Search Results (86)

Phosphoric acid-doped polybenzimidazole membranes are a leading fluorine-free electrolyte platform for high-temperature proton exchange membrane fuel cells, enabling proton transport under anhydrous conditions. However, recent evidence shows that conductivity, mechanical stability, and acid retention are intrinsically coupled, preventing independent optimization of these properties. This review establishes a unified framework in which membrane performance is governed by a multidimensional design space defined by acid doping level, activation energy (E_a), hydrogen-bond network topology, and mechanical confinement. Conductivity is shown to scale with both carrier density and hopping energetics, while mechanical stability decays with increasing ADL due to acid-induced plasticization, described through a semi-empirical relationship. Analysis across molecular architectures, including molecular weight control, crosslinking, backbone modification, topological design, and free-volume engineering, demonstrates that performance emerges from a balance between transport efficiency and structural stability. Device-level benchmarking further reveals that similar conductivity values can correspond to orders-of-magnitude differences in voltage decay rate, confirming that durability is governed primarily by mechanical confinement and acid mobility rather than σ alone. A multivariate stability corridor is identified, within which phosphoric acid-doped polybenzimidazole membranes achieve σ ≈ 0.14–0.20 S·cm⁻¹ while maintaining low degradation rates under realistic high temperature proton exchange membrane conditions. Based on this framework, quantitative design rules are derived linking acid doping level, activation, topology, and mechanical properties. This work shifts membrane design from conductivity-driven optimization toward predictive structure–property–durability engineering, providing a basis for the development of next-generation HT-PEM fuel cells with sustained long-term performance. Full article

This study reports the intermediate-temperature proton exchange membrane (IT-PEM) based on an oligomeric vinyl sulfonic acid (OVS)-infiltrated crosslinked porous polybenzimidazole (cp-PBI) framework. The cp-PBI membrane, fabricated via ZIF-8-templated porosity and covalent crosslinking, provides a mechanically robust and chemically stable host matrix that enables high uptake and uniform distribution of OVS throughout the membrane bulk. In situ oligomerization of vinyl sulfonic acid yields a wax-like OVS ionomer with high proton density and reduced mobility, effectively suppressing ionomer leaching while maintaining efficient proton transport under anhydrous conditions. The resulting membrane exhibits high proton conductivity of 8.4 × 10⁻³ S cm⁻¹ at room temperature and 2.6 × 10⁻² S cm⁻¹ at 110 °C without any external humidification. Compared to dense PBI and conventional phosphoric acid (PA)-doped systems, the composite membrane demonstrates significantly enhanced ionomer retention, with only 2.3 wt% loss under compressive conditions and improved stability under humid environments. These results highlight the synergistic effect of a porous crosslinked host and viscous oligomeric ionomer, providing a promising strategy for designing stable, high-performance IT-PEMs. Full article

Perfluorosulfonic acid (PFSA) membranes, exemplified by Nafion, suffer dehydration-induced degradation at elevated temperatures, although modifications enhance their conductivity and performance. Sulfonated aromatic polymers (SAPs) exhibit weaker phase separation, yielding narrow, tortuous ion channels and lower conductivity than their PFSA membrane counterparts at equivalent ion exchange capacity; however, excessive sulfonation causes swelling and mechanical instability, offset by cost advantages. Phosphoric acid-doped polybenzimidazole (PBI) offers superior thermal stability and high conductivity, with recent advances in polybenzimidazole derivatives and composites driving medium-to-high temperature proton-exchange membrane fuel cell innovation. This review summarizes progress in three major medium-to-high temperature proton-exchange membrane fuel cell categories—perfluorosulfonic acid, sulfonated polymers, and PBI-based membranes—while addressing challenges and future goals for enhanced performance. Full article

High-temperature proton exchange membranes (HT-PEMs) are critical components of high-temperature fuel cells, facilitating proton transport and acting as a barrier to fuel and electrons; however, their performance is hampered by persistent issues of phosphoric acid leaching and oxidative degradation. Herein, a novel HT-PEM with abundant hydrogen bond network is constructed by incorporating nanoscale polyhedral oligomeric silsequioxane functionalized with eight pendent sulfhydryl groups (POSS-SH) into poly(4,4′-diphenylether-5,5′-bibenzimidazole) (OPBI) matrix. POSS, a cage-like nanostructured hybrid molecule, features a well-defined silica core and highly designable surface organic groups, offering unique potential for enhancing membrane performance at the molecular level. Through controlled reactions between sulfhydryl groups and allyl glycidyl ether (AGE), two functional POSS crosslinkers—octa-epoxide POSS (OE-POSS) and mixed sulfhydryl-epoxy POSS (POSS-S-E)—were synthesized. These were subsequently used to fabricate crosslinked OPBI membranes (OPBI-OE-POSS and OPBI-POSS-S-E) via epoxy–amine coupling. The OPBI-POSS-S-E membranes demonstrated exceptional oxidative stability, which is attributed to the free radical scavenging ability of the retained sulfhydryl groups on the nano-sized POSS framework. After soaking in Fenton’s reagent at 80 °C for 108 h, the OPBI-POSS-S-E-20% membrane retained 79.4% of its initial weight, significantly surpassing both the OPBI-OE-POSS-20% and pristine OPBI membranes. The PA-doped OPBI-POSS-S-E-20% membrane achieved a proton conductivity of 50.8 mS cm⁻¹ at 160 °C, and the corresponding membrane electrode assembly delivered a peak power density of 724 mW cm⁻², highlighting the key role of POSS as a nano-modifier in advancing HT-PEM performance. Full article

High-temperature proton exchange membrane systems (HT-PEM) based on polybenzimidazole (PBI) membranes are a promising technology offering significant advantages over their low-temperature counterparts. A key challenge limiting its long-term durability is the leaching of phosphoric acid (PA) from the membrane during operation. This work introduces, for the first time, the strategy of modifying polybenzimidazole (PBI) membranes with amino-functionalized porous aromatic frameworks (PAF-20-NH₂) to fundamentally enhance their PA retention and operational stability, a critical challenge for high-temperature PEM technologies. We propose that the synergistic combination of the framework’s nanoscale porosity and the specific interaction of its amino groups create an unprecedented network for acid immobilization via reinforced hydrogen bonding. A comprehensive study of the membranes’ physicochemical and structural properties reveals that PAF-20-NH₂ modification results in a significant and quantitatively demonstrated improvement in acid retention capacity, directly translating into a notable increase in proton conductivity compared to both pristine PBI and membranes modified with the non-functionalized PAF-20. These findings establish a new, highly effective pathway for the rational design of next-generation high-performance PBI-based membranes. Full article

The design of the chemical structure of ion-conductive membranes is critical to enhance proton/vanadium ion selectivity and the performance of vanadium redox flow batteries (VRFBs). Herein, camphorsulfonic acid is proposed as a novel proton-conductive group and grafted on polybenzimidazole (PBICa). The pendant sulfonic acid group on the end of the grafted side chains is flexible to promote the aggregation of ionic clusters at even a relatively low ion-exchange capacity (IEC) of 2.14 mmol g⁻¹. The formation of these high-quality clusters underscores the remarkable efficacy of this structural strategy in driving nanoscale phase separation, which is a prerequisite for creating efficient proton-conducting pathways. The bulky and non-coplanar architecture of the camphorsulfonic acid group helps to increase the proportion of free volume compared with the conventional sulfonated polybenzimidazole, which not only promotes water uptake to facilitate proton transport but also exerts a sieving effect to effectively block vanadium ion permeation. The well-formed ionic clusters, together with the expanded free volume architecture, endow the membrane with both high proton conductivity (30.5 mS cm⁻¹) and low vanadium ion permeability (0.15 × 10⁻⁷ cm² s⁻¹), achieving excellent proton/vanadium ion selectivity of 9.85 × 10⁹ mS s cm⁻³, which is about 5.6-fold that of a Nafion 212 membrane. Operating at 200 mA cm⁻², the PBICa-based VRFB achieves an energy efficiency of 78.4% and a discharge capacity decay rate of 0.32% per cycle, outperforming the Nafion 212-based battery (EE of 76.9%, capacity decay of 0.79% per cycle). Full article

Intermediate-temperature (IT) proton-exchange membranes (PEMs) play vital roles in hydrogen and direct liquid fuel cells, electrolyzers, and other electrochemical membrane reactors at elevated temperatures of higher than 150 °C. This article reports the fabrication and performance assessment of a type of new IT polymer–inorganic composite (PIC) PEMs that were made of cerium ultraphosphate (CeP₅O₁₄-CUP) as the durable solid-state proton conductor and undoped polybenzimidazole (PBI) as the high-temperature (HT) polymeric binder. The proton conductivity and electrochemical performance of the PIC PEMs were characterized at 200 °C with varying membrane thickness, processing parameters, and operating conditions using a single-stack hydrogen fuel cell connected to a fuel cell test station. Experimental results show that the PIC membranes (with CUP of 75 wt.%) carried high mechanical flexibility and strength as well as noticeably reduced water uptake of 4.4 wt.% compared to pristine PBI membranes of 14.0 wt.%. Single-stack hydrogen fuel cell tests at 200 °C in a humidified hydrogen and air environment showed that the proton conductivity of the PIC PEMs was measured up to 0.105 S/cm, and the electrochemical performance exhibited its dependence upon the membrane thickness with the power density of up to 191.7 mW/cm². Discussions are made to explore performance dependence and improvement strategies. The present study expects the promising future of the IT-PIC-PEMs for broad applications in high-efficiency electrochemical energy conversion and value-added chemical production at elevated temperatures of 200 °C or higher. Full article

Polybenzimidazole (PBI), a high-performance polymer known for its exceptional thermal stability and chemical resistance, was processed by solution electrospinning to manufacture fibrous non-woven membranes. The process was repeated under different conditions by adjusting four main settings: the polymer solution concentration, the flow rate, the voltage applied between the needle and the collector, and the separating distance. To clarify the interplay between process parameters and material properties, a Design of Experiment (DOE) approach was used to systematically analyze the effects of said parameters on microstructural properties, including fiber diameter, porosity, and air permeability, pointing out that the increase in viscosity improves fiber uniformity, while optimizing the applied voltage and the needle–collector distance enhances jet stability and solvent evaporation, crucial for defect-free fibrous microstructures. Post-processing via calendering further refined the membrane texture and properties, for example by reducing porosity and air permeability without significantly altering the fibrous morphology, particularly at low lamination ratios. Thermal and mechanical evaluations highlighted that the obtained electrospun PBI membranes exhibited enhanced flexibility, but lower tensile strength compared to cast films due to the underlying open pore microstructure. This integrated approach—combining experimental characterization, DOE-guided optimization, and post-processing via calendering—provides a systematic framework for tailoring PBI membranes for specific applications, such as filtration, fuel cells, and molecular sieving. The findings highlight the potential of PBI-based electrospun membranes as versatile materials, offering high thermal stability, chemical resistance, and tunable properties, thereby establishing a foundation for further innovation in advanced polymeric membrane design and applications for energy and sustainability. Full article

Supercapacitors are advanced energy storage devices renowned for their rapid energy delivery and long operational lifespan, making them indispensable across various industries. Their relevance has grown in recent years due to the adoption of environmentally friendly materials. One such material is bacterial nanocellulose (BNC), produced entirely from microbial sources, offering sustainability and a bioprocess-driven synthesis. In this study, BNC was synthesized using a symbiotic microbial community. After production and purification, pristine BNC membranes, with an average thickness of 80 microns, were impregnated with an alkali-alcohol meta-polybenzimidazole (PBI) solution. This process yielded hybrid BNC/PBI membranes with improved ion-transport properties. The BNC membranes were then doped with a 6 M KOH solution, to enhance OH⁻ conductivity, and characterized using optical microscopy, ATR FT-IR, XRD, CVT, BET analysis, and impedance spectroscopy. Both BNC and BNC/PBI membranes were tested as separators in laboratory-scale symmetric supercapacitor cells, with performance compared to a commercial Viledon^® separator. The supercapacitors employing BNC membranes exhibited high specific capacitance and excellent cycling stability, retaining performance over 10,000 charge/discharge cycles. These findings underscore the potential of BNC/KOH membranes for next-generation supercapacitor applications. Full article

Novel AB-Polybenzimidazole (AB-PBI)/TiO₂ nanocomposite membranes have been prepared using a synthetic green chemistry approach. Modified Eaton’s reagent (methansulfonic acid/P₂O₅) was used as both reaction media for microwave-assisted synthesis of AB-PBI and as an efficient dispersant of partially agglomerated titanium dioxide powders. Composite membranes of 80 µm thickness have been prepared by a film casting approach involving subsequent anti-solvent inversion in order to obtain porous composite membranes possessing high sorption capacity. The maximal TiO₂ filler content achieved was 20 wt.% TiO₂ nanoparticles (NPs). Titania particles were green synthesized (using a different content of Mentha Spicata (MS) aqueous extract) by hydrothermal activation (150 °C), followed by thermal treatment at 400 °C. The various methods such as powder X-ray diffraction and Thermogravimetric analyses, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and Energy-dispersive X-ray spectroscopy, Electronic paramagnetic resonance, Scanning Electron Microscopy and Transmission Electron Microscopy have been used to study the phase and surface composition, structure, morphology, and thermal behavior of the synthesized nanocomposite membranes. The photocatalytic ability of the so-prepared AB-Polybenzimidazole/bio-TiO₂ membranes was studied for decolorization of Reactive Black 5 (RB5) as a model azo dye pollutant under UV light illumination. The polymer membrane in basic form, containing TiO₂ particles, was obtained with a 40 mL quantity of the MS extract, exhibiting the highest decolorization rate (96%) after 180 min of UV irradiation. The so-prepared AB-Polybenzimidazole/TiO₂ samples have a powerful antibacterial effect on E. coli when irradiated by UV light. Full article

This review discusses the progress of research on sulfonated poly(ether ether ketone) (SPEEK) and its composite membranes in proton exchange membrane fuel cells (PEMFCs). SPEEK is a promising material for replacing traditional perfluorosulfonic acid membranes due to its excellent thermal stability, mechanical property, and tunable proton conductivity. By adjusting the degree of sulfonation (DS) of SPEEK, the hydrophilicity and proton conductivity of the membrane can be controlled, while also balancing its mechanical, thermal, and chemical stability. Researchers have developed various composite membranes by combining SPEEK with a range of organic and inorganic materials, such as polybenzimidazole (PBI), fluoropolymers, and silica, to enhance the mechanical, chemical, and thermal stability of the membranes, while reducing fuel permeability and improving the overall performance of the fuel cell. Despite the significant potential of SPEEK and its composite membranes in PEMFCs, there are still challenges and room for improvement, including proton conductivity, chemical stability, cost-effectiveness, and environmental impact assessments. Full article

High-temperature polymer-electrolyte membrane fuel cells (HT-PEMFCs) are a very important type of fuel cells since they operate at 150–200 °C, making it possible to use hydrogen contaminated with CO. However, the need to improve the stability and other properties of gas-diffusion electrodes still impedes their distribution. Self-supporting anodes based on carbon nanofibers (CNF) are prepared using the electrospinning method from a polyacrylonitrile solution containing zirconium salt, followed by pyrolysis. After the deposition of Pt nanoparticles on the CNF surface, the composite anodes are obtained. A new self-phosphorylating polybenzimidazole of the 6F family is applied to the Pt/CNF surface to improve the triple-phase boundary, gas transport, and proton conductivity of the anode. This polymer coating ensures a continuous interface between the anode and proton-conducting membrane. The polymer is investigated using CO₂ adsorption, TGA, DTA, FTIR, GPC, and gas permeability measurements. The anodes are studied using SEM, HAADF STEM, and CV. The operation of the membrane–electrode assembly in the H₂/air HT-PEMFC shows that the application of the new PBI of the 6F family with good gas permeability as a coating for the CNF anodes results in an enhancement of HT-PEMFC performance, reaching 500 mW/cm² at 1.3 A/cm² (at 180 °C), compared with the previously studied PBI-O-PhT-P polymer. Full article

The use of immiscible polymer blends in gas separations is limited due to uncontrollable phase separation. In contrast, compatibilized immiscible polymer blends can be used as precursors with controlled morphologies that allow for a unique pore architecture. Herein, an immiscible polymer blend (1:1) comprising polybenzimidazole (PBI) and the copolyimide 6FDA-DAM:DABA [3:2], derived from reacting 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 2,4,6-trimethyl-1,3-phenylenediamine (DAM) and 3,5-diaminobenzoic acid (DABA), were combined with durene diamine as a compatibilizer. The compatibilizer helped reduce the 6FDD domain sizes from 5.6 µm down to 0.77 µm and induced a more even 6FDA distribution and the formation of continuous thin-selective PBI layers. The carbon–carbon composite membranes derived from the compatibilized immiscible polymer blends showed a 3-fold increase in both H₂ permeability and H₂/CO₂ selectivity compared to the membranes derived from non-compatibilized polymer blends. The H₂ permeability of the compatibilized immiscible polymer blends increased from 3.6 to 27 Barrer, and their H₂/CO₂ selectivity increased from 7.2 to 20. The graphitic domain size of the carbon–carbon composite membranes derived from the polymer blends also increased from 6.3 nm for the non-compatibilized blend to 10.0 nm for the compatibilized blend. Full article

A high phosphoric acid uptake and retention capacity are crucial for the high performance and stable operation of phosphoric acid/polybenzimidazole (PA/PBI)-based high-temperature proton exchange membranes. In this work, amine end-functionalized side-chain grafted PBI (AGPBI) with different grafting degrees are synthesized to enhance both the phosphoric acid uptake and the acid retention ability of the accordingly formed membranes. The optimized acid–base membrane exhibits a PA uptake of 374.4% and an anhydrous proton conductivity of 0.067 S cm⁻¹ at 160 °C, with the remaining proton conductivity percentages of 91.0% after a 100 h stability test. The accordingly fabricated membrane electrode assembly deliver peak power densities of 0.407 and 0.638 W cm⁻² under backpressure of 0 and 200 kPa, which are significantly higher than 0.305 and 0.477 W cm⁻² for the phosphoric acid-doped unmodified PBI membrane under the same conditions. Full article

Nanofibrous membranes have gained interest for their small pore size, light weight, and excellent filtration. When produced from high-performance polymers, nanofibrous membranes also benefit from excellent mechanical properties, thermal resistance, and chemical resistance. Electrospinning is a common method of producing high-performance nanofibres. However, there are still major challenges with the dissolution and electrospinning of these polymers, as well as in the performance of the resulting nanofibres, which is often less than what would be expected from a conventional high-performance fibre. This review assesses the state of progress in the electrospinning of five high-performance fibres: meta-aramid (m-aramid), para-aramid (p-aramid), polyamide-imide (PAI), polybenzoxazole (PBO), and polybenzimidazole (PBI). Polymers that can be readily dissolved in organic solvents, such as m-aramid, PAI, and PBI, have been more widely researched for electrospinning compared to those that can only be spun from precursors or dissolved in non-volatile solvents. Major focuses within the literature include optimizing the electrospinning process and improving the mechanical performance of the nanofibres. This review demonstrates a clear need for more standardized characterization methods and consideration for the longevity of the nanofibrous membranes. Future research should also focus on scale-up methods of electrospinning so that the benefits of nanofibres made from high-performance polymers can be leveraged by the industry. Full article