Microphase-separated Morphology Research Articles

Bifunctional Imidazole Cross‐Linked Anion Exchange Membrane Based on Quaternized Chitosan With High Performance

ABSTRACTDeveloping novel anion‐exchange membranes (AEMs) that feature superior hydroxide conductivity and excellent alkaline stability poses a major challenge. Among different kinds, cross‐linked AEMs enjoy the highest popularity, thanks to their uncomplicated fabrication procedures and outstanding stability. However, it is noteworthy that in the majority of instances, the employment of covalent cross‐linking methods often plunges AEMs into a conductivity‐stability conundrum. That is to say, when efforts are made to boost the conductivity, the stability tends to be compromised, and conversely, attempts to enhance stability might adversely affect conductivity. To tackle the conductivity‐stability issue faced by conventional covalent cross‐linked AEMs, within this research, innovative bifunctional imidazole cross‐linking agents that carry imidazole cations were synthesized using N‐(3‐aminopropyl)‐imidazole and 3‐chloropropylamine. Following that, these agents were then utilized to manufacture high‐performance cross‐linked quaternized chitosan (QCS) membranes. The bifunctional cross‐linker was able to furnish an ionic 3‐D network, further promoting the formation of microphase separation morphology and a densely cross‐linked structure, thereby bringing about both excellent conductivity and alkaline stability. The as‐prepared QCS‐MI0.3 AEM exhibited a relatively low swelling ratio of 29.7% at 80°C, along with outstanding conductivity reaching 128.83 mS cm−1 at the same temperature. Moreover, it demonstrated remarkable alkaline stability, with 92% of its conductivity retained after being immersed in 6 M KOH at 80°C for 168 h. Meanwhile, the single cell built upon the QCS‐MI0.3 AEM likewise showcased remarkable fuel cell performance, achieving a power output of 518.08 mW cm−2 at 80°C, and exhibited excellent durability as well. This research effort devised a novel approach for synthesizing high‐performance cross‐linked AEMs, which further augmented the application potential of QCS‐based AEMs in the realm of fuel cells.

The Effect of Various Functional Groups on the Morphology and Performances of Crosslinked Addition‐Type Poly(Norbornene)s‐Based Anion Exchange Membranes

ABSTRACTTo investigate the effect of different functional groups on the morphology and properties of crosslinked anion exchange membranes (AEMs), a series of novel partially crosslinked addition‐type poly(norbornene)s‐based AEMs were prepared by flexibly grafting N‐methylpyrrolidinium, N‐methylpiperidinium, N‐methylmorpholinium, and 1, 2‐dimethylimidazolium onto an addition‐type poly(norbornene)s backbone. The well‐developed microphase separation morphology was observed for all the prepared crosslinked AEMs using AFM and SAXS. The AEM with N‐methylpyrrolidine groups (CL‐aPNB‐TMHDA‐MPY) constructed more uniform and wider ion transport channel, exhibiting the highest hydroxide conductivity of 122.0 mS cm−1 at 80°C. The AEM‐tethering N‐methylpiperidine cations (CL‐aPNB‐TMHDA‐MPRD) exhibited the best alkaline stability and achieved 90.61% conductivity retention even after being soaked in 1 M NaOH at 80°C for 1008 h. Meanwhile, the order of alkaline stability was CL‐aPNB‐TMHDA‐MPRD>CL‐aPNB‐TMHDA‐MPY>CL‐aPNB‐TMHDA‐DMMI>CL‐aPNB‐TMHDA‐NMM. The peak power density of a H2/O2 fuel cell equipped with CL‐aPNB‐TMHDA‐MPY, CL‐aPNB‐TMHDA‐MPRD, CL‐aPNB‐TMHDA‐NMM, and CL‐aPNB‐TMHDA‐DMMI were 247.3, 218.1, 185.9, and 178.0 mW cm−2 at 80°C, respectively. These results of the comparison of AEMs with different cation groups give some insights for designing high‐performance AEMs in future.

Molecular Characterization of PFSA Ionomer Dispersions and Their Aggregated Structures

Perflurosulfonic acid (PFSA) ionomers are widely used in numerous polymer electrolyte-based electrochemical devices including fuel cells and water electrolyzers. The majority of the state-of-the-art PFSA ionomers consist of chemically robust hydrophobic perfluorocarbon backbone and vinyl ether side chains terminated with hydrophilic sulfonic acid groups, which are highly incompatible. Therefore, such architecture allows hydrophobic-hydrophilic microphase-separated morphologies in a membrane to induce fast proton conduction. However, dispersion-cast ionomers cannot necessarily offer good performance over long periods, and thus it is important to understand the ionomer dispersion in molecular scale as well as aggregated state to correlate the dispersion characteristic with the performance of final dispersion-cast membrane film. Here, we investigate the physical characteristics of PFSA ionomer dispersions, with a particular focus on the molecular weight of ionomers. A series of commercial ionomers with various compositions were obtained and characterized in terms of equivalent weight (EW) and melt flow index (MFI). Ionomer dispersion was produced by screening various aqueous/alcohol and polar solvents with varying concentrations dispersing temperature, to achieve nanodispersion with an aggregate diameter being smaller than 20 nm, as confirmed by the light scattering measurement. Furthermore, size-exclusion chromatography (SEC) of ionomers was performed to determine the molar mass distribution of ionomers, in addition to providing information on the aggregation number of ionomer chains in the dispersion state. Additional characterization of the ionomer dispersion with multiangle light scattering (MALS) provided an estimate of the absolute molar mass of the ionomers, which implements the possible inaccuracy of the molecular weight obtained from SEC arising from the ionomer-column interaction. Combining these results allows correlation between the hydrodynamic radius of ionomer dispersion as a function of molecular weight (or MFI) values. Moreover, ionomer nanodispersion was cast into membrane film for rheological and morphological characterization to further establish the correlate between the physical properties of ionomer dispersion and membrane.

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-diazabicyclo[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 h 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.

Quaternized poly(aryl imidazolium) containing bulky binaphthyl group as proton exchange membrane for high-temperature fuel cells

The low power output and high phosphoric acid (PA) leakage are the main constraints restricting the commercialization of PA-doped high-temperature proton exchange membranes (HT-PEMs). Ionized imidazoles have been shown to be an effective strategy to improve PA retention, however, less research has been conducted on the fractional free volume (FFV) of the backbone of the main chain on PA loss. Herein, novel imidazolium ions polymer (PQBN-4-IM) material with bulky binaphthyl (BN) group was prepared as PA-doped HT-PEM using a one-step superoxid acid catalyzed polycondensation and subsequent methylation process. The rigidity and hydrophobicity of the BN group promote PQBN-4-IM PEM to produce more obvious microphase separation morphology and large FFV, which is beneficial for forming better ion transport channels and excellent PA interaction. Notably, the PA-doped PQBN-4-IM (PQBN-4-IM/PA) membrane has the highest proton conductivity (90.26 mS cm−1, 180 ℃) and peak power density (PPD) (802.5 mW cm−2, 180 ℃) than PQTP-4-IM/PA and m-PBI/PA HT-PEMs. Moreover, the PQBN-4-IM/PA membrane has higher PA retention at 80 ℃/40 % relative humidity (RH), 40 ℃/60 % RH, or immersed in water due to enhancement on ion-pair interactions by microstructure. Under the accelerated stress test (AST) of the fuel cell (FC), the PQBN-4-IM/PA membrane loses only 12.22 % of PPD after 200 cycles at 80 ℃, which exhibits higher PPD retention than that of the PQBP-4-IM/PA (70.23 %), PQTP-4-IM/PA (74.36 %) and m-PBI/PA (65.25 %) membranes, and shows excellent durability of cell performance for more than 1000 h without significant voltage decay at 160 °C. Thus, the outstanding performance suggests that the microstructure and morphology of imidazolium ions polymer membranes significantly influence proton conductivity, performance, and the durability of a cell.

Tuning poly(isatin biphenyl) anion exchange membranes by copolymerization and branching

The cardo structure and long side chain of poly(isatin biphenyl) are conducive to the motion and aggregation of cations over mainchain type membranes, therefore it is used as the pristine membrane. It is well known that random copolymerization and branching can effectively modify the configuration and properties of polymers. Herein, we use random copolymerization and branching to improve the behaviors of poly(isatin biphenyl) anion exchange membranes (AEMs). High-curvature random copolymers (QPIDBP-n) and high free volume branched polymers (b-QPIBP-x) are synthesized via polycondensation. The random copolymerization results in the formation of a twisted chain structure, while the introduction of branching agent leads to the formation of orderly stacking of chains. Both of these approaches have been demonstrated to boost the microphase-separated morphology of the pristine polymer. A series of QPIDBP-n and b-QPIBP-x are tested and an optimal ratio is explored. QPIDBP-40 and b-QPIBP-5 exhibit high overall performance. Among the as-prepared membranes, b-QPIBP-5 exhibits the highest conductivity (80 °C, 160.7 mS cm−1) with a swelling ratio of 20.7 %. The residual conductivity of b-QPIBP-5 is 93.1 % after the 1200 h alkali stability test. The cell assembled by b-QPIBP-5 achieves a peak power density of 680 mW cm−2. Moreover, the b-QPIBP-5 based cell holds 88.6 % voltage after the in-situ stability test for 50 h.

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.

Understanding the shape-memory mechanism of thermoplastic polyurethane by investigating the phase-separated morphology: A dissipative particle dynamics study

Shape-memory polyurethanes (SMPUs) are promising materials that change shape in response to external heat. These polymers have a dual-segment structure: a hard segment for netpoint and a soft segment for molecular switch. Understanding the molecular behavior of each segment and microphase-separated morphology is crucial for comprehending the shape-memory mechanism. This study aimed to understand the shape-memory behavior by observing the phase separation of SMPU using mesoscale models based on dissipative particle dynamics (DPD) simulations. The SMPU copolymer was modeled using 4,4′-diphenylmethane diisocyanate (MDI, hard segment) and poly(ethylene oxide) (PEO, soft segment). By calculating segment solubility and repulsion parameters, we found that the hard-segment domain changes from isolated form to a lamellar and interconnected structure and eventually to a continuous form as its content increases. Combining these insights with shape-memory performance models can enhance our understanding of better SMPU design and contribute significantly to the optimization of smart stimuli-responsive materials.

Vat photopolymerization of poly(styrene-b-isoprene-b-styrene) triblock copolymers

Vat photopolymerization (VPP) additive manufacturing (AM) produces complex geometries with micron-scale resolution and smooth surface finish from a wide range of photocrosslinkable polymeric precursors. However, mass transport limitations typically constrain VPP amenable precursors to viscosities less than 10 Pa·s. Reactive oligomers and monomers comprise the majority of VPP polymeric precursors, which result in highly crosslinked and brittle 3D objects upon printing. This work describes colloidal high molecular weight ABA triblock copolymers, or latex, as a feedstock for aqueous photoreactive compositions to enable AM of thermoplastic elastomers (TPE). Photorheological analysis determined 15 wt% aqueous reactive monomers and oligomers generated a structural scaffold that achieved sufficiently high modulus to maintain feature fidelity for iterative layer formation. Subsequent thermal post-processing removed water and promoted polymeric particle coalescence throughout the scaffold resulting in an interpenetrating network (IPN) that exhibited an isotropic dimensional shrinkage of 25 %. Small-angle X-ray scattering (SAXS) confirmed microphase-separated morphologies typical of triblock copolymers, revealing a characteristic length scale of 30 nm. Using commercially available VPP printers, ABA triblock copolymer poly(styrene-b-isoprene-b-styrene) latex yielded printed elastomers with precise feature fidelity and tensile extensibility exceeding 800 %.

Engineering Biodegradable Polyurethanes with Precisely Controlled Hierarchical Structures to Access Shape Memory Effect and Enhanced Bioactivities.

Biodegradable polymers with shape memory effects (SMEs) offer promising solutions for short-term medical interventions, facilitating minimally invasive procedures and subsequent degradation without requiring secondary surgeries. However, achieving a good balance among desirable SMEs, mechanical performance, degradation rate, and bioactivities remains a significant challenge. To address this issue, we established a strategy to develop a versatile biodegradable polyurethane (PPDO-PLC) with tunable hierarchical structures via precise chain segment control. Initial copolymerization of l-lactide and ε-caprolactone sets a tunable Tg close to body temperature, followed by block copolymerization with poly(p-dioxanone) to form a hard domain. This yields a uniform microphase-separation morphology, ensuring robust SME and facilitating the development of roughly porous surface structures in alkaline environments. Cell experiments indicate that these rough surfaces significantly enhance cellular activities, such as adhesion, proliferation, and osteogenic differentiation. Our approach provides a methodology for balancing biodegradability, SMEs, three-dimensional (3D) printability, and bioactivity in materials through hierarchical structure regulation.

Exploring the effects of flexibility of monomers on poly (isatin monomer-co-biphenyl) anion exchange membranes

To investigate the effect of the monomer with different flexibility and rigidity on the random copolymer, we prepare anion exchange membranes (AEMs) with a similar copolymerization ratio containing different monomers. The results show that the introduction of rigid dibenzofuran, moderately flexible diphenyl ether and flexible bibenzyl affects the conformation and morphology of the polymers, further tuning the overall performance of the AEMs. The three random copolymers exhibit better microphase-separated morphology and conductivity than the homopolymer owing to their more twisted conformation. It is found that the incorporation of flexible monomers has an advantage in holding size consistence and flexibility. Overall, the integration of bibenzyl monomer has the most positive impact on the membrane characteristics, the QPIBBP-40 AEM with flexible units possesses the highest OH− conductivity (80 °C, 159.6 mS cm−1) and an excellent mechanical stability (elongation at break: 48.2 %, tensile strength: 15.6 MPa). The wet-stated QPIBBP-40 AEM maintains an inferior swelling ratio (80 °C, 10.8 %), indicating that it possesses good size consistence and ionic conductivity simultaneously. The highest output power density of the QPIBBP-40 AEM based fuel cell is 655 mW cm−2.

Mechanically Robust, Durable, and Multifunctional Hyper-Crosslinked Elastomer Based on Metal-Organic-Cluster Crosslinker: The Role of Topological Structure.

Polymer materials formed by conventional metal-ligand bonds have very low branch functionality, the crosslinker of such polymer usually consists of 2-4 polymer chains and a single metal ion. Thus, these materials are weak, soft, humidity-sensitive, and unable to withstand their shape under long-term service. In this work, a new hyperbranched metal-organic cluster (MOC) crosslinker containing up to 16 vinyl groups is prepared by a straightforward coordination reaction. Compared with the current typical synthesis of metal-organic cages (MOCs) or metal-organic-polyhedra (MOP) crosslinkers with complex operations and low yield, the preparation of the MOC is simple and gram-scale. Thus, MOC can serve as a high-connectivity crosslinker to construct hyper-crosslinked polymer networks. The as-prepared elastomer exhibits mechanical robustness, creep-resistance, and humidity-stability. Besides, the elastomer possesses self-healing and recyclability at mild condition as well as fluorescence stability. These impressive comprehensive properties are proven to originate from the hyper-crosslinked topological structure and microphase-separated morphology. The MOC-driven hyper-crosslinked elastomers provide a new solution for the construction of mechanically robust, durable, and multifunctional polymers.

High conductive and dimensional stability proton exchange membranes with an all-carbon main chain and densely sulfonated structure

Sulfonated polyarylene membranes are demonstrated to be efficient as proton exchange membranes (PEMs) for proton exchange membrane fuel cells (PEMFCs) in clean energy conversion systems. In this study, we design and synthesize a series of sulfonated polyarylene with all-carbon backbones and densely sulfonated pendant groups, which can be prepared by copolymerization of 1,3-Disulfonic acid benzaldehyde, 1,1,1-trifluoroacetone and biphenyl under superacid-catalyzed conditions. Rigid, hydrophobic backbone and hydrophilic side chains make the membrane form good microphase separation morphology. The PEMs exhibit high proton conductivity (404 mS cm−1) and excellent dimensional stability (swelling ratio lower than 24% and water uptake lower than 40%) at 80 °C. Moreover, the PEMs show good oxidization stability (the retaining weight rate of membrane up to 99.2% for 1 h oxidative treatment), and the oxidization stability and degradation mechanism of Ar3CH in polymer backbone are also studied. The H2/O2 fuel cell assembled with PEMs exhibited a maximum peak power density of 560 mW cm−2. It indicates that all-carbon main chain and densely sulfonated structure show great potential for improving the performance of PEMs.

Facilitated belt for ion transport by comb-shape Poly(terphenyl piperidone) carried with macrocyclic crown ether as anchor in anion exchange membrane

To ensure efficient ion transport in anion exchange membranes (AEMs) for hydrogen production, it is essential to develop efficient ion transport pathways. Utilization of intermolecular interactions induced by embedded macrocycles is an attemptable approach. Self-aggregated channels can be constructed with this force serving as a driving force for stepped-up ion transport. Herein, we present a delicate strategy to polymerize the macro crown ether in the backbone and graft flexible alkyl long chains to prepare comb-type copolymers as AEMs. The macrocycle dynamically traps ammonium ions as an anchor which accelerates the aggregation of ionic phases. The resulting AEMs show favorable membrane-forming ability and tensile strength. As the side chain length increases, the microphase-separated morphology develops well and formed ‘belt’-like channels in the poly(terphenyl piperidone)-5-bis-quaternary ammonium (PTCP-5-bisQA) membrane, exhibiting a hydroxide conductivity of 78.1 mS/cm at 80 °C. The alkaline durability of PTCP-5-bisQA AEM is explored by nuclear magnetic hydrogen spectrum (1H NMR) investigation at 80 °C for 720 h. Furthermore, the PTCP-5-bisQA based electrolyzer reaches a current density of 330 mA/cm2 at 1.85V by 1 wt% potassium hydroxide solution circulation. A life endurance observation is carried out on this electrolyzer for a 100h operation with performance degradation rate of 40.1 mV/h.

Design and Synthesis of Comb‐Like Bisulfonic Acid Proton Exchange Membrane with Regulated Microstructure

AbstractThe design and synthesis of proton exchange membranes (PEMs) with controllable microstructure and sulfonation degree play a crucial role in enhancing their performance and expanding their application. In this study, the disulfonic acid monomer is designed and prepared to synthesize the comb‐like disulfonic PEMs with controllable ion exchange capacity. The results show that the side chain structure and more concentrated sulfonic acid groups facilitate the aggregation of sulfonic acid groups in the polymer, improve the microphase separation morphology of PEMs, and increase the ionic conductivity. The proton conductivity of the DS‐PXIDI‐60 membrane is approximately 300 mS cm−1. The PEMs with controllable microstructure are prepared by introducing comonomers, including 9,9‐dimethylxanthrene, biphenyl, and p‐terphenyl, with different reactivity, spatial structure, and solubility. Biphenyl is copolymerized to form a copolymer with an alternating structure, and 9, 9‐dimethylxanthrene is copolymerized to form a random copolymer. In addition, it is worth noting that p‐terphenyl is copolymerized to form a microblock structure of the copolymer, with more excellent comprehensive properties. DS‐PXITp‐60 exhibits better performance than Nafion 212 in redox­flow batteries and fuel cells. Therefore, such molecular design and synthesis strategies provide a reference guide for the development of high‐performance PEMs.

Novel Fluorinated Anion Exchange Membranes Based on Poly(Pentafluorophenyl-Carbazole) with High Ionic Conductivity and Alkaline Stability for Fuel Cell Applications.

Constructing good microphase separation structures by designing different polymer backbones and ion-conducting groups is an effective strategy for improving the ionic conductivity and chemical stability of anion exchange membranes (AEMs). In this study, a series of AEMs based on the poly(pentafluorophenylcarbazole) backbone grafted with different cationic groups are designed and prepared to construct well-defined microphase separation morphology and improve the trade-off between the properties of AEMs. Highly hydrophobic fluorinated backbone and alkyl spaces enhance phase separation and construct interconnected hydrophilic channels for anion transport. The ionic conductivity of the PC-PF-QA membrane is 123 mS cm-1 at 80°C, and the ionic conductivity of the PC-PF-QA membrane decreased by only 6% after 960h of immersion at 60°C in 1M NaOH aqueous solution. The maximum peak power density of the single cell based on PC-PF-QA is 214mW cm-2 at 60°C.

Advancing Ion Selective Membranes with Micropore Ion Channels in the Interaction Confinement Regime.

Ion exchange membranes allowing the passage of charge-carrying ions have established their critical role in water, environmental, and energy-relevant applications. The design strategies for high-performance ion exchange membranes have evolved beyond creating microphase-separated membrane morphologies, which include advanced ion exchange membranes to ion-selective membranes. The properties and functions of ion-selective membranes have been repeatedly updated by the emergence of materials with subnanometer-sized pores and the understanding of ion movement under confined micropore ion channels. These research progresses have motivated researchers to consider even greater aims in the field, i.e., replicating the functions of ion channels in living cells with exotic materials or at least targeting fast and ion-specific transmembrane conduction. To help realize such goals, we briefly outline and comment on the fundamentals of rationally designing membrane pore channels for ultrafast and specific ion conduction, pore architecture/chemistry, and membrane materials. Challenges are discussed, and perspectives and outlooks are given.

Oligo (ethylene glycol)-grafted poly(terphenyl indole piperidinium) with high water diffusivity for anion exchange membrane fuel cells

The water diffusivity of polymeric anion exchange membranes (AEMs) plays a critical role in determining the AEM fuel cells (AEMFCs) performance because it generates an imbalance in the amount of water at the anode and cathode. However, the correlation between water diffusivity and the chemical structure of AEMs remains unclear. This study focuses on a series of oligo(ethylene glycol) (OEG) functionalized poly(arylene indole piperidinium) AEMs, in which OEG grafts are directly attached onto the polymer backbones. The polar and flexible OEG side chains afford a microphase-separated morphology, close polymer-chain packing, and extra sites for water–ion transport, resulting in high ion-exchange-capacity (IEC)-normalized conductivity, improved water diffusivity, and dimensional stability. Moreover, these side chains provide excellent ex-situ stability in a 1 M NaOH solution (80 °C) for 1080 h, surpassing the stability of its alkyl side chain counterpart (PITP-C10Q85) by a significant margin. The resultant PITP-OEG-85 with the highest water diffusivity exhibits a highest peak power density of 1.23 W cm−2 at 80 °C despite its low IEC value and conductivity. In-situ durability tests of this membrane at 0.2 A cm−2 for 24 h revealed the degradation of piperidinium under harsh conditions (70 % anode relative humidity at 60 °C). This work opens a new avenue for designing highly conductive and alkali-stable AEM materials with high water diffusivity to realize high-performance AEMFCs.

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.

Ultramicroporous crosslinked polyxanthene-poly(biphenyl piperidinium)-based anion exchange membranes for water electrolyzers operating under highly alkaline conditions.

Anion exchange membrane water electrolyzers (AEMWEs) suffer from low efficiencies and durability, due to the unavailability of appropriate anion exchange membranes (AEM). Herein, a rigid ladder-like polyxanthene crosslinker was developed for the preparation of ultramicroporous crosslinked polyxanthene-poly(biphenyl piperidinium)-based AEMs. Due to the synergetic effects of their ultramicroporous structure and microphase-separation morphology, the crosslinked membranes showed high OH- conductivity (up to 163 mS cm-1 at 80 °C). Furthermore, these AEMs also exhibited moderate water uptake, excellent dimensional stability, and remarkable alkaline stability. The single-cell AEMWE based on QPBP-PX-15% and equipped with non-noble catalysts achieved a current density of 3000 mA cm-2 at 2.03 V (compared to PiperION's 2.26 V) in 6 M KOH solution at 80 °C, which outperformed many AEMWEs that used platinum-group-metal catalysts. Thus, the crosslinked AEMs developed in this study showed significant potential for application in AEMWEs fed with concentrated alkaline solutions.