Ion-sieve Effect Research Articles

Fundamentals and Implication of Point of Zero Charge (PZC) Determination for Activated Carbons in Aqueous Electrolytes.

The point of zero charge (PZC) is a crucial parameter for investigating the charge storage mechanisms in energy storage systems at the molecular level. This paper presents findings from three different electrochemical techniques, compared for the first time: cyclic voltammetry (CV), staircase potentio electrochemical impedance spectroscopy (SPEIS), and step potential electrochemical spectroscopy (SPECS), for two activated carbons (ACs) with 0.1molL-1 aqueous solution of LiNO3, Li2SO4, and KI. The charging process of AC operating in aqueous electrolytes appears as a complex phenomenon - all ionic species take an active part in electric double-layer formation and the ion-mixing zone covers a wide potential region. Therefore, the so-called PZC should not be considered as an absolute one-point potential value, but rather as a range of zero charge (RZC). SPECS technique is found to be a universal and fast method for determining RZC, as applied here together with the EQCM. In most cases, the RZC covers a potential range from ≈100 to ≈200mV and the correlation of the range with the carbon microtexture is clear, highlighting the role of the ion-sieving effect. It is postulated that PZC for porous materials in aqueous electrolytic solutions should be considered instead as RZC.

High-Current Water-Enabled Electricity Generation in Mushrooms via Synergistic Ion Sieving and Adsorption.

Water-enabled electricity generation (WEG), which harvests energy from the natural water cycle, is a novel strategy for producing green electricity. Taking advantage of the ion sieving effect based on evaporation-induced water flows in charged nanopores, various WEG devices have been developed. Here, we report that a carbonized mushroom produces a record-high current output of up to 96.7 μA, which is attributed to a unique ion adsorption effect combined with an ion sieving effect. Specifically, the natural gradient potential from root to cap in a mushroom caused by tissue differentiation adsorbs different ions, enhancing the traditional ion sieving current. In synergy with the two effects, the mushroom can operate under a broad range of concentrations (0 to 0.6 mol L-1) and represents significant improvements in current, duration, and total charge transfer. These findings reveal the hidden talent of mushrooms as natural materials for WEG, providing inspiration for the development of high-performance WEG devices.

Self-Standing Covalent Organic Polymer Membrane with High Stability and Enhanced Ion-Sieving Effect for Flow Battery.

Fabrication of ion-conducting membranes with continuous sub-nanometer channels holds fundamental importance for flow batteries in achieving safe integration of renewable energy into grids. Self-standing covalent organic polymer (COP) membranes provide feasibility due to their rapid and selective ion transport. However, the development of a scale-up possible, mechanically robust and chemically stable membranes remains a significant challenge. Herein, using irreversible strong secondary amine linkage, we propose a self-standing COP membrane with sub-nanometer pores ranging from 4.5 to 6.4 Å, by a simple and efficient in-situ polymerization approach. This membrane exhibits enhanced selectivity for proton and vanadium ions, especially excellent electrochemical stability, delivering an energy efficiency of over 80% at the current density of 200 mA cm-2 over 1000 cycles for an all-vanadium redox flow battery (VFB). This study provides novel insights for COP-based ion-sieving membranes in sustainable energy fields.

Free-standing COF nanofiber in ion conductive membrane to improve efficiency of vanadium redox flow battery

The ion sieving effect of the porous two-dimensional covalent organic frameworks (COFs) in vanadium redox flow battery (VRFB) was greatly restricted by the brittleness and easy agglomeration of COFs in ion conductive membranes. Herein, the strategy of free-standing COF nanofiber as continuous ion conductive pathways is proposed to maximize the selective ion conduction of COFs. The free-standing TFP-TAPA electrospun COF nanofiber mat was fabricated by an in-situ growth-template etching method, densified with sulfonated polybenzimidazole (SPBI) and continuously dispersed in the membrane. Fibrillization gives rigid COF materials excellent flexibility to be freely bent, induces the orientated aggregation of sulfonic acid groups via hydrogen bonding for proton hopping, as well as the long-range vanadium ions repelling barrier via the sieving pores (6 Å) and Donnan effect of the imine groups in COF. The TFP-TAPA COF nanofiber continuous membrane shows 3 folds of H+/Vn+ selectivity over Nafion212, achieves excellent VRFB energy efficiency of about 80.5 % at 200 mA cm−2, which surpasses most state-of-the-art COFs based ion conductive membranes for VRFBs.

Simultaneous improvement of wetting resistance and permeability in membrane distillation using MXene-foam coating layer with heterostructural channels

To alleviate global water scarcity, membrane distillation (MD) has been identified as a promising technology for desalination. However, there exists a trade-off effect between membrane permeability and anti-wetting performance, impeding the intensive application of MD. To address this problem, inspired by the ion-sieving effect and the special nanostructure of aquaporins to break the trade-off between permeability and selectivity, a porous MXene coating layer with heterostructural channels in fusiform shape was designed on a PVDF membrane through a hydrazine-induced approach. The coating layer was in a foam shape with hydrophobic surfaces and outstanding stability in water. The delicate-designed fusiform channels endowed the membrane with enhanced permeability (the average flux of the optimum modified membrane was 55.59 kg/m2h with a temperature gradient of 60 °C (feed temperature: 70 °C and permeate temperature: 10 °C) and flow velocity of 400 ml/min, nearly 2.5 times as high as that of the virgin membrane) and resistance to simultaneous sault induced and foulant-induced wetting performance. This paper proposed a novel strategy for engineering porous nanostructures with dual-spacing channels on the membrane surface to ensure high permeability and stable excellent desalination performance.

Impact of Faradaic Interlayer Confinement and Carbon-Centered Macrostructure Designs for Ion Capture and the Recovery of Elements.

Environmental protection associated with renewable energy is among the most critical challenges for translational ion-capture based on capacitive storage of ions in electrical double layers at the interface of electrode and electrolyte. Electric double-layer capacitance with charge induction and faradaic pseudo-capacitance with charge transfer classifies the capacitance of the electrochemical interface. The electrochemical interface in most energy technologies involves porous and pseudocapacitive redox materials that offer varying degrees of electrolyte confinement. In this review, we discuss the factors affecting water desalination, such as the effect of nanopores for ion capture, the ion sieving effect, the effect of hydration energy, and hydration radius in the carbon sub-nanometer pore. Moreover, the surface phenomena of electrodes, including carbon corrosion, and the potential of zero charge to control the oxidation of carbon electrodes are explained along with protection mechanisms. The various capacitive deionization (CDI) operations and the corresponding electrochemical cell technologies are briefly introduced, including the significance of double-layer charging materials with faradaic intercalation, which suffer less from co-ion expulsion. Finally, we revisit the effects of various nanoarchitectures and the construction of capacitive deionization electrodes for clean water technology.

Dual-Functional V2 C MXene Assembly in Facilitating Sulfur Evolution Kinetics and Li-Ion Sieving toward Practical Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are considered as one of the most promising candidates to achieve an energy density of 500Wh kg⁻1 . However, the challenges of shuttle effect, sluggish sulfur conversion kinetics, and lithium-dendrite growth severely obstruct their practical implementation. Herein, multiscale V2 C MXene (VC) with a spherical confinement structure is designed as a high-efficiency bifunctional promotor for the evolution of sulfur and lithium species in Li-S batteries. Combining synchrotron X-ray 3D nano-computed tomography (X-ray 3D nano-CT), small-angle neutron scattering (SANS), and first-principle calculations, it is revealed that the activity of VC can be maximized by tuning the scale, and the as-attained functions are conducted as follows: (i) the VC acts as the efficient lithium polysulfide (LiPS) scavenger due to the large number of active sites; (ii) the VC exhibits significantly improved electrocatalytic function for the Li2 S nucleation and decomposition reaction kinetics owing to the scale effect; and (iii) the VC can regulate the dynamic behavior of Li-ions and thus stabilize the lithium plating/stripping effectively on account of the unique ion-sieving effect.

Self-repairing interphase reconstructed in each cycle for highly reversible aqueous zinc batteries

Aqueous zinc (Zn) chemistry features intrinsic safety, but suffers from severe irreversibility, as exemplified by low Coulombic efficiency, sustained water consumption and dendrite growth, which hampers practical applications of rechargeable Zn batteries. Herein, we report a highly reversible aqueous Zn battery in which the graphitic carbon nitride quantum dots additive serves as fast colloid ion carriers and assists the construction of a dynamic & self-repairing protective interphase. This real-time assembled interphase enables an ion-sieving effect and is found actively regenerate in each battery cycle, in effect endowing the system with single Zn2+ conduction and constant conformal integrality, executing timely adaption of Zn deposition, thus retaining sustainable long-term protective effect. In consequence, dendrite-free Zn plating/stripping at ~99.6% Coulombic efficiency for 200 cycles, steady charge-discharge for 1200 h, and impressive cyclability (61.2% retention for 500 cycles in a Zn | |MnO2 full battery, 73.2% retention for 500 cycles in a Zn | |V2O5 full battery and 93.5% retention for 3000 cycles in a Zn | |VOPO4 full battery) are achieved, which defines a general pathway to challenge Lithium in all low-cost, large-scale applications.

Reducing Irreversible Performance Losses via a Graphene Oxide Buffer Layer for Proton-Exchange Membrane Fuel Cells.

Alloy catalysts are promising for proton-exchange membrane fuel cells but are difficult to realize high-durability operation because the dissolution of Pt-M (M = Co, Ni, etc.) metals inevitably accelerates irreversible performance degradation. Here, we propose a buffer layer solution that inserts a trace layer of a graphene oxide (GO) film between the PEM and the alloy catalyst layer to mitigate the poison effect. To distinguish the irreversible and reversible losses, two typical recovery procedures (shutdown and JRC-based protocols) being part of a fuel cell dynamic load cycle durability test are characterized. The electrochemical evaluation reveals that GO-1 μg/cm2 enables a higher initial performance and stability. Furthermore, the GO buffer layer design allows the realization of membrane electrode assemblies with a highly homogeneous current density distribution and a low accessible mass transport resistance. Thanks to the ion sieving effect in the GO buffer layer, high anti-poisoning and stability during the accelerated stress test process are ensured.

Minimize the trade-off between wetting resistance and water permeance in membrane distillation with ion-sieving coating layer

• An ion-sieving layer was introduced into the MD system for anti-wetting. • Swelling of ion-sieving layer was mitigated by intercalating Ca 2+ ions. • The trade-off between wetting resistance and water permeance was overcome. • Mass transport in janus, omniphobic and ion-sieving membrane was discussed. The conventional hydrophobic membranes in membrane distillation system are prone to be wetted by surfactants. Meanwhile, there is a trade-off between wetting resistance and water permeance on advanced membrane materials, such as Janus membrane and omniphobic membrane. To overcome this dilemma, a composite membrane with ion-sieving layer was fabricated by self-assembling MXene nanosheets on the commercial PTFE membrane. The coating layer exhibited ordered subnanometer channels, and the stability can be further enhanced by intercalating Ca 2+ ions between the two-dimensional MXene pieces. The experiments using SDS-NaCl solution and realistic wastewater demonstrated that such modification can provide an excellent anti-wetting property without sacrificing the permeate flux. The anti-wetting property can be attributed to the ion-sieving effect, which created an energy barrier by the partial dehydration of ions. Simultaneously, the ion-sieving layer has a much lower water transfer resistance than the coating layer on conventional Janus membrane due to its ordered nanostructure, and the hydrophobic substrate can provide a larger effective evaporation interface compared with the omniphobic membrane. This article attempts to provide an insight into the novel membrane distillation system coupled with ion-sieving effect, and paves the way for developing advanced membranes for treating wastewater with low surface tension contaminants.

Selective recovery of strontium from oilfield water by ion-imprinted alginate microspheres modified with thioglycollic acid

The efficient recovery of Sr2+ from brine is a great challenge due to the interference of a large number of coexisting ions. Herein, a new-type spherical Sr2+ adsorbent with a diameter of about 2–3 mm was developed by the ion-imprinting method using low-cost and high hydrophilic sodium alginate (SA). It was found that although SA could be granulated in HCl solution, it showed no adsorption ability for Sr2+. However, when SA was ion-imprinted with Sr2+ and then eluted with HCl, the material exhibited excellent adsorption performance. Especially, after modification with thioglycollic acid, the maximum adsorption capacity reached approximately 177 mg·g−1, which was far higher than that of the spherical materials reported at present. The Sr2+ in the material could be eluted easily with 0.05 mol·L−1 HCl at an eluent dosage of only 0.02 L·g−1, and the Sr2+ concentration in the eluate was nearly 25 times higher than that in the original solution. Because of the ion-sieve effect, the developed adsorbent presented high stability and selectivity when used for Sr2+ recovery from oilfield water. The attenuation of adsorption capacity was only 0.42% after five adsorption-desorption. The separation factors between Sr2+ and other ions were all higher than 54, indicating that the selective recovery of Sr2+ is almost unaffected by coexisting Na+, K+, Mg2+, and Ca2+. All these properties suggest that the proposed material has excellent properties and can be used as a candidate for selective recovery of Sr2+ from oilfield water or other liquid strontium resources.

Ions Exclusion by the Bio-Inspired WS2 Lamellar Membrane Under Different Driving Forces

In recent years, lamellar membranes composed of 2D materials have drawn attention for membrane separation, as these contain nanoscale capillaries suitable to reject hydrated ions present in sea water. Slight surface chemistry modification of such nanoscale capillaries has been observed to further enhance the ion sieving effect. Herein, we report on a biofunctionalized WS2 membrane which consists of peptide-intercalated layer-stacked porous WS2 nanosheets. The intercalated peptides are responsible to modify the surface chemistry of nano-channels. The performance in terms of both ion sieving and water permeance of the membrane is found to be improved after peptide intercalation when tested under different electro-kinetic driving forces (concentration gradient and pressure difference). The membrane excludes ∼ 99 % of the salt ions (Na+, K+, Cl-, Mg+2) while maintaining higher water permeance than the industrialized membrane. The membrane is also found to be highly stable under aqueous medium and does not swell when used for longer period of time. Moreover, the membrane is tested for antifouling resistance and more than 85 % flux recovery rate is observed. This membrane works good in different pH values as well. These results suggest applicability in water purification systems.

Investigation of the mechanism of metal–organic frameworks preventing polysulfide shuttling from the perspective of composition and structure

The inhibition of polysulfides by a MOF composite separator with an ion sieve effect, and physical and chemical adsorption is illustrated.

Исследование природных лантансодержащих цеолитов методом растровой электронной микроскопии

Методами растровой электронной микроскопии и энергодисперсионной рентгеновской спектроскопии установлено распределение ионов лантана в структуре природных цеолитов – стильбита, шабазита, анальцима, мезолита. Показано, что ионы лантана по поверхности зерна цеолита локализованы неравномерно, концентрируясь на различных структурных дефектах в составе кристаллической фазы.

Heteroatom doped porous carbon sheets derived from protein-rich wheat gluten for supercapacitors: The synergistic effect of pore properties and heteroatom on the electrochemical performance in different electrolytes

Developing high-performance biomass-derived carbons and understanding the relationship between their structures and performance are highly desired for carbon-based supercapacitors. Herein, a wheat gluten-derived carbon with porous sheet-like structure, high specific surface area, and oxygen- and nitrogen-based heteroatom groups is fabricated. Their pore properties and heteroatom doping amount are adjusted through controlling the activation temperature. In aqueous electrolyte there is a significant synergistic effect between pore properties and heteroatom amount on the electrochemical performance of the gluten-derived carbon; while their performance is mainly determined by their pore properties in ionic liquid electrolytes. Besides, whatever in the aqueous and ionic liquid electrolytes ion sieving effect also affects their capacitive performance. The gluten-derived carbon prepared at 700 °C with reasonable pore properties and heteroatom amount shows the highest specific capacitance of 350 F g−1 at 0.5 A g−1 in 6 mol L−1 KOH. But the gluten-derived carbon prepared at 800 °C with the highest specific surface area of 2724 m2 g−1 possesses a high specific capacitance of 197 F g−1 at 0.25 A g−1 in the ionic liquid electrolyte. This work can provide a guideline for optimizing the performance of biomass-derived carbons through matching their pore properties and heteroatom with different electrolytes.

Ion Sieving Effect of Pillared Graphene Materials in Electrochemical Capacitors

Electrical double-layer capacitors (EDLCs), commonly known as supercapacitors, store energy through reversible adsorption of electrolytic ions on the charged electrode surfaces.1 Extensive work on carbide-derived carbons (CDCs), ACs and templated carbons revealed that the sub-micro pores (< 1 nm) contribute significantly to the overall charge storage.2 , 3 Carbon materials with uni-modal pore size distribution curves (PSD) are essential for such a focused analysis.4 However, the difficulties in synthesizing such carbon materials and obtaining their PSDs reliably through gas sorption have hampered the progress.5 Meanwhile, research on graphene derivatives for charge storage in SCs has shown promising advances owing to good surface areas and electrical conductivities. However, much of the current research is devoted to improving the material porosity with a focus on PSDs, similar to the research on ACs.6 Surprisingly, little attention has been devoted towards exploring the possible confinement of the electrolytic ions into the unique layered structures of graphitic materials. An analysis of materials with varied inter-graphene sheets distance (d-spacing) in SCs would assess the possibility of such confinement. In this context, this study is aimed at understanding the consequences of interlayer spacing on electrochemical charge storage. A class of graphene-like materials with varying d-spacing have been synthesized using alkyl diamines cross-linking and are characterized for their application in SCs. Electrochemical analysis of the materials in SCs using electrolytes containing tetraalkylammonium cations of different sizes (alkyl: ethyl, propyl, butyl and hexyl) showed limitations of ion adsorption in different materials. The PSD curves of the materials show no presence of sub-micro pores (< 1 nm) and thus relate the observed ion limitation to d-spacing. Hence, this work demonstrates that the inter-layer galleries in graphene like materials indeed confine electrolyte ions based on the size constrictions. A correlation between the d-spacing and the electrolyte ion sizes is established and a condition for maximum capacitances versus d-spacing for a specific electrolyte is being investigated. [1] Simon, P.; Gogotsi, Y. Nat Mater 2008, 7 (11), 845–854. [2] Merlet, C.; Péan, C.; Rotenberg, B.; Madden, P. A.; Daffos, B.; Taberna, P.-L.; Simon, P.; Salanne, M. Nat. Commun. 2013, 4, 3701-3707. [3] Raymundo-Piñero, E.; Kierzek, K.; Machnikowski, J.; Béguin, F. Carbon 2006, 44 (12), 2498–2507. [4] Kondrat, S.; Pérez, C. R.; Presser, V.; Gogotsi, Y.; Kornyshev, A. A. Energy Environ. Sci. 2012, 5 (4), 6474–6479. [5] Béguin, F.; Presser, V.; Balducci, A.; Frackowiak, E. Adv. Mater. 2014, 26 (14), 2219–2251. [6] Li, C.; Shi, G. Adv. Mater. 2014, 26 (24), 3992–4012.

Highly selective core-shell structural membrane with cage-shaped pores for flow battery

A blend membrane with the core-shell structure was designed and prepared for vanadium flow batteries (VFBs). The core is the membrane manufactured by poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) and polyvinylpyrrolidone (PVP) anion exchange resin, while the shell is composed of cage-shaped pores induced by VO2+ treatment. The high ion selectivity of PVDF-HFP/PVP blend membranes with the core-shell structure is assured by the ion sieving effect of cage-shaped pores and Donnan exclusion effect of anion exchange resin. The convection mechanism of charge carriers across pores on the surface and surface layers, together with the Grotthuss mechanism across the deep-seated anion exchange membrane jointly contributes to high ion conductivity of blend membranes. A great balance between high ion selectivity and high ion conductivity can thus be achieved. Moreover, the formation of cage-shaped pores can remedy the loss of chemical stability caused by anion exchange groups in PVP. A VFB with the resultant membrane could achieve a columbic efficiency of 98.16%, and an energy efficiency of 88.01% at 80 mA cm−2, much higher than those of Nafion 115. This core-shell structural blend membrane is an entirely novel concept to combine advantages of porous membranes and ion exchange membranes, while avoid their drawbacks simultaneously.

Anion Selectivity of Layered Double Hydroxides: Effects of Crystallinity and Charge Density

Layered double hydroxides (LDHs) have long been thought to have low selectivity for NO3–. In contrast, it has recently been reported that LDHs with certain compositions show high selectivity for NO3–. The reason for the high selectivity has been unclear, although the ion sieve effect has been proposed as a possible mechanism. Moreover, small LDHs have been reported to show good anion exchanging ability. Given this background, a systematic study was conducted using Mg‐Al LDHs with two different crystallinities. High‐crystallinity LDHs with lager particle sizes clearly showed selectivity changes that depended on the Mg/Al molar ratio, compared with low‐crystallinity LDHs with smaller particle sizes. When the Mg/Al ratio increased, selectivity of high‐crystallinity LDHs for SO42– and F– decreased, whereas that for NO3– increased. In the case of F–, the diameter of which is smaller than the height of the flat orientation of NO3–, this result indicates that an ion sieve effect is not the only factor that determines selectivity. Other factors, such as the interactions of NO3– with the interlayer surface and with interlayer water, may also be involved.

The characteristics of resin/carbon composite electrode and application in selective adsorption of vanadium(IV) by capacitive deionization

The characteristics and adsorption performances of three kinds of resin/mineral active carbon (Resin/AC-m) composite electrodes, the pure AC-m electrode and the resins were comparatively investigated. The Resin/AC-m composite electrodes have lower specific capacitance and higher resistance than the AC-m electrode, but their hydrophilia, specific surface areas and microspores content can be largely improved due to the addition of the resins, which is beneficial to the ions adsorption on the electrodes. The hydrated radius of VO2+ is smaller than that of Fe3+ and Al3+, then VO2+ is easier to pass through the microspores of the D860/AC-m electrode and adsorbed by the composite electrode. Thus, the D860/AC-m electrode presents the highest adsorption capacity and the strongest selectivity for VO2+, which may be resulted from the combined actions of the ion-sieve effect of the composite electrode material and the affinity of the resin for VO2+. Multiple adsorption-regeneration cycles proved that the performance of the D860/AC-m electrode can remain stable in long-term operation, indicating it may be suitable for cycle use in CDI. This study may provide a promising method for separation and recovery of ions from complex solutions.

A novel electric-field-accelerated ion-sieve membrane system coupling potential-oscillation for alkali metal ions separation

A novel electric-field-accelerated ion-sieve membrane (EISM) system with potential-oscillation was set up for the selective separation of the alkali metal ions. The ion-sieve membrane was fabricated by coating a polypyrrole/polystyrenesulfonate composite on the stainless steel wire mesh (PPy/PSS/SSWM). In the EISM system, an external electric filed was applied by introducing a constant cell voltage on the two sides of the ion-sieve membrane to accelerate the directed transport of target ions through the membrane. Meanwhile, an extra pulse potential was applied on the PPy/PSS/SSWM membrane to adjust the ion binding ability of the PPy/PSS composite toward cations. As such, an enhanced “ion sieving effect” of the EISM system was achieved through the synergistic function of the constant cell voltage and potential oscillation, which resulted in the rapid transport of target cation across the membrane in a “leap-frogging” way. It is found that when an extra pulse potential of ±1.0 V (pulse width of 60 s) was applied on the EISM, the permeation flux of K+ ions was increased by 7.42-fold with a constant cell voltage of 5 V. The permselectivities of the PPy/PSS/SSWM membrane for K+/Li+ and K+/Cs+ reached 3.29 and 3.45 respectively based on the optimized amplitude (±1.0 V) and frequency (pulse width of 60 s) of pulse potential.