Quaternary Ammonium Polysulfone Research Articles

Correlation between the Humidity-Dependent Surface Microstructure and Macroconductivity of Anion Exchange Membranes.

Anion exchange membrane (AEM) fuel cells have gained significant interest in recent years due to their promising applications in cost-effective and environmentally friendly energy conversion. Among various factors that affect their performance, water content plays an important role in the conductivity and stability of AEMs. However, the effect of the hydration level on the microstructure of AEMs and the correlation between the microstructure and macroconductivity have not been systematically investigated. In this work, four AEMs, quaternary ammonia polysulfone, quaternary ammonia poly(N-methyl-piperidine-co-p-terphenyl) (QAPPT), and bromoalkyl-tethered poly(biphenyl alkylene)s PBPA and PBPA-co-BPP, have been studied by atomic force microscopy and electrochemical impedance spectroscopy to elucidate the correlation between the humidity-dependent surface microstructure and macroconductivity of the AEMs. We obtained phase images by atomic force microscopy and identified hydrophilic and hydrophobic domains by fitting the distribution curve of phase images, which reasonably distinguishes hydrophilic domains from hydrophobic domains of the membrane surface, and thus, the surface hydrophilic area ratio and average size could be quantitatively analyzed. The conductivities of the membranes were then measured by electrochemical impedance spectroscopy at various humidities. The joint results from atomic force microscopy and electrochemical measurements help clarify the effect of the hydration level on the microphase separation and ionic conduction of the membranes.

Constructing proton selective pathways using MOFs to enhance acid recovery efficiency of anion exchange membranes

Efficient recovery of acids from industrial wastewater containing metal ions is crucial for resource recycling and environmental safety. Dialysis based on anion exchange membranes (AEMs) is a promising method for acid recovery but typically suffers from low selectivity. Herein, we develop highly stable AEMs based on metal-organic frameworks (MOFs) to improve the acid recovery performance. For membranes based on quaternary ammonium polysulfone (QAPSF) and quaternary ammonium poly (2,6-dimethyl-1,4-phenylene oxide) (QPPO), embedded MOFs can provide selective proton transport paths because of a precise size-sieving effect and abundant hydrogen-bonding networks, thus improving both the acid dialysis selectivity and flux. Remarkably, the QPPO membrane incorporated with 20 wt% UiO-66 exhibits a high dialysis coefficient of 16 mm/h and a separation factor of 683. The MOF-hybrid AEMs are sufficiently stable and retain their original structure and morphology after dialysis tests. In addition, molecular dynamics simulations suggest that the competitive Fe2+ ions are immobile and present a high energy barrier to diffuse in UiO-66, whereas water molecules can hop between the cavities of MOFs, thereby facilitating fast proton conduction and thus improving proton selectivity. Therefore, Zr-MOFs can be incorporated as porous sieving fillers into AEMs to develop advanced hybrid membranes for acid recovery.

Constructing highly utilizable Fe-N4 single-atom sites by one-step gradient pyrolysis for electroreduction of O2 and CO2

Fe-N4 single-atom catalysts (SACs) have been investigated extensively in various energy conversion reaction. However, large amount of untouchable Fe-N4 sites buried in the dense carbon skeletons greatly restrict the maximization of catalytic performance. Therefore, rational construction of catalyst nanostructure to effectively expose Fe-N4 single atom sites is eagerly desired. Here, we report a one-step gradient pyrolysis method by using quaternary ammonia polysulfone (QAPS) polymer with a lower carbonization temperature to segregate precursor particles (ZIF-8 and polyaniline) to construct mesopores at 4–9 nm, thereby tellingly increasing the accessibility of Fe-N4 single atom sites. Nitrite reduction method revealed that the prepared catalyst had a three-fold increase in active sites density compared to catalyst without QAPS. Thus, it exhibits a terrific peak power density (1.15 W cm−2) in proton exchange membrane fuel cells and a superior CO partial current density (121 mA cm−2) with 99 % Faradaic efficiency for CO at 0.5 V in flow cells.

Highly conductive anion exchange membranes based on polymer networks containing imidazolium functionalised side chains

Two novel types of anion exchange membranes (AEMs) having imidazolium-type functionalised nanofibrous substrates were prepared using the facile and potentially scalable method. The membranes’ precursors were prepared by graft copolymerization of vinylbenzyl chloride (VBC) onto syndiotactic polypropylene (syn-PP) and polyamide-66 (PA-66) nanofibrous networks followed by crosslinking with 1,8-octanediamine, thermal treatment and subsequent functionalisation of imidazolium groups. The obtained membranes displayed an ion exchange capacity (IEC) close to 1.9 mmol g–1 and ionic (OH-) conductivity as high as 130 mS cm–1 at 80 °C. This was coupled with a reasonable alkaline stability representing more than 70% of their original conductivity under accelerated degradation test in 1 M KOH at 80 °C for 360 h. The effect of ionomer binder on the performance of the membrane electrode assembly (MEA) in AEM fuel cell was evaluated with the optimum membrane. The MEA showed a power density of as high as 440 mW cm−2 at a current density is 910 mA cm−2 with diamine crosslinked quaternized polysulfone (DAPSF) binder at 80 °C with 90% humidified H2 and O2 gases. Such performance was 2.3 folds higher than the corresponding MEA performance with quaternary ammonium polysulfone (QAPS) binder at the same operating conditions. Overall, the newly developed membrane was found to possess not only an excellent combination of physico-chemical properties and a reasonable stability but also to have a facile preparation procedure and cheap ingredients making it a promising candidate for application in AEM fuel cell.

Molecular dynamics simulation of alkaline electrolyte diffusion in anion exchange membrane

During the operation of alkaline direct liquid fuel cells, the alkaline electrolyte is usually needed in the anode electrode to accelerate the electrochemical reaction kinetics of the liquid fuel. However, the crossover of the alkaline solution in the anode through the anion exchange membrane to the cathode can increase the transfer resistance of the oxygen in the cathode. In order to reduce the crossover of the alkaline solution, the diffusion process of the alkaline solution in the anion exchange membrane needs to be fully understood. In this work, interface models of anion exchange membrane-alkaline electrolytes are established based on the cell structure of the quaternary ammonium polysulfone (QAPS) membrane to simulate the dynamic process of the alkaline solution in the membrane. The effect of the type and the concentration of the alkaline solution on the transportation of the metal ions and OH− in the membrane are studied. The results show that the agglomeration of Na+ is formed more easily than K+ in the interface model. Because of the strong interaction of Na+ on OH−, OH− ions appear to be concentrated, resulting in that the diffusion coefficients of the metal ion and OH− in the in Na+ solution are lower than those in the K+ solution. In addition, with the raised concentration of electrolyte solution, the aggregation degrees of the metal ions and OH− can be increased, which means an enlarged mass transfer resistance of the components. Furthermore, by adding a polytetrafluoroethylene (PTFE) layer on the QAPS membrane, the distribution of metal ions tends to be concentrated, and the number of hydrophilic channels in the QAPS membrane is reduced, which significantly increases the alkali resistance of the anion exchange membrane.

Tailoring polyethersulfone/quaternary ammonium polysulfone ultrafiltration membrane with positive charge for dye and salt selective separation

AbstractPolyethersulfone (PES)/quaternary ammonium polysulfone (QAPSf) blend ultrafiltration (UF) membranes with positive charge were fabricated by nonsolvent induced phase separation (NIPS) for use in dye and salt selective separation. QAPSf was synthesized by nucleophilic substitution with chloromethylated polysulfone (CMPSf). The effect of the PES/QAPSf mass ratio on the morphology and performance of blend UF membranes were studied. The membranes' zeta potentials gradually changed from negative to positive with decreases in the PES/QAPSf mass ratio. At PES/QAPSf mass ratios of 30:70 and 10:90, the zeta potentials of the membranes reached +1.8 mV and + 5.9 mV, respectively. Additionally, the contact angles of the membranes decreased from 74° to 52° as the QAPSf content increased from 0 wt% to 90 wt%. Furthermore, the membrane with a PES/QAPSf mass ratio of 30:70 showed a high water permeance (181.4 LMH bar−1) and excellent dye and salt selective separation performance. The rejection ratios reached 99.1%, 87.8%, 99.6%, and 92.4% for dyes Congo red, methyl blue, Alixin blue 8GX, and basic blue 24, respectively, while those for salts Na2SO4, MgSO4, MgCl2, and NaCl were ≤ 10%. In addition, the PES/QAPSf membranes showed excellent antifouling performance and good operating stability with dye‐salt mixtures of various pHs and salt concentrations.

The effect of material on bipolar membrane fuel cell performance: A review

Bipolar membrane fuel cell (BPMFC) was firstly discovered in 2000 that composed of two-layered ionic conducting membranes. The importance of BPMC development is its ability to humidify the cell when operating at a high current density that eliminates the use of the external humidification system. It is able to self-humidify the cell because of water formation at the intermediate layer from the reaction of hydrogen ion (H+) with hydroxide ion (OH−). Up to now, there is no commercial bipolar membrane (BPM) in water formation configuration for the fuel cell humidifying purpose. Thus, the researcher had come out with a composition of proton exchange membrane with anion exchange membrane by the hotpressing method that allows them to carry the proton and anion simultaneously in a single cell. There are a few of polymeric-based PEM and AEM material had been selected for developing BPM such as Nafion, FumaPEM FAA3, quaternary ammonium polysulfone (QAPSF), and quaternary ammonium poly(phenylene)oxide (QAPPO). This review aims to determine the effect of material selection and design for developing BPM toward its performance in fuel cell based on published works. Besides, the potentialities of polymeric-based material are discussed, pointing out the main positive and negative effect of this BPM for fuel cell applications. As a case study, the use of different types of PEM and AEM material for BPM is particularly stressed, pointing out the main properties for its applications in BPMFC.

Preparation of acid block anion exchange membrane with quaternary ammonium groups by homogeneous amination for electrodialysis-based acid enrichment

Proton leakage defect of anion exchange membrane (AEM) seriously restricts the applications of electrodialysis (ED) in acid enrichment. Different from conventional scheme in which weak base groups are usually introduced, strong base AEMs are endowed with acid block property by the specific design of membrane microstructure in this work. Firstly, as confirmed by 1H NMR and FTIR, a series of quaternary ammonium polysulfone containing long alkyl side chains pendant are synthesized for AEM preparation. Small Angle X-ray Scattering experiments show that ionic domains form a distinct and well-separated phase. The introduced hydrophobic side chains strengthen the hydrophobic matrix and then restrict AEM water uptake. Besides, some interesting confinement effects are observed, for examples, the reinforcement of Donnan exclusion for H+ and facilitated transport of counter-ions. Furthermore, influences of pendant carbon chain length and ion exchange capacity are investigated. Notably, ED measurements show as-prepared AEMs indeed display excellent acid block performance, a current efficiency of almost 100% under certain condition, which substantially exceeds that of conventional AEM fabricated by heterogeneous aminaiton. This observation demonstrates an unprecedented result that novel strong base AEM with both outstanding acid block performance and membrane conductivity can be achieved by constructing phase separation microstructure.

Microscopic phase-segregated quaternary ammonia polysulfone membrane for vanadium redox flow batteries

Anion-exchange membranes have been investigated for vanadium redox flow batteries. However, their commercial application is plagued by the low transportation efficiency of anions in the membranes. Inspired by a strategy for constructing an ionic highway in alkaline anion-exchange membranes to accelerate the migration of anions. Thus, a well-segregated phase morphology is achieved to construct three-dimensional anion channels via architectural design of amphiphilic quaternary ammonium polysulfone with hydrophobic hexane side chains. This unique morphology gives the membrane enhanced conductivity with less water uptake, and this thereby enables the vanadium redox flow battery that is fabricated with the microscopic phase-segregated membrane to have better voltage and energy efficiency under current densities in the range of 60–150 mA cm−2. Furthermore, the vanadium redox flow battery using the microscopic phase-segregated membrane has excellent cycling stability. These investigations provide a universal strategy for developing of anion-exchange membranes that have high-conductivity and are stable for use in vanadium redox flow batteries.

Constructing an internally cross-linked structure for polysulfone to improve dimensional stability and alkaline stability of high performance anion exchange membranes

The preparation of quaternary ammonium polysulfone anion exchange membranes (AEMs) with good dimensional stability and alkaline stability is an urgent problem to solve. In response, a series of cross-linked based on polysulfone and 4, 4′-trimethylenedipiperidine (TMDP) as crosslinkers with different degrees AEMs were developed in this work through a simple process. Among the fabricated AEMs, CAPSF-5 exhibits superb alkaline stability in a 1 M KOH aqueous solution at 60 °C for 15 days, whereas the non-crosslinked APSF membrane became tremendously brittle within 24 h and could not be further studied under the same conditions. In addition, even at 60 °C, CAPSF-5 demonstrates a superior dimensional stability compared to the non-crosslinked APSF membrane due to the formation of a dense internal network structure. These observations demonstrate that crosslinked CAPSF membranes can be a viable strategy to improve the deficiency of the polysulfone backbone, especially in terms of alkaline stability.

Understanding mass and charge transports to create anion-ionomer-free high-performance alkaline direct formate fuel cells

The disadvantage of anion ionomer that possesses low hydroxide conductivity, and thermal and chemical instability hinders the development of the high-performance anion-exchange membrane direct liquid fuel cells. Instead of adding additional base and synthesizing high-conductivity ionomer material, by gaining insight into species transports, herein, we propose an anion-ionomer-free anion-exchange membrane direct formate fuel cell (AEM DFFC). Experimental result reveals that this conceptual anion-ionomer-free AEM DFFC can operate stably within a 6-h constant-current discharge at 10 mA cm−2, mainly because formate hydrolysis renders a high OH− conductivity. It was also found that the anion-ionomer-free AEM DFFC yields a peak power density as high as 41 mW cm−2 at 40 °C, 40% higher than that of the conventional quaternary ammonia polysulfone anion-ionomer AEM DFFC. This can be attributed to the fact that the OH−-containing formate solution facilitates the mass and charge transports, thereby enlarging the triple-phase boundary for both anodic formate oxidation reaction and cathodic oxygen reduction reaction.

Constructing interconnected ionic cluster network in polyelectrolyte membranes for enhanced CO2 permeation

Membranes with fast CO2 transport pathways have attracted intense attention due to their outstanding CO2 permeability, showing potential for industrial application. Regulating the spatial distribution of CO2-philic groups in polymer-based membranes is expected to be a promising strategy to achieve the fast CO2 transport pathways. In membrane matrix, the interconnected network of concentrated domains of CO2 facilitated transport groups provides membranes with specific CO2 transport pathways and finally leads to their high separation performance. In this study, a novel kind of polyelectrolyte membrane, quaternary ammonium polysulfone with interconnected ionic clusters, is prepared to enhance the CO2 permeability. The hydrophilic quaternary ammonium groups tend to aggregate spontaneously to create ionic clusters. Furthermore, under humidified conditions, these ionic clusters are connected by water to form an ionic cluster network in the membrane matrix. The ionic cluster network plays the crucial role in accelerating the selective transport for CO2 molecules over CH4 by the reversible interaction between CO2 and ion pairs. By tuning the quaternization degree of polysulfone, a series of polyelectrolyte membranes with different size of ionic clusters were developed. Membranes with hydrated ionic clusters (5–9 nm) show dramatic enhancement in CO2 separation performance, especially in CO2 permeability. The as-prepared quaternary ammonium polysulfone membrane with 8.98 nm ionic clusters exhibited the high CO2 permeability of 1109.44 Barrer and a high CO2/CH4 selectivity of 29.70, which exceeds 2008 Robeson upper bound limit. The optimized separation performance of QA-PSf membranes is attractive for potential application such as CO2 capture from flue gas and natural gas.

A polysulfone-based anion exchange membrane for phosphoric acid concentration and purification by electro-electrodialysis

A series of quaternary ammonium polysulfone (QAPSU) anion exchange membranes used the chlorotrimethylsilane instead of toxic chloromethyl methyl ether and quaternized-functionalized by trimethylamine ethanol solution were prepared. The effect of chloromethylation reaction time on membrane morphologies and physiochemical properties such as ion exchange capacity, water swelling, and membrane area resistance, mechanical and thermal stabilities was investigated. When being applied in electro-electrodialysis (EED) for purifying phosphoric acid solution, the QAPSU membranes exhibit high purification efficiency, especially all the metal ions (Fe, Mg, Ca) removal rates reach over 60%, which suggests that the QAPSU membranes have a high potential for EED application.

Improved Electrochemical Performance of Alkaline Batteries Using Quaternary Ammonia Polysulfone-Functionalized Separators

Flow-permeable separators underwent surface modification, and their performances were evaluated to determine the impact of an ion-exchange coating on the electrochemical properties of sandwich diffusion batteries. A zinc–alkaline system was used to evaluate this performance at high discharge rates and diffusion overpotentials across the separator. An alkaline-resistant anion-exchange polyelectrolyte was synthesized based on a quaternary ammonia polysulfone system to utilize the coated separators for faster ion and counterion transport, and the obtained functionalized separators were compared with stationary inert porous separators. Accordingly, the discharge behavior of primary battery systems for both inactive and functionalized separators was introduced. According to discharge profiles, the practical voltage range, specific capacity, and utilization of active materials were improved, and ionic conduction was enhanced and verified by electrochemical impedance spectroscopy. Different commercial filter papers were examined to determine the optimal polymer–substrate compatibility.

Bipolar Interfacial Polyelectrolyte Membrane Fuel Cell Ⅱ: Optimization of Cathode Catalyst Layer

Bipolar fuel cell (BPFC) is a new kind polymer electrolyte membrane fuel cell (PEMFC) with acidic-alkaline bipolar interface formed by acidic and alkaline polyelectrolyte both used in one cell. BPFC has shown some novel characterizations: (1) water generated at the bipolar interface would provide the possibility to devise self-humidification over the entire cell, which would simplify the water manager system; (2) alkaline cathode with facilitated electrokinetics allows for the use of lower catalyst loading or non-noble catalysts, such as silver and nickel. In our previous work, the effect of bipolar membrane electrode configuration on the cell output performance was evaluated and the optimal configuration was achieved. The BPFC with optimal membrane electrode configuration has been operated under completely self-humidifying conditions for prolonged periods successfully. However, there exists a big gap with the cell performance between BPFC and the state-of-art PEMFC. In order to improve the fuel cell performance, optimization of the membrane electrode configurations and further advances in fabricating bipolar interface had been conducted in our previous work. Another issue that affects the performance of the fuel cell is the structure and composition of the catalyst layer. Since the oxygen reduction reaction (ORR) at cathode influenced the fuel cell performance a lot, the improvement of electrode was mainly focused on the cathode catalyst layer. In the present work, thin hydrophilic electrode and thick hydrophobic electrode were used as cathode for BPFC. The influence of ionomer binder, quaternary ammonium polysulfone (QAPSF) in thin hydrophilic electrode and polytetrafluoroethylene (PTFE) in thick hydrophobic electrode, concentration on BPFC performance was studied. The results indicated that the optimal content of QAPSF in thin hydrophilic cathode was 20 wt%, and the peak power density of BPFC reached to 186.1 mW/cm at 25 °C without humidification. While the PTFE in the thick hydrophobic cathode was also 20 wt% with a peak power density of 461.5 mW/cm at 40 °C without humidification. Due to the high demand of alkaline cathode for drainage, the thick hydrophobic electrode behaved better than thin hydrophilic electrode in BPFC.

Constructing ionic highway in alkaline polymer electrolytes

Alkaline polymer electrolytes (APEs) are an emerging material that enables the use of nonprecious-metal catalysts in electrochemical energy technology, such as fuel cell and water electrolysis. Yet the OH− conduction in APE has been of much lower efficiency than the H+ conduction in its acidic counterpart (typically Nafion), leading to a large dissipative loss in energy conversion applications. Here we report that, by properly constructing ion-aggregating structures in APE, a OH− conducting highway can be built, such that the OH− conduction in APE becomes as efficient as the H+ conduction in Nafion (greater than 0.1 S cm−1 at 80 °C under moderate ion-exchange capacity 1.0 mmol g−1). The optimal approach to constructing such an ionic highway is first screened computationally using coarse-grained molecular dynamics (CGMD) simulations, and then implemented experimentally based on a quaternary ammonia polysulfone (QAPS) model system. The resulting ordered structure of ion assembly has been unambiguously revealed by both the theoretically calculated structure factor and experimental results of TEM and SAXS. These findings have not only furthered our understanding about the ionic channels in APE, but also provided a general strategy for the rational design of polymer electrolytes.

Alkaline polymer electrolyte fuel cell with Ni-based anode and Co-based cathode

Alkaline polymer electrolyte fuel cells (APEFCs) are a new class of fuel cell that has been expected to combine the advantages of alkaline fuel cells (AFCs) and polymer electrolyte fuel cells (PEFCs). In recent decade, APEFCs have drawn much attention in the fuel cell world. While great efforts have been devoted to the development of high-performance alkaline polymer electrolytes (APEs), prototypes of APEFC using nonprecious metal catalysts in both the anode and the cathode have not been well implemented, except for our previous report where Ni–Cr was used as the anode catalyst and Ag was employed as the cathode catalyst. In the present work, we report our recent progress in this regard. The self-crosslinked quaternary ammonia polysulfone (xQAPS), a high-performance APE that possesses both good ionic conductivity and extremely high dimensional stability, is applied as both the electrolyte membrane and the ionomer impregnated in the electrodes. Carbon-supported Co-polypyrrole (CoPPY/C) is employed as the cathode catalyst and a new Ni-based catalyst, W-doped Ni, is used as the anode catalyst, which features in high oxidation tolerance. H2–O2 and H2-air APEFCs are thus fabricated and show a decent performance with peak power density being 40 and 27.5 mW/cm2 at 60 °C, respectively.

Ultrathin composite membrane of alkaline polymer electrolyte for fuel cell applications

To minimize the ohmic loss in the cell voltage of fuel cells, the electrolyte should be made as thin as possible, in particular when alkaline polymer electrolytes (APEs) are employed, where both the mobility and the concentration of OH− are relatively low. A practical strategy for fabricating thin APE membranes is to impregnate APE ionomers into an ultrathin, rigid framework (such as a porous PTFE film), so that high ion conduction is achieved by the APE with a high ion-exchange capacity (IEC), while good mechanical stability is provided by the robust host. Our previous study has realized a prototype of an APE fuel cell (APEFC) using this kind of composite membrane but we found later that the APE component, quaternary ammonium polysulfone (QAPS), will leach out gradually under fuel cell operating conditions because of the poor interaction between the QAPS guest and the PTFE host. To address this problem, we demonstrate in the present work a new approach for making ultrathin composite membranes of APEs. The APE ionomer (TQAPS) is impregnated into a porous PTFE film, followed by a self-crosslinking process, so as to form a semi-interpenetrating network. The resulting ultrathin composite membrane (xQAPS@PTFE, 25 μm thick) is highly tolerant to leaching in 80 °C water and possesses low area resistance (0.09 Ω cm2), a low swelling degree (3.1% at 60 °C) and high mechanical strength (31 MPa). Making use of such an xQAPS@PTFE membrane, the H2–O2 APEFC exhibits a peak power density of 550 mW cm2 at 60 °C under 0.1 MPa of back pressure.

Quaternary ammonia polysulfone-PTFE composite alkaline anion exchange membrane for fuel cells application

The quaternary ammonia polysulfone (QAPS) alkaline anion exchange membrane (AAEM) was previously prepared successfully. The QAPS membrane showed good ionic conductivity but poor mechanical strength and high swelling ratio. This study focused on membrane mechanical strength and dimensional stability by PTFE membrane enhancement, which increases the mechanical strength by five times and decreases the swelling ratio by 50%. The fuel cell with the resulted thinner QAPS/PTFE composite membrane with catalyst coated membrane (CCM) as the electrode showed a high power output, and the peak power density of 315 mW cm−2 was achieved at 50 °C.

Computational modeling of structure and OH-anion diffusion in quaternary ammonium polysulfone hydroxide – Polymer electrolyte for application in electrochemical devices

Using computational approaches we predict the microstructure of high-performance alkaline polymer, quaternary ammonium polysulfone hydroxide (QAPS-OH) membranes, dry and with ∼14wt% water uptake. The microstructure can be described as a hydrophobic polymer backbone penetrated by a network of three-dimensional interlinked hydrophilic channels of different diameters. Mobile OH-anions are distributed inside the channels. OH diffusion coefficients and corresponding activation energy were calculated from our molecular dynamics simulations of the QAPS-OH membrane at different temperatures. The predicted values are consistent with available experimental data. Possible mechanisms of the OH-anion diffusion have been discussed.