Phosphoric Acid Doping Research Articles

Quaternary ammonium-biphosphate ion-pair based copolymers with continuous H+ transport channels for high-temperature proton exchange membrane

Phosphoric acid (PA)-doped polymer electrolyte membranes are the most promising materials for high-temperature proton exchange membranes (HT-PEMs). However, their development is subject to the compromise between proton conductivity and phosphoric acid (PA) doping level. Here, an ether-free QPAF-4 membrane (a copolymer containing perfluoroalkylene and fluorenyl groups with pendant ammonium groups) is directly doped with phosphoric acid and studied as HT-PEMs. Due to the intrinsic micro-phase separation structure of QPAF-4 matrix and strong interaction of quaternary ammonium (QA)-PA, the PA-doped membranes possess high proton conductivity and eminent PA retention at comparatively low PA doping level, respectively. The QPAF-4 membrane with 150% PA uptake (QPAF-4-150%PA) offers a proton conductivity of 52 mS cm−1 at 160 °C. As expected, the single cell with QPAF-4-150%PA membrane shows the maximum peak power density of 683 mW cm−2 at 160 °C under anhydrous condition. Meanwhile, the single cell exhibits excellent durability over a period of 60 h with only a slight reduction in voltage of 3.1%. These results indicate that the as-prepared PA-doped quaternized polymer with micro-phase separation structure seems to offer a promising way to develop performing and long-life HT-PEMs with low PA doping levels.

Enhanced proton conductivity and stability of polybenzimidazole membranes at low phosphoric acid doping levels via constructing efficient proton transport pathways with ionic liquids and carbon nanotubes

Polybenzimidazole (PBI) membrane doped with phosphoric acid (PA) usually requires the high PA doping level (ADL) to ensure excellent proton conductivity, however, the loss of PA can lead to dramatical attenuation of fuel cell performance. Herein, we develop a facile way to enhance the proton conductivity and stability of poly[2,2′-(p-oxydiphenylene)-5,5′-benzimidazole (OPBI) membranes at much low ADL (about 80% of OPBI membrane) via construction of proton transport pathways between ionic liquids (ILs), carbon nanotubes (CNTs) and PA. Owing to the anionic and cationic structures of ILs and the adsorption of CNTs on PA, abundant proton transport pathways can be constructed to guarantee superior proton conductivity and durability of hybrid OPBI membrane (ILs/CNTs/OPBI) with low ADL. The as-prepared 10%-ILs/NH2-CNTs/OPBI hybrid membrane exhibits the highest proton conductivity (130.8 mS cm−1) and stability (above 119 mS cm−1 after 228 h test) at 160 °C, much better than other ILs/CNTs/OPBI hybrid membranes and OPBI membranes. More importantly, a fuel cell based on ILs/NH2-CNTs/OPBI membrane achieves the highest power density of 508 mW cm−2 at 160 °C, 2.7 times higher than that of OPBI membranes (189 mW cm−2). Good durability of a single cell with ILs/NH2-CNTs/OPBI membranes is also confirmed in steady-state and restart tests.

Polybenzimidazole membrane crosslinked with quaternized polyaniline as high-temperature proton exchange membrane: Enhanced proton conductivity and stability

Despite the phosphoric acid (PA) doped polybenzimidazole (PBI) membrane demonstrates excellent proton conductivity, the higher loss rate of PA and the lower mechanical strength at high PA doping level (ADL) will lead to a significant deterioration of its performance. The traditional cross-linking method can construct compact PBI molecular structure to enhance the mechanical properties, but it prevents the doping of PA in PBI membrane, thus reducing the ADL. Herein, we prepare cross-linked poly[2,2′-(p-oxydiphenylene)-5,5′-benzimidazole] (OPBI) membranes with polyaniline (PANI) cross-linker containing different quaternary ammonium (QA) group contents to balance the relationship between ADL and mechanical properties. Based on the aniline-diphosphate ion pair constructed by PANI and PA, more QA-diphosphate ion pairs are constructed through tuning the content of alkaline QA group in PANI to increase ADL and reduce the loss of PA. Quaternized PANI cross-linked OPBI membranes (QPANI-OPBI) exhibit superior mechanical properties, high ADL and proton conductivity. The cross-linked membrane containing QA group at a molar ratio of 0.30 to the OPBI repeating unit (0.30-QPANI-OPBI) exhibits the smallest PA loss rate of 15.2% after 120 h even at the highest ADL of 17.2. The 0.30-QPANI-OPBI membrane exhibits much better proton conductivity and peak power density than OPBI membrane at high temperature (160 °C), which are respectively 145.6 mS cm−1 and 459 mW cm−2. Our present work demonstrates that the quaternized PANI would be a promising cross-linker to prepare the PA-PBI membrane with excellent properties as High-temperature proton exchange membrane (HT-PEM).

Nitrogen Dense Distributions of Imidazole Grafted Dipyridyl Polybenzimidazole for a High Temperature Proton Exchange Membrane.

The introduction of basic groups in the polybenzimidazole (PBI) main chain or side chain with low phosphoric acid doping is an effective way to avoid the trade-off between proton conductivity and mechanical strength for high temperature proton exchange membrane (HT-PEM). In this study, the ethyl imidazole is grafted on the side chain of the PBI containing bipyridine in the main chain and blended with poly(2,2′-[p-oxydiphenylene]-5,5′-benzimidazole) (OPBI) to obtain a series of PBI composite membranes for HT-PEMs. The effects of the introduction of bipyridine in the main chain and the ethyl imidazole in the side chain on proton transport are investigated. The result suggests that the introduction of the imidazole and bipyridine group can effectively improve the comprehensive properties as HT-PEM. The highest of proton conductivity of the obtained membranes under saturated phosphoric acid (PA) doping can be up to 0.105 S cm−1 at 160 °C and the maximum output power density is 836 mW cm−2 at 160 °C, which is 2.3 times that of the OPBI membrane. Importantly, even at low acid doping content (~178%), the tensile strength of the membrane is 22.2 MPa, which is nearly 2 times that of the OPBI membrane, the proton conductivity of the membrane achieves 0.054 S cm−1 at 160 °C, which is 2.3 times that of the OPBI membrane, and the maximum output power density of a single cell is 540 mW cm−2 at 160 °C, which is 1.5 times that of the OPBI membrane. The results suggest that the introduction of a large number of nitrogen-containing sites in the main chain and side chain is an efficient way to improve the proton conductivity, even at a low PA doping level.

Synthesis and characterization of phosphonated polybenzimidazole membranes with improved proton conductivity for high-temperature proton exchange membrane applications

The study has synthesized a novel dicarboxylic acid monomer with phosphonate group, 2-((diethoxyphosphoryl)methyl)-[1,1′-biphenyl]-4,4′-dicarboxylic acid (PMDA), and then successfully prepared a series of polybenzimidazole polymers containing methyl-phosphonic acid group and ether group (POPBI-x) via the polycondensation between PMDA, 4,4′-oxybis (benzoic acid) (OBBA) and 3,3′-diaminobenzidine (DAB) in polyphosphoric acid (PPA)/phosphorus pentoxide (P2O5). Meanwhile, the smooth membranes were fabricated via the solution-casting method. Results of TGA, the Fenton’s reagent immersing test, and the tensile test showed that the POPBI-x membranes possessed good thermo-oxidative stability and mechanical properties. Moreover, compared to poly[2,2′-(p-oxydiphenylene)-5,5′-benzimidazole] (OPBI), POPBI-x had a significant enhancement in the phosphoric acid doping level, PA retention ability, and proton conductivity after doped with phosphoric acid (PA) because the methyl-phosphonic acid groups on the backbones enriched the hydrogen bonding interactions between the polymer chain and phosphoric acid. Notably, the POPBI-19 exhibited a high phosphoric acid doping level of approximately 11.3 and excellent proton conductivity of approximately 0.0523 S cm−1 at 180°C under anhydrous conditions.

Tröger's base polymer blended with poly(ether ketone cardo) for high temperature proton exchange membrane fuel cell applications

Developing membrane electrolyte materials with high performance and low cost is a key factor in promoting the application and commercialization of the high temperature proton exchange membrane fuel cell (HT-PEMFC). In this work, a Tröger's base (TB) polymer is synthesized from commercially available and low-cost 4,4′-diamine-3,3′-dimethyl-biphenyl (DMBP) and dimethoxy methane in trifluoroacetic acid via a one-pot TB polymerization reaction under mild conditions. The obtained polymer is composited by TB unit and DMBP moiety (named as DMBP-TB), which occupies a good organic solubility, high thermal stability and excellent chemical resistance. Due to the built-in bicyclic amine rings and intrinsic microporous structure, the pure DMBP-TB membrane exhibits a remarkable phosphoric acid (PA) doping content as high as 1077% in 85 wt% PA solution at room temperature. However, the excessive swelling and poor mechanical integrity hinder the PA doped DMBP-TB membrane as the HT-PEM. Thus, the commercial and low-cost engineering thermoplastic of poly(ether ketone cardo) (PEKC) is employed as the enhanced material to prepare DMBP-TB blend membranes. The DMBP-TB/50%PEKC/149%PA membrane displays an anhydrous conductivity of 0.061 S cm−1 at 180 °C and a tensile strength of 8.7 MPa at room temperature, which enables H2–O2 fuel cell with a peak power density of 536 mW cm−2 at 180 °C without backpressure, suggesting the utility for HT-PEMFCs.

Polyethersulfone/polyvinylpyrrolidone/boron nitride composite membranes for high proton conductivity and long-term stability high-temperature proton exchange membrane fuel cells

Proton exchange membranes have excellent proton conductivity and long-term endurance vital for high-temperature proton exchange membrane fuel cells (HT-PEMFCs). Herein, a polyethersulfone (PES)/polyvinylpyrrolidone (PVP)/boron nitride (BN) (PES–PVP–BN) composite membrane was fabricated successfully. The well-dispersion of BN nanosheets in the PES–PVP–BN composite membrane was demonstrated by scanning electron microscopy and energy dispersive X-ray spectrometry mapping. Benefiting from the interaction force between BN nanosheets with phosphoric acid (PA), the PA doping level (ADL) and conductivity of the blend membrane have been improved. In addition, the interaction force between the PVP@BN system and PA has been demonstrated by theoretical calculations, which enhances the anchoring effect of BN to PA compared with the PES–PVP membrane significantly. Thus, the PES–PVP–0.5% BN composite membrane exhibited the best proton conductivity (107.42 mS cm−1) and peak power density (359 mW cm−2) at 160 °C under the same device operation conditions. Furthermore, the PES–PVP–0.5% BN composite membrane exhibited outstanding long-term stability during a 100 h test, demonstrating the PES–PVP–BN composite membrane as a candidate material for HT-PEMFC applications.

An Imidazolium Type Ionic Liquid Functionalized Ether-Free Poly(terphenyl piperidinium) Membrane for High Temperature Polymer Electrolyte Membrane Fuel Cell Applications

Development of high temperature polymer electrolyte membranes is essential for advanced energy conversion and storage technologies. Herein, an imidazolium type ionic liquid (BPMIm) with a long side-chain of 5-bromopentyl is synthesized and employed as the quaternization reagent for ether-free poly(p-terphenyl-co-N-methyl-piperidine) (PTP). Grafting the flexible long side-chain imidazolium group into the ether-free polymer backbone not only improves the polymer solubility in organic solvents but also provides acid-base interaction sites for the following phosphoric acid doping that supports proton conductivity at above 100 °C. Compared with pure and iodomethane quaternized PTP membranes (i.e. PTP and PTP-Me), the prepared imidazolium ionic liquid grafted PTP membrane (i.e. PTP-PMIm) exhibits an enhanced phosphoric acid uptake and hence a superior anhydrous proton conductivity of 138 mS cm−1 at 180 °C. The technical feasibility of the PTP-PMIm membrane is demonstrated in H2-air fuel cells at temperatures from 160 °C–200 °C, which reaches a high peak power density of around 456 mW cm−2 at 200 °C at ambient pressure.

The performance and durability of high-temperature proton exchange membrane fuel cells enhanced by single-layer graphene

Single-layer graphene (SLG) obtained by chemical vapor deposition is applied between membrane and electrodes by a wet chemical transfer method to study its effect on the performance and durability of polybenzimidazole membranes in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). After accelerated stress testing (AST), the membrane electrode assembly (MEA) loaded with SLG at different positions exhibits higher peak power density, lower electrode resistances, and larger electrochemical active surface area than pure polybenzimidazole membranes with high phosphoric acid doping level. The peak power density of the MEAs with both cathode and anode loaded with SLG is 480 mW cm-2 after AST, while those based on pure membranes is 249 mW cm-2. Lab-based X-ray micro-computed tomography combined with Raman spectroscopic mapping was applied for the first time to study the effect of SLG on controlling phosphoric acid leaching. In addition, samples containing SLG on an ultra-thin membrane (7.5 µm) were also tested to explore its influence on hydrogen crossover. After 100 h of galvanostatic discharging, the hydrogen crossover of samples loaded with single-layer graphene on the anode does not exceed 1.75 × 10−4 mol s-1, which is much lower than that of MEAs made using pure ultra-thin membranes (8.16 ×10−4 mol s-1).

Impact of Membrane Phosphoric Acid Doping Level on Transport Phenomena and Performance in High Temperature PEM Fuel Cells.

In this work, a three-dimensional mathematical model including the fluid flow, heat transfer, mass transfer, and charge transfer incorporating electrochemical reactions was developed and applied to investigate the transport phenomena and performance in high-temperature proton exchange membrane fuel cells (HT-PEMFCs) with a membrane phosphoric acid doping level of 5, 7, 9, 11. The cell performance is evaluated and compared in terms of the polarization curve. The distributions of temperature, oxygen mass fraction, water mass fraction, proton conductivity, and local current density of four cases are given and compared in detail. Results show that the overall performance and local transport characteristics are significantly affected by the membrane phosphoric acid doping level.

Graphene-Based Materials for High Temperature Fuel Cell Applications

High-Temperature Hydrogen Proton Exchange Membrane (HT-PEMFC) operates at temperatures up to 200 oC using Phosphoric Acid (PA) doped Poly[2,2′-m-(phenylene)-5,5′-benzimidazole] (PBI) membrane. PBI does not have a good proton conductivity by itself it should doped with PA to establish a complete network of hydrogen bond (Grotthuss mechanism). HT-PEMFC and PBI performance depends on the doping level of PA and consequently of Physico-chemical properties of this acid [1,2].One of the main advantages of these fuel cells is that PA has a low vapour pressure at these temperatures allowing long-term operation of these fuel cells without any electrolyte loss, which is one of the principal aspect defined by US Department of Energy as 2015 targets [1,2]. Additionally, the PA is an excellent proton conductor material being comparable to typical Nafion membranes and without the necessity of additional gas humidification due to the fast Grotthus mechanism. However, PBI/PA membranes exhibit PA migration form cathode to anode at the high current density and high temperatures. This loss of PA and its redistribution within the Membrane Electrode Assembly (MEA) have a range of potential implications for fuel cell degradation such as decreasing of PA doping level resulting in increased membrane resistance, lower proton conductivity and as a consequence, decreasing performance and lifetime [1,2].To stop the PA leaching from the cathode side and consequently to reduce the negative effects produced on the fuel cell, we propose to use a barrier to avoid PA leaching. Single Layer Graphene (SLG) has a 2D hexagonal structure, which acts a since material to block all atoms and molecules from passing through except protons, as has been proved by Hu et al.[3] SLG has been already used on low temperature PEM fuel cells to reduce fuel crossover and improve the efficiency of the fuel cell [4]. However, despite the advantageous properties of SLG, it is still presenting some drawbacks, notably due to the complex process to proceed it and its high cost. These limitations leave an open window to Graphene based materials such a Graphene Oxide, which has attractive properties to as filler materials in PBI membranes due to its chemical functionalization and its non-porous structure leading to additional resistance for mass transport and increases the tortuosity of the permeation pathways allowing a higher selectivity [5].This work presents two different approaches to stop the PA leaching in HT-PEMFC by incorporating SLG and GO-composite membranes into the MEA. The addition of the SLG produced by Chemical Vapour Deposition (CVD) has demonstrated no change in the proton conductivity, supporting the hypothesis that SLG is a good proton conductor [3]. In addition to that, SLG has extraordinary barrier properties, leading a decrease of the PA leaching and enhancing the HT-PEMFC performance as well as the membrane degradation.Although positive results have been obtained by adding SLG into the fuel cells, GO-composite membrane have been also evaluated within the MEA. Exfoliated Graphene Oxide has been synthesized by electrochemical exfoliation of graphite and has been incorporated as a filler into the PBI, obtaining successful results in terms of performance and long term work.

Mechanically robust and highly conductive polymer electrolyte membranes comprising high molecular weight poly[2,2′-(bipyridyl)-bibenzimidazole] and graphene oxide

Promising proton exchange membranes comprising a nitrogen-rich and a high molecular weight poly[2,2′-(bipyridyl)-bibenzimidazole] (BipyPBI) polymer as a substrate and graphene oxide (GO) as a filler were successfully fabricated. The synergism of GO on the membrane physicochemical properties, including the acid doping level, acid retention capability, water uptake, swelling degree, mechanical properties, proton conductivity, oxidative stability, and the hydrogen permeability was studied. The results of the study confirmed the fabrication of mechanically robust and highly conductive proton exchange membranes. Regarding the phosphoric acid (PA) doping level, the BipyPBI/GO membrane reached 17 mol of PA per monomeric unit of BipyPBI (an increase of around 69% in PA-doping level compared to the bare BipyPBI membrane). The proton conductivity at 60 °C under anhydrous conditions increased from 0.002 S cm−1 to 0.019 S cm−1 (around 10-folds increase) when 4 wt% of GO was incorporated into the BipyPBI matrix. In addition, the conductivity reached 0.045 S cm−1 at 140 °C. The activation energy of the proton conduction decreased from 45.6 kJ mol−1 for the bare BiPyPBI to 12 kJ mol−1 for the composite membranes, indicating an improved proton mobility where the GO worked as a carrier-bridge for a smooth proton transfer into the polymer matrix. Furthermore, the H2 permeability reached 1.3 Barrer at 140 °C, indicating the fabrication of tightly-packed membranes. These results provide a very promising membrane for fuel cell applications.

New high-performance bulky N-heterocyclic group functionalized poly(terphenyl piperidinium) membranes for HT-PEMFC applications

The development of high-performance high temperature proton exchange membranes (HT-PEMs) is a huge challenge that impedes the application of HT-PEM fuel cell (HT-PEMFC). Herein, novel bulky basic group grafted ether-free poly(terphenyl piperidinium) membranes are proposed for HT-PEMFC. Through a simple one-step polymerization, the poly(terphenyl piperidine) (PTP) polymer is synthesized. In order to improve the phosphoric acid (PA) uptake and solubility of PTP in organic solvents, both benzimidazole and pyridine side chains are functionalized into the PTP backbone. Comparing with methyl and methylene pyridine grafted PTP membranes (PTP-Me and PTP-Py), the methylene benzimidazole side chain grafted membrane (PTP-BeIm) exhibits an excellent PA doping content of 215 wt% and a high conductivity of 0.088 S cm−1 at 180 °C under anhydrous condition. The H2–O2 fuel cell based on PTP-41%BeIm/215%PA displays a high peak power density of around 1 W cm−2 at 180 °C without any backpressure, which is about 1.5 times higher than that of PBI/342 wt%PA based cell. Thus, this work develops a facile and low-cost approach on the preparation of high-performance HT-PEMs.

Preparation of highly porous heat‐resistant polybenzoxazole network films and their electrical conductivities

AbstractHighly porous rigid polybenzoxazole (PBO) network films were prepared using a precursor‐mediated fabrication method. The obtained PBO network films possessed high porosities of ~40%, as calculated from their apparent densities. In addition, the 5%‐weight‐loss temperatures of the films were ≥570°C under nitrogen atmosphere, demonstrating an excellent thermal stability. The electrical conductivities of the obtained PBO network films and phosphoric‐acid‐doped PBO network films were also evaluated. In addition, PBO network films containing pyridine rings were prepared and subjected to phosphoric acid doping. The resultant films were found to exhibit the highest conductivities of the films considered in this study owing to proton conduction both between phosphate groups and between the pyridine rings. The highest conductivity was found for a film prepared from a phosphoric‐acid‐doped PBO network containing pyridine rings, that is, 2.09 × 10−1 S/cm at 150°C, which was higher than that of Nafion™. Therefore, these films can be used at higher temperatures than that of Nafion™.

Constructing stable continuous proton transport channels by in-situ preparation of covalent triazine-based frameworks in phosphoric acid-doped polybenzimidazole for high-temperature proton exchange membranes

Phosphoric acid (PA)-doped high-temperature proton exchange membranes (HTPEMs) suffer from low efficiency of proton transport and severe PA leakage. Constructing a stable continuous proton transport channel may be a promising method to address the above issues. Herein, a stable proton transport channel was constructed for the first time by in-situ preparing covalent triazine-based frameworks (CTFs) in polybenzimidazole under a mild trifluoromethanesulfonic acid (TFA) catalysis condition. The membranes were prepared with CTFs loading from 10% to 40%, and the properties of the membranes were characterized carefully. The membrane containing 30% CTFs showed some attractive properties, such as high conductivity (74.8 mS cm−1) under low PA doping level (167.1%), low volume swelling (71.8%), and high PA retention ability (89.5%). Importantly, under the same PA doping level, the single fuel cell assembled with the composite membranes showed a higher peak power density (534.4 mW cm−2) than that of poly [2,2′-(p-oxydiphenylene)-5,5′-benzimidazole] (OPBI) (325.2 mW cm−2). The results prove that constructing a stable proton transport channel can improve the properties of the membranes and the prepared membranes can potentially be used as HTPEMs.

Thermodynamic Optimization of a High Temperature Proton Exchange Membrane Fuel Cell for Fuel Cell Vehicle Applications

In this paper, a finite time thermodynamic model of high temperature proton exchange membrane fuel cell (HT-PEMFC) is established, in which the irreversible losses of polarization and leakage current during the cell operation are considered. The influences of operating temperature, membrane thickness, phosphoric acid doping level, hydrogen and oxygen intake pressure on the maximum output power density Pmax and the maximum output efficiency ηmax are studied. As the temperature rises, Pmax and ηmax will increase. The decrease of membrane thickness will increase Pmax, but has little influence on the ηmax. The increase of phosphoric acid doping level can increase Pmax, but it has little effect on the ηmax. With the increase of hydrogen and oxygen intake pressure, Pmax and ηmax will be improved. This article also obtains the optimization relationship between power density and thermodynamic efficiency, and the optimization range interval of HT-PEMFC which will provide guidance for applicable use of HT-PEMFCs.

HT-PEMs based on carbazole grafted polybenzimidazole with high proton conductivity and excellent tolerance of phosphoric acid

A set of grafted AmPBI-Car-X membranes based on amino polybenzimidazole (AmPBI) and 9-(4-Bromobutyl)-9H-carbazole (Car) have been synthesized. The membranes are applied to high temperature-proton exchange membranes (HT-PEMs). Due to its large volume and rigid structure, the obtained membranes can maintain enough mechanical strength and lower swelling while absorbing more phosphoric acid (PA). Among them, AmPBI-Car-10 has the best comprehensive performance. When its PA doping level (ADL) reaches 10.5, its proton conductivity is as high as 125.3 mS cm-1 under anhydrous conditions at 180 °C, which is 2.7 times compare with pristine AmPBI (47 mS cm-1). Moreover, AmPBI-Car-10 has a lower swelling ratio of 156.7%, which is lower than that of AmPBI while being doped with more PA. The power density of AmPBI-Car-X is higher than many reported membranes at 350 mA cm-2. It is worth noting that the conductivity of AmPBI-Car-10 membrane can still reach 94.9 mS cm-1 at 180 °C after the PA retention test under 160 °C non-humidity for 240 h.

Facile synthesis and properties of poly(ether ketone cardo)s bearing heterocycle groups for high temperature polymer electrolyte membrane fuel cells

Novel high temperature polymer electrolyte membranes (HT-PEMs) are fabricated from commercial and low-cost poly (ether ketone cardo) (PEK-Cardo). Rather than normal chloromethylation and quaternization procedure to introduce basic groups into poly (arylene ether)s, three different long side-chain basic groups are grafted into PEK-Cardo through a facile one-step lactamization between the cardo phenolphthalein type moiety in PEK-Cardo and amino compounds (i.e. 1-(3-aminopropyl) imidazole (APIm), 1-(3-aminopropyl) pyrrolidin-2-one (APy) and 3-(dimethylamino)-1-propylamine). The obtained lactamized PEK-Cardo membranes exhibit excellent phosphoric acid doping capability and the physicochemical properties are optimized by adjusting the chemical structure and grafting degree of side-chain basic groups. Fuel cell results demonstrate a big potential for HT-PEM fuel cell applications. Thus, this proposal provides a new, straightforward and low-cost method to prepare high-performance HT-PEMs.

Simultaneously enhancing proton conductivity and mechanical stability of the membrane electrolytes by crosslinking of poly(aromatic ether sulfone) with octa-amino polyhedral oligomeric silsesquioxane

The trade-off between proton conductivity and mechanical property is a critical issue to phosphoric acid (PA) doped high temperature proton exchange membranes (HT-PEMs) for using as the electrolytes in various devices. Uniformly introducing additives into polymer matrix is required for improvements on the properties of the polymer membranes. Herein, the hydrophilic and acidophilic octa-amino polyhedral oligomeric silsesquioxane (OA-POSS) is synthesized for using as a filler and a crosslinker concurrently to prepare HT-PEMs based on poly(aromatic ether sulfone) (PAES). The PA doped membrane with a crosslinking degree of 10% exhibits a proton conductivity of 97.4 mS cm−1 at 180 °C without humidifying, and an enhanced tensile stress of 8.5 and 2.4 MPa under ambient atmosphere and 110 °C, respectively, which are about 60% and 70% higher than those of the pristine quaternary ammonium PAES membrane. A peak power density of 461 mW cm−2 is achieved by the membrane at 200 °C by fueling the fuel cell with non-humidified H2 and O2 without backpressure. Comprehensive characterizations on the structure, PA doping level, anhydrous proton conductivity, as well as dimensional stability and PA retention ability of the prepared membranes are made.

Polybenzimidazoles via polyamidation: A more environmentally safe process to proton conducting membrane for hydrogen HT-PEM fuel cell

The article presents a new environmentally safe synthetic approach towards durable polybenzimidazole proton-conducting membrane via polyamidation at ambient conditions and subsequent thermal heterocyclization of films cast from reaction solution followed by phosphoric acid doping. The method avoids exhausts, acid waste and inorganic salts, compared with the existing methods and technologies, allowing to minimize the negative environmental impact related to the process. The membrane possesses an excellent proton conductivity of 105 mS cm−1 and good mechanical properties and has been successfully tested in high temperature polymer electrolyte membrane fuel cells. An extremely low hydrogen crossover through the membrane of 0.040 mA cm−2 at 180 °C has been registered compared with quite high 4–5 mA cm−2 for Celazole® m-PBI.