Anhydrous Proton Exchange Membranes Research Articles

Molecular Complexation of Polymers and Metal Oxide Clusters for Semicrystalline, Thermoplastic Anhydrous Proton Exchange Membranes in Fuel Cells.

With the manipulation of surface charges and loadings, 1 nm super-acidic metal oxide clusters can co-crystallize with poly(ethylene glycol) (PEG) at molecular scale for thermoplastic anhydrous proton exchange membranes (PEMs). The coexistence of crystalline and amorphous regions endows the PEMs with a high Young's modulus and high flexibility, while the noncovalent complex interactions enable facile preparation and (re)processing. Furthermore, the diffusive dynamics of PEG chains is slowed by the confinement effect, while the local segmental dynamics is accelerated due to the transition of the chain conformation from helix to zigzag when confined in the crystalline framework. This greatly facilitates proton transportation in the crystalline region for an excellent anhydrous proton conductivity of 4.5 × 10-3 S cm-1 at 90 °C. The balanced proton conductivity, mechanical strength, and processability of the PEMs contribute to the promising power density of H2/O2 fuel cells assembled with co-crystalline PEMs at high temperatures under dry conditions.

New anhydrous proton exchange membranes based on polypyrrolone (PPy) for high-temperature polymer electrolyte fuel cells

Polypyrrolone (PPy) possesses excellent heat resistance and mechanical properties, moreover, the N-heterocycle contained in the PPy allows the absorption of phosphoric acid (PA) for proton conduction. In the present work, PPy is synthesized by a two-step method and evaluated for the first time as the polymeric material for high temperature proton exchange membranes (HT-PEMs). The PA-doped PPy membrane reaches a peak power density of 582 mW cm−2 at 160 °C under fully anhydrous conditions, besides, the fuel cell exhibits excellent durability over a period of 300 h with a load voltage decay of only 0.032% per hour and remains 0.647 V after the test. Further, the PPy-impregnated polyimide (PI) nanofiber mat composite membrane (PI@PPy) with an optimal thickness is fabricated with enhanced dimensional stability, of which acid swelling ratio noticeably declined by 51% in area and 25% in volume. A higher peak power density (634 mW cm−2) and less cell voltage reduction is also observed in the composite membrane, benefits from the trade–off between proton conductivity and PA retention ability. The results of the present study may contribute to further studies on polypyrrolone-based HT-PEMs and composite membranes.

Researching proton conduction behavior at subzero temperature of lamellar anhydrous proton exchange membranes

For proton exchange membranes (PEMs), many studies have been going into the anhydrous PEMs with the working temperature exceeding 110 °C and the humidified PEMs below 80 °C. However, the PEMs fracture can cause cold start failure while the fuel cell vehicles are exposed to a colder climate for a long-time parking. In this study, low temperature PEMs (LTPEMs) with the lamellar structure was constructed through the well-ordered dispersion of Kevlar nanofibers, thioglycollic acid capping cadmium telluride (CdTe) nanocrystals and polyurethane (PU) polymer, expecting to enhance the mechanical property and improve the proton conductivity at subzero temperature. The successful preparation of the LTPEMs with spin coating technique and layer by layer self-assembly technique was determined by the structure analysis and the property measurement. The compact microstructure was constructed owing to electrostatic attraction and intermolecular hydrogen bonding. In the prepared (Kevlar/CdTe)25/(PU/CdTe)100 membrane, Kevlar nanofibers provided the support and PU molecular chains guaranteed enough flexibility. Furthermore, a massive amount of CdTe nanocrystals could tolerate low temperature condition, which was derived from the high proton conductivity at subzero temperature. Specifically, the (Kevlar/CdTe)25/(PU/CdTe)100/PA membrane exhibited the proton conductivity values of (2.23 ± 0.39) × 10−2 S/cm at −30 °C, (6.59 ± 0.15) × 10−2 S/cm at 0 °C and (1.73 ± 0.04) × 10−1 S/cm at 30 °C. Most importantly, the fine proton conductivity stability was revealed from the proton conductivity values of 3.72 × 10−2 S/cm at −30 °C after a thirty-cycle heating/cooling process and 3.53 × 10−2 S/cm at −30 °C after a 1020 h non-stop test. Furthermore, there was a slight decrease on the tensile stress with PA molecules doping owing to the compact microstructure.

Local proton hopping mechanism in imidazolium-based plastic crystal: an ab initio molecular dynamics study

Abstract Protic organic ionic plastic crystals (POIPCs) are promising solid-state proton conductor materials in anhydrous proton exchange membrane fuel cells, due to their mechanical flexibility and high ionic conductivity in the plastic crystal phase. In typical POIPCs, the ions are orientationally disordered while the centers of mass are ordered (positional order) like the crystal phase. The local disorder provides more degrees of freedom for the translational and rotational diffusion of ions, thus enhancing proton conduction either via the vehicle mechanism or the Grotthuss mechanism. Yet the local dynamics and the interactions of the cations and anions during the proton transfer process are far from being fully understood. Here, we performed Car–Parrinello molecular dynamics (CPMD) simulation on the imidazolium methanesulfate ([ImH][CH3SO3]) unit cell. By artificially creating one proton hole, we found that a proton can hop directly between the cations. Though the anion is not directly involved in proton hopping, the oxygen atom in the sulfonate group interacts with the proton and has a synergetic motion along with the proton hopping process. This indicates the structural disorder of imidazolium rings and the aid of an anion can facilitate Grotthuss-type proton hopping in imidazolium-based POIPCs.

Development of 1,2,3-Triazole Based Ionic Liquid Doped Sulfonated Polysulfone (SPSU) Electrolytes for Anhydrous Proton Exchange Membrane Applications

In this study, triazole based ionic liquid doped sulfonated polysulfone (SPSU) composite membranes were evaluated for high temperature proton exchange membrane fuel cell (PEMFC) systems. SPSU obtained by sulfonation of aromatic polysulfone (PSU) polymer matrix was used in the preparation of composite electrolytes. Sulfonated polymer matrices were doped with three different triazole-based ionic liquids (TIL-1, TIL-2 and TIL-3) synthesized within the scope of the study and composite membrane series were formed. Structural, thermal and mechanical characterizations were performed by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA), respectively. Proton conductivities were measured over a wide temperature range (380-450 K) and the effectiveness of composite membranes in high temperature PEMFC systems was evaluated. As a result of TGA analysis, all triazole based ionic liquid doped membrane series exhibited high thermal resistance. It was observed that the proton conductivity of the composite structures was greatly improved with high temperature proton conductivity measurements (8.05 mS/cm for SPSU; 58.1 mS/cm for SPSU/TIL-3(1.0)) and the obtained membranes could be an alternative in high temperature PEMFCs.

Alkaline polymers of intrinsic microporosity: high-conduction and low-loss anhydrous proton exchange membranes for energy conversion

Polymers of intrinsic microporosity, with high volume and capillary force, can meet the requirements of PA adsorption and retention for HT-PEMs. The widespread and interconnected microstructure realized state-of-the-art HT-PEMs with fast proton transfer.

Constructing anhydrous proton exchange membranes through alternate depositing graphene oxide and chitosan on sulfonated poly(vinylidenefluoride) or sulfonated poly(vinylidene fluoride-co-hexafluoropropylene) membranes

The proton exchange membranes (PEMs) have been constructed through alternate depositing chitosan (CS) and graphene oxide (GO) on the membrane substrates of sulfonated poly(vinylidenefluoride) (SPVDF) or sulfonated poly(vinylidene fluoride-co-hexafluoropropylene) (SPVDF-HFP). Phosphoric acid (PA) doped membranes were formed owing to the intermolecular hydrogen bonds, which were expected to work as PEMs in high temperature proton exchange membrane fuel cells (HTPEMFCs). The prepared layer-by-layer (LBL) depositional composite membranes showed the fine capacity to combine PA molecules with the lower dimension swelling. As expected, SPVDF(CS/GO)50/PA and SPVDF-HFP(CS/GO)50/PA membranes respectively exhibited higher proton conductivity values of 2.34 × 10−1 S/cm and 1.56 × 10−1 S/cm at 140 °C. Furthermore, the proton conductivity values of 3.52 × 10−1 S/cm and 2.25 × 10−1 S/cm at 140 °C in a 500-hour non-stop test could correspond to the negligible leakage of the depositional layers from the composite membranes. Because the doped PA molecules entered the gaps between the depositional layers, the prepared PA doped membranes possessed the enhanced mechanical strength owing to the compacted structure. Most interestingly, the prepared LBL deposited membranes could retain the better tensile stress even if PA molecules were doped with the formation of SPVDF(CS/GO)50/PA and SPVDF-HFP(CS/GO)50/PA membranes. Meanwhile, the proper thermal stability, methanol permeability and proton conductivity stability of the prepared membranes could suggest that the strategy of alternate depositing the functional components on membrane substrates is substantially more effective at improving the grade of PEMs. In our opinion, the fine balance on proton conductivity and mechanical property could make them stand out from other candidates as PEMs for HTPEMFCs.

Chain end-termination of p-polybenzimidazole by bulk segment for efficient electrochemical power generation and hydrogen separation

We investigated the effects of hydrogen separation using high-temperature anhydrous proton-exchange membrane fuel-cell technology. Various acid-doped para-polybenzimidazole (p-PBI)-chain end-tethered amine-polyhedral oligomeric silsesquioxane (NH2-POSS) membranes were prepared via a unique sol–gel transition method termed as the poly(phosphoric acid) process. The resulting NH2-POSS-capped p-PBI membranes exhibited a higher phosphoric acid-doping level (128–223.5%) and proton conductivity (0.23–0.29Scm−1 at 160°C and 0% relative humidity) than the parent p-PBI membrane. The chemical chain end-termination of p-PBI with cage-like NH2-POSS significantly enhanced the electrochemical H2/CO2 and H2/CO separation at 160°C. The hydrogen separation of the NH2-POSS-capped p-PBI system required a relatively small amount of energy, and the system exhibited a good dynamic response. The favorable interfacial interaction between the NH2-POSS and the p-PBI host, high thermomechanical stability, and good fuel-cell and hydrogen-separation performance at high temperatures up to 160°C indicate the applicability of the NH2-POSS-capped p-PBI membranes to electrochemical power generation and hydrogen pumps for practical industrial applications in harsh and extreme environments.

Constructing anhydrous proton exchange membranes based on cadmium telluride nanocrystal-doped sulfonated poly(ether ether ketone)/polyurethane composites

Cadmium telluride (CdTe) nanocrystals with thiol stabilizers have been applied widely in the fields of energy storage and transformation. The aim of this work is to develop anhydrous proton exchange membranes (PEMs) by introducing CdTe nanocrystals bearing thioglycolic acid (tga) or mercaptopropionic acid (mpa) stabilizers into sulfonated poly(ether ether ketone) (SPEEK) and polyurethane (PU) systems. In the prepared SPEEK/PU/CdTe membranes, CdTe nanocrystals could provide desirable properties such as improving mechanical strength and enhancing proton conductivity by combining with phosphoric acid (PA) molecules. Successful preparation of SPEEK/PU/CdTe/PA membranes was demonstrated by the identification of high and stable proton conductivity and satisfactory thermal/chemical stability and mechanical properties. The fine appearance of membranes revealed uniform dispersion of components. Measurements of properties showed that the SPEEK(74%)/PU/CdTe-mpa(20/60/20)/100%PA membrane as a candidate anhydrous PEM is promising for use in high-temperature proton exchange membrane fuel cells. Specifically, the recommended membrane showed a proton conductivity of 1.18 × 10−1 S cm−1 at 160 °C and 3.96 × 10−2 S cm−1 at 100 °C, lasting for 600 h, and a tensile stress of 14.6 MPa at room temperature. Mixing inorganic CdTe nanocrystals with polymers to form inorganic/organic composite membranes is effective for producing anhydrous PEMs with cheaper polymers without functional groups to conduct protons.

Synthesis and Properties of Phosphoric-Acid-Doped Polybenzimidazole with Hyperbranched Cross-Linkers Decorated with Imidazolium Groups as High-Temperature Proton Exchange Membranes.

Highly phosphoric-acid (PA)-doped polybenzimidazole (PBI) membranes exhibit good proton conductivity at high temperatures; however, they suffer from reduced mechanical properties and loss of PA molecules due to the plasticity of PA and the weak interactions between PA and benzimidazoles, especially with the absorption of water. In this work, a series of PBIs with hyperbranched cross-linkers decorated with imidazolium groups (ImOPBI-x, where x is the weight ratio of the hyperbranched cross-linker) as high-temperature proton exchange membranes are designed and synthesized for the first time. We observe how the hyperbranched cross-linkers can endow the membranes with improved oxidative stability and acceptable mechanical performance, and imidazolium groups with strong basicity can stabilize the PA molecules by delocalization and hydrogen bond formation to endow the membranes with an enhanced proton conductivity and a decreased loss of PA molecules. We measured a high proton conductivity of the ImOPBI-x membranes, ranging from 0.058 to 0.089 S cm−1 at 160 °C. In addition, all the ImOPBI-x membranes displayed good mechanical and oxidative properties. At 160 °C, a fuel cell based on the ImOPBI-5 membrane showed a power density of 638 mW cm−2 and good durability under a hydrogen/oxygen atmosphere, indicating its promising use in anhydrous proton exchange membrane applications.

Investigation on carbon nanotube oxide for anhydrous proton exchange membranes application

ABSTRACTThe widespread participation of polymers in the membrane preparation has been considering to be critical for the development of proton exchange membranes (PEMs). For the polymers without functional groups to conduct protons, the introduction of proton conduction carriers with the formation of composite membranes is an effective strategy to prepare PEMs with the outstanding proton conductivity. However, there remains a potential risk of the components leaking from composite membranes due to the lack of the interaction force. Here, the composite of carbon nanotube oxide (OCNT) assembling with cadmium telluride (CdTe) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate (bmimPF6) was introduced into the system of phosphoric acid (PA) doping poly(vinylidene fluoride) (PVDF) with the formation of PVDF/OCNT‐CdTe‐bmimPF6/85%PA membranes. PA molecules are anchored by the inorganics of OCNT‐CdTe‐bmimPF6 and are stabilized in membranes. The high and stable proton conductivity values at the elevated temperature are obtained comparing the reported PVDF/bmimPF6/PA membranes. Specifically, the proton conductivity value reached 1.28 × 10−1 S/cm at 160 °C and the value is stable 1.70 × 10−2 S/cm at 120 °C lasting for 350 h. The fine stability in components could make the membranes extricate from the predicament of proton conductivity decline exceeding 120 °C under anhydrous conditions in PVDF/bmimPF6/PA membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48833.

High temperature anhydrous proton exchange membranes based on chemically-functionalized titanium/polybenzimidazole composites for fuel cells

We herein report an effective way to fabricate high-performance polybenzimidazole (PBI) nanocomposite membranes using sulfophenylated titanium oxide (s-TiO2) nanoparticles for application in high temperature polymer electrolyte membrane fuel cell (HT-PEMFC). The s-TiO2, multifunctional inorganic proton conductors that can improve proton conductivity and cell performance of PBI, was obtained through the surface modification. The PBI nanocomposite membranes were doped with phosphoric acid (PA) for performance evaluation. Properties such as PA doping level, proton conductivity, PA retention and cell performance were evaluated and compared to neat PBI. PA doped PBI-sTP2 (2 wt% TiO2) showed the highest doping of 12.1 and proton conductivity of 0.096 S/cm at 150 °C. In the cell test, peak power density of 621 mW/cm2 was obtained, roughly 30% better performance compared to neat PBI (471 mW/cm2).

Constructing multilayered membranes with layer-by-layer self-assembly technique based on graphene oxide for anhydrous proton exchange membranes

Layer-by-layer (LBL) self-assembly technique could nanoscopically construct the layered membranes and it has attracted more attention in the field of bionics, clean energy and microelectronics. The aim of this research to develop the multilayered membranes with the ordered deposition of components using LBL self-assembly technique. Successful preparation of anhydrous proton exchange membranes (PEMs) based on graphene oxide (GO) as polyanions, polyurethane (PU) and poly(diallyldimethylammonium chloride) (PDDA) as polycations have been demonstrated by identification of the ordered distribution of components and compact structure. While the prepared membranes were immersed into phosphoric acid (PA) solution, PA molecules were combined with the formation of PA doped membranes. In spite of PA dominating the proton conduction, the decreased proton conduction resistance is revealed from the lower activation energy owing to the multilayered structure. Specifically, the proton conductivity of 1.83 × 10−1 S/cm at 150 °C was obtained for (PU/GO/PDDA/GO)200/60%PA membranes. Moreover, the proton conductivity stability measurement demonstrated the component and mechanical stability, showing 1.47 × 10−1 S/cm at 120 °C and 1.83 × 10−1 S/cm at 140 °C. The result revealed that LBL self-assembly technique could provide a promising strategy to prepare multilayered membranes as membrane electrolytes using in high temperature proton exchange membrane fuel cells.

Fabrication of layered membrane electrolytes with spin coating technique as anhydrous proton exchange membranes

Spin coating technique is a simple and effective method to fabricate layered membranes and it has been widely used in the field of energy storage and transformation, biomaterials and electronics. The aim of this work is to develop anhydrous proton exchange membranes (PEMs) based on cheap polymers bearing the simple structure with spin coating technique. Successful fabrication of anhydrous PEMs based on polyvinylidene fluoride (PVDF) polymer, cadmium telluride (CdTe) nanocrystals and phosphoric acid (PA) molecules has been demonstrated by identification of high and stable proton conductivity. Specifically, (PVDF-CdTe-PA)5/85%PA membranes present the maximum proton conductivity of 7.70 × 10−2 S/cm at 160 °C and 1.42 × 10−2 S/cm at 140 °C lasting 620 h. The decreased proton conduction resistance is revealed from the drastic reduction of activation energy (Ea) owing to the layered structure and the adsorption of PA molecules. The introduction of CdTe nanocrystals to form the organic/inorganic composite membranes that is substantially more effective at improving proton conductivity and stiffness, showing great promise in solving the dilemma of proton conductivity and mechanical property. This study provides the support to exploit anhydrous PEMs with more cheap polymers using spin coating technique.

Phosphoric acid doped high temperature proton exchange membranes based on comb-shaped polymers with quaternized graft architectures

A series of poly(arylene ether ketone)-g-quaternized 4-vinylbenzyl chloride copolymers (PAEK-g-QVBC-x) containing locally and densely quaternized side chains were synthesized. The PAEK-g-QVBC membranes were obtained by solution casting from their reaction mixture and then doped with phosphoric acid (PA) to be used as advanced anhydrous high temperature proton exchange membranes. Compared to the commercial PA doped polybenzimidazole membrane and other main-chain-type quaternized hydrocarbon polymer membranes with the similar proton conductivity, these PA-PAEK-g-QVBC-x membranes possess much lower PA doping level, extremely lower volume swelling ratio, and higher dimensional and oxidative stability. Among them, PA-PAEK-g-QVBC-6.4 membrane with the PA doping level in weight of 101.7% has the highest proton conductivities of 31 mS cm−1 at 120 °C and 65 mS cm−1 at 200 °C, respectively. Surprisingly, its volume swelling ratio is only 7.8%, which is far less than other reported PA doped membranes. The preliminary fuel cell test shows that PA-PAEK-g-QVBC-6.4 membrane has the peak power density of 53 mW cm−2 at 100 °C without any humidification. The results indicate that the anhydrous proton exchange membranes based on comb-shaped polymers with quaternized graft architectures have the potential to resolve the dilemma between demand of high PA doping levels to achieve high proton conductivity and the dimensional and mechanical stability of largely swollen membranes for high temperature fuel cells.

Membrane preparation from hyperbranched perfluorinated polymers

ABSTRACTIn this research, membrane formation with hyperbranched perfluorinated polymers (HBFP) was investigated. To create a tough membrane, HBFP was blended and crosslinked with a tougher linear polymer. Blending only or crosslinking only was not sufficient to create a tough membrane, but combining blending with crosslinking was successful. Miscibility, phase separation, and thermal and mechanical properties were evaluated for a variety of systems. By using a toughening linear polymer with lower polarity, reduced phase separation and improved mechanical properties were seen. Overall, imidazole‐containing HBFPs produced the clearest and toughest blends. These new hyperbranched ionomers and copolymers are strong candidates for future use in anhydrous proton exchange membranes. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 961–972

New anhydrous proton exchange membranes based on fluoropolymers blend imidazolium poly (aromatic ether ketone)s for high temperature polymer electrolyte fuel cells

The blend polymer membranes were synthesized from the methylimidazolium poly (aromatic ether ketone) (MeIm-PAEK) and fluoropolymers (PVDF and PVDF-HFP) with excellent thermal stability and improved dimensional stabilities for high-temperature polymer electrolyte fuel cells. The MeIm-PAEK exhibited good compatibility with PVDF or PVDF-HFP without phase separation. High phosphoric acid doping contents of the blend membranes were achieved at elevated temperatures with acceptable swellings. The acid doped blend membranes displayed lower dimensional swellings and higher mechanical strength compared to the MeIm-PAEK membrane, which allowed the blend membranes to obtain higher acid doping contents and proton conductivities. The MeIm-PAEK/10%PVDF membrane with a phosphoric acid doping content of 700 wt% showed a proton conductivity as high as 0.192 S cm−1 at 180 °C under the non-humidified condition and a tensile strength of 4.3 MPa at room temperature.

Phosphoric acid doped hydrophobic ionic liquid-based composite membranes for anhydrous proton exchange membrane application

In this study, phosphoric acid doped hydrophobic ionic liquid-based composite membranes are successfully synthesized and characterized.

Anhydrous proton conducting poly(vinyl alcohol) (PVA)/ poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS)/1,2,4-triazole composite membrane

The design and fabrication of anhydrous proton exchange membranes are critically important for high temperature proton exchange membrane fuel cell (HT-PEMFC) operating between 100 and 200 °C. Herein, we demonstrate a novel proton conducting membrane consisting of poly(vinyl alcohol) (PVA), poly (2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) and 1,2,4-triazole, which was fabricated by physical blending, casting and solvent evaporation techniques. The in-situ chemical cross-linking was performed by glutaraldehyde (GA) to improve the water management of the membranes. The molecular structure of the membranes and intermolecular interactions between the constituents were confirmed by Fourier-transform infrared spectroscopy (FT-IR). The surface and cross-section morphologies of the membranes were observed by scanning electron microscopy (SEM). The thermal stability performance of the membranes was studied with thermogravimetric analysis (TGA). In order to determine the physico–chemical properties of the membranes, water uptake (WU), dimensional change and ion exchange capacity (IEC) tests were carried out. The proton conductivities of composite membranes increase with the temperature and the temperature dependencies exhibit an Arrhenius behavior. Proton conductivity measurements revealed an optimum ratio between PAMPS and 1,2,4-triazole content to achieve higher proton conductivity. In anhydrous state at 150 °C, the highest proton conductivity measured was 0.002 S/cm for PVA:PAMPS:1,2,4-triazole (1:1:1) composition. Overall, our investigation showed that 1,2,4-triazole is a promising proton carrier reagent above 100 °C when it is embedded into appropriate host polymers.

Side-chain-type quaternized naphthalene-based poly(arylene ether ketone)s for anhydrous high temperature proton exchange membranes

The PA/Q-SCT-NPAEK-xx membranes with good proton conductivity, mechanical and thermal stabilities were prepared successfully.