of solutes in the interfacial layer are difficult to be analyzed, giving rise to diversified separation results that are challenging to explain using traditional nanofiltration separation theory. Four Salvia divinorum phenolic acid components—sodium salvinorin, protocatechuic aldehyde, rosmarinic acid, and salvianolic acid B—which have gradient relative molecular masses and dissociation constants, were selected as the objects of study. The nanofiltration separation parameters, such as membrane flux and permeation rate of the Salvia divinorum phenolic acids and their variability with the monomer solution under the complex solution environment were systematically analyzed. Based on the correlation between the concentration of the interfacial layer and the initial concentration, membrane flux and mass transfer coefficient in the theory of concentration polarization, the concentration of the interfacial layer of the nanofiltration membrane was calculated. This was combined with the state of association characterized by the distribution of particle sizes in the solution, the research model based on the ‘Associative State-Interfacial Competition-Separation Behavior’ was constructed, and the competitive and synergistic membrane separation regulations of the constituents of salvia phenolic acids were clarified. In acidic solutions, van der Waals forces dominate the interfacial competition, and of the four phenolic acids, salvinorin acid B diffused most easily to the membrane surface, showing that the component with the larger relative molecular mass inhibited the penetration of the smaller component; In alkaline solution, Coulomb force and Van der Waals force together dominate the interfacial competition, and the more acidic sodium salvinorin, etc., would preferentially react with hydroxide. At the same time, combined with the feature that the more molecular states in the particle size distribution of the solution are more likely to form aggregates, it was proven that the dissociation of protocatechuic acid aldehyde was inhibited, and its molecular state was more complete. It was shown that the more acidic sodium salvinorin and others facilitated the less acidic protocatechuic aldehyde to pass through the membrane.

Comparison and optimization of electrochemical and thermal performances of SOFC with different configurations of a metal foam flow field

The effects of different configurations of a metal foam flow field on current density and temperature gradient of a single channel solid oxide fuel cell (SOFC) are investigated, and the overall performance of the optimum configuration is optimized. First, model A (conventional channel-rib flow field) is compared with three different configurations (i.e., model B with metal foam flow field only at anode, model C with that only at cathode, and model D at both). Although model C achieves the highest current density, its temperature is also fairly high. Although model B achieves the lowest temperature gradient, its current density is also fairly low. Model D performs well in both current density and temperature gradient. Then, the effect of electrode thickness and metal foam thickness on the performance of model D is investigated. The Ohmic polarization of model D remains almost constant with different electrode thicknesses, and its concentration polarization decreases as the electrode thickness decreases, which is totally different from the channel-rib flow field. Moreover, a thinner cathode causes lower activation overpotential, whereas a thinner anode causes higher activation overpotential. In general, a thick anode, a thin cathode, and thin metal foam can maximize the current density of model D, while a thick electrode and metal foam can always reduce the temperature gradient. Finally, the Taguchi method and gray relational analysis are used to optimize the current density and temperature gradient of model D. The current density of an optimized model is 3.27% higher than that of the original model with a temperature gradient of 9.05 K/cm.

Developing high-flux dense Janus membrane with robust wetting and scaling resistance: A systematic comparison with Omniphobic membranes

Membrane wetting, scaling and low flux are challenging obstacles for membrane distillation (MD). However, the lack of advanced membranes capable of achieving both high flux and high wetting/scaling resistance constrains MD potential applications. Herein, a dense Janus membrane (JM) was facilely developed by co-depositing a dense PVA/PDA layer on a highly porous PTFE substrate to overcome this dilemma and systematically compared with omniphobic PTFE substrates with varied pore sizes for the first time. Results showed that, unlike flux-resistance “trade-off” observed for PTFE substrates, dense JM effectively resisted 0.4 mM SDS at a high flux of 56.8 LMH and retarded membrane scaling by 20 mM oversaturated gypsum. Robust wetting resistance was primarily attributed to the sieving effect of the sub-nanometer surface layer, which greatly protected substrate from SDS adsorption and feed intrusion, and was less affected by severe surface concentration polarization and relatively low substrate LEP than PTFE substrates. Strongly polar PVA/PDA layer provided a much more thermodynamically unfavorable continuous interface for gypsum adhesion than PTFE substrates, which played a key role in determining anti-scaling behavior. In contrast, gypsum still tended to rapidly cause membrane scaling in stagnant zones within PTFE substrates when flux was increased. This study shall provide new insights in designing high-performance membranes for robust hypersaline wastewater treatment, and highlighting dense JMs with a macroporous substrate and a highly hydrophilic dense surface layer as ideal alternatives.

A Carrier Phase Ultrafiltration and Backflow Recovery Technique for Purification of Biological Macromolecules.

A simple carrier phase based ultrafiltration technique that is akin to liquid chromatography and is suitable for medium-to-large volume sample preparation in the laboratory is discussed in this paper. A membrane module was integrated with a liquid chromatography system in a "plug and play" mode for ease of sample handling, and recovery of species retained by the membrane. The sample injector and pump were used for feed injection and for driving ultrafiltration, while the sensors and detectors were used for real-time monitoring of the separation process. The concentration of retained species was enriched by utilizing controlled concentration polarization. The recovery of the retained and enriched species was enhanced by backflow of carrier phase through the membrane using appropriate combination of valves. The backflow of carrier phase also cleaned the membrane and limited the extent of membrane fouling. Proof-of-concept of the proposed technique was provided by conducting different types of protein ultrafiltration experiments. The technique was shown to be suitable for carrying out protein fractionation, desalting, buffer exchange and concentration enrichment. Adoption of this approach is likely to make ultrafiltration easier to use for non-specialized users in biological research laboratories. Other advantages include enhanced product recovery, significant reduction in the number of diavolumes of buffer needed for conducting desalting and buffer exchange, minimal membrane fouling and the potential for repeated use of the same module for multiple separation cycles.

Conformal coating of PbO2 around boron doped diamond coated carbon felt positive electrode for stable and high-capacity operation of soluble lead redox flow battery

The commercialization of soluble lead redox flow battery (SLRFB) is challenging due to its limited cycle life, lower areal capacity, Pb dendrite formation, and positive electrode corrosion. However, improvements are made to a certain extent by employing additives chemistry in terms of electrolyte modification. One of the major problems in SLRFB is carbon corrosion at higher current densities. Therefore, electrode modification, specifically on the positive side, is required to improve the cyclability of SLRFB further. There is minimal literature on this aspect.Given this, efforts are being made to enhance the electrochemical performance of SLRFB by employing a boron doped diamond (BDD) coated carbon felt (CF) as the positive electrode. The BDD coated CF electrode possesses a high surface area (7.1 m2g−1) compared to bare CF (0.6 m2g−1), i.e., BDD creates porous morphology, which enables a high mass transfer and hence reduces concentration polarisation. BDD coating on the CF delays the OER and reduces the overpotential for PbO2 deposition/dissolution. The cell with BDD coated CF electrode is successfully cycled for >300 charge/discharge cycles @ 40 mA cm−2 with average coulombic efficiency (CE), voltage efficiency (VE) and energy efficiency (EE) of 97 %, 71 % and 69 % respectively. The EE is improved by 8 % in the presence of BDD coated CF as compared to CF electrode. SLRFB cell with BDD coated CF electrode has reached 80 mAh cm−2 areal capacity.

Extending the applicability of concentration polarization-enabled “click” hydrogel coating of desalination membranes

Reverse osmosis (RO) systems continually struggle with membrane fouling, leading to diminished membrane permeability and therefore elevated energy requirements. Building on prior own research, this study presents further development of an in situ antifouling coating technique for commercial RO flat sheet membranes and spiral-wound modules, deploying a concentration polarization-driven reactive (“click”) coating formation process. Utilizing this approach, zwitterionic (self-synthesized polyacrylates) and nonionic (functionalized “clickable” poly(vinyl alcohol)) coating materials were employed. Relying on comprehensive statistical analysis and the design of experiments (DOE) framework for lab-scale experiments, essential parameters that dictate the efficiency of the coating process were identified. By modulating the extent of concentration polarization, precise control over the permeance of modified membranes and spiral-wound modules was achieved. A robust correlation emerged between the relative permeance change (RPC) post-modification and the relative end permeance change (REPC) during modification. This correlation serves as basis for the real-time prediction and adjustment of final membrane performance, enabled by online flux monitoring during the modification and stopping it a preset REPC value—a relationship substantiated through extensive experiments on both lab-scale and pilot plant platforms. In performance comparisons, the modified membranes consistently surpassed unmodified variants in both selectivity and antifouling resilience. With successful upscaling to commercial TW30-2521 modules in a pilot plant setting, a significant step toward industrial readiness has been made. Overall, this work introduces a scalable, predictable, and controllable in situ coating method for RO membranes and modules that enables balancing enhanced anti-fouling functionality with preserved flux performance at uncompromised solute rejection.

Pressure retarded osmosis enhanced by micro-nano bubbles: Coupling effects of operation conditions and mass transfer resistance analyses

The concentration polarization is one of the bottlenecks of pressure retarded osmosis (PRO) for industrial-scale application. Micro-nano bubbles (MNBs) could form a strong repulsion and shear force on the membrane surface, thus, the degree of concentration polarization is reduced, and hence, both the water flux and power density could be increased. In this paper, the synergistic effects of MNBs with concentration, temperature, water and air flow rates, pressure, and spacers were investigated through membrane cell scale experiments. A numerical model with trans-membrane heat flux and MNBs effects is built and validated by the experiment results. The mechanism of strengthening effect of MNBs could be explained. A maximum promotion of 6.28 % was achieved for concentration combination of 0.171–1 mol/L. However, the promotion ratio of water flux was deceased significantly with higher temperature (<1 % for 45 °C) and higher pressure (nearly zero for 7 bar). The light MNBs would be pushed away from membrane under larger water flux with larger osmotic pressure difference. The variations of mass transfer resistances, and the thicknesses of boundary layers were discussed. Moreover, the key variables that have significant impacts on the metrics of PRO process were identified through partial least squares analysis.

Performance enhancement of vanadium redox flow battery with novel streamlined design: Simulation and experimental validation

Electrolyte utilization and the consequent concentration polarization significantly limit the potential increase in power density and contribute to electrode degradation in vanadium redox flow batteries during cycling. This study investigates a novel curvature streamlined design, drawing inspiration from natural forms, aiming to enhance the performance of vanadium redox flow battery cells compared to conventional square and rectangular flow-through cell designs. The simulated 3D single-cell model shows a notably superior uniformity in both current and species' concentration distribution within the streamlined design compared to the square and rectangular shapes. Experimental analysis conducted on 3D-printed flow frames demonstrated 2 % enhanced energy efficiency and 47 % improved capacity when compared to rectangular design at 150 mA cm−2, all achieved with minimal increase in pressure drop.

An Ion-Pumping Quasi-Solid Electrolyte Enabled by Electrokinetic Effects for Stable Aqueous Zinc Metal Batteries.

The practical application of aqueous zinc (Zn) metal batteries (ZMBs) is hindered by the complicated hydrogen evolution, passivation reactions, and dendrite growth of Zn metal anodes. Here, an ion-pumping quasi-solid electrolyte (IPQSE) with high Zn2+ transport kinetics enabled by the electrokinetic phenomena to realize high-performance quasi-solid state Zn metal batteries (QSSZMBs) is reported. The IPQSE is prepared through the in situ ring-opening polymerization of tetramethylolmethane-tri-β-aziridinylpropionate in the aqueous electrolyte. The porous polymer framework with high zeta potential provides the IPQSE with an electrokinetic ion-pumping feature enabled by the electrokinetic effects (electro-osmosis and electrokinetic surface conduction), which significantly accelerates the Zn2+ transport, reduces the concentration polarization and overcomes the diffusion-limited current. Moreover, the Zn2+ affinity of the polymer and hydrogen bonding interactions in the IPQSE changes the Zn2+ coordination environment and reduces the amount of free H2O, which lowers the H2O activity and inhibits H2O-induced side reactions. Consequently, the highly reversible and stable Zn metal anodes are achieved. The assembled QSSZMBs based on the IPQSE display excellent cycling stability with high capacity retention and Coulombic efficiency. The high-performance quasi-solid state Zn metal pouch cells are demonstrated, showing great promise for the practical application of the IPQSE.

Forward osmosis for concentrating lithium-enriched brine: From membrane performance to system design

Using concentrated salt-lake brine as the draw solution (DS), forward osmosis (FO) has been proposed as the low carbon footprint concentration technology for extracting water from lithium-enriched brine. From membrane modules to a process, there exist tremendous risks when considering total cost in time and investment for a trial. To address this issue, a bridge between the FO membrane/ module characteristics and a FO system design is highly desirable. This study for the first time developed a system design model using hollow fiber (HF) FO membrane modules for FO concentration of lithium-enriched brine. The concentration polarization along the module, the membrane structural parameters (S), crossflow velocity, and DS concentration were the main factors considered in the model. The effect of all factors on module water flux and total membrane area was systematically investigated for a typical industrial output of 10 k ton of Li2CO3. A master curve of the water flux verse feed concentration for the tailor-made HF modules was utilized as the basis. On a module scale, the structural parameter S is of first importance and indicates requirement of FO membranes with low S. The crossflow velocity has relatively small impact to the membrane area, but not negligible. On a system scale, the empirical equation of the structural parameters and crossflow velocity on the theoretical minimum system membrane area was summarized. The results show that increasing the stages can reduce the number of modules and required DS flow. Increasing DS dilution rate in system design efficiently utilizes the osmotic pressure of DS. The present model serves as a practical solution for process optimization and FO membrane selection. The methodology is valuable for other FO applications using HF FO membranes.

Investigating Li-Ion Depletion during Fast Charging with Operando FTIR

Lithium-ion concentration polarization and slow ionic transport in the electrolyte phase hinder fast charging of electric vehicle batteries and can cause cell degradation. Although pseudo-2D (P2D) models capture concentration polarization phenomena during fast charging, experimental measurements of Li-ion concentration in the electrolyte phase have been limited. In this research, Fourier transform infrared spectroscopy (FTIR) and attenuated total reflection (ATR) were used to collect operando optical measurements of Li-ion concentration in a high-loading graphite/NMC811 full cell with 1.2M LiPF6 in 3/7 (wt./wt.) ethylene carbonate (EC)/ethyl methyl carbonate (EMC). For this research, an optically accessible operando battery was developed that enables real-time measurements of Li-ion concentration at the back of the graphite anode near the current collector. Significant Li-ion concentration changes up to 0.5M were observed during charging at 1C, 2C, and 3C, as well as discharging at C/2, and compared with a P2D model. Both the model and the experiments showed Li-ion depletion and sinuous fluctuations at the graphite/current collector interface that indicate non-ideal behavior. These gradients likely develop due to insufficient electrolyte transport properties. This research enables novel Li-ion concentration measurements with FTIR. This research also validates P2D model physics for measuring and analyzing Li-ion concentration polarization at fast charging rates.