Charge Layer Research Articles

(Invited) First Principles Treatments of Heterogeneous Electrocatalysis – Reactivity Trends and Electrocatalyst Structure

Advances in the theoretical understanding of electrochemical systems have, over the past decade, led to growing use of periodic Density Functional Theory studies to treat a surprisingly large ensemble of electrocatalytic reactions, ranging from carbon dioxide electroreduction to oxygen evolution. Many such studies have employed simplified models of the electrochemical environment to determine reactivity trends across a broad space of catalytic materials, while other efforts have focused on developing detailed descriptions of electrochemical phenomena, such as the structure of electrochemical double layers, on model catalyst structures. An emerging challenge is to combine these approaches to ultimately enable theoretical design of electrocatalysts for reactions of significantly expanded chemical and materials complexity.In this talk, I will begin by discussing how we have applied strategies from computational heterogeneous catalysis to design enhanced electrocatalysts for the classic oxygen reduction reaction. In such treatments, we have effected highly detailed analyses of the catalyst surface structure and have employed machine learning-based methods to describe interactions between the various ORR reaction intermediates that are present at significant surface coverages. I will then explore challenges in obtaining more detailed descriptions of the electrocatalytic reaction environment, including the structure of catalysts with solid/solid interfaces, the distribution of charges in electrochemical double layers, and the structure and entropy of solvents near the electrocatalyst surface. I will conclude with some perspectives on how these complexities may be incorporated into traditional computational catalyst screening approaches to identify improved materials for more complex electrocatalytic systems.

Deconvoluting Surface Modification Effects on Flow Battery Electrode Performance by Impedance Spectroscopy

Flow batteries have proliferated over the past decade, both in installed capacity and in the diversity of systems being developed for grid storage applications. As a long duration energy storage technology, flow batteries offer the distinct advantage of independent scaling of energy capacity through their liquid electrolytes, and of power capacity through stack design. Across flow battery systems, improving the design of reactor stacks to achieve high power densities at acceptable energy conversion efficiencies remains an important lever for lowering overall levelized costs of storage. In pursuit of this aim, understanding the reaction kinetics on the surfaces of porous carbon electrodes is key [1]. However, traditional techniques such as voltammetry, impedance spectroscopy, and cell performance must be utilised with caution to avoid convoluting observations of surface kinetics with other effects.Previous studies on vanadium flow batteries have used impedance spectroscopy to circumvent this issue, utilising the shared dependence of double layer capacitance and charge transfer conductance [2]. In recent years, DRT analysis of impedance spectra has also been used to further study electrode treatments for vanadium systems [3]. Building on these works, we use impedance spectroscopy combined with other techniques to deconvolute the effects of electrode treatments ex-situ before demonstrating the modified electrode performance in flow cells. The accompanying abstract image illustrates how different electrode modifications can manifest comparative differences in identified faradaic features in impedance spectra. As the most well studied system, we first apply our analysis to electrodes for vanadium electrolytes, validating our method and previous studies on electrode modifications. Following this, we apply our approach to capture a range of behaviours by studying redox active species with faster kinetics, such as recently developed organic species [4].The results of this work aim to improve the evaluation of reaction kinetics for different redox active species and electrode treatments. By doing so, we seek to further understand surface reaction mechanisms and how they can be harnessed to improve stack and electrolyte performance.[1] T. V. Sawant, C. S. Yim, T. J. Henry, D. M. Miller, and J. R. McKone, ‘Harnessing Interfacial Electron Transfer in Redox Flow Batteries’, Joule, vol. 5, no. 2, pp. 360–378, Feb. 2021, doi: 10.1016/j.joule.2020.11.022.[2] H. Fink, J. Friedl, and U. Stimming, ‘Composition of the Electrode Determines Which Half-Cell’s Rate Constant is Higher in a Vanadium Flow Battery’, J. Phys. Chem. C, vol. 120, no. 29, pp. 15893–15901, Jul. 2016, doi: 10.1021/acs.jpcc.5b12098.[3] K. Köble et al., ‘Revealing the Multifaceted Impacts of Electrode Modifications for Vanadium Redox Flow Battery Electrodes’, ACS Appl. Mater. Interfaces, vol. 15, no. 40, pp. 46775–46789, Oct. 2023, doi: 10.1021/acsami.3c07940.[4] J.-M. Fontmorin, S. Guiheneuf, T. Godet-Bar, D. Floner, and F. Geneste, ‘How anthraquinones can enable aqueous organic redox flow batteries to meet the needs of industrialization’, Current Opinion in Colloid & Interface Science, vol. 61, p. 101624, Oct. 2022, doi: 10.1016/j.cocis.2022.101624. Figure 1

(Invited) Advances in Modeling Ion Transport in Micropores and Charging Behavior of Porous Electrodes: Merging Molecular Insights with Machine Learning for Energy Storage

Electric double layer (EDL) charging is a complex process coupling electro-osmotic flow, surface reactions, and ion concentration gradients. The charging dynamics depends on the properties of electrolyte and electrode structure, as well as initial and boundary conditions. While molecular dynamics (MD) simulations and first-principles calculations can encompass all factors, their computational demands are substantial even for simple electrochemical systems such as electrolytes near a planar surface. This presentation explores recent advancements in modeling ion transport in micropores and the charging behavior of porous electrodes with different theoretical and simulation methods. Illustrative examples will be discussed on the integration of molecular modeling and machine-learning techniques to enhance our understanding of complex electrochemical processes and improve the design of energy storage devices.

Corrosion Behavior of FeCoNiCrAl High-Entropy Alloy in Molten NaNO3-KNO3

Molten nitrates are the main heat transfer fluid (HTF) for concentrated solar power (CSP) systems. However, due to the instability of molten nitrates at high temperatures, the corrosiveness of the molten nitrates poses high requirements for the structural material used in CSP. Therefore, it is urgent to develop highly corrosion-resistant materials. In this study, the corrosion behavior of FeCoNiCrAl high entropy alloys (HEA) in molten NaNO3-KNO3 (60 wt% to 40 wt%) under argon at 600°C is investigated by mass loss and electrochemical methods. The results show that the FeCoNiCrAl HEA experienced severe mass loss during the 100 h immersion due to the high oxygen partial pressure and the galvanic corrosion effect. The corrosion products of FeCoNiCrAl HEA in the melt consist of Fe2O3, Cr2O3, FeCr2O4, and NaFeO2. After immersion for 100 h, an outer layer dominated by porous iron oxides and an inner more compact Cr-rich layer are formed. Furthermore, both of the oxide layers are gradually thickened with the extension of the corrosion time, and the process is manifested by the increased value of the oxide layer resistance Rox and charge transfer resistance Rt in the electrochemical impedance spectra. At the same time, compared with the Rt of 316L stainless steel, it can be seen that with the extension of corrosion time, the Rt of FeCoNiCrAl HEA is larger and shows better corrosion resistance in the same corrosive environment. In addition, FeCoNiCrAl HEA shows a higher corrosion potential and a lower corrosion current density than 316L in molten nitrates at 600°C.

Complex conductivity as a tool to investigate the electrical behavior between graphene oxide and reduced graphene in supercapacitors: Correlation between the electrical properties

The storage mechanisms of solid-solid supercapacitors based on graphene oxide (rGO/GO/rGO) were explored by Zhang Q et al. (Zhang et al., 2014) [1], using Density Functional Theory (DFT) and Impedance Spectroscopy (EIS) to elucidate the unusual capacitive behavior of GO sandwich films. Their study revealed alternating charged layers without diffusion zones. Analysis of complex impedance (Z*) data, ranging from 10−3 to 3.106 Hz, was conducted using an equivalent circuit, though this was limited to Nyquist plot data.To further investigate charge storage mechanisms, the current study delved deeper into complex impedance (Z*) and conductivity (σ*). A theoretical approach identified relaxation processes in the imaginary parts of (Z″) and (σ'') across frequencies. Extrapolation up to 3.10^9 Hz and deconvolution confirmed three distinct relaxation processes in Z* and σ*, similar to Cole-Cole relaxation, which describes Maxwell-Wagner-Sillars (MWS) relaxation. This reflects local electrical interactions between active sites on molecular chains and counterions, creating induced dipolar moments or diffusion processes.The identified relaxations at low, medium, and high frequencies correspond well with DFT results, attributed to specific regions: graphene oxide (GO), the (rGO/GO) interface, and reduced graphene (rGO). Key parameters extracted from each relaxation, such as relaxation time, ionic strength, and conductivity values at different frequencies, showed good correlation. This approach, based on deep conductivity (σ*) analysis, effectively highlighted the charge conduction and storage mechanisms in rGO/GO/rGO supercapacitor films.

Charge separation at liquid interfaces

We present a theory for phase-separated liquid coacervates with salt, taking into account spatial heterogeneities and interfacial profiles. We find that charged layers of alternating sign can form around the interface while the bulk phases remain approximately charge neutral. We show that the salt concentration regulates the number of layers and the amplitude of the layer's charge density and electrostatic potential. Such charged layers can either repel or attract single-charged molecules diffusing across the interface. Our theory could be relevant for artificial systems and biomolecular condensates in cells. Our work suggests that interfaces of biomolecular condensates could mediate charge-specific transport similar to membrane-bound compartments. Published by the American Physical Society 2024

Control of work functions of nanophotonic components

Work function is an essential material’s property playing important roles in electronics, photovoltaics, and more recently, in nanophotonics. We have studied effects of organic, and inorganic dielectric materials on work functions of Au films in single layered, and multilayered structures. We found that measured work function of metallic surfaces can be affected by dielectric materials situated 10–100 nm away from the metallic surface. We have found that, (i) the glass underneath ~ 50 nm gold slab reduces the work function of gold, (ii) Rh590:PMMA increases the work function of a gold film deposited on top of the polymer, and (iii) reduces it if Rh590:PMMA is deposited on top of Au. (iv) With increase of the Rh590 concentration in PMMA, n, the work function first decreases (at n < 64 g/l), and then increases (at n > 64 g/l). (v) The work function of a Fabry–Perot cavity or an MIM waveguide is almost the same as that of single Au films of comparable thickness. The experimental results can be qualitatively explained in terms of a simple model taking into account adhesion of charged molecules to a metallic surface, and formation of a double layer of charges accelerating or decelerating electrons exiting the metal and decreasing or increasing the work function.

Preparation of PVA-based charged mosaic membrane using screen-printed method and evaluation of ion transport properties

In this study, a polyvinyl alcohol (PVA)-based charged mosaic membrane (CMM) with a stripe-shaped charged structure from PVA-modified block copolymers was fabricated on a non-fabric support using a screen-printed method. The membrane structure of the stained CMM indicated that the striped negatively (N)- and positively (P)-charged layers with 20 μ m thickness were formed on the support. The domain sizes of the N and P layers were 173 and 203 μ m, respectively. Membrane potential measurements revealed that the charge density in the N layers of the fabricated CMM (CM-1) was almost the same as that in the P layers. A diffusion dialysis test indicated that the CM-1 had an electrolyte permselectivity of 986 between 0.1 M KCl and 0.1 M sucrose; a value which is approximately 20 times higher than that of Desalton® which is the only commercially available CMM. A water permeation test showed that CM-1 exhibited negative osmosis, which is a unique behavior of CMMs with high electrolyte permselectivity. Absolute flux in the negative osmosis was maximum when the electrolyte concentration was 0.1 M. A piezo dialysis test at an initial concentration of 500 ppm NaCl and applied pressure of 0.7 MPa, indicated that the rejection of CM-1 yielded negative value, confirming that the membrane can desalt salty water via piezo dialysis.

A novel nanofiltration membrane with a dual-charged layer to simultaneously remove anions and cations from acid mine drainage

A novel nanofiltration (NF) membrane with a positively and negatively dual-charged layer was finely designed in this study. The membrane was prepared by co-deposition of 4-tert-butylpyrocatechol (TBC) and polyethyleneimine (PEI) and electrostatic interaction to assemble positively and negatively charged functional layers on a substrate which is polyamide (PA)-based NF membrane. The NF membrane achieved excellent retention capacity through the combined effects of Donnan repulsion and electrostatic field trapping. The prepared membrane had a dense but thin surface layer with an average pore size of 0.84 nm, enabling an improved membrane flux of 8.66 L/(m2·h·bar) and high rejection to divalent inorganic salt ions (93.56 % Mg2+, 99.56 % SO42-). The membrane was used to treat acid mine drainage (AMD) and achieved an excellent retention capacity for ions in AMD (93.25 % Mg2+, 91.58 % Ca2+, 94.22 % Mn2+, 95.96 % SO42-), meeting industrial wastewater discharge standards. In addition, the NF membrane demonstrated good anti-fouling performance during the AMD treatment and significant potential for environmental remediation applications.

In situ polymerization of a poly(3,4-ethylenedioxythiophene):poly(sodium–styrennesulfonate) conductive layer for electro-assisted ultrafiltration and fouling mitigation

Electrification can enhance the antifouling performance of ultrafiltration membranes and improve the sustainability of membrane technologies. The design of high-performance conductive membrane materials remains one of the core technologies in electro-assisted ultrafiltration. Here, conductive PVDF/PEDOT:PSS composite membranes were prepared via in situ chemical oxidation polymerization on a PVDF surface. The PVDF/PEDOT:PSS membranes were subsequently used for electro-filtration to study the effect of the applied potential on humic acid fouling. When a voltage of 3 V was applied, the PVDF/PEDOT:PSS20 membrane was continuously polluted for 5 cycles. The results showed that after simple hydraulic cleaning, the membrane flux recovery rate reached 91 %. Compared with that of the PVDF membrane, the irreversible fouling of the PVDF/PEDOT:PSS20 membrane decreased by 65 %. The modified Poisson Boltzmann equation indicates that applying cathodic potential on the surface of PEDOT:PSS conductive layer increases the cumulative concentration of counter ions on the membrane surface and the thickness of the charged layer, thereby promoting the migration of peak forces on the membrane surface to the bulk solution, changing the fouling behaviour of HA from cake filtration to standard blocking.

Magnetic field-assisted electrochemical additive manufacturing of nickel structure: Growth mechanism and microstructural evolution

The microstructure and crystal texture of magnetically assisted electrochemical additive manufacturing parts play crucial roles in their mechanical properties and applications. This paper elucidates the electrocrystallization process of electrochemical additive manufacturing by constructing a magnetically assisted setup and exploring both nucleation mechanisms and growth kinetics. The electrochemical behavior of the system was analyzed using electrochemical methods under different magnetic field strengths. Nickel structures with aspect ratios of 7.0 and 8.2 were fabricated using the experimental setup, and their morphology, crystal texture, and microstructure were characterized. The results showed that without applying a magnetic field, the nucleation mechanism followed three-dimensional instantaneous nucleation under diffusion control. Under magnetic field conditions, forced convection, double layer charging, and hydrogen evolution reactions were combined to modify the S-H nucleation model, demonstrating that the magnetic field can significantly enhance the nucleation rate and number of nuclei. The initial growth of the microstructure did not exhibit preferential solid orientation, primarily forming refined equiaxed grains. Subsequently, a characteristic pentagonal structure developed, followed by spiral dislocation growth, with a significant transformation of equiaxed grains into columnar crystals. The crystal orientation eventually evolved to <110>, with many twin boundaries, among which Σ3 grain boundaries accounted for more than 55 %. Applying a magnetic field improved processing efficiency, altered the morphology and texture of the material, refined the grains, and increased the types of twins. These results provide theoretical and experimental support for electrochemical additive manufacturing.

NiO/vermiculite composites prepared for photocatalytic degradation of methanol-water solution and hydrogen generation

A novel eco-friendly NiO/Vm clay based photocatalysts were synthesized from two vermiculites (Vm1 and Vm2) and nickel(II) nitrate hexahydrate (Ni(NO3)2·6H2O salt precursor by the chemical precipitation without and with the sodium hydroxide (NaOH) or ammonium hydroxide (NH4OH, 28% NH3 in H2O) as precipitation agents (Synthesis A) in comparison with the solid-state thermal decomposition (Synthesis B) at 600 °C. Structural properties of all specimens were characterized by X-ray fluorescence, scanning electron microscopy, X-ray diffraction, infrared (IR) and Raman spectroscopy. The photocatalytic performance of NiO/Vm composites was evaluated under UV radiation (λ = 254 nm) for decomposition of methanol-water to hydrogen over 4-h and the stable yield of hydrogen over the 24-h periods. The NaOH and NH4OH affected the NiO crystallite size and therefore the photocatalytic activity during 4 h. Different 2:1 layer charge of Vm1 (0.82 e−) and Vm2 (0.40 e−) and the specific surface area of Vm1 (about 43 m2/g) and Vm2 (about 34 m2/g) supported H2 yield of 628.2 μmol/gcat. and 596.8 μmol/gcat., close to 657.0 μmol/gcat. produced in the presence of commercial photocatalyst TiO2 Evonik P25. Crystalline NiO precipitated and anchored in NiO/Vm composites contained smaller crystallites than those in free NiO. Vermiculite silica surface supports coverage of NiO by hydrogen bonding to Si-OH groups influencing the geometry of the NiO crystal structure (disorder NiO(X)). The heterojunction with Si-O-Ni bonding, at which electrons transfer from Vm to NiO cause enriching electron density in NiO and favoring its photocatalytic activity. Photocatalytic hydrogen generation from methanol–water mixture at the presence of all specimens indicated the main product H2 and minimum by-products CH4 and CO. The stable hydrogen production for 24 h was confirmed only in the presence NiO/Vm1–24 while maintaining the NiO(X) in small crystallites. The thermal solid-state procedure provided the gradual dehydration of vermiculites and Ni(NO3)2·6H2O to the same amount and crystallinity of NiO in NiO/Vm1 and NiO/Vm2 composites. The results of this work confirm that vermiculites mixed layer structures with different negative layer charge play a dominant role as semiconductors for anchored NiO. The photocatalytic activity of NiO/vermiculite composites can be harnessed to treat wastewater containing organic contaminants.

Active microparticle propulsion pervasively powered by asymmetric AC field electrophoresis

HypothesisSymmetry breaking in an electric field-driven active particle system can be induced by applying a spatially uniform, but temporally non-uniform, alternating current (AC) signal. Regardless of the type of particles exposed to sawtooth AC signals, the unevenly induced polarization of the ionic charge layer leads to a major electrohydrodynamic effect of active propulsion, termed Asymmetric Field Electrophoresis (AFEP). ExperimentsSuspensions containing latex microspheres of three sizes, as well as Janus and metal-coated particles were subjected to sawtooth AC signals of varying voltages, frequencies, and time asymmetries. Particle tracking via microscopy was used to analyze their motility as a function of the key parameters. FindingsThe particles exhibit field-colinear active propulsion, and the temporal reversal of the AC signal results in a reversal of their direction of motion. The experimental velocity data as a function of field strength, frequency, and signal asymmetry are supported by models of asymmetric ionic concentration-polarization. The direction of particle migration exhibits a size-dependent crossover in the low frequency domain. This enables new approaches for simple and efficient on-chip sorting. Combining AFEP with other AC motility mechanisms, such as induced-charge electrophoresis, allows multiaxial control of particle motion and could enable development of novel AC field-driven active microsystems.

Anisotropic Dual S‐Scheme Heterojunctions Mimic Natural Photosynthetic System for Boosting Photoelectric Response

AbstractThe design of heterojunctions that mimic natural photosynthetic systems holds great promise for enhancing photoelectric response. However, the limited interfacial space charge layer (SCL) often fails to provide sufficient driving force for the directional migration of inner charge carriers. Drawing inspiration from the electron transport chain (ETC) in natural photosynthesis system, we developed a novel anisotropic dual S‐scheme heterojunction artificial photosynthetic system composed of Bi2O3−BiOBr−AgI for the first time, with Bi2O3 and AgI selectively distributed along the bicrystal facets of BiOBr. Compared to traditional semiconductors, the anisotropic carrier migration in BiOBr overcomes the recombination resulting from thermodynamic diffusion, thereby establishing a potential ETC for the directional migration of inner charge carriers. Importantly, this pioneering bioinspired design overcomes the limitations imposed by the limited distribution of SCL in heterojunctions, resulting in a remarkable 55‐fold enhancement in photoelectric performance. Leveraging the etching of thiols on Ag‐based materials, this dual S‐scheme heterojunction is further employed in the construction of photoelectrochemical sensors for the detection of acetylcholinesterase and organophosphorus pesticides.

Anisotropic Dual S-Scheme Heterojunctions Mimic Natural Photosynthetic System for Boosting Photoelectric Response.

The design of heterojunctions that mimic natural photosynthetic systems holds great promise for enhancing photoelectric response. However, the limited interfacial space charge layer (SCL) often fails to provide sufficient driving force for the directional migration of inner charge carriers. Drawing inspiration from the electron transport chain (ETC) in natural photosynthesis system, we developed a novel anisotropic dual S-scheme heterojunction artificial photosynthetic system composed of Bi2O3-BiOBr-AgI for the first time, with Bi2O3 and AgI selectively distributed along the bicrystal facets of BiOBr. Compared to traditional semiconductors, the anisotropic carrier migration in BiOBr overcomes the recombination resulting from thermodynamic diffusion, thereby establishing a potential ETC for the directional migration of inner charge carriers. Importantly, this pioneering bioinspired design overcomes the limitations imposed by the limited distribution of SCL in heterojunctions, resulting in a remarkable 55-fold enhancement in photoelectric performance. Leveraging the etching of thiols on Ag-based materials, this dual S-scheme heterojunction is further employed in the construction of photoelectrochemical sensors for the detection of acetylcholinesterase and organophosphorus pesticides.

Effects of polar discontinuities and stacking sequences on ferromagnetic properties at La0.67Sr0.33MnO3/SrCuO2 interfaces

Polar discontinuities occur in oxide heterostructures due to varying net charges in the sub-unit cell layers. These polar discontinuities lead to structural reconstruction and often create diverse functionalities. This work constructs polar discontinuous in La0.67Sr0.33MnO3/SrCuO2 (LSMO/SCO) heterostructures on a (001)-orientated SrTiO3 (STO) substrate under different configurations. By changing the growth order of LSMO and SCO, we found two different compensating mechanisms for polar discontinuity. When LSMO is grown on SCO, interfacial polarity discontinuities result in the generation of a large number of oxygen vacancies within the LSMO film. Thus, the LSMO magnetism deteriorates. For the SCO/LSMO/SCO trilayer, the SCO capping layer can recover the LSMO magnetism. The scanning transmission electron microscope results show an atomic reconstruction at the SCO-on-LSMO interface and several oxygen vacancies at the SrO sublayer. The interface reconfiguration releases the polar energy, thereby inhibiting the generation of oxygen vacancies and improving the ferromagnetism of the LSMO film. Our work studies the impact of polar discontinuity at the interface, providing insights into the effects of interface polar discontinuities on functional materials.

Quantitative Analysis of the Synergy of Doping and Nanostructuring of Oxide Photocatalysts.

In this paper, the effect of doping and nanostructuring on the electrostatic potential across the electrochemical interface between a transition metal oxide and a water electrolyte is investigated by means of the Poisson-Boltzmann model. For spherical nanoparticles and nanorods, compact expressions for the limiting potentials at which the space charge layer includes the whole semiconductor are reported. We provide a quantitative analysis of the distribution of the potential drop between the solid and the liquid and show that the relative importance changes with doping. It is usually assumed that high doping improves charge dynamics in the semiconductor but reduces the width of the space charge layer. However, nanostructuring counterbalances the latter negative effect; we show quantitatively that in highly doped nanoparticles the space charge layer can occupy a similar volume fraction as in low-doped microparticles. Moreover, as shown by some recent experiments, under conditions of high doping the electric fields in the Helmholtz layer can be as high as 100 mV/Å, comparable to electric fields inducing freezing in water. This work provides a systematic quantitative framework for understanding the effects of doping and nanostructuring on electrochemical interfaces, and suggests that it is necessary to better characterize the interface at the atomistic level.

Tailor-Made Heterocharged Covalent Organic Framework Membrane for Efficient Ion Separation.

Pore size sieving, Donnan exclusion, and their combined effects seriously affect ion separation of membrane processes. However, traditional polymer-based membranes face some challenges in precisely controlling both charge distribution and pore size on the membrane surface, which hinders the ion separation performance, such as heavy metal ion removal. Herein, the heterocharged covalent organic framework (COF) membrane is reported by assembling two kinds of ionic COF nanosheets with opposite charges and different pore sizes. By manipulating the stacking quantity and sequence of two kinds of nanosheets, the impact of membrane surface charge and pore size on the separation performance of monovalent and multivalent ions is investigated. For the separation of anions, the effect of pore size sieving is dominant, while for the separation of cations, the effect of Donnan exclusion is dominant. The heterocharged TpEBr/TpPa-SO3H membrane with a positively charged upper layer and a negatively charged bottom layer exhibits excellent rejection of multivalent anions and cations (Ni2+, Cd2+, Cr2+, CrO4 2-, SeO3 2-, etc). The strategy provides not only high-performance COF membranes for ion separation but also an inspiration for the engineering of heterocharged membranes.

An Asymptotic Analysis of Space Charge Layers in a Mathematical Model of a Solid Electrolyte

An Asymptotic Analysis of Space Charge Layers in a Mathematical Model of a Solid Electrolyte

PA/APVC nanofiltration membrane from reactive positively charged substrate membrane

Efficient Li+ and Mg2+ from natural seawater and salt lakes using nanofiltration is essential for efficient extraction of lithium resources and to address the global energy shortage. The combination of size sieving and the Donnan effect is crucial for optimal selectivity. We proposed a positively charged reactive support layer to design dual positively charged layer to enhance the magnesium-lithium separation. The positively charged support layer was prepared by ammoniating the PVC membrane with PEI, and then reacted with TMC to successfully prepare a dual positively charged layer PA/APVC nanofiltration membrane with high Li+/Mg2+ selectivity. The reactive support layer not only established a covalent bond connection with the PA layer, which increased the stability of the active layer, but also showed a positive charge (23.59 mV at pH=7) after ammonization, which further enhanced the Mg2+ repulsion from 82.57 % to 98.56 %. Furthermore, the highest separation factor achieved was 23.34 when a mixed solution containing Mg2+ and Li+ in a mass ratio of 50:1 was utilized, which was 13.48 times that of commercial nanofiltration membranes. The utilization of a reactive substrate membrane in the fabrication process of the PA/APVC membrane offers innovative prospects for future investigations on magnesium-lithium separation, contributing to the advancement of nanofiltration membranes.