Polybenzimidazole Membranes Research Articles

Investigation of Ceria based Heterostructure Composite Mixed Matrix Membrane with Polybenzimidazole for Polymer Electrolyte Fuel Cell Application at High Temperature

In recent years Ceria based heterostructure composites are considered as one of the highest performing solid state ionic conductors, therefore we wanted to leverage the benefits of using these materials for high temperature Proton Exchange Membrane Fuel Cells (PEMFCs). In this study a Polybenzimidazole (PBI)/Ceria carbonate CHC (Ceria based heterostructure composite) membrane was prepared by drop casting method and tested as an electrolyte for a high temperature H2/Air PEMFC application in anhydrous condition. Inorganic composite of ceria and alkali metal carbonates (Li2CO3, Na2CO3) was prepared by solid state route to obtain Ceria carbonate CHC. X-Ray diffraction (XRD) study confirmed the formation of the heterostructure and their successful incorporation into the PBI membranes. Homogeneity of fillers inside the membrane was further verified by Energy Dispersive X-Ray Analysis (EDAX) and Scanning Electron Microscopy (SEM). 5wt% of inorganic powder induced inside the PBI fillers reduced the phosphoric acid uptake of composite membrane (∼17% less) compared to pristine PBI membrane, which ultimately resulted into a lower swelling and dimensional change of the composite membrane. Thermal robustness of the phosphoric acid doped composite and pristine PBI membranes was investigated by thermogravimetric analysis (TGA) which showed that the prepared membranes were gone under a less than 10% reduction in weight up till 200ºC, ensuring their validity of application in high temp PEM fuel cells. The added inorganic functionalities resulted in a slight increase in the proton conductivity of PA doped composite PBI membranes i.e., 42.3 mS cm-1 at 180 ºC while for pristine PBI membrane it is 36 mS cm-1 at same temperature. A single cell with composite PBI membranes outperformed a pristine PBI membrane resulted into a ∼120% higher peak power density i.e., 320.88 mW cm-2. The composite membrane also displayed the excellent durability and showed a less than 10-4 mV/h degradation in cell potential till 180 ºC.

Proton direct transport channels incorporated with protonated porphyrin hyper-crosslinked structures for high proton conductivity HT-PEMs

The trade-off between the mechanical properties and proton conductivity of phosphoric acid (PA)-doped polybenzimidazole (PBI) membranes presents a significant challenge to their development and practical application as high-temperature proton exchange membranes (HT-PEMs). In this study, we prepared hyper-crosslinked poly[2,2′-(p-oxydiphenylene)-5,5′-benzimidazole] (OPBI) membranes with porphyrins (TBPP) containing a substantial amount of halogen. The combination of the protonation effect of porphyrin and the support of the hyper-crosslinked structure results in TBPP-OPBI crosslinked membranes exhibiting excellent mechanical strength and proton conductivity at high PA doping levels (ADLs). In particular, the TBPP-15-OPBI crosslinked membrane exhibits high proton conductivity of 244 mS cm−1 at 180 °C, which is 3.64 times greater than that observed in the OPBI membrane. The H2/air fuel cells based on the TBPP-15-OPBI crosslinked membranes exhibit a peak power density of 521.1 mW cm−2 at 160 °C without humidification and back pressure, as well as excellent durability (over 100 h). Thus, this work provides a straightforward and feasible structural design approach to comprehensively enhance the performance of PA-PBI proton exchange membranes.

Regulating Molecular Interactions in Polybenzimidazole Membrane for Efficient Vanadium Redox Flow Battery.

The tightly bonded structure of polybenzimidazole (PBI) membrane is the origin of its poor proton conductivity, which severely hinders achieving a cost-effective membrane for vanadium redox flow battery (VRFB). It desires a strategy to relax the membrane structure to significantly improve the proton conductivity and maintain its structure stability. Therefore, this work proposes a novel strategy through regulating molecular interactions within PBI membrane to loosen up the structure of PBI membrane and dramatically enhance the proton conductivity. The interactions in PBI membrane are switched by DMSO/water and acid through sequentially treating membrane with these solutions. The efficient PBI membrane prepared using this strategy demonstrates an outstanding performance for VRFB, with the proton conductivity enhanced by 3850% (from 1.9 to 76.3 mS cm-1), and VRFB achieves a high energy efficiency of 80.5% under 200 mA cm-2. More importantly, this work shed lights on the structure-property relationship of PBI membrane, and the mechanism in enhancing proton conductivity is unraveled, which is of great significance for the development of VRFB membranes.

Enhanced Organic Solvent Nanofiltration Membranes with Double Permeance via Laser‐Induced Graphitization of Polybenzimidazole

AbstractThis study investigates the fabrication of organic solvent nanofiltration (OSN) membranes through laser‐induced graphitization of polybenzimidazole (PBI). Employing a CO2 laser, the polymer is converted into graphene, resulting in controlled submicron‐scale porous 3D structures, a feat not achievable with traditional methods such as chemical crosslinking. The effectiveness of this process hinges on precise adjustments of laser parameters, such as fluence, to attain the ideal graphitization levels. The findings indicate that partial graphitization, as opposed to excessive, is crucial for preserving the membrane's microstructure and enhancing its functional properties. The partially graphitized PBI‐LIG (Polybenzimidazole ‒ Laser‐induced Graphene) membranes achieved up to 94% rejection of Congo red from ethanol, with an ethanol permeance rate of 12.14 LMH bar−1—nearly twice that of standard PBI membranes. Additionally, these membranes showcased outstanding chemical stability and solvent resistance, maintaining over 99% structural integrity and experiencing <1% weight loss after prolonged exposure to various industrial solvents over a week. These results highlight the potential of laser‐graphitized PBI membranes for applications in harsh chemical conditions, paving the way for further optimization of high‐performance OSN membranes. This research advances membrane technology, merging laser engineering with materials science, and contributes to environmental sustainability and industrial efficiency.

Complexion-induced Cu2+ coordinated phase separation PBI membrane for lithium metal batteries

The uncontrolled dendritic lithium production issues and the highly reactive behavior of lithium with electrolytes has limited use of lithium metal batteries. Herein, we utilized a straightforward method of the Complexion-Induced Phase Separation (CIPS) to fabricate a Cu2+ coordinated polybenzimidazole (PBI) membrane for a lithium metal battery. CIPS offer improved control over the structure and composition of the membrane, potentially leading to improved selectivity in ion transport, enhancing the safety and longevity of the battery. The formation mechanism and influencing elements of PBI-Cu are analyzed through experimental analysis and density functional theory calculations (DFT). The PBI-Cu membrane is effective in facilitating reversible lithium stripping and plating processes, suppressing dendrite formation, and promoting stable long-term cycling. Notably, the PBI-Cu cell demonstrated stable cycling conditions for over 200 h at a very high current density of 4 mA cm−2. The impressive rate performance was also confirmed during Li//LiFePO4 full cell operation, where it maintained a stable capacity of 120 mAh g−1 for more than 300 cycles. This research provides an in-depth insight into membrane design and paves the way for its application in various other energy-related technologies.

Sulfonating and polyhedral oligomeric silsesquioxane crosslinking in one step to build multiple proton pathways for proton exchange membrane fuel cells over a wide temperature range

Developing proton exchange membrane fuel cells (PEMFCs) operating over a wide temperature range can avoid additional internal/external heating or cooling devices for the PEMFCs operating. Polybenzimidazole (PBI) doped with phosphoric acid (PA) exhibits significant potential in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). Nevertheless, the traditional PA-PBI membranes are limited to operating within 140∼180 °C. In this work, a sulfonated polyhedral oligomeric silsesquioxane crosslinked polybenzimidazole membrane enriched pyridine and diazafluorene (CSPBI-X) is prepared where the sulfonation and crosslinking are accomplished by one-step heating. The theoretical calculations confirm that PA molecules have strong interactions with sulfonic acid groups and nitrogen-containing groups, enabling the membrane to achieve proton conductivity in a wide temperature range (80–180 °C). Moreover, the cross-linked sulfonated membranes have excellent PA retention ratio as high as 83.8% under 80 °C and 40% relative humidity for 120 h. Remarkably, with the acid doping level of 7.6, the proton conductivity of the CSPBI-20 membrane reaches 0.0491 S cm−1 and 0.145 S cm−1 at 80 °C and 180 °C in dry state, respectively. The highest power density of the CSPBI-20 at 80, 100, 120, 140, 160, and 180 °C is 257.3, 362.9, 485.3, 604.6, 755.3, and 956.1 mW cm−2, respectively.

Sulfonated polybenzimidazole membrane with graphene oxide additive for 2,3-butanediol/water separation: A molecular simulation

Membrane separation for 2,3-butanediol (2,3-BDO) recovery from fermentation broth is highly valued for sustainable and renewable processes, but it requires efficient membrane materials. This work evaluates the sulfonated polybenzimidazole (sPBI) and its graphene oxide (GO) doped composite membrane for separating 2,3-BDO and water via atomistic simulations. Density functional theory calculations are applied to identify various forms of sPBI structures and quantify their binding interactions with 2,3-BDO and water. Classical molecular dynamic simulations are used to evaluate the structural changes, diffusivity, and selectivity of 2,3-BDO and water in different sPBI models, GO surfaces, and GO-doped sPBI composite models. Our results suggest that sPBI slightly increases the crystallinity of the membrane structures, enhances the adsorption strength for both 2,3-BDO and water, and improves the water/2,3-BDO selectivity by 2–3 times. The GO surfaces display a maximum selectivity at a surface coverage of 0.1–0.15 for both hydroxyl and epoxy surface groups. The addition of GO flakes to sPBI creates new interaction sites for 2,3-BDO and water at the interface of sPBI and GO, and the water/2,3-BDO selectivity of GO-doped sPBI models is further increased up to 3 times. This work illustrates how the integrated addition of sPBI and GO flakes offers a promising approach to selective separation of 2,3-BDO and water, providing theoretical guidance for polybenzimidazole-based membranes in the potential application of 2,3-BDO recovery.

Pd2+-coordinated polybenzimidazole membranes with fast and selective ion transport for alkaline aqueous organic redox flow battery

The advancement of aqueous organic redox-flow batteries (AORFBs) is impeded by the lack of efficient, low-resistance, and highly selective ion-conducting membranes (ICMs). Although polybenzimidazole (PBI) is one of the most promising low-cost non-fluorinated ion-conducting membranes, it remains challenging to design stable PBI membranes with fast and selective ion transport channels. Here, we engineer the chemical structure of PBI and regulate the ion transport channels to prepare highly conductive and selective Pd2+-coordinated membranes with grafting and crosslinking structures. In this design, the positively charged quaternary ammonium groups on the side chain improve the conductivity of OH−, while the continuous cross-linked network formed by ionic bonds between quaternary ammonium groups and deprotonated imidazole groups significantly enhances the membrane's mechanical properties. Furthermore, the coordination of Pd2+ with PBI and plasticization of PBI chain by trifluoroacetate anions expand the molecular free volume while inducing local contraction. Consequently, the QPBI-xPBI-Pd membrane enables fast charge carrier transport and suppresses the diffusion of active substances. The AORFBs assembled with the QPBI-10PBI-Pd membranes exhibit high coulombic efficiency (99.6 %) and energy efficiency (77.67 %) at 100 mA cm−2, maintaining excellent stability for 500 cycles. This study provides an innovative strategy to design high-performance PBI membranes for RFBs, thereby advancing the viability of RFBs in the realm of large-scale energy storage technologies.

Ionomeric Binders for High Temperature Proton Exchange Membrane Fuel Cells.

High-temperature proton exchange membrane fuel cell (HT-PEMFC) based on phosphoric acid doped polybenzimidazole membrane (PBI/PA) operating at 120-200 °C can provide insensitivity to carbon monoxide (CO) and simplified managements of water and heat and thus attract significant global attention. However, one significant drawback is its low utilization of precious metal catalysts resulted from the PA poisoning and inefficient three-phase boundary. Studies of binder materials in catalyst layers for HT-PEMFC are gradually emerging and there are few literature reviews on this important topic. The purpose of this review is to describe the various types of binders based on their molecular structure and electrochemical properties, with particular emphasis on catalyst layer for fuel cells. Importantly, this review provides a better understanding of relationship between fuel cell performance and the gas permeability and conductivity of different binders. Then, future directions of research and development in binder materials of HT-PEMFC are pointed out.

Asymmetric porous polybenzimidazole membrane with tunable morphology for vanadium flow battery (VFB)

Polybenzimidazole (PBI) membranes have attracted much attention for flow batteries due to their good chemical stability. However, the high area resistance (AR) of dense PBI limits its further development in VFBs. Herein, we design a sintering method to remove the phthalates with different molecular structures in the ternary system (PBI as polymer, N-methylpyrrolidone as solvent, and phthalates as non-solvent). Asymmetric PBI membranes with adjustable and disconnected pores, as well as ultrathin-dense layers, are prepared. This series of porous membranes shows excellent overall performance in VFBs. Among them, the porous NPBI-DBP-200 membrane (0.139 Ω cm2) with DBP as the non-solvent exhibits a lower AR compared to the dense NPBI (0.489 Ω cm2). At a current density of 200 mA cm−2, the energy efficiency (EE) of a single cell assembled with the NPBI-DBP-200 membrane (EE = 78.26 %) has improved by 26.37 % compared to the dense NPBI membrane (EE = 61.93 %). In addition, the porous NPBI-DBP-200 membrane has excellent in-situ stability, and the single cell can operate stably for 1800 cycles at the current density of 120 mA cm−2. This work presents a novel, easy-to-use technique for preparing high-performance porous PBI membranes with adjustable pore morphology.

Imidazole and triazine framed porous aromatic framework with rich proton transport sites for high performance high-temperature proton exchange membranes

Phosphoric acid-doped polybenzimidazole (PA-PBI) membranes for high-temperature proton exchange membranes (HT-PEMs) exhibit low proton conductivity under low phosphoric acid loading and poor mechanical properties under high phosphoric acid loading. In order to overcome these disadvantages, a novel kind of porous aromatic framework framed with imidazole and triazine groups (PAF-227) was designed and synthesized, phosphoric acid (PA) was incorporated into PAF-227 by utilizing vacuum-assisted infusion to yield the product PAF-227-PA. Subsequently, this dopant was combined with polybenzimidazole (OPBI) to create the PAF-227-PA/OPBI composite high-temperature proton exchange membranes (HT-PEMs). The PAF-227-PA/OPBI exhibited high proton conductivity (0.24 S cm−1) at 200 °C, as well as a favorable mechanical property (6.73 MPa) and a high PA absorption rate (250.2 %), and the peak power density of the fabricated fuel cells was significantly increased to 678.21 mW cm−2 at 200 °C with the Pt loading of 0.3 mg cm−2. The basic sites of PAF-227 framed with rigid imidazole and triazine groups can anchoring the PA to achieve a high PA retention rate through the acid-basic interaction with PA, and provide sufficient proton conduction sites by forming hydrogen bonds with PA, and synergized with OPBI membranes to form a multiple hydrogen bond and proton transfer network for enhanced mechanical properties and dimensional thermal stability. Thus, this work provided a novel approach to the preparation of HT-PEMs, which exhibited excellent overall performance for HT-PEMs fuel cells.

Side-chain vertical imidazole backbone enhances phosphoric acid uptake in Poly(2,5-benzimidazole) membranes for high-temperature PEMFCs

PA-doped polybenzimidazole membranes dominate high-temperature proton exchange membranes (HT-PEMs), but the current membranes have poor PA uptake ability, which directly affects the operational efficiency and stability of fuel cells. In this work, it is proposed that a series of grafted polybenzimidazole membranes containing benzimidazole side chains were successfully prepared by grafting 2-chloromethyl benzimidazole to the backbone of poly (2,5-benzimidazole) (ABPBI) via nucleophilic substitution reaction. All these membranes exhibited excellent mechanical properties, oxidative stability, and thermal stability. The introduction of benzimidazole side chains not only increased the free volume of the membranes to store more PA but also added additional basic sites to form hydrogen bonds with PA molecules and constructed a dense hydrogen bonding network, which greatly enhanced the PA uptake of the membranes and accelerated the proton conduction to reduce the activation energy. The proton conductivity of the PA-doped g-ABPBI-50% membrane reached 0.122 S cm−1 at 180 °C under humidity-free conditions, while the peak power density of the PA-doped g-ABPBI-30% membrane was as high as 0.372 W cm−2 at 160 °C, which was 1.75 times higher than that of the pure ABPBI membrane. These results highlight the potential of this grafted membrane for high-temperature proton exchange membrane fuel cells (HT-PEMFCs) applications.

The chemical crosslinking effect of polybenzimidazole/polyvinyl alcohol blend membranes for proton exchange membrane fuel cells: An experimental study

AbstractIn this survey, the different weight ratios of polybenzimidazole (PBI)/polyvinyl alcohol (PVA) blend polymer membranes were produced using the solution‐casting method. The crosslinking agents of phosphoric acid (PA) and glutaraldehyde (GA) were studied separately to prevent the PVA water solubility in the PBI/PVA blend membrane structure. The GA crosslinking (24 h) successfully prevented membrane solubility, reducing it to below 1%. The chemically crosslinked blend membrane (Cr‐PBI/PVA‐9:1) has the highest proton conductivity result which is 0.209 S cm−1 at 80°C and it has excellent oxidative stability since the membrane only lost 4% of its weight in a Fenton agent after 96 h. The Cr‐PBI/PVA‐9:1 also has higher proton conductivity than the commercial PBI membrane (0.122 S cm−1 at 80°C). The glass transition temperature of the synthesized Cr‐PBI/PVA‐9:1 blend membrane is greater than the synthesized PBI membrane (390°C). The current density and power density measured at 0.6 V for the synthesized Cr‐PBI/PVA‐9:1 membrane were found to be 504 mA cm−2and 251 mW cm−2. This work sheds light on the potential use of PVA in PEMFC applications by mixing PVA with a high‐temperature polymer like PBI and crosslinking the membrane with a prepared GA crosslinking agent.

Enhancing PA-PBI Composite Membrane with Metal Oxides Incorporation for HT-PEMFC Operating Above 200 oc

High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are renowned for their excellent CO tolerance and rapid reaction kinetics [1]. Among the various membrane types, phosphoric acid doped polybenzimidazole (PA-PBI) membranes, phosphoric acd (PA) acts as a proton conductor, facilitating proton transfer through hydrogen bond rearrangement between PA molecules and the PBI backbone [2]. However, the operating temperature of PA-PBI membrane-based HT-PEMFC is constrained by the condensation of PA, limiting their use to below 180 oC and posing a significant challenge for achieving efficient operation above 200 oC.Recent research endeavors have focused on enhancing PA-PBI membranes by incorporating metal oxides to extend their operational temperature range beyond 180 oC. The addition of metal oxides into PA solution leads to the formation of metal hydrogen phosphate, effectively preventing PA evaporation at elevated temperatures ( > 180 oC) and maintaining membrane performance without degradation. Furthermore, the presence of metal oxides facilitates proton transfer to the metal hydrogen phosphate surface, thereby improving ionic conductivity even at temperatures exceeding 200 oC.In this study, we present the synthesis of poly(2,2’-(1,4-phenylene)-5,5’ bibenzimidaozle) (pPBI) composite membranes through an in-situ method, where various metal oxides (SnO2, TiO2, ZrO2) are introduced into the synthesis solution. Through systematic investigation, we evaluate the impact of these metal compounds on fuel cell performance and durability at high temperatures exceeding 200 oC. Our findings shed light on the potential of metal oxide-modified PA-PBI composite membranes for advancing the performance and reliability of HT-PEMFCs in demanding operating conditions.

(Digital Presentation) Graphene as Barriers to Prevent Phosphoric Acid Leaching in High-Temperature PEMFCs

High-temperature PEMFCs running at 120-200℃ with the simplified water management has attracted more attention [1]. However, phosphoric acid molecules in polybenzimidazole membrane electrolyte (PA/PBI) are easily leaching to electrodes, which block pores of carbon fiber electrodes and impact gas transfer. Finally, the power density and durability of PEMFCs are extremely reduced [2].Graphene is a kind of two-dimensional (2D) structure of honeycomb lattice material and can block the penetration of almost all molecules and atoms, which is able to prevent PA molecules leaching as [3]. Our group has investigated a nitrogen-modified reduced graphene oxide (NrEGO) prepared by the electrochemical exfoliation, which has shown excellent performance in enhancing the activity and stability of catalysts [4]. Meanwhile, our previous research developed a single layer graphene loaded electrode. The power density of high-temperature PEMFCs is improved compared with commercial cells after accelerated stress test [5].Therefore, this work used NrEGO flakes as barriers to prevent phosphoric acid leaching to gas diffusion layer with lower Pt loading. In the present results, when the ratio of NrEGO and CB is 2 to 3 and the Pt loading is 0.25 mgPt/cm2, the cell improves 20% of the maximum power density and shows more stable with a decay of voltage by only 0.02 mV/h, which is quiet lower compared with that of 1.14 mV/h in commercial Pt/C.

Highly acid-stable high-temperature proton exchange membrane: Azide-based polymeric ionic liquids for the enhancement of amino-polybenzimidazole

Polybenzimidazole (PBI) is commonly used for high-temperature proton exchange membranes. However, it is undeniably challenging for phosphoric acid (PA)-doped PBI membranes to have both high proton conductivity and excellent long-term stability. In this study, a series of polymer ionic liquid composite PBI membranes were fabricated. These membranes are made using two azide-functional ionic liquids and amino-polybenzimidazole, adjusting the amount of the two ionic liquids. The ionic pairs offered by the ionic liquids positively impact the transportation of protons and the stability of PA through the replacement of anions. It is noteworthy that crosslinked amino-polybenzimidazole membranes containing functional polymeric ionic liquids have proton conductivity of up to 131.7 mS cm−1 at 180 °C, and the PA retention after 240 h at 160 °C under humidity-free conditions is 86.5 %. In addition, the membrane is used in membrane electrodes with hydrogen and oxygen at the anode and cathode, respectively, exhibiting a peak power density of 694.6 mW cm−2 at 160 °C. And the voltage decay rate is 0.28 mV h−1 after long-term test. The findings indicate that membranes made of functional polymeric ionic liquids crosslinked with amino-polybenzimidazoleprovide a new strategy to enhance fuel cell durability.

Improving the performance and long-term durability of high-temperature PEMFCs: A polyvinylpyrrolidone grafting modification strategy of polybenzimidazole membrane

This study introduces an innovative approach to graft Polyvinylpyrrolidone (PVP) onto Polybenzimidazole (PBI) to synthesise Proton Exchange Membranes (PEMs) with high performance and durability. As a widely used hydrophilic polymer in industry, PVP can add numerous nitrogen-containing functional groups to the membrane to enhance its phosphoric acid (PA) binding ability. In this work, Polybenzimidazole-graft-polyvinylpyrrolidone (PVP-g-PBI) polymers with varying grafting degrees were synthesized and tested to investigate the impact of the grafting modification on the membrane's proton conductivity, thermal properties, and electrochemical performance. With the introduction of PVP side chains, the fuel cell showed enhanced PA uptake and substantial improvements in peak power density. Notably, PBI-g-PVP membranes with a grafting degree of 22.4 % achieved a peak power density enhancement up to 1312 mW cm⁻2 at 160 °C, a 59.6 % increase over pristine PBI membranes. Due to the increased PA binding sites in the membrane, the PBI-g-PVP PEMs exhibit better PA adsorption ability and long-term durability than pristine membranes. The accelerated stress test (AST) demonstrated that the PBI-g-PVP membranes maintain a peak power density of 1105 mW cm⁻2 after a 70-h test, equivalent to 183.9 % of the pristine PBI membrane. The improved fuel cell performance and durability of PBI-g-PVP PEMs underscore the potential of this grafting strategy.

High-performance polybenzimidazole composite membranes doped with nitrogen-rich porous nanosheets for high-temperature fuel cells

Traditional phosphoric acid (PA) doped polybenzimidazole (PBI) membranes encounter many issues when used in high-temperature proton exchange membrane fuel cell (HT-PEMFC), including the loss of PA within the membrane and limitations on conductivity. The mixed matrix membranes (MMMs) synergistically combine the advantages of pore fillers and polymer matrix, making them promising candidates for HT-PEMs. Interface compatibility is the main factor affecting the further development of MMMs. This research presented OPBI composite membranes filled with porous nanosheets, featuring average pore diameters of 2.83 nm, 3.38 nm, and 2.60 nm, respectively. The high aspect ratio and plentiful nitrogen components of the nanosheets increase the π-π and hydrogen bonding interactions with the polymer matrix, resulting in outstanding interface compatibility and mechanical properties of MMMs. The results of theoretical calculations indicate that there is a stronger interaction energy between the nanosheets and PA molecules, and the abundant pore structure within the nanosheets facilitates the absorption of PA molecules, leading to the formation of a continuous PA network. Consequently, MMMs exhibited enhanced proton conductivity, as well as improved PA absorption and retention. Furthermore, the effect of pore size distribution of nanofillers on the performance of MMMs were investigated. Membranes composed of nanosheets with large pore size showed a higher conductivity of 176.7 mS cm−1 at 200 °C, leading to excellent performance and stability in assembled H2/O2 fuel cells. This work offers valuable insights into the design of MMMs and high-performance HT-PEMs.

A soluble highly-sulfonated polybenzimidazole with high molecular weight as membrane for vanadium flow battery with enhanced performance and long-term stability

A series of novel sulfonated polybenzimidazole (SPBI) membranes containing flexible double ether segments, having high ion exchange capacity (IEC), good solubility as well as high molecular weight, are designed for vanadium flow batteries (VFBs). The bis-ether structure of self-synthesized sulfonic acid monomer, 4,4'-((2-sulfo-1,4-phenylene)bis(oxy))dibenzoic acid, improves the solubility of produced SPBI and the microphase separation structure of prepared membrane by disrupting the regularity of the backbone through a non-planar structure and attenuating the interchain stacking effect of the polymer backbone. Such a highly reactive bis-ether monomer also leads to high molecular weights (2.37−2.82 dL g−1). The copolymerization using another sulfonic acid monomer, Monosodium-5-Sulfoisophthalate monomer, leads to a high IEC of up to 2.08 mmol g−1. As a result, the SPBI membrane shows a low area resistance of 0.21 Ω cm2 and a low vanadium ion permeability of 3.36 × 10−9 cm2 s−1. The VFB cell employing SPBI membrane achieves a very high energy efficiency exceeding 82 % at 200 mA cm−2. In addition, an ultra-long lifetime of over 3400 cycles is accomplished.

High-performance imidazole-containing polymers for applications in high temperature polymer electrolyte membrane fuel cells

This work focuses on the development of high temperature polymer electrolyte membranes (HT-PEMs) as key materials for HT-PEM fuel cells (HT-PEMFCs). Recognizing the challenges associated with the phosphoric acid (PA) doped polybenzimidazole (PBI) membranes, including the use of carcinogenic monomers and complex synthesis procedures, this study aims to develop more cost-effective, readily synthesized, and high-performance alternatives. A series of superacid-catalyzed polyhydroxyalkylation reactions have been carefully designed between p-terphenyl and aldehydes bearing imidazole moieties, resulting in a new class of HT-PEMs. It is found that the chemical structure of aldehyde-substituted N-heterocycles significantly impacts the polymerization reaction. Specifically, the use of 1-methyl-2-imidazole-formaldehyde and 1H-imidazole-4-formaldehyde monomers leads to the formation of high-viscosity, rigid, and ether-free polymers, denoted as PTIm-a and PTIm-b. Membranes fabricated from these polymers, due to their pendent imidazole groups, exhibit an exceptional capacity for PA absorption. Notably, PTIm-a, carrying methylimidazole moieties, demonstrates a superior chemical stability by maintaining morphology and structural stability during 350 h of Fenton testing. After being immersed in 75 wt% PA at 40 °C, the PTIm-a membrane reaches a PA content of 152%, maintains a good tensile strength of 13.6 MPa, and exhibits a moderate conductivity of 50.2 mS cm−1 at 180 °C. Under H2/O2 operational conditions, a single cell based on the PTIm-a membrane attains a peak power density of 732 mW cm−2 at 180 °C without backpressure. Furthermore, the membrane demonstrates stable cycle stability over 173 h within 18 days at a current density of 200 mA cm−2, indicating its potential for practical application in HT-PEMFCs. This work highlights innovative strategies for the synthesis of advanced HT-PEMs, offering significant improvements in membrane properties and fuel cell performance, thus expanding the horizons of HT-PEMFC technology.