Alkaline Stability Research Articles

Bis-cationic crosslinked anion exchange membranes based on carbazole-containing polyaromatics with excellent ionic conductivity for alkaline water electrolysis

As the core component in anion exchange membrane water electrolyser (AEMWE), anion exchange membrane (AEM) directly determines the electrolysis performance and long-term durability of AEMWE. Herein, we synthesized novel poly(carbazole-p-terphenylpiperidine) (PCTP-x) copolymers and then prepared a series of bis-cationic cross-linked AEMs (QPCTP-x-bpip) using the Menshutkin reaction between the cross-linker 4,4′-trimethylenebis(1-methylpiperidine) and the alkyl bromide on the polymer side chains. For comparison, non-crosslinked AEMs containing alkylpiperidinium side chains (QPCTP-x-pip) were prepared via a grafting reaction of alkyl bromide with 1-methylpiperidine. The bis-cationic crosslinked membrane exhibited high hydroxide conductivity of 190.0 mS cm−1, and demonstrated outstanding alkaline stability in a 1 M KOH solution at 80 °C, retaining more than 90 % of the initial hydroxide conductivity and tensile strength after 2200 h alkaline treatment. Meanwhile, the flexural carbazole backbone enhanced polymer solubility, enabling the utilization of QPCTP-20-pip as an anion exchange ionomer (AEI) in AEMWE. For the water electrolysis testing, AEMWE employing QPCTP-20-bpip as the AEM and QPCTP-20-pip as the AEI exhibited excellent performance, achieving a current density of 2910 mA cm−2 at 2.0 V using a 1 M KOH feed at 80℃. Moreover, the voltage increase during the in-situ durability test over 200 h was a mere 0.65 mV/h, demonstrating its promising potential for AEMWE applications.

Pd@CuInP2S6 Core-Shell Nanospheres with Exceptional Hydrogen Evolution Capability and Stability in Both Alkaline and Acidic Media under Large Current Density Exceeding 1000mAcm-2.

By combining Pd with 2D layered crystal CuInP2S6 (CIPS) via laser irradiation in liquids, low-loading Pd@CIPS core-shell nanospheres are fabricated as an efficient and robust electrocatalysts for HER in both alkaline and acidic media under large current density (⩾1000mAcm-2). Pd@CIPS core-shell nanosphere has two structural features, i) the out-shell is the nanocomposite of PdHx and PdInHx, and ii) there is a kind of dendritic structure on the surface of nanospheres, while the dendritic structure porvides good gas desorption pathway and cause the Pd@CIPS system to maintain higher HER activity and stability than that of commercial Pt/C under large current densities. Pd@CIPS exhibits very low overpotentials of -218 and -313mV for the large current density of 1000mAcm-2, and has a small Tafel slope of 29 and 63mVdec-1 in 0.5mH2SO4 and 1mKOH condition, respectively. Meanwhile, Pd@CIPS has an excellent stability under -10 and -500mAcm-2 current densities and 50000 cycles cyclic voltammetry tests in 0.5mH2SO4 and 1mKOH, respectively, which being much superior to that of commercial Pt/C. Density functional theory (DFT) reveals that engineering electronic structure of PdHx and PdInHx nanostructure can strongly weaken the Pd─H bonding.

Organic and Metal–Organic Polymer-Based Catalysts—Enfant Terrible Companions or Good Assistants?

This overview provides insights into organic and metal–organic polymer (OMOP) catalysts aimed at processes carried out in the liquid phase. Various types of polymers are discussed, including vinyl (various functional poly(styrene-co-divinylbenzene) and perfluorinated functionalized hydrocarbons, e.g., Nafion), condensation (polyesters, -amides, -anilines, -imides), and additional (polyurethanes, and polyureas, polybenzimidazoles, polyporphyrins), prepared from organometal monomers. Covalent organic frameworks (COFs), metal–organic frameworks (MOFs), and their composites represent a significant class of OMOP catalysts. Following this, the preparation, characterization, and application of dispersed metal catalysts are discussed. Key catalytic processes such as alkylation—used in large-scale applications like the production of alkyl-tert-butyl ether and bisphenol A—as well as reduction, oxidation, and other reactions, are highlighted. The versatile properties of COFs and MOFs, including well-defined nanometer-scale pores, large surface areas, and excellent chemisorption capabilities, make them highly promising for chemical, electrochemical, and photocatalytic applications. Particular emphasis is placed on their potential for CO2 treatment. However, a notable drawback of COF- and MOF-based catalysts is their relatively low stability in both alkaline and acidic environments, as well as their high cost. A special part is devoted to deactivation and the disposal of the used/deactivated catalysts, emphasizing the importance of separating heavy metals from catalysts. The conclusion provides guidance on selecting and developing OMOP-based catalysts.

Impact of functionalized titanium oxide on anion exchange membranes derived from chemically modified PET bottles

The accessibility of newly affordable materials has drawn significant attention to the anion exchange membrane (AEM) technology. However, developing a high-performance AEM with excellent hydroxide conductivity and long-term durability is still challenging. The present work aims to improve the overall properties of AEMs synthesized by chemical modification of Polyethylene terephthalate (PET) bottles as the starting material. The modified PET structure was confirmed using IR, NMR, and HPLC-ESIMS analyses. AEMs were developed by incorporating quaternary ammonium (QA) functional groups into the modified PET structure, necessary for transporting anionic species (OH−). In addition, TiO2 nanoparticles grafted with silane coupling agents containing amine functional groups were synthesized via the sol-gel method and embedded in the polymer matrix. Then, the prepared nanocomposite membranes were thoroughly characterized, and the results displayed an overall improvement in the membrane's physicochemical properties. The composite membrane with 3wt% content of nanoparticle (NC3 %/M-PETm) showed remarkable conductivity, reaching 126 mS/cm at 80 °C, doubling the value of pristine membranes (64 mS/cm) while also displaying alkaline stability, retaining up to 92.2 % of conductivity after 20 days in harsh 2 M KOH at 80 °C. These results proved the suitability of these membranes for electrochemical energy applications. This innovative approach offers potential cost savings in preparing the new membranes while aligning with sustainable and circular economy principles.

Impact of side chain length on the properties and alkaline fuel cell performance of OEG-grafted poly(terphenyl piperidinium) anion exchange membranes

In designing comb-shaped anion exchange membranes (AEMs), replacing alkyl side chains with ethylene glycol (EG)-based ones significantly enhances membrane properties and boosts AEM fuel cell performance. Although much research has focused on optimizing the placement of EG segments within the polymer matrix, the effect of EG chain length remains less explored. In this work, a series of poly(terphenyl piperidinium) AEMs with N-oligo(ethylene glycol) (OEG) terminal pendants having two to five EG repeating units were prepared by simple post-polymerization quaternization. The membrane properties showed a strong correlation with the length of the OEG side chains, influenced by both chemical composition and phase behavior. Among the OEG-grafted AEMs, PTP-OEG3 with moderate three EG repeating units, exhibited the best properties due to a careful balance between EG and cationic groups, leading to a favorable microphased separation. It achieved high hydroxide conductivity (114 mS cm−1 at 80 °C in water), robust mechanical strength (tensile strength >52 MPa), and good ex situ alkaline stability. As a result, the AEM fuel cells with the property-balanced PTP-OEG3 membrane achieved the highest peak power density of 976 mW cm−2. The in situ stability of these AEMs was also investigated. Evidently, understanding the optimal EG side chain length is an important criterion for designing AEM materials for alkaline fuel cells.

Ruthenium-doped dual-phase cobalt catalysts for enhanced electrocatalytic hydrogen evolution

Controlling the structural sensitivity and selectivity of metal catalysts in reactions, such as the hydrogen evolution reaction (HER) on cobalt crystals, remains a challenging issue in heterogeneous catalysis. In this study, we introduced a straightforward approach to tuning the phase composition of hexagonal close-packed cobalt (HCP-Co) and face-centered cubic cobalt (FCC-Co) in a core–shell Co/C catalyst through the incorporation of Ru atoms. The HER performance was evaluated by controlling the contents of HCP-Co and FCC-Co phases in the catalysts. Single-atom Ru-doped cobalt catalysts containing dual-phase HCP and FCC were prepared by a mechanical ball-milling zeolitic imidazolate framework (ZIF-67) with appropriate ruthenium chloride, followed by a pyrolysis process. The doping of Ru resulted in changes in the contents of the HCP-Co and FCC-Co phases, which significantly boosted the HER activity of the catalysts. The obtained biphasic Ru-Co/C catalyst demonstrated ultra-low HER overpotential and promising stability in alkaline and acidic media, outperforming single-phase cobalt and commercial Pt/C catalysts. Theoretical calculations revealed the synergistic catalysis effect of biphasic cobalt on HER. These findings, which indicated that significant activity dependence on the crystallographic structure, may inspire new design concepts for efficient metal electrocatalysts.

High stable poly (terphenyl-co-fluorene quinuclidinium) anion exchange membrane for alkaline water electrolysis

Developing anion exchange membranes (AEMs) is an effective way to reduce the cost of water electrolyser systems and fuel cell systems because of the no requirement of platinum-group-metal (PGM) catalysts. However, low conductivity and poor stability are the bottlenecks that constrain its development. In this work, we propose a series of performance enhanced poly (terphenyl-co-fluorene quinuclidinium) (TPFQ) AEMs. The hydroxide conductivity of TPFQ-10 reached 178.5 mS cm−1 at 80 °C. The rigid fluorene group gives the membrane better dimensional stability (swelling ratio: 7.7% in pure water and 1.2% in 10 M NaOH at 80 °C for TPFQ-10). In particular, the membranes exhibit extremely high alkaline stability, with almost no conductivity loss over more than 2000 h in a 10 M NaOH solution. The AEM water electrolysers (AEMWEs) with nickel-alloy foam electrodes shows an excellent current density of 2.32 A cm−2 at 2.0 V. The AEMWEs can work steadily at a current density of 0.5 A cm−2 in 5 M NaOH at 80 °C for more than 500 h, with a low voltage rising rate of 56 μV h−1.

Ionic nanoporous membranes from self-assembled liquid crystalline brush-like imidazolium triblock copolymers.

There is a need to generate mechanically and thermally robust ionic nanoporous membranes for separation and fuel cell applications. Herein, we report a general approach to the preparation of ionic nanoporous membranes through custom synthesis, self-assembly, and subsequent chemical manipulations of ionic brush block copolymers. We synthesized polynorbornene-based triblock copolymers containing imidazolium cations balanced by counter anions in the central block, side-chain liquid crystalline units, and sidechain polylactide end blocks. This unique platform comprises: (1) imidazolium/bis(trifluoromethanesulfonyl)imide (TFSI) as the middle block, which has an excellent ion-exchange ability, (2) cyanobiphenyl liquid crystalline end block, a sterically hindered hydrophobic segment, which is chemically stable and immune to hydroxide attack, (3) polylactide brush-like units on the other end block that is easily etched under mild alkaline conditions and (4) a polynorbornene backbone, a lightly crosslinked system that offers mechanical robustness. These membranes retain their morphology before and after backbone crosslinking as well as etching of polylactide sidechains. The ion exchange performance and dimensional stability of these membranes were investigated by water uptake capability and swelling ratio. Moreover, the length of the carbon spacer in the imidazolium/TFSI central block moiety endowed the membrane with improved ionic conductivity. The ionic nanoporous materials are unusual due to their singular thermal, mechanical, alkaline stability and ion transport properties. Applications of these materials include electrochemical actuators, solid-state ionic nanochannel biosensors, and ion-conducting membranes.

Novel Anion Exchange Membrane Design Strategies Toward Improved Water Electrolysis Performance

Long-term energy storage is crucial for transitioning from fossil fuels to renewable energies due to the fluctuating energy generation of renewable energy sources such as solar or wind.[1,2] Water electrolysis could produce hydrogen from water and electricity from renewable energy resources, thus solving the energy storage problem.[3] Recent research aims to combine the advantages of alkaline water electrolysis (AWE) and the zero-gap architecture of proton exchange membrane water electrolysis (PEMWE). Limitations of this so-called AEMWE are the lower hydroxide conductivity compared to proton conductivity and, consequently, lower current densities. Furthermore, the chemical stability of AEMs still limits their technical applicability.[4–6] Sustainion®, a commercially available AEM, is a 4-vinylbenzyl chloride styrene copolymer quaternized with 1,2,4,5-tetramethylimidazole.[5,7] Sustainion® shows excellent performance in AEMWE and CO2 electrolysis.[7–9] However, on other polymer systems, it was found that the conductivity and alkaline stability could be increased if the cationic group is separated from the backbone by an alkyl spacer.[10–12] Furthermore, other cationic groups or polymer backbones also offer several advantages. In this study, we demonstrate some new membrane synthesis approaches aiming to enhance the performance of AEMs in electrochemical water-splitting devices. The demonstrated approaches involve attaching different side chains, which may vary in length or the presence of heteroatoms like oxygen. Furthermore, cationic groups like sterically protected imidazoliums are attached to these side chains to study their influence on long-term stability. Finally, our synthetic approaches comprise different membrane preparation strategies such as blending, crosslinking, or applying block-copolymers. The novel polymers are characterized by state-of-the-art methods of polymer chemistry and are further investigated regarding their applicability in AEMWE. Finally, their ionic conductivity, alkaline stability, ion exchange capacity, and the respective performance in AEMWE are investigated.[1] G. A. Lindquist, Q. Xu, S. Z. Oener, S. W. Boettcher, Joule 2020, 4, 2549.[2] A. Kiessling, J. C. Fornaciari, G. Anderson, X. Peng, A. Gerstmayr, M. Gerhardt, S. McKinney, A. Serov, A. Z. Weber, Y. S. Kim, B. Zulevi, N. Danilovic, J. Electrochem. Soc. 2022, 169, 24510.[3] N. Du, C. Roy, R. Peach, M. Turnbull, S. Thiele, C. Bock, Chemical reviews 2022, 122, 11830.[4] S. Gottesfeld, D. R. Dekel, M. Page, C. Bae, Y. Yan, P. Zelenay, Y. S. Kim, J. Power Sources 2018, 375, 170.[5] D. Henkensmeier, M. Najibah, C. Harms, J. Žitka, J. Hnát, K. Bouzek, J. Electrochem. Energy Convers. Storage 2021, 18.[6] N. Chen, Y. M. Lee, Prog. Polym. Sci. 2021, 113, 101345.[7] Z. Liu, S. D. Sajjad, Y. Gao, H. Yang, J. J. Kaczur, R. I. Masel, Int. J. Hydrog. Energy 2017, 42, 29661.[8] J. J. Kaczur, H. Yang, Z. Liu, S. D. Sajjad, R. I. Masel, Front. Chem. 2018, 6, 263.[9] R. I. Masel, Z. Liu, S. Sajjad, ECS Trans. 2016, 75, 1143.[10] H.-S. Dang, P. Jannasch, Macromolecules 2015, 48, 5742.[11] S. Miyanishi, T. Yamaguchi, Polym. Chem. 2020, 11, 3812.[12] S. P. Ertem, E. B. Coughlin, Macromol. Rapid Commun. 2022, 43, e2100610.

Enhanced Local Ion Transport in High-Performance Anion Exchange Membrane Water Electrolyzers Via Quaternary Ammonium-Functionalized Metal-Organic Framework Electrocatalysts

Anion-exchange membrane water electrolyzers (AEMWEs) present a multitude of advantages, particularly in the utilization of non-platinum group (non-PGM) catalysts. While diverse catalysts have demonstrated notable electrocatalytic activity in alkaline conditions, the integration of the ionomer with the electrocatalyst at the active catalyst layer is crucial for enhancing overall AEMWE performance in practical device demonstrations by improving mass transport. However, the intrinsic instability of polymeric ionomers, leading to physical detachments or alkaline (chemical) degradation, poses a challenge that can potentially diminish performance. In this study, drawing inspiration from the aforementioned ionomer chemistry, we introduce non-PGM NiFe-based metal-organic frameworks (MOFs) incorporating quaternary ammonium (QA) cation moieties covalently functionalized to benzenedicarboxylic acid (BDC) ligands as promising electrocatalysts for the oxygen evolution reaction (OER) in alkaline environments. Three specifically designed functional groups with varying ion exchange capacities (IEC) and alkaline stability—trimethylamine (TMA), N-methylpyrrolidine (C4N), and N-methylpiperidine (C5N)—were directly tethered to BDC ligands. The alkaline OER activity of Ni2Fe1-QA-MOF was meticulously assessed using rotating disk electrodes and AEMWE devices. These directly tethered QA groups markedly facilitated improved ionic transport of OH- ions at the catalyst/electrolyte interfaces compared to BDC ligands, ultimately leading to a significant enhancement in half-cell activity and AEMWE performance. In-situ IR/RAMAN spectroscopy revealed that QA moieties highly promoted local ionic transport at the interfaces, as evidenced by characteristic peaks indicating a robust interaction between QA and OH- ions. Unexpectedly, QA moieties not only contributed to ionic transport in local environments but also induced oxidation states of Ni metal sites, while Fe sites exhibited no changes during the applied potential in the OER region, as comprehensively revealed by synchrotron X-ray absorption spectroscopy (XAS). In comparison with conventional NiFe layered double hydroxide (LDH) structures, we posit that the substantial structural transformation of Ni moieties can be attributed to an increased degree of M-O bond interaction, enhanced by the local interaction between QA and OH- ions. Density functional theory (DFT) calculations also validate the balanced adsorption of OER intermediates on QA-MOFs. Finally, QA-NiFe-MOF was directly synthesized on a porous transport layer (PTL), and its AEMWE performance was evaluated without the use of any ionomer. At 1.0 M KOH, C4N, C5N, and TMA-based NiFe MOFs exhibited current densities of 9.35 A/cm2, 9.11 A/cm2, and 7.6 A/cm2, respectively. These current densities surpassed those of bare BDC-NiFe MOF and commercial IrO2 anode catalysts, which exhibited only 7.39 A/cm2 and 6.4 A/cm2, respectively. Consequently, we emphasize that the facilitation of local ionic transport could yield remarkable AEMWE performance, even in the absence of conventional polymeric ionomers.

Tetrazole-Containing Polyelectrolytes: A New Class of Ion-Solvating Membranes for Alkaline Water Electrolysis

Alkaline ion-solvating membranes, such as those based on polybenzimidazole (PBI), offer high ion conductivity and good gas barrier properties, making them promising for next-generation alkaline water electrolyzers.1 However, the stability of commonly used PBI derivatives is limited due to gradual backbone degradation. Consequently, alternative PBI chemistries and other polymer options like poly(vinyl alcohol),2 and carboxylate functionalized styrene-ethylene-butylene copolymers are being explored to address this inherent stability issue.3 In this study, we present the synthesis and characterization of a novel type of ion-solvating membranes for alkaline water electrolyzers. These membranes are based on tetrazole functionalized polymers derived from poly(styrene-co-acrylonitrile). A one-step click-type [3+2] cycloaddition reaction was utilized to introduce tetrazole pendants by converting acrylonitrile groups in poly(styrene-co-acrylonitrile). The degree of functionalization was controlled by adjusting the content of acrylonitrile units in the polymer. Subsequent treatment in aqueous KOH solution led to the formation of negatively charged tetrazolide pendants with high ionization degrees.The alkaline stability of the tetrazolides was evaluated using both DFT simulations and model compound studies, demonstrating remarkable stability with no degradation observed for over 3000 hours in 25 wt.% KOH at 80 °C. Physicochemical properties such as electrolyte uptake, swelling behavior, thermal stability, and ion conductivity were assessed for the synthesized polymers. The electrolyte-imbibed membranes exhibited high ion conductivity, reaching up to 90 mS cm-1 in 15 wt% KOH at 80 °C. Electrolysis operation using these membranes showed stable performance for 600 hours with no signs of degradation. 1 D. Aili, M. R. Kraglund, S. C. Rajappan, D. Serhiichuk, Y. Xia, V. Deimede, J. Kallitsis, C. Bae, P. Jannasch, D. Henkensmeier, J. O. Jensen, ACS Energy Letters, 2023, 1900–1910. 2 Y. Xia, S. C. Rajappan, D. Serhiichuk, M. R. Kraglund, J. O. Jensen, D. Aili, J Memb Sci 2023, 680, 121719. 3 D. Serhiichuk, D. Tian, M. R. Almind, Z. Ma, Y. Xia, M. R. Kraglund, C. Bae, J. O. Jensen, D. Aili ACS Applied Energy Materials 2024 7 (3), 1080-1091 Figure 1 Tetrazolation of poly(styrene-co-acrylonitrile) and formation of corresponding potassium tetrazolide following equilibration in aqueous KOH. Figure 1

Anion exchange membrane with enhanced alkaline stability through radiation grafting of ETFE for solid polymer electrolytes

AbstractSolid polymer electrolyte membranes are considered as the nub of many electrochemical devices. Given the climate crisis and related concerns, the evolution of new membrane materials to support the sustainable systems is inevitable. Building on recent advances with the radiation technique and polymer chemistry, herein, anion exchange membranes (AEMs), ETFE‐g‐1VIm/4VP, were fabricated through graft copolymerization of vinyl heterocyclic monomer binary mixture, such as 1‐vinylimidazole (1‐VIm) and 4‐vinylpyridine (4‐VP) onto ethylene tetrafluoroethylene (ETFE), a main polymer backbone without aryl ether bonds. The grafting reaction was achieved at 60°C and then followed by quaternization as a subsequent step. The effects of various reaction grafting conditions were investigated. The ETFE‐g‐1VIm/4VP AEM were characterized w.r.t the morphological and structural features. The dense surface of the grafted membranes is proved by field emission‐scanning electron microscopy (FE‐SEM) images, which also show that the vinyl entities are clearly distributed in the prepolymer, which may lead to a continuous ion transport channel. AEMs processed from the highest graft yield showed good hydroxide conductivity at 90°C, reaching 16.9 mS/cm due to the presence of more transport sites. The same membrane has a relatively good alkaline stability, which is studied through weight percentage method and FT‐IR. Hence, we assume that the introduction of multi‐cationic moieties, pyridinium and imidazolium, contributes to the performance of anion exchange membranes and makes a perfect balance, especially the hydrophilicity and hydrophobicity. These data highlight the potential of the copolymer as an anion exchange membrane for wide spectra of electrochemical applications.Highlights AEMs based on ETFE‐g‐1VIm/4VP are developed via radiation grafting. The membrane exhibits remarkable alkaline stability. FT‐IR, SEM, and weight percentage methods were used to prove the alkaline stability. The membrane has the potential to be used for different electrochemical applications.

Development and characterization of engineering plastic diaphragm for alkaline water electrolysis

Research on carbon dioxide free energy sources is increasing due to climate change, with green hydrogen gaining significant attention for its eco-friendly production process. This study focused on creating a diaphragm for alkaline water electrolysis using the TIPS method, utilizing the engineering thermoplastics PEEK and PPS for their excellent mechanical properties and heat resistance. DPK was employed as a diluent, and the phase diagram was established by measuring the crystallization temperature and cloud point based on polymer content. The morphology of the diaphragm, both surface and cross-section, was observed using an SEM, while tensile strength, alkaline stability, and permeability tests assessed its suitability for alkaline electrolysis conditions. The diaphragm with a polymer content of 20 wt% demonstrated a mechanical strength of 31.9 MPa, making it viable for operational use in alkaline electrolysis. All the diaphragms exhibited exceptional alkali resistance, with weight changes of less than 1 % in a 25 to 30 wt% KOH solution. Additionally, permeability tests indicated that permeability decreased as polymer content increased. Electrochemical evaluations revealed that the 20 wt% polymer content diaphragm achieved the best performance, delivering 188.7 mA/cm². This study confirms the potential of using these diaphragms in efficient and sustainable alkaline water electrolysis systems.

Bioadhesive-Inspired Ionomer for Membrane Electrode Assembly Interface Reinforcement in Fuel Cells.

Anion exchange membrane fuel cells promise a sustainable and ecofriendly energy conversion pathway yet suffer from insufficient performance and durability. Drawing inspiration from mussel foot adhesion proteins for the first time, we herein demonstrate catechol-modified ionomers that synergistically reinforce the membrane electrode assembly interface and triple-phase boundary inside catalyst layers. The resulting ionomers present exceptional alkaline stability with only slight ionic conductivity declines after treatment in 2 M NaOH aqueous solution at 80 °C for 2500 h. Adopting catechol-modified ionomer as both anion exchange membrane and binder achieves a single-cell performance increase of 34%, and more importantly, endows fuel cell operation at a current density of 0.4 A cm-2 for over 300 h with negligible performance degradation (with a cell voltage decay rate of 0.03 mV h-1). Combining theoretical and experimental investigations, we reveal the molecular adhesion mechanism between the catechol-modified ionomer and Pt catalyst and illuminate the effect on the catalyst layer microstructure. Of fundamental interest, this bioadhesive-inspired strategy is critical to enabling knowledge-driven ionomer design and is promising for diverse membrane electrode assembly configurational applications.

Alkaline stability of polyester nanofiltration membranes prepared by interfacial polymerization

Polyester nanofiltration membranes typically outperform traditional polyamide alternatives in fouling resistance, water flux, and chlorine tolerance. However, their alkali resistance remains poorly understood. This study investigates the stability of polyester membranes, prepared via interfacial polymerization of eight hydroxyl monomers with TMC, in alkaline conditions (pH 12.4). We systematically recorded changes in water flux and solute rejection and employed SEM, AFM, zeta-potential, contact angle analysis, and XPS to examine physicochemical structural changes during hydrolysis. The findings reveal that most membranes are susceptible to alkaline hydrolysis, evidenced by increased water flux and decreased rejection rates. Specifically, membranes derived from pyrogallol-based hydroxyl monomers exhibited the greatest instability, whereas those incorporating sodium alginate demonstrated remarkable stability. After immersion in water, the water flux of the TA membrane increased from 8.4 to 21.2 Lm−2h−1bar−1 and the rejection rate decreased from 36.6 % to 12.1 %. the water flux of PG membrane was from 22.0 to 54.2 Lm−2h−1bar−1, while the rejection rate decreased from 60.2 % to 22.7 %. DFT calculations corroborate these observations, linking ester bond energies with membrane stability. This study not only advances our understanding of polyester nanofiltration membrane properties but also highlights critical vulnerabilities in alkali environments, guiding future improvements.

Graphene oxide nanosheets reinforced quaternized poly(2,6-dimethyl-1,4-phenylene oxide) composite membranes with enhanced hydroxide ions conduction at subzero temperature

The realization of high hydroxide ion conductivity on the premise of enough alkaline stability is basic of the practical application of anion exchange membranes (AEMs). In this research, we propose a facile way to enhance the hydroxide ion conductivity at subzero temperature through constructing multilayered microstructures of AEMs. Graphene oxide (GO) nanosheets and 3,6-diazaspiro[5.5]undecane bromide (DSUBr) are alternately deposited on the surface of a quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO) membrane with the layer by layer self-assembly process. Multilayered and compact microstructures are retained even if the prepared QPPO/(GO/DSUOH)5 membranes are immersed in 2 M KOH solution for 300 h. The hydroxide ions conduction resistance is reduced, deriving from the well-ordered dispersion of components. For example, the QPPO/2-(GO/DSUOH)5 membrane exhibits the hydroxide ion conductivities of 0.922 mS/cm at −25 °C and 58.5 mS/cm at 80 °C. Furthermore, the prepared AEMs possess the enhanced hydroxide ion conductivity owing to the fine dimension and component stabilities. After the ten-cycle hydroxide ion conductivity stability test, the retention rates of hydroxide ion conductivity are 99.4 % at −25 °C and 105 % at 30 °C. Additionally, the residual hydroxide ion conductivity reaches 61.6 mS/cm at 80 °C in 2 M KOH solution for 624 h. A single fuel cell equipped with the QPPO/2-(GO/DSUOH)5 membrane exhibits the maximum power densities of 80.8 mW/cm2 at 30 °C and 351.6 mW/cm2 at 60 °C.

Effect of branching degree of quaternized poly(p-terphenyl isatin) on the performance of anion exchange membrane water electrolyzers

Anion exchange membrane (AEM) is a vital component of an anion exchange membrane water electrolyser (AEMWE). Herein, we reported a series of quaternized poly(p-terphenyl isatin) (Q-PPI-bx) AEMs with the branching architecture and microporous structure by incorporating bulky rigid 1,3,5-triphenyl monomer through a superacid polycondensation reaction. It was found that the introduction of branching and microporous structures provided the membranes with a larger free volume and distinct microphase separation morphology, thus resulting in a higher OH− ionic conductivity (158.7 mS cm−1 at 80 °C). At the same time, the AEMs exhibited good mechanical properties and good alkaline stability (retention of 85 % for 1500 h in 1 M KOH at 80 °C). In addition, the current density of Q-PPI-b10 AEM was 1.14 A cm−2 at 2 V in AEMWE. During the in-situ endurance experiment at current density of 0.2 A cm−2, the voltage remained stable for 170 h. These findings underscore the potential of novel branched AEMs for application in AEMWE systems with enhanced performance and durability, thus contributing to the advancement of efficient and sustainable water electrolysis technology.

Highly durable anion exchange membranes with sustainable mitigation of hydroxide attacks for water electrolysis

Low hydroxide conductivity and insufficient alkaline stability are the main problems currently facing anion exchange membranes (AEMs). Conventional quaternary ammonium groups have limited resistance to attack by hydroxide roots. In this paper, quaternary ammonium-type (Cn-PFCO (n = 2, 5)) perfluoroanion exchange polymers with carbonyl side chains were synthesized. The C5–PFCO exhibited an impressive conductivity of 113.4 mS cm−1 at 80 °C, and remarkably, it retained 86.87% of its initial conductivity even after 15 days of immersion in a 1 M KOH aqueous solution. This excellent alkali resistance is due to the generation of intermediate oxygen anions from OH− and carbonyl groups through a reversible reaction. These anions effectively reduce the likelihood of SN2 attack by diminishing the electrostatic potential of the QA groups from Density Functional Theory (DFT) calculations. The electrostatic potential of C2–PFCO is 6.28 eV, while it decreases to 2.69 eV after the formation of intermediate anions. Furthermore, we also used the prepared AEM for pure water electrolysis to explore its performance. The electrochemical performance of AEMWE exhibited remarkable results when supplied with pure water, demonstrating an impressive current density of 262 mA cm−2 at 1.9 V. This study introduces a novel strategy for concurrently enhancing hydroxide conductivity and alkali resistance in AEMs by analyzing the potential for further improvement in AEMs' alkali resistance.

β-Cyclodextrin-enabled, densely cross-linked anion-exchange membranes for fuel cell applications

Polyarylpiperidinium anion exchange membranes (AEMs) have been widely studied in anion exchange membrane fuel cells and alkaline electrolyzed water due to their excellent alkali resistance stability. In this work, we report the design and fabrication of poly(p-triphenylene-piperidinyl) (PTP) AEMs quaternized and cross-linked by bromo-β-cyclodextrin (β-CD-Br7). In this type of membranes, the densely cross-linked and quaternized sites derived from β-CD-Br7 can help to construct continuous ion transport channels to facilitate ion conduction. Although the ion exchange capacity (IEC) tended to decrease with increasing cross-linking degree, the qPTP-CD5 membrane with 5 % cross-linking (IEC = 2.3 mmol g−1) produced the most significant microphase separation and the highest conductivity (125.6 mS cm−1 at 80 °C). The membrane also exhibited impressive alkaline stability, with 94.6 % conductivity retention in 1 M NaOH at 80 °C after 1000 h and 90.7 % conductivity retention after 1500 h. Finally, the peak power density of the fuel cell assembled with qPTP-CD5 membranes was 1.216 W cm−2 at 80 °C and there was no significant voltage degradation when operated at 200 mA cm−2 current density for 40 h. This work demonstrates that β-CD can function as a good “platform” for simultaneous cross-linking and quaternization to fabricate high performance AEM.

Prussian Blue Analogues Derived Bimetallic CoNi@NC as Efficient Oxygen Reduction Reaction Catalyst for Mg‐Air Batteries

The magnesium‐air (Mg‐air) batteries are regarded as a highly promising system for electrochemical energy conversion and storage, owing to exceptional energy density, notable safety and eco‐friendliness. The development of high‐performance and durable non‐noble metal catalysts for the cathodic oxygen reduction reaction (ORR) is crucial for advancing the practical use of Mg‐air batteries. The synergistic interaction between different metals in bimetallic catalysts is an effective strategy for enhancing the activity and stability of the catalysts. Herein, various prussian blue analogues (PBA) were selected as precursors to synthesis the bimetallic CoNi@NC, monometallic Co@NC and Ni@NC catalysts due to tunable chemical compositions. Compared with Co@NC and Ni@NC, the bimetallic CoNi@NC pyrolyzed at 600°C (CoNi@NC‐600) exhibits outstanding ORR performances and stability in alkaline (0.1 M KOH) and neutral (3.5 wt% NaCl) electrolytes. Following 5000 CV cycles, the half‐wave potentials for CoNi@NC‐600 show only minor negative shifts of 8 and 7 mV, respectively. Meanwhile, the CoNi@NC‐600 possesses the similar ORR reaction mechanism and activity with Pt/C. The primary Mg‐air battery assembled with CoNi@NC‐600 displays better discharge performances than that of Co@NC and Ni@NC. This study lays the foundation for future investigations into the advancement of non‐precious bimetallic catalysts for ORR in Mg‐air batteries.