Concentration Polarization Research Articles

HighlightsElectrochemical phase-field model.Concurrent electrochemical reaction, heat transfer, separator thermal deformation.Dependence of dendrite descriptors on separator thermophysical parameters.Thermal conductivity, thermal deformation, and thermal shutdown of separator.

The effects of pretreatment pH value, operating pressure, and concentration factors on the performance of nanofiltration membrane concentration and the recovery of phosphorus-containing wastewater were systematically studied. A novel pretreatment strategy using solid sodium hydroxide was developed to adjust the feed solution pH, achieving optimal solid removal and minimized conductivity at pH = 5. Unlike conventional calcium-based methods, this approach avoids excessive chemical sludge formation and mitigates membrane scaling, enhancing system stability. Experimental results demonstrate that both phosphorus rejection and desalination efficiency are significantly influenced by feed solution pH, operating pressure, and concentration ratio. While increasing pH and pressure improve total phosphorus (TP) rejection and desalination rates, these benefits are accompanied by reduced membrane flux due to elevated osmotic pressure and intensified concentration polarization. The membrane exhibited optimal performance at a feed pH of 5 and an operating pressure of 3 MPa, with sustained flux and enhanced separation efficiency. Under these conditions, when the wastewater was concentrated fivefold at 25 °C, the TP rejection rate and desalination efficiency reached 92.9% and 91.8%, respectively.

We demonstrate how magnetic nanoparticles, through field-induced chaining and the resulting non-Newtonian magnetorheological behavior, substantially modulate ion concentration polarization in converging microchannels. Rather than direct magnetic trapping, it is the altered fluid rheology under applied magnetic fields that governs the extent of depletion and enrichment.. A coupled Poisson-Nernst-Planck and Navier-Stokes model was extended with a Bingham-like constitutive law to capture non-Newtonian rheology. Simulations reveal that the electric force to viscous force parameter C1, inverse of bulk concentration parameter C2, MR coupling parameter C3 and transport parameter Pe jointly regulate enrichment. For Newtonian fluids, the enrichment factor (EF) saturates at EF ≈ 3, whereas MR fluids exhibit up to a 3-fold enhancement (EF ≈ 10) at high C3. Mesh refinement and enrichment-window sensitivity tests indicate numerical uncertainties of 5-7%. These results demonstrate how magnetic-field-tunable rheology can synergistically amplify ICP-based preconcentration, offering a strategy to design next-generation microfluidic enrichment platforms.

Electrocatalysis is a powerful approach to accelerate sulfur redox kinetics in lithium-sulfur (Li-S) batteries. However, in practical high sulfur loading and thick cathodes, the severe concentration polarization induced by the rapid depletion of local lithium ions (Li+) greatly restricts catalysis and battery performance, representing an engineering challenge in a closed microelectrochemical reactor. Here, an electrolyte-dispersible Li+-reservoir catalyst is proposed to sustain the local Li+ concentration to ensure the continuous electrochemical reaction in the battery with an energy density of over 400 Wh kg-1. Such a catalyst is realized by anchoring single cobalt atoms onto uniformly dispersed carbon quantum dots (Co-CQD). The negatively charged CQD strongly attracts and enriches Li+ around the Co catalytic sites by robust electrostatic interactions, ensuring a continuous Li+ supply during the catalytic reactions. Moreover, Co-CQDs are homogeneously dispersed in the electrolyte and distributed in thick electrodes, promoting bulk-phase Li+ distribution and effectively eliminating concentration polarization. As a result, this strategy lowers the sulfur conversion activation energy in thick cathodes from 1.27 to 0.72 eV and enables the battery to maintain a high reversible capacity of 13.5 mAh cm-2 under a high sulfur loading of 13 mg cm-2, outperforming conventional catalysts under identical conditions. Moreover, an Ah-level pouch cell delivers a high energy density of 513 Wh kg-1, offering a scalable strategy to overcome ion transport bottlenecks in thick cathodes for practical Li-S batteries.

Seawater desalination is a key technological approach to address the global problem of water scarcity. Spacers in water treatment membrane modules play a critical role in the water treatment process. The use of a spacer improves fluid dynamics, enhances heat and mass transfer efficiency, and effectively mitigates concentration polarization, reduces fouling risks, and increases the long-term operational stability of the system as a whole. Although numerous novel spacer designs have been proposed in recent years, their large-scale commercialization still faces significant challenges. This review summarizes the critical strategies for improving hydraulic performance, mitigating scaling issues, and enhancing heat and mass transfer performance of spacers. It focuses on structural innovations that aim to optimize spacer performance and meet the diverse demands of various desalination methods. On the basis of a comprehensive analysis of spacer performance in typical application scenarios, it summarizes the limitations of current research, identifies future research directions, and highlights the potential of novel spacer designs to improve desalination efficiency. This review enhances understanding of the role of spacers in desalination systems and offers new research directions for future developments in seawater desalination technology.

This paper presents a novel batch Forward Osmosis (FO) process for hydropower generation. It focuses on analyzing the parameters needed to make the proposed osmotic power plant implementable with currently available technology. Starting from the solution–diffusion model and using flow and mass balance equations, the equations that describe the behavior of the system over time are obtained. Membrane orientation, concentration polarization, reverse solute flux, and membrane fouling are not considered. The equations for calculating the operation time for the charging and discharging stages are obtained. Also, an equation for calculating the required membrane area to make the duration of the two stages the same is obtained. The results indicate that a volume of approximately 30.4 m3 discharging through a 0.84 inch diameter outflow jet towards a turbine could generate an energy of 25 kw·h. The discharging stage would take 12 h, and with a membrane with a water permeability constant Am=1.763·10−12 m/(s·Pa), the charging stage would require a membrane superficial area Arm=1·104 m2 to have the same duration. The proposed osmotic power plant, whose working principle is based on volume change over time, contrary to pressure retarded osmosis, whose working principle requires expending energy to extract energy from the salinity gradient, could deliver greater net produced energy with comparatively lower operational costs as it does not require high-pressure pumps or energy recovery devices as are required in pressure-retarded osmosis. The use of several tanks that charge and discharge alternatively can make the system generate energy as if it were a continuous process.

Rejection of geosmin and 2-methylisoborneol by polyamide membranes in drinking water treatment: Performance-energy efficiency evaluation and practical implications.

The potential of reverse electrodialysis for harvesting osmotic energy is severely limited by ion concentration polarization (ICP), a phenomenon that restricts power output and confines the technology to the laboratory scale (< 0.4 µW). This challenge is overcome with an ionic liquid confined porous MXene (IPM) system that integrates strategies across two scales. At the microscopic level, sub-nanometer channels are engineered using porous MXene and confined ionic liquids to reduce mass transfer resistance and optimize ion transport. Concurrently, at the macroscopic level, a micropore array design spatially decouples the diffusion interfaces to effectively suppress the ICP effect. This dual-scale approach increases power density by 53.6% and achieves a maximum output power of 3.47 µW, which is nearly ten times higher than that of similar work. The work demonstrates a robust pathway for overcoming critical power limitations, advancing osmotic energy conversion toward industrial renewable energy applications.

The purification and treatment of water have assumed greater significance in the context of sustainable development. Nevertheless, the conventional theory of concentration polarization inherently imposes constraints on the effective regulation and precise manipulation of ionic transport for electrochemical-based technology. In this work, we propose an extraordinary concentration enrichment mediated by a line charge down to tens of micrometers, allowing continuous extraction in shear flow. The spatiotemporal evolution of the solute concentration is experimentally observed under various applied voltages and flow rates in a microfluidic-based electrochemical device. Through numerical simulations and scaling analysis, we elucidate the trade-offs between key physical parameters to optimize enrichment performance. Furthermore, we demonstrate the cation separation in multicomponent electrolytes and the effective removal of plastic particles and cells in solutions. This portable water purification concept may extend options for drinking water access in disaster response or infrastructure-constrained environments.

Membrane distillation crystallization (MDCr) is an approach for treating hypersaline wastewaters and enabling zero-liquid-discharge (ZLD) systems. However, its performance is often inhibited by concentration polarization, scaling, and membrane wetting. Heterogeneous seeding has been proposed to shift crystallization into the bulk phase, yet its quantitative influence on flux stability, wetting resistance, and crystal growth remains poorly understood. This study investigates air-gap MDCr (AGMDCr) of 300 g L−1 NaCl using polypropylene (PP) and polytetrafluoroethylene (PTFE) membranes under seeded and unseeded conditions. Introducing 0.1 g L−1 SiO2 seeds (30–60 µm) enhanced steady-state permeate flux by 41% and maintained salt rejection ≥ 99.99%, indicating effective suppression of wetting. Seeding shifted the crystal size distribution from fine (mean 50.6 µm, unseeded) to coarse (230–340 µm), consistent with reduced primary nucleation and preferential growth on seed surfaces. At 0.6 g L−1, the flux decreased relative to 0.1–0.3 g L−1, consistent with near-wall solids holdup and hindered transport at high seeding concentration. The PTFE membrane exhibited a 47% higher flux than PP, primarily due to its reduced thermal resistance and optimized module geometry at the same flow rate. These results demonstrate that appropriately sized and dosed SiO2 seeding effectively stabilizes flux and suppresses wetting in MDCr.

Abstract The aspiration for Mars necessitates the development of higher‐energy/power‐density battery systems to safeguard both planetary missions and terrestrial sustainability efforts. Li‐CO2 batteries stand out due to their ultrahigh theoretical energy density and the in situ utilization of Martian CO2 resources. However, the application prospects are constrained by limited reversible capacity and significant concentration polarization. Herein, 3D printing (3DP) technology is employed to fabricate hierarchical porous ultrathick electrodes with dual ion/gas channels, markedly optimizing CO2 mass transfer and surface reaction kinetics. Surprisingly, it achieves a record‐breaking comprehensive improvement (even over ten‐fold), including rapid charging rates (10 mA cm−2), remarkable discharge capability (386.7 mWh cm−2), and ultrahigh cyclic capacity (10 mAh cm−2). By mimic of the Martian CO2 flow as external mass transfer assistance, the areal power density can even reach up to 133 mW cm−2 at 100 mA cm−2. Meanwhile, the 3DP electrode exhibits excellent temperature tolerance (−80 to 180 °C) and can operate for over 200 Martian solar days at ‐80 °C without external heating. A proof‐of‐concept pouch cell with extraordinary energy efficiency (96.4%) proves its potential for multi‐scenario energy storage. This scalable electrode fabrication renders Mars‐capable Li‐CO2 batteries no longer just a concept.

The cycle life of aqueous zinc-ion batteries (AZIBs) is hindered by the unstable Zn anode interface, causing uncontrolled dendrite growth and side reactions. Herein, for the first time, a hierarchical nanostructure-engineered hydrogel interphase layer is developed via a facile and precisely controlled copolymerization-induced microphase separation (CIMS) strategy, which enables multi-level Zn2+-buffering to stabilize the Zn anode interface: 1) The nanoconfinement effect, combined with the hydrophobicity ofmethylacryloyloxypropyl cage-type polyhedral oligomeric silsesquioxane (MP-POSS), facilitates [Zn(H2O)6]2+ desolvation while blocking water and SO4 2- penetration, achieving an optimal balance between enhanced Zn2+ transport and minimized side reactions; 2) CIMS between polar comonomers and MP-POSS creates hierarchical molecular clusters within the hydrogel. These self-assembled domains homogenize Zn2+ flux and reduce interfacial concentration polarization, realizing dendrite-free Zn deposition. After modification, symmetric cells achieve exceptionally long lifespan exceeding 5500h (1mA cm-2) and 1500h (10mA cm-2). Asymmetric cell demonstrates an impressive Coulombic efficiency of 99.6% after 3600 cycles. MnO2 and V2O5 full cells retain 85.4% and 84.7% capacity retention after 1000 (1 A g-1) and 2000 (5 A g-1) cycles, respectively. This research unveils a novel multi-level Zn2+-buffering mechanism based on gel polymer hierarchical nanostructure engineering and provides a feasible strategy for advancing grid-scale AZIBs.

Water desalination is essential to address global water scarcity, and forward osmosis (FO) has emerged as a promising method due to its low energy demand. However, FO membrane performance is limited by internal concentration polarization and defects in the polyamide (PA) active layer when using highly porous supports. In this work, PA thin-film composite membranes were fabricated on microfiltration membrane supports modified with a sacrificial zeolitic imidazolate framework (ZIF-67) interlayer. The interlayer reduced pore size and provided a uniform reaction interface for controlled interfacial polymerization while being easily removed by water after PA formation. By tuning cobalt and imidazole concentrations, we tailored the interlayer density and its effect on PA morphology and FO performance. The optimized membrane achieved a water flux of 25.5 LMH with a reverse salt flux of 4.27 gMH (active layer facing feed). Notably, by increasing the support pore size to 450 nm, the water flux further increased to 40.1 LMH. These findings highlight the effectiveness of a removable ZIF-67 interlayer in engineering high-performance FO membranes.

This study presents a novel sustainable approach to desalination by integrating tidal energy with reverse osmosis (RO) technology, enhanced by Kenics static mixers (KSM) to improve mass transfer. A three-dimensional computational fluid dynamics (CFD) model analyzes the optimized ROKSM configuration, featuring three rows of KSM at a 30° twist angle, achieving a 1.6-fold increase in the Sherwood number (from 8.5 to 13.6 at Re = 300) and a 23% increase in water flux (from 13 to 16 L/m²h) by reducing concentration polarization. However, this comes with a 4.7-fold increase in pressure drop, partially mitigated by Energy Recovery Devices (ERDs), resulting in a net specific energy consumption of 2.2–2.5 kWh/m³. Tidal energy from global sites (600–1700 kW) provides feed pressures of 17–80 bar, with energy storage and pressure regulation ensuring stable RO operation despite tidal fluctuations. Techno-economic analysis indicates a potential levelized cost of water (LCOW) reduction of 15–20% (to 0.45–0.65 $/m³) under realistic conditions, though challenges in intermittency and costs require further validation. The integrated approach, validated with less than 5% error against experimental data, demonstrates significant potential for sustainable freshwater production, offering a scalable solution for coastal regions worldwide.

Abstract Salinity gradient energy extracted with the reverse electrodialysis technique is attracting great interest and has been suggested as a promising renewable and stable energy source. However, the reverse electrodialysis relies on highly charge‐selective membranes, causing a range of problems including the selectivity–permeability trade‐off, strong concentration polarization, and strict requirement on the material structure, severely limiting its viability for large scale applications. We demonstrate these problems may be addressed by adopting the diffusio–osmosis process to generate power using sulfonated covalent framework membranes (COF), which does not require any charge selectivity. As a result, the membrane shows much higher power density compared to similar‐sized membranes and enables much higher scalability. Remarkably, the generator has loose requirement on material structure and could largely maintain its power generation performance even when a substantial number of pinholes are present. This could make the material fabrication significantly easier than before. We expect our work to advance the practical application of salinity gradient energy extraction.

A critical factor in enhancing unitized regenerative fuel cell (URFC) performance lies in optimizing the material properties of the gas diffusion layer (GDL). In this study, the effects of GDL electrical conductivity and porosity are investigated, utilizing a self-developed multi-physical two-phase model. The model is operated under typical URFC conditions, including a temperature of 353.15 K, atmospheric pressure. The GDL thickness is fixed at 3 × 10−4 m, with porosity varied between 0.4 and 0.8 and electrical conductivity ranging from 300 to 1250 S/m. The results indicate that URFC performance is constrained in both operating modes when the electrical conductivity is below 300 S/m. Increasing the conductivity to 1000 S/m results in a notable improvement in electrical performance, though further increases had minimal additional impact. In contrast, the effect of porosity is more pronounced in FC mode compared to electrolytic cell (EC) mode. Higher porosity levels enhance oxygen transport to the catalyst layer (CL), particularly when the concentration polarization occurs. This research identifies optimal GDL parameters (porosity of 0.6 and conductivity of 1000 S/m) that can improve the round-trip (RT) energy efficiency of URFCs, offering valuable insights for future studies.

Salinity gradient energy extracted with the reverse electrodialysis technique is attracting great interest and has been suggested as a promising renewable and stable energy source. However, the reverse electrodialysis relies on highly charge-selective membranes, causing a range of problems including the selectivity-permeability trade-off, strong concentration polarization, and strict requirement on the material structure, severely limiting its viability for large scale applications. We demonstrate these problems may be addressed by adopting the diffusio-osmosis process to generate power using sulfonated covalent framework membranes (COF), which does not require any charge selectivity. As a result, the membrane shows much higher power density compared to similar-sized membranes and enables much higher scalability. Remarkably, the generator has loose requirement on material structure and could largely maintain its power generation performance even when a substantial number of pinholes are present. This could make the material fabrication significantly easier than before. We expect our work to advance the practical application of salinity gradient energy extraction.

Introduction: Jet electrodeposition technology has proven effective for enhancing metal substrate surface properties. This study employed the technique to fabricate Ni- Al2O3 composite coatings on stainless steel substrates, aiming to improve their mechanical performance and tribological characteristics. Methods: The Ni- Al2O3 coating was generated by using the univariate control method and changing the parameters of current density and Al2O3 concentration, respectively. Comprehensive characterization was performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) for microstructural analysis, while microhardness and wear resistance were systematically evaluated using a Vickers hardness tester and reciprocating tribometer, respectively. Results: Through systematic optimization of deposition parameters, optimal performance was achieved at a jet velocity of 150 L/h, current density of 130 A/dm², and Al2O3 concentration of 20 g/L. The resulting coatings exhibited exceptional mechanical properties, including a maximum hardness of 547 HV, a remarkably low friction coefficient of 0.14, and minimal wear loss (0.6 mg). Discussion: The performance enhancement is mainly due to the fact that at the optimal current density, this density balances the cathode overpotential, promotes grain refinement, and simultaneously avoids concentration polarization and tip effects. This synergistic effect is further amplified by the incorporation of Al2O3 nanoparticles, which refine Ni-based particles by increasing nuclear sites, serve as the carrier hard phase, and provide abrasive polishing during the deposition process. However, excessive Al2O3 can cause particle agglomeration, reduce the uniformity of the microstructure, and thereby lower the performance of the coating. Forced convection in jet electrodeposition is crucial for maintaining the dispersion of nanoparticles. Conclusion: This study successfully determined optimal jet electrodeposition parameters for highperformance Ni- Al2O3 coatings. The resulting coatings exhibit excellent mechanical and tribological properties. The method’s scalability and performance suggest strong commercial patentability in wear-resistant coatings.

Engineering a symmetric and positively charged forward osmosis membrane without internal concentration polarization for heavy metal recovery

Power generation by reverse electrodialysis (RED) is a promising technology based on sustainable salinity gradient energy. This study performed numerical simulations using a three-dimensional multi-physical model of a RED cell pair with emphasis on chevron-profiled membranes. The simulations revealed the hydrodynamics and electrochemical behaviors during the RED process and the effects of chevron-profiled membranes on stack performance. The results indicated that the chevron corrugations of chevron-profiled membranes induce periodically upward and downward fluid motion similar to the role of spacers, leading to improved fluid mixing and reduced concentration polarization. Furthermore, these microstructures increased the membrane surface area available for mass transfer and shortened the transport path of ions crossing flow channels, resulting in enhanced ion transport and decreased electrical resistance. Comparisons among RED stacks with different configurations revealed that the RED stack with chevron-profiled membranes exhibits considerably higher net power density than stacks with wave-profiled membranes or woven spacers.