Stable Anion Exchange Membranes Research Articles

Alkaline stable cross-linked anion exchange membrane based on steric hindrance effect and microphase-separated structure for water electrolyzer

This study focuses on the development of cross-linked anion exchange membranes (AEMs) based on polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS), known for its ether free backbone and excellent chemical stability. The cross-linked SEBS (X-SEBS-BC) membranes were synthesized using an eco-friendly method with SnCl4 under mild conditions. A cross-linking agent, 1,4-diazbicyclo[2.2.2]octane (DABCO), was employed to enhance ion conducting channels and improve alkaline stability by preventing degradation. The resulting membranes exhibited low swelling, high conductivity, and significant chemical stability in alkaline environments. This is achieved through the rigid cage-like structure of DABCO, which hinders syn-periplanar conformational changes and protects against the degradation of SN2 and ylide reactions. Their well-defined microphase-separated morphology, observed through TEM, supports effective ion transport. Notably, the X-SEBS-BC-0.81 membrane showed excellent alkaline stability, with minimal degradation in 3 M KOH over 30 days at 30 °C and 3.3% degradation in 1 M KOH over 600 hours at 50 °C. In water electrolysis tests, this membrane demonstrated superior performance (0.95 Acm−2 at 2.0 V), surpassing the commercial FAA-3-50 membrane by 82%. These findings highlight the potential of X-SEBS BC membranes for advanced AEM applications, particularly in water electrolysis..

Electrochemical activation of Pt electrode for efficient and stable anion exchange membrane ammonia electrolyzer

Replacing the oxygen evolution reaction in water electrolysis with ammonia oxidation reaction enables low voltage hydrogen production. Pt is a promising catalyst for the ammonia oxidation reaction due to its superior dehydrogenation and low affinity for *N, but Nads poisoning deactivates the Pt surface. This study proposes a method to improve ammonia oxidation performance and stability through electrochemical activation, introducing cathodic corrosion and recovery conditions. The half-cell results showed a peak current density of 74.2 mA cm−2 and retention ratio of 17 %. Adjusting the lower and upper cell voltage in a membrane electrode assembly based single cell optimized surface cleaning and inhibits further poisoning by O/OHads above 0.75 Vcell. Furthermore, incorporation of recovery conditions can enhance the stability of poisoned electrode compared to that in chronoamperometry test. The results of pulsed ammonia electrolysis tests incorporating recovery conditions suggested a novel approach to practical hydrogen production by stabilizing catalysts with a 83 % Faradaic efficiency at 0.1 A cm−2

Highly conductive and stable anion exchange membranes with dense flexible alkyl ether linkages and 1,2,4,5-tetramethylimidazolium for water electrolysis

Anion exchange membranes (AEMs) are key core materials in water electrolysis, requiring excellent conductivity and chemical durability. In this study, the suspended dense alkyl ether linkages and 1,2,4,5-tetramethylimidazolium ions with high stability are introduced into the polymer structure (PAES-FTMI-x, x = 0.15–0.30) for AEMs. The obtained AEMs with ion exchange capacity of 1.22–1.74 mmol g−1 exhibit high conductivity and dimensional stability. Their hydroxide ionic conductivity and swelling ratio are in the range of 76.28–113.17 mS cm−1 and 9.7%–17.0 % at 80 °C, respectively. The conductivity retention for the representative sample PAES-FTMI-0.25 achieves 90.6 % after soaked in 2 mol L−1 NaOH and 80 °C for 480 h. The assemble water electrolyzer based on PAES-FTMI-0.25 shows 734.97 mA cm−2 of current density at 2 mol L−1 NaOH and 2.0 V of voltage when the temperature is RT. It also has good durable stability at a current density of 500 mA cm−2 for 480 h with only 0.02 V decrease of voltage. This work would provide an effective strategy for the collaborative design and modification of AEMs for alkaline electrolyzed water.

Dimensionally Stable Anion Exchange Membranes Based on Macromolecular-Cross-Linked Poly(arylene piperidinium) for Water Electrolysis.

The advancement of anion exchange membranes (AEMs) with superior ionic conductivity has been greatly hindered due to the inherent "trade-off" between membrane swelling and ionic conductivity. To resolve this dilemma, macromolecular covalently cross-linked C-FPVBC-x AEMs were fabricated by combining partially functionalized ether-bond-free polystyrene (FPVBC) with poly(arylene piperidinium). The results from atomic force microscopy reveal that an increase in the ratio of FPVBC promotes the fabrication of microphase separation morphology, resulting in a high ionic conductivity of 40.15 mS cm-1 (30 °C) for the C-FPVBC-1.7 membrane. Molecular dynamics simulations further examine the ionic conduction effect of cross-linked AEMs. Besides, the unique cross-linking structure significantly improves mechanical and alkaline stability. After treatment in 1 M KOH at 50 °C for 1200 h, the C-FPVBC-1.7 membrane shows only a 6.9% decrease in conductivity. The C-FPVBC-1.7 AEM-based water electrolyzer achieves a high current density of 890 mA cm-2 at 2.4 V (80 °C) and maintains good stability, enduring over 100 h at 100 mA cm-2 (50 °C). These results demonstrate the significant potential of macromolecularly cross-linked AEMs for practical applications in water electrolysis.

A monolithic Co-FeCo8S8 electrode for stable anion exchange membrane water electrolyzer driven by fluctuating power supply

Integrating water electrolysis and green electricity offers a promising approach towards sustainable and clean energy. However, such a system demands electrodes that can swiftly and stably adapt to fluctuating power...

Activation of low-cost stainless-steel electrodes for efficient and stable anion-exchange membrane water electrolysis

A cost-effective activation method was developed to enhance the performance of commercial stainless steel (SS) as a bifunctional electrocatalyst for the AEM water electrolyzer, exhibiting remarkable durability at 5.0 A (1.0 A cm−2) for 250 h.

Electrochemical reconstruction of non-noble metal-based heterostructure nanorod arrays electrodes for highly stable anion exchange membrane seawater electrolysis

Direct seawater electrolysis for hydrogen production has been regarded as a viable route to utilize surplus renewable energy and address the climate crisis. However, the harsh electrochemical environment of seawater, particularly the presence of aggressive Cl−, has been proven to be prone to parasitic chloride ion oxidation and corrosion reactions, thus restricting seawater electrolyzer lifetime. Herein, hierarchical structure (Ni,Fe)O(OH)@NiCoS nanorod arrays (NAs) catalysts with heterointerfaces and localized oxygen vacancies were synthesized at nickel foam substrates via the combination of hydrothermal and annealing methods to boost seawater dissociation. The hierarchical nanostructure of NiCoS NAs enhanced electrode charge transfer rate and active surface area to accelerate oxygen evolution reaction (OER) and generated sulfate gradient layers to repulsive aggressive Cl−. The fabricated heterostructure and vacancies of (Ni,Fe)O(OH) tuned catalyst electronic structure into an electrophilic state to enhance the binding affinity of hydroxyl intermediates and facilitate the structural transformation into amorphous γ-NiFeOOH for promoting OER. Furthermore, through operando electrochemistry techniques, we found that the γ-NiFeOOH possessing an unsaturated coordination environment and lattice-oxygen-participated OER mechanism can minimize electrode Cl− corrosion enabled by stabilizing the adsorption of OH* intermediates, making it one of the best OER catalysts in the seawater medium reported to date. Consequently, these catalysts can deliver current densities of 100 and 500 mA cm−2 for boosting OER at minimal overpotentials of 245 and 316 mV, respectively, and thus prevent chloride ion oxidation simultaneously. Impressively, a highly stable anion exchange membrane (AEM) seawater electrolyzer based on the non-noble metal heterostructure electrodes reached a record low degradation rate under 100 μV h−1 at constant industrial current densities of 400 and 600 mA cm−2 over 300 h, which exhibits a promising future for the non-precious and stable AEMWE in the direct seawater electrolysis industry.

In Situ Electrochemical Restructuring B-Doped Metal-Organic Frameworks as Efficient OER Electrocatalysts for Stable Anion Exchange Membrane Water Electrolysis.

Metal organic frameworks (MOFs) are promising as effective electrocatalysts toward oxygen evolution reaction (OER). However, the origin of OER activity for MOF-based electrocatalysts is still unclear because of their structure reconstruction during electrocatalysis process. Here, a novel MOF (B-MOF-Zn-Co) with spherical superstructure is developed by hydrothermal treatment of zeolitic imidazolate framework-Zn, Co (ZIF-Zn-Co) using boric acid. The resultant B-MOF-Zn-Co shows high OER activity with a low overpotential of 362mV at 100mA cm-2. Remarkably, B-MOF-Zn-Co displays excellent stability with only 3.6% voltage delay over 300h at 100mA cm-2 in alkaline electrolyte. Surprisingly, B-MOF-Zn-Co thoroughly transforms into B-doped CoOOH (B-CoOOH) during electrolysis process, which isserved as actual active material for high OER electrocatalytic performance. The newly-formed B-CoOOH possesses lower energy barrier of potential-determining step (PDS) for OOH* formation compared with CoOOH, benefiting for high OER activity. More importantly, B-MOF-Zn-Co based anion exchange membrane water electrolytic cell (AEMWE) demonstrates continuously durable operation with stable current density of 200mA cm-2 over 300h, illustrating its potential application in practice water electrolysis. This work offers an in situ electrochemical reconstruction strategy for the development of stable and effective OER electrocatalysts toward practice AEMWE.

A high performance, stable anion exchange membrane for alkaline redox flow batteries

The development of cost-effective, safe, and low-corrosion alkaline aqueous redox flow batteries, such as alkaline zinc-iron flow batteries, has motivated the research of hydrocarbon-based anion exchange membranes. These membranes, characterized by their positively charged functional groups, facilitate the transport of hydroxide anions (OH−) in alkaline environments, rendering them as potential alternatives to conventional proton exchange membranes in emerging alkaline redox flow batteries. Herein, a facilely synthesized anion exchange membrane (AEM) with superior chemical stability in alkaline media and outstanding ion conductivity has been developed for use in an alkaline redox flow battery. The membrane consists of a partially imidazolium substituted poly (vinylbenzyl chloride) polymer matrix and low molecular weight polyethylene glycol (PEG) additive. The membrane provides positively charged polymer backbone with hydroxide anion as counter ions. The additive PEG not only augments membrane flexibility through interaction with the rigid polymer backbone, but also enhances the conductivity through conducting ions by the alkalized-ether functionality. The optimized anion exchange membrane demonstrates better ionic conductivity of 58.2 mS cm−1 and comparable permeability compared with commercially Nafion117 membrane, enabling promoted energy efficiency (83.5 %), coulombic efficiency (99.85 %) and excellent stability (280 cycles with negligible capacity degradation) of a zinc-iron flow battery at 80 mA cm−2.

Initial Degradation Issues in AEMWE and the Importance of Catalyst/Ionomer Binding

With the recent development of highly alkaline stable anion exchange membranes (AEMs) and ionomers (AEIs), anion exchange membrane water electrolyzer (AEMWE) has garnered attention due to its ability to achieve high hydrogen production rate at a low cost. The performance of AEMWE is determined by the anode catalyst layer, which can be made up of either a mixture of metal nanoparticles and polymer binders or a single metal. Although the integral metal has high mechanical properties, its performance is limited due to low electrochemical surface area and difficulties in mixing with binders, which makes it unsuitable for use in pure water. Catalyst layers made up of a combination of metal nanoparticles and polymeric binders can achieve high performance with a large surface area, but they often have low durability due to detachment of the anode catalyst layer from the porous transport layer substrate during water electrolysis. To prevent this, the anode catalyst layer must have high physical stiffness and it can be achieved by the strong bonding between the metal nanoparticles and the ionomer binder. This presentation investigates the phenomenon of initial performance degradation in AEMWE with an anode catalyst layer composed of metal nanoparticles, highlights the significance of the physical stiffness of the anode catalyst layer, and proposes that the issue can be resolved by introducing a polymer binder with high adhesion between the metal nanoparticles and the ionomer binder.

Activation of Commercial Stainless-Steel Electrodes for Highly Efficient and Stable Anion-Exchange Membrane Electrolysis

Commercial stainless steel (SS) is gaining interest as a promising electrode material to be widely used for green hydrogen production from alkaline water electrolysis. Herein, low-cost 304-type SS meshes (SM) were engineered through a simple 2-step activation process, i.e., chemical etching and electrochemical activation. The modified electrodes exhibited comparable hydrogen and oxygen evolution reaction properties with commercially, noble metal-based electrodes available. The modified stainless steel-based electrodes were assembled and tested in an AEM electrolyzer cell, which displays more than 300 mV-voltage drops compared to the bare stainless steel-based cells. The in-situ impedance spectroscopy revealed a significant decrease in the resistances due to interfacial contact, charge transfer, and mass transport. In addition, we identified nanocrystalline Fe-NiCr2O4 and nanocrystalline Ni(OH)2/Fe(OH)2 active species for SS used in hydrogen and oxygen evolution side respectively which could explain the significantly higher performance. In addition, we also developed an electrolyzer system to assess the long-term durability of our cell reactors in which our cells exhibited exceptional durability at 5.0 A (1.0 A cm-2) for 250 h. Our results exemplify that such an approach has the potential for upscaling and deployment in the next-generation, low-cost AEM electrolysis for green hydrogen production.

Tailoring highly stable anion exchange membranes with graft molecular structure ordering using reversible addition-fragmentation chain transfer polymerization for alkaline fuel cells

The radiation-induced grafting is used to prepare a variety of anion-exchange membranes (AEM) based on poly(ethylene-co-tetrafluoroethylene) (ETFE) utilizing a reversible addition-fragmentation chain transfer (RAFT) agent. The copolymerization process is controlled by the RAFT agent, resulting in AEMs with a restricted molecular weight dispersion. As a result, RAFT-AEMs exhibit decreased water uptake and reduced swelling. A significant improvement in thermal and mechanical characteristics is evidenced, while the conductivity remains practically unaltered. Anion-exchange membrane fuel cell (AEMFC) tests revealed that conventional RIG-AEMs and RAFT-AEMs with low RAFT content (5 wt%) have comparable beginning-of-life performances (∼0.95 W cm−2). However, for higher RAFT contents, the performance trends to decrease indicating an imbalance in water management. Furthermore, short-term stability tests suggest that RAFT-AEMs are able to operate highly stable, with a conductivity rate loss of 0.05% h−1, which represents an improvement of 160% in comparison to conventional RIG-AEM. AFM analysis demonstrated that structural ordering molecular and morphology tailor the fundamental properties of ETFE-based AEMs, combining enhanced performance and stability for alkaline fuel cell applications.

(Invited) New Membranes for Preventing Crossover in Non-Aqueous Redox Flow Batteries

Non-aqueous redox flow batteries have been considered as an alternative battery technology for grid storage due to the ability to operate at higher potentials with organic solvents. However, there are no commercial ion exchange membranes capable to handling these non-aqueous redox flow batteries, because they swell or degrade over time. This paper will discuss strategies for synthesizing stable anion exchange membrane separators for non-aqueous redox flow batteries to prevent crossover and improve long term stability.

Highly conductive and robustly stable anion exchange membranes with a star-branched crosslinking structure

In order to improve the ionic conductivity and durability of anion exchange membranes (AEMs), novel ether free AEMs are prepared based on 6-bromo-1-hexanol quaternized poly(terphenyl piperidine)s by construction of a star-branched crosslinking structure via a crosslinker of 1,3,5-tris(bromomethyl)benzene. The star-branched crosslinking network enhances the dimensional stability and mechanical property without occupying the active sites for cation production. Suitable microphase separations with ionic cluster spacing within 19.68–20.72 nm are formed according to the SAXS results. The proposed AEMs exhibit hydroxide ion (OH‾) conductivity ranging from 118 to 136 mS cm−1 at 80 °C. The dense crosslinking structure and flexible side chains endow the AEMs with excellent resistance against the attack of OH‾ ions. About 80% of the conductivity retention rate is achieved after immersing the AEMs in 1 mol L−1 KOH aqueous solutions at 80 °C for 1600 h. A single H2/O2 fuel cell employing the prepared membrane as the electrolyte exhibits a peak power density of 639 mW cm−2 at 60 °C without back pressure.

Highly conductive and dimensionally stable anion exchange membranes enabled by rigid poly(arylene alkylene) backbones

Dimensionally and chemically stable anion exchange membranes with excellent ion conductivity are highly desired in electrochemical energy conversion technologies. Herein, we present a design using rigid arylene units, i.e., p-tetraphenylene and p-terphenylene, to suppress the water sorption of quaternized poly(arylene alkylene) membranes with high ion contents. Of note, side chain double-quaternary ammonium (QA) functionalized poly(q-tetraphenylene-co-p-terphenylene alkylene) membrane P(4PA-co-3PA)-D100 with the IEC value as high as 2.93 mmol g−1 showed very limited water uptake and swelling at 80 °C of 75 wt% and 14 %, respectively. Meanwhile, the immiscibility of hydrophilic double-cation side chain and the hydrophobic poly(arylene alkylene) backbone drives the formation of phase-separated morphology. As a result, P(4PA-co-3PA)-D100 showed an exceptional conductivity of 227.8 mS cm−1 at 80 °C with activation energy of 10.5 kJ mol−1. Despite the rigid poly(arylene alkylene) backbone with highly chemical durability and oxidative stability, the tandem tethered double cation in the side chain showed a 11 % QA moiety loss after a 1000-h treatment in 2 M NaOH at 80 °C. Moreover, a good peak power density of 550 mW cm−2 at the current density of 1.06 A cm−2 was achieved for P(4PA-co-3PA)-D100 with the gases flow of 200 mL min−1. This work demonstrates that, in addition to the approach of cross-linking, the highly conductive AEMs with excellent dimensional stability can be achieved by improving the rigidity of polymer backbones.

Highly Ion-Conductive and Alkaline Stable Anion Exchange Membranes Containing Bulky Aryl Units and Symmetric bis-Piperidinium Branches

The challenge in developing high-performance anion exchange membranes (AEMs) involves achieving high ion conductivity while maintaining sufficient alkaline and mechanical stability. In this work, an aromatic monomer [bis(4′-(1,5-dibromopentan-3-yl)phenyl)-1,4-terphenyl (BBTP)] with a bulky aryl unit and symmetric dibrominated branches was first designed and synthesized. Then, BBTP was used to prepare aryl ether-free AEMs (QPTPDP-x-OH) via the superacid-catalyzed polyhydroxyalkylation and Menshutkin reactions. Due to the several structural advantages of BBTP, QPTPDP-x-OH membranes reached high hydroxide conductivity up to 161.5 mS cm–1 at 80 °C while maintaining good dimensional stability. Moreover, the membranes exhibited high alkaline stability with the conductivity retention above 80% after soaking in 5 M NaOH at 80 °C for 1200 h. In addition, QPTPDP-30-OH membranes achieved a peak power density of 407.8 mW cm–2 in H2–O2 fuel cells at 60 °C. The design strategy used in this work provided insights into the development of next-generation AEMs with high performance.

Chemically stable anion exchange membrane with 2,6-protected pendant pyridinium cation for alkaline fuel cell

In alkaline environment, cationic membranes regularly experience degradation because of OH− attack on the cation in anion exchange membrane fuel cells (AEMFCs). Unlike quaternized amine (alicyclic and aliphatic) cations, aromatic cations are unaffected by Hofmann ß-elimination, however, because of planar geometry they are highly susceptible to nucleophilic substitution reaction. A series of polysulfone (PSU) based anion exchange membranes (AEMs) was fabricated carrying pendant pyridinium cation with different substituent groups to shield the cation against OH− ions attack. The pyridinium cations were C-2 substituted, C-4 substituted and simultaneously C-2 and C-6 substituted with either –NH2, –OH or –CH3. Chloromethylation, azidation and CuAAC reactions were employed to synthesize the copolymers. The collaborative analysis of 1H NMR and FT-IR spectroscopy was used to confirm the successful preparation of the desired product. All membranes exhibited adequate thermo-mechanical stabilities and sufficient hydration level without any serious swelling at all ranges of temperature (20–80 °C). The highest recorded ionic conductivity, peak power density and current density were 59.6 mS cm−1, 486.8 mW cm−2 and 1481.8 mA cm−2 respectively. The alkaline stability results suggest that simultaneous protection of pyridinium cation at C-2 and C-6 turns the membrane thoroughly resistant to OH− attack while the ones with exposed cations degrade at accelerated rate at elevated temperature. This study is aimed at providing a broader understanding of designing durable AEMs with promising performance by exploring the influence of changes in structural configuration of aromatic cations with different functional groups on the overall performance of AEMs and how the cations withstand the nucleophilic attack in AEMFCs.

Highly Conductive and Ultra Alkaline Stable Anion Exchange Membranes by Superacid-Promoted Polycondensation for Fuel Cells

A series of anion exchange membranes (4-QPPAF-TMA) were prepared by a metal-free, superacid-promoted polymerization reaction. The polymers were obtained with high molecular weight (Mn = 9.5–19.6 kDa, Mw = 44.9–622.5 kDa). 4-QPPAF-TMA membranes exhibited high hydroxide ion conductivity (up to 115 mS cm–1) at 80 °C, reasonable water absorbability (45% water uptake at 30 °C for 1.7 meq g–1), low to moderate dimensional swelling (5–15% at 30–80 °C for 1.7 meq g–1), and mechanical robustness (12.8 MPa maximum stress and 32% elongation at break for 1.7 meq g–1). Furthermore, 4-QPPAF-TMA membranes exhibited excellent alkaline stability in 8 M KOH at 80 °C for 1000 h, maintaining high conductivity (105 mS cm–1, 97% remaining). density functional theory (DFT) calculations suggested that the unique molecular configuration of the pendant ammonium head groups was responsible for high resistivity to the hydroxide ion attack. A fuel cell was operated with the 4-QPPAF-TMA membrane and an ionomer using a non-PGM cathode catalyst (Fe–N–C) to achieve a peak power density of 215 mW cm–2 accountable for 860 mW mg–1 Pt at a 590 mA cm–2 current density and 0.40 V (Pt–C cathode achieved 370 mW cm–1 at 810 mA cm–2 and 0.50 V). The fuel cell was operated at constant current density (15 mA cm–2) for 240 h with −0.79 mV h–1 average cell voltage decay. The postdurability analyses revealed that the membrane did not deteriorate while the degradation of the cathode catalysts/ionomer caused the performance loss.

Physically and Chemically Stable Anion Exchange Membranes with Hydrogen-Bond Induced Ion Conducting Channels.

Anion exchange membranes (AEMs) with desirable properties are the crucial components for numerous energy devices such as AEM fuel cells (AEMFCs), AEM water electrolyzers (AEMWEs), etc. However, the lack of suitable AEMs severely limits the performance of devices. Here, a series of physically and chemically stable AEMs have been prepared by the reaction between the alkyl bromine terminal ether-bond-free aryl backbone and the urea group-containing crosslinker. Morphology analyses confirm that the hydrogen bonding interaction between urea groups is capable of driving the ammonium cations to aggregate and further form continuous ion-conducting channels. Therefore, the resultant AEM demonstrates remarkable OH- conductivity (59.1 mS cm-1 at 30 °C and 122.9 mS cm-1 at 90 °C) despite a moderate IEC (1.77 mmol g-1). Simultaneously, due to the adoption of ether-bond-free aryl backbone and alkylene chain-modified trimethylammonium cation, the AEM possesses excellent alkaline stability (87.3% IEC retention after soaking in 1 M NaOH for 1080 h). Moreover, the prepared AEM shows desirable mechanical properties (tensile stress > 25 MPa) and dimensional stability (SR = 20.3% at 90 °C) contributed by the covalent-bond and hydrogen-bond crosslinking network structures. Moreover, the resulting AEM reaches a peak power density of 555 mW cm-2 in an alkaline H2/O2 single fuel cell at 70 °C without back pressure. This rational structural design presented here provides inspiration for the development of high-performance AEMs, which are crucial for membrane technologies.

Superior Performance and Durability Water Electrolysis with a Highly Conductive and Stable Anion-Exchange Membrane

The commercialization of anion-exchange membrane water electrolysis (AEMWE) is important to produce low-cost and high-purity hydrogen. However, water electrolysis with an anion-exchange membrane (AEM) has limitations such as its poor stability and ionic conductivity, leading to low durability and performance of AEMWE. In this study, we developed superior-performance and stable AEMWE by employing an AEM without aryl-ether backbone structure. To achieve superior -performance and durable AEMWE, the effect of various parameters that is suitable for the adapted AEM was estimated. As a result, the AEM adapted in this work showed much better and was more durable than the conventional AEM (FAA-3). Moreover, it exhibited high efficiency under pure water feeding conditions. These results were contributed to high-efficient and durable AEM caused by its absence of aryl-ether backbone. This work suggests the potential use of polyphenylene structure as aryl-ether free backbone of AEM on AEMWE under alkaline solution and/or pure water condition.