High Molecular Weight Polybenzimidazole Membranes for High Temperature PEMFC

High temperature operation of proton exchange membrane fuel cells under ambient pressure has been achieved by using phosphoric acid doped polybenzimidazole (PBI) membranes. To optimize the membrane and fuel cells, high performance polymers were synthesized of molecular weights from 30 to 94 kDa with good solubility in organic solvents. Membranes fabricated from the polymers were systematically characterized in terms of oxidative stability, acid doping and swelling, conductivity, mechanical strength and fuel cell performance and durability. With increased molecular weights the polymer membranes showed enhanced chemical stability towards radical attacks under the Fenton test, reduced volume swelling upon the acid doping and improved mechanical strength at acid doping levels of as high as about 11 mol H₃PO₄ per molar repeat polymer unit. The PBI‐78kDa/10.8PA membrane, for example, exhibited tensile strength of 30.3 MPa at room temperature or 7.3 MPa at 130 °C and a proton conductivity of 0.14 S cm^–1 at 160 °C. Fuel cell tests with H₂ and air at 160 °C showed high open circuit voltage, power density and a low degradation rate of 1.5 μV h^–1 at a constant load of 300 mA cm^–2.     

A PBI‐Sb0.2Sn0.8P2O7‐H3PO4 Composite Membrane for Intermediate Temperature Fuel Cells

Fine particles of a solid proton conductor Sb_0.2Sn_0.8P₂O₇ were incorporated in PBI‐H₃PO₄ membranes with 20 wt.%. In SEM figures, the Sb_0.2Sn_0.8P₂O₇ particles exhibited even and uniform distribution in the PBI‐Sb_0.2Sn_0.8P₂O₇ membrane. Influences of the immersing time and the concentration of H₃PO₄ solution for immersion on H₃PO₄ loading level were investigated. H₃PO₄ loading level was found an important factor on membrane conductivity. Incorporation of Sb_0.2Sn_0.8P₂O₇ in the PBI‐H₃PO₄ membrane resulted in greater membrane conductivities. In the single cell tests, the peak power density of the membrane electrode assembly (MEA) with the PBI‐Sb_0.2Sn_0.8P₂O₇‐H₃PO₄ membrane was also greater than that of a MEA with PBI‐H₃PO₄ membrane. One MEA using PBI‐Sb_0.2Sn_0.8P₂O₇‐H₃PO₄ membrane achieved a peak power density of 0.67 W cm^–2 at 175 °C with H₂/O₂ and exhibited satisfactory stability.     

Effects of organically modified nanoclay on the transport properties and electrochemical performance of acid‐doped polybenzimidazole membranes

Nanocomposite polyelectrolyte membranes based on phosphoric acid (H₃PO₄) doped polybenzimidazoles (PBIs) with various loading weights of organically modified montmorillonite (OMMT) were prepared and characterized for direct methanol fuel cell (DMFC) applications. X‐ray diffraction analysis revealed the exfoliated structure of OMMT nanolayers in the polymeric matrices. An H₃PO₄–PBI/OMMT membrane composed of 500 mol % doped acid and 3.0 wt % OMMT showed a membrane selectivity of approximately 109,761 in comparison with 40,500 for Nafion 117 and also a higher power density (186 mW/cm²) than Nafion 117 (108 mW/cm²) for a single‐cell DMFC at a 5M methanol feed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A polymer electrolyte membrane for high temperature fuel cells to fit vehicle applications

Poly(tetrafluoroethylene) PTFE/PBI composite membranes doped with H₃PO₄ were fabricated to improve the performance of high temperature polymer electrolyte membrane fuel cells (HT-PEMFC). The composite membranes were fabricated by immobilising polybenzimidazole (PBI) solution into a hydrophobic porous PTFE membrane. The mechanical strength of the membrane was good exhibiting a maximum load of 35.19 MPa. After doping with the phosphoric acid, the composite membrane had a larger proton conductivity than that of PBI doped with phosphoric acid. The PTFE/PBI membrane conductivity was greater than 0.3 S cm⁻¹ at a relative humidity 8.4% and temperature of 180 °C with a 300% H₃PO₄ doping level. Use of the membrane in a fuel cell with oxygen, at 1 bar overpressure gave a peak power density of 1.2 W cm⁻² at cell voltages >0.4 V and current densities of 3.0 A cm⁻². The PTFE/PBI/H₃PO₄ composite membrane did not exhibit significant degradation after 50 h of intermittent operation at 150 °C. These results indicate that the composite membrane is a promising material for vehicles driven by high temperature PEMFCs.     

Preparation and Characterisation of Proton Exchange Membranes Based on Crosslinked Polybenzimidazole and Phosphoric Acid

Crosslinked polybenzimidazole (PBI) was synthesised via free radical polymerisation between N‐vinylimidazole and vinylbenzyl substituted PBI. The degree of crosslinking increases with increasing content of the crosslinker. The phosphoric acid doping behaviour, mechanical properties, proton conductivity and acid migration stability of crosslinked PBI and linear PBI are discussed. The results show that the acid doping ability decreases with increasing degree of crosslinking of PBI. The introduction of N‐vinylimidazole in PBI is beneficial to its oxidation stability. The mechanical stability of crosslinked PBI/H₃PO₄ membrane is better than that of linear PBI/H₃PO₄ membrane. The proton conductivity of the acid doped membranes can reach ∼10^–4 S cm^–1 for crosslinked PBI/H₃PO₄ composite membranes at 150 °C. The temperature dependence of proton conductivity of the acid doped membranes can be modelled by an Arrhenius relation. The proton conductivity of crosslinked PBI/H₃PO₄ composite membranes is a little lower than that of linear PBI/H₃PO₄ membranes with the same acid content. However, the migration stability of H₃PO₄ in crosslinked PBI/H₃PO₄ membranes is improved compared with that of linear PBI/H₃PO₄ membranes.     

A Quaternary Polybenzimidazole Membrane for Intermediate Temperature Polymer Electrolyte Membrane Fuel Cells

A quaternary ammonium polybenzimidazole (QPBI) membrane was synthesized for applications in intermediate temperature (100–200 °C) hydrogen fuel cells. The QPBI membrane was imbibed with phosphoric acid to provide suitable proton conductivity. The proton conductivity of the membrane was 0.051 S cm^–1 at 150 °C with the PA acid loading level of 3.5 PRU (amount of H₃PO₄ per repeat unit of polymer QPBI). The QPBI membrane was characterized in terms of composition, structure and morphology by NMR, FTIR, SEM, and EDX. The fuel cell performance with the membrane gave peak power densities of 440 and 240 mW cm^–2 using oxygen and air, respectively, at 175 °C.     

Methanol permeability and proton conductivity of polybenzimidazole and sulfonated polybenzimidazole

The preparation of sulfonated polybenzimidazole (sPBI) by the grafting of (4‐bromomethyl) benzenesulfonate onto polybenzimidazole (PBI) has been investigated. The methanol permeability and proton conductivity of PBI and sPBI have been studied, and the effects of methanol concentration and temperature on the methanol permeability of PBI and sPBI membranes are discussed. The results showed that the PBI membrane is a good methanol barrier. Methanol permeability in this membrane decreases with increasing methanol concentration and increases with increasing temperature. The temperature‐dependence of methanol permeability of PBI and sPBI membranes is of the ‘Arrhenius type’. Methanol permeation of sPBI is less sensitive to temperature than that of PBI. However, sPBI is a poorer methanol barrier when compared to PBI. Methanol permeability in sPBI membranes increases with increasing methanol concentration and temperature. The proton conductivity of sPBI is 4.69 × 10^?4 S cm^?1 at room temperature in the hydrated state. The DC conductivity of sPBI–H₃PO₄ increases with increasing temperature. Proton transport in sPBI–H₃PO₄ is less sensitive to temperature than that in PBI–H₃PO₄. Copyright © 2004 Society of Chemical Industry     

Performance evaluation of sodium alginate–Pebax polyion complex membranes for application in direct methanol fuel cells

A novel polyion complex membrane was synthesized for direct methanol fuel cell application through the blending of the natural biopolymer sodium alginate (SA) with the synthetic polymer Pebax [poly(ether‐block ‐amide)]. The blend was covalently crosslinked with glutaraldehyde (GA) and sulfonated with sulfuric acid (H₂SO₄), after which characterization by Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffractometry, thermogravimetric analysis, and universal testing machine techniques was carried out. The SA–Pebax–GA–H₂SO₄ membrane exhibited a high ion‐exchange capacity of 2.1 mequiv/g, an optimum water sorption of 17.3%, and a low methanol sorption of 9.5%. A desirably low methanol permeability of 9.25 × 10^?8 cm²/s and a high proton conductivity of 0.067 S/cm were obtained as against corresponding values of 1.82 × 10^?6 cm²/s and 0.077 S/cm reported for a commercial Nafion 117 membrane. Moreover, a high selectivity of 6.5 × 10⁵ Ss/cm³ with a power density of 0.17 W/cm² was achieved with the indigenous blend membrane at a potential of 0.34 V. Molecular dynamics simulation was performed along with the estimation of fractional free volume to explain the transport behavior of water and methanol molecules through the membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44485.     

A PFSA Composite Membrane with Sulfonic Acid Functionalized TiO2 Nanotubes for Polymer Electrolyte Fuel Cells and Water Electrolysers

Titanate nanotubes (TiO₂‐NT) were functionalized with sulfonic acid functional groups and characterized with Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD). Results confirmed that sulfonic acid groups were grafted onto TiO₂‐NT with a uniform distribution. When the functionalized titanate nanotube (F‐TiO₂‐NT) was incorporated in perfluorosulfonic acid membranes, the membrane conductivity and water uptake were improved. Polymer electrolyte membrane (PEM) fuel cells using 5 wt.% F‐TiO₂‐NT incorporated composite membrane exhibited a peak power density of 429 mW cm^–2 with non‐humidified O₂ at 90 °C, which is about four times higher than that with Nafion 117 membrane at identical conditions. PEMWE with 5 wt.% F‐TiO₂‐NT incorporated composite membrane achieved 1,000 mA cm^–2 current density at voltages below 1.6 V at 90 °C without back pressurizing.     

Proton Conducting Membranes Based on Poly(2,2′‐imidazole‐5,5′‐bibenzimidazole)

Poly(2,2′‐imidazole‐5,5′‐bibenzimidazole) (PBI‐imi) was synthesized via the polycondensation between 3,3′,4,4′‐tetraaminobiphenyl and 4,5‐imidazole‐dicarboxylic acid. Effects of the reaction conditions on the intrinsic viscosity of the synthesized polymers were studied. The results show that the molecular weight of the polymers increases with increasing monomer concentration and reaction time, and then levels off. With higher reaction temperature, the molecular weight of the polymer is higher. With the additional imidazole group in the backbone, PBI‐imi shows improved phosphoric acid doping ability, as well as a little higher proton conductivity when compared with widely used poly[2,2′‐(m‐phenylene)‐5,5′‐bibenzimidazole] (PBI‐ph).Whereas, PBI‐imi and PBI‐ph have the similar chemical oxidation stability. PBI‐imi/3.0 H₃PO₄ composite membranes exhibit a proton conductivity as high as 10^–4 S cm^–1 at 150 °C under anhydrous condition. The temperature dependence of proton conductivity of acid doped PBI‐imi can be modeled by an Arrhenius equation.     

Synthesis and Properties of Random Copolymers of Functionalised Polybenzimidazoles for High Temperature Fuel Cells

A series of polybenzimidazoles (PBIs) incorporating main chain sulphonic acid groups were synthesised as random copolymers with p‐PBI in varying ratios using polyphosphoric acid (PPA) as both the polymerisation solvent and polycondensation reagent. The PPA process was used to produce high molecular weight phosphoric acid (PA) doped PBI gel membranes in a one‐step procedure. These membranes exhibit excellent mechanical properties (0.528–2.51 MPa tensile stress and 130–300% tensile strain) even at high acid doping levels [20–40 mol PA/PRU (polymer repeat unit)] and high conductivities (0.148–0.291 S cm^–1) at elevated temperatures (>100 °C) with no external humidification, depending on copolymer composition. Fuel cell testing was conducted with hydrogen fuel and air or oxygen oxidants for all membrane compositions at temperatures greater than 100 °C without external feed gas humidification. Initial studies showed a maximum fuel performance of 0.675 V for the 25 mol% s‐PBI/75 mol% p‐PBI random copolymer at 180 °C and 0.2 A cm^–2 with hydrogen and air, and 0.747 V for the same copolymer at 180 °C and 0.2 A cm^–2 with hydrogen and oxygen.     

Polybenzimidazole/inorganic composite membrane with advanced performance for high temperature polymer electrolyte membrane fuel cells

In this work, Al–Si was synthesized via a sol–gel process and introduced in poly 2,2′‐m‐(phenylene)‐5,5′‐bibenzimidazole (PBI). As a result, a series of five Al–Si/PBI composite (ASPBI) membranes (0, 3, 6, 9, and 12 wt%) were developed and characterized for application in high temperature polymer electrolyte membrane fuel cells (HT‐PEMFCs). The chemical and morphological structure of ASPBI membranes were analyzed by Fourier transform infrared spectroscopy, X‐ray diffractometer, and scanning electron microscopy. According to the doping level test and thermogravimetric analysis, as the concentration of Al–Si increased, the doping level increased up to 475% due to the affinity and interaction between Al and phosphoric acid (PA). Moreover, the proton conductivity, current density at 0.6 V, and maximum power density of ASPBI membranes increased up to 0.31 S cm⁻¹, 0.320 A cm⁻², and 0.370 W cm⁻², respectively, because the increased concentration of Al–Si allows the membranes to hold more PA. Alternatively, as the amount of Al–Si increased, the tensile strength of PA‐doped and ‐undoped membranes decreased. This was caused by both excess PA and aggregation, which can cause serious degradation of the membrane and induce cracks. Furthermore, the PA‐doped and ‐undoped ASPBI12 had the lowest tensile strength of 11.6 and 77.2 MPa. The improved proton conductivity and single cell performance of ASPBI membranes implies that these membranes are possible candidates for HT‐PEMFC applications. However, further studies seeking to enhance the compatibility between PBI and Al–Si and optimize the amount of filler should be performed. POLYM. COMPOS., 38:87–95, 2017. © 2015 Society of Plastics Engineers     

Ionically Cross‐Linked Proton Conducting Membranes for Fuel Cells

For improving stability without sacrificing ionic conductivity, ionically cross‐linked proton conducting membranes are fabricated from Na⁺‐form sulfonated poly(phthalazinone ether sulfone kentone) (SPPESK) and H⁺‐formed sulfonated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (SPPO). Ionically acid‐base cross‐linking between sulfonic acid groups in SPPO and phthalazone groups in SPPESK impart the composite membranes the good miscibility and electrochemical performance. In particular, the composite membranes possess proton conductivity of 60–110 mS cm⁻¹ at 30 °C. By controlling the protonation degree of SPPO within 40–100 %, the composite membranes with favorable cross‐linking degree are qualified for application in fuel cells. The maximum power density of the composite membrane reaches approximately 1100 mW cm⁻² at the current density of 2800 mA cm⁻² at 70 °C.     

High Polymer Content 3,5‐Pyridine‐Polybenzimidazole Copolymer Membranes with Improved Compressive Properties

Three series of polybenzimidazole (PBI) copolymers (3,5‐pyridine‐r‐2OH‐PBI, 3,5‐pyridine‐r‐para‐PBI, and 3,5‐pyridine‐r‐meta‐PBI) were polymerized and cast into membranes by the polyphosphoric acid (PPA) process. Monomer pairs with high and low solubility characteristics were used to define phase stability‐processing windows for preparing membranes with high temperature membrane gel stability. Creep compliance of these membranes (measured in compression at 180 °C) generally decreased with increasing polymer content. Membrane proton conductivities decreased linearly with increasing membrane polymer content. Fuel cell performances of some high‐solids 3,5‐pyridine‐based copolymer membranes (up to 0.66 V at 0.2 A cm^–2 following break‐in) were comparable to para‐PBI (0.68 V at 0.2 A cm^–2) despite lower phosphoric acid (PA) loadings in the high solids membranes. Long‐term steady‐state fuel cell studies showed 3,5‐pyridine‐r‐para‐PBI copolymers maintained a consistent fuel cell voltage of >0.6 V at 0.2 A cm^–2 for over 2,300 h. Phosphoric acid that was continuously collected from the long‐term study demonstrated that acid loss is not a significant mode of degradation for these membranes. The PBI copolymer membranes' reduced high‐temperature creep and long‐term operational stability suggests that they are excellent candidates for use in extended lifetime electrochemical applications.     

Polyaniline salt containing dual dopants,pyrelenediimide tetracarboxylic acid,and sulfuric acid: Fluorescence and supercapacitor

Storage of energy is considered as the most germane technologies to address the future sustainability. In this study, aniline was chemically oxidized with a controlled concentration of pyrelenediimide tetracarboxylic acid (PDITCA) by ammonium persulfate to polyaniline salt (PANI‐H₂SO₄‐PDITCA), with nanorods morphologies, having a sensibly decent conductivity of 0.8 S cm^?1, wherein H₂SO₄ was generated from ammonium persulfate during polymerization. PANI‐H₂SO₄‐PDITCA salt showed bathochromic fluorescence shift (595 nm) compared to PDITCA (546 nm). The Brunauer–Emmett–Teller surface area of the PANI‐H₂SO₄‐PDITCA‐25 and PANI‐H₂SO₄‐PDITCA‐50 were 18.3 and 21.4 m² g^?1, respectively. Furthermore, its energy storage efficiency was evaluated by supercapacitor cell configuration. The composite PANI‐H₂SO₄‐PDITCA‐50 showed capacitance 460 F g^?1 at 0.3 A g^?1 and large cycle life 85,000 cycles with less retention of 77% to its original capacitance (200 F g^?1) even at a better discharge rate of 3.3 A g^?1. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45456.     

Synthesis and characterization of polybenzimidazole/α‐zirconium phosphate composites as proton exchange membrane

To improve the high‐temperature performance of proton exchange membranes, the polybenzimidazole (PBI)/α‐zirconium phosphate (α‐Zr(HPO₄)₂·nH₂O, α‐ZrP) proton exchange composite membranes were prepared in this study. PBI polymer containing a large amount of ether units has been synthesized from 3,3′‐ diaminobenzidine (DAB) and 4,4′‐oxybis (benzoic acid) by a direct polycondensation in polyphosphoric acid. The polymer exhibited a good solubility in most polar solvents. Inorganic proton conductor α‐ZrP nanoparticles have been obtained using a synthesis route involving separate nucleation and aging steps (SNAS). The effects of α‐ZrP doping content on the composite membrane performance were investigated. It was found that the introduction of ZrP improved the thermal stability of the composite membranes. The PBI/ZrP composite membranes exhibited excellent mechanical strength. The composite membrane with 10 wt% ZrP showed the highest proton conductivity of 0.192 S cm^?1 at 160°C under anhydrous condition. The proton conducting mechanism of the PBI/ZrP composite membranes was proposed to explain the proton transport phenomena. The experimental results suggested that the PBI/ZrP composite membranes may be a promising polymer electrolyte used in high temperature proton exchange membrane fuel cells (HT‐PEMFCs) under anhydrous condition. POLYM. ENG. SCI., 56:622–628, 2016. © 2016 Society of Plastics Engineers     

Modification of sulfonated poly(ether ether ketone) membranes by impregnation with the ionic liquid 1‐butyl‐3‐methylimidazolium tetrafluoroborate for proton exchange membrane fuel cell applications

Sulfonated poly(ether ether ketone) (SPEEK) membranes were modified by impregnation with the ionic liquid (IL) 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMI.BF₄) by immersion into an IL aqueous solution for different periods of time. The modified membranes were investigated by thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), ion exchange capacity (IEC), and conductivity. The SPEEK membrane immersed into the IL aqueous solution for 2 min showed greater dimensional and thermal stability than the pristine SPEEK membrane, and achieved higher decomposition temperatures. It also presented a higher conductivity value (1.0 mS cm^?1), indicating that BMI.BF₄ is a promoter of proton conductivity. The membrane electrode assembly (MEA) produced reached maximum values of power density of 0.13 W cm^?2 and current density of 0.54 A cm^?2 during fuel cell operation. The results indicate that the SPEEK membrane modified by immersion for 2 min is promising for use in a proton exchange membrane fuel cell. Its performance yielded values very close to those obtained with Nafion, which reaches maximum values of power density of 0.19 W cm^?2 and current density of 0.77 A cm^?2. POLYM. ENG. SCI. 56:1037–1044, 2016. © 2016 Society of Plastics Engineers     

Oxidation of SO2 in a Trickle Bed Reactor Packed with Activated Carbon at Low Liquid Flow Rates

In this study, the oxidation of SO₂ on activated carbon (AcC) by using distilled water and air was carried out in a laboratory scale trickle bed reactor (TBR). Distilled water and air containing 1.7 % (v/v) SO₂ were fed co‐currently downward through a fixed bed of AcC particles in a range of 1–7 cm³/s and 10–27 cm³/s respectively. H₂SO₃/H₂SO₄ solutions were the products obtained in the liquid phase. Steady‐state experiments were performed in a column of 0.15 m packing height and 0.047 m column diameter at 20 °C and atmospheric pressure. Experimental reaction rates of this study were compared with those of other studies on the basis of plug flow model of Mata‐Smith given in literature.     

Fabrication of BaZr0.1Ce0.7Y0.2O3 – δ ‐Based Proton‐Conducting Solid Oxide Fuel Cells Co‐Fired at 1,150 °C

Dense proton‐conducting BaZr_0.1Ce_0.7Y_0.2O_{3 – δ} (BZCY) electrolyte membranes were successfully fabricated on NiO–BZCY anode substrates at a low temperature of 1,150 °C via a combined co‐press and co‐firing process. To fabricate full cells, the LaSr₃Co_1.5Fe_1.5O_{10 – δ}–BZCY composite cathode layer was fixed to the electrolyte membrane by two means of one‐step co‐firing and two‐step co‐firing, respectively. The SEM results revealed that the cathode layer bonded more closely to the electrolyte membrane via the one‐step co‐firing process. Correspondingly, determined from the electrochemical impedance spectroscopy measured under open current conditions, the electrode polarisation and Ohmic resistances of the one‐step co‐fired cell were dramatically lower than the other one for its excellent interface adhesion. With humidified hydrogen (2% H₂O) as the fuel and static air as the oxidant, the maximum power density of the one‐step co‐fired single cell achieved 328 mW cm^–2 at 700 °C, showing a much better performance than that of the two‐step co‐fired single cell, which was 264 mW cm^–2 at 700 °C.     

Pr Doped Barium Cerate as the Cathode Material for Proton‐Conducting SOFCs

BaCe_0.8Pr_0.2O₃ (BCP20) and BaCe_0.6Pr_0.4O₃ (BCP40) powders are successfully synthesized through the Pechini method and used as the cathode materials for proton‐conducting solid state oxide fuel cells (SOFCs). The prepared cells consisting of the structure of a BaZr_0.1Ce_0.7Y_0.2O_3–δ (BZCY7)‐NiO anode substrate, a BZCY7 anode functional layer, a BZCY7 electrolyte membrane, and a cathode layer, are measured from 600 to 700 °C with humidified hydrogen (∼3% H₂O) as the fuel and static air as the oxidant. The electricity results show that the cell with BCP40 cathode has a higher power density, which could obtain an open‐circuit potential of 0.99 V and a maximum power density of 378 mW cm^–2 at 700 °C. The polarization resistance measured at the open‐circuit condition of BCP40 is only 0.16 Ω cm² at 700 °C, which was less than BCP20.