Proton conducting membrane containing room temperature ionic liquid

A new proton conducting membrane containing room temperature ionic liquid: 2,3-dimethyl-1-octylimidazolium trifluoromethanesulfonylimide (DMOImTFSI) and polyvinylidenefluoride-co-hexafluoropropylene (PVdF-HFP) has been developed in the present work. The addition of bis(trifluoromethanesulphonyl)imide (HN(CF₃SO₂)₂) to this membrane results in an increase in conductivity by one order of magnitude at 25 °C. The membrane shows a conductivity of 2.74 × 10⁻³ S/cm at 130 °C along with good mechanical stability. The membrane was tested in a commercial fuel cell test station at 100 °C with dry hydrogen and oxygen gas reactants using Pt/C electrodes. The membrane containing the ionic liquid has been found to be electroactive for hydrogen oxidation and oxygen reduction at the platinum electrode and can be developed for use in proton exchange membrane fuel cell (PEMFC) under non-humid conditions at elevated temperatures.     

Inorganic membranes and membrane reactors

The inorganic membrane reactor is a combined unit operation of chemical reactions and membrane separations. By having a membrane reactor, the downstream separation load can be reduced. Also, the yields can be increased and conversion can be improved for equilibrium limited reactions. However, many of the industrial chemical reactions take place at high temperature that the conventional polymeric membranes cannot withstand. A great deal of research has been done recently to develop ion-conducting ceramic membranes. Many of these have been successfully employed to form membrane reactors for many industrially relevant chemical reactions, such as hydrogenation, dehydrogenation, oxidation, coupled reactions, and decomposition reactions. An overview is given for the area of inorganic membrane preparations and membrane reactors. Many examples of petrochemical interests are presented, including hydrocarbon conversions and fuel cell applications.     

Phosphonated poly(arylene ether)s as potential high temperature proton conducting materials

The preparation and characterization of new phosphonated polymeric ionomers based on a fully aromatic poly(arylene ether) backbone with applications as proton exchange membranes for fuel cell is reported. The high-molecular-weight polymers were obtained by the polycondensation of the phosphonated monomers with decafluorobiphenyl in high yields with inherent viscosities up to 0.58 dL g⁻¹. The hydrolysis of the phosphonated ester into phosphonic acid groups was carried out quantitatively under acidic conditions. The polymers were studied by TGA after hydrolysis and showed10% weight loss above 430 °C. Membranes with total ion-exchange capacities above 6 meq/g showed proton conductivities of approximately92 mS/cm at 25 °C and 100% relative humidity increasing to ca.150 mS/cm at 140 °C. Their conductivity under dry condition showed values over 2 mS/cm at 120 °C which upon doping with phosphoric acid jumped to nearly 100 mS/cm.     

Hydrogen generation in a Pd membrane fuel processor: assessment of methanol-based reaction systems

The feasibility of a Pd membrane fuel processor that integrates several methanol-based chemistries and hydrogen purification steps is assessed. The assessment involves membrane reactor simulations to determine the effects of operating and design parameters on performance metrics including hydrogen utilization, hydrogen productivity, device volume, and Pd requirements. Methanol decomposition (direct and oxidative) on Pd/SiO₂, methanol steam reforming (MSR) on Cu/ZnO/Al₂O₃, and methanol partial oxidation (MPOX) on Cu/Al₂O₃ are evaluated. The membrane reactor model includes detailed treatments of the catalytic kinetics from the literature, accounts for reaction on the Pd membrane and hydrogen permeation inhibition by site blockage, among other features. The simulations reveal that a maximum in the hydrogen productivity occurs at an intermediate value of the space velocity, implying a trade-off between reactor size, methanol conversion and hydrogen utilization. The assessment involves a determination of the Pd membrane surface to reactor volume ratio that maximizes productivity and the requisite Pd to realize that productivity. We show that MSR on Cu/ZnO and MPOX on Cu are promising reaction systems to practice the membrane concept for fuel processing, whereas direct methanol decomposition is reaction limited, making it infeasible. Several approaches for improving membrane fuel processor performance are evaluated and discussed. We show that oxygen addition can increase the hydrogen productivity in the Pd system, while water addition is beneficial for the MPOX system. The extent of enhancement in both cases depends on supply rate and kinetic factors.     

Catalyst Layer Models for Proton Exchange Membrane Fuel Cells

This paper presents two simple catalyst layer models – the macro‐homogeneous model and the agglomerate model for the proton exchange membrane (polymer) fuel cell using hydrogen gas as the feedstock. The former is solved analytically whereas the latter is solved numerically. The emphasis of this research is to parameterize factors affecting the performance of the fuel cell with simple approach without going into detailed catalyst layer modeling.     

The effect of dip-coating parameters on the thickness and uniformity of BCZYZ electrolyte layer on porous NiO-BCZYZ tubular supports

The effect of dip-coating parameters on the coating thickness and uniformity have been investigated for BaCe_0.7Zr_0.1Y_0.16Zn_0.04O_3-δ (BCZYZ) electrolyte on porous NiO-BCZYZ tubular supports. The calculated thicknesses of electrolyte using both pre-fired and full fired tubes' dimensions and both wet and dry weight gains have been compared to the measured ones using Scanning Electron Microscopy (SEM) analysis after full firing. The calculated thicknesses using pre-fired tubes’ dimensions using both wet and dry weight gains are found in a good agreement with the measured thicknesses. The minimum coating thickness of 20.49 ± 3.36 μ with 16% standard deviation (StDev) is achieved using 1.91 mm s^?1 (20 step.s^-1) withdrawal speed and 30 s dwell time. The most uniform coating layer is obtained using that withdrawal speed and 60 s dwell time, leading 23.14 ± 1.69 μ coating thickness and the minimum StDev% of 7%. Using the polynomial fit between StDev% and dwell time, the minimum StDev% can be achieved at that withdrawal speed has been determined as 80 s. The coating parameters have been optimized as 1.91 mm s^?1 withdrawal speed and 80 s dwell time for BCZYZ electrolyte on porous Ni/NiO-BCZY tubular supports.     

Fuel Cells,Advanced Reactors and Smart Catalysis: The Exploitation of Ceramic Ion‐Conducting Membranes

Membrane reactors are of great interest in the chemical industries because they offer the possibility of improved yields, improved selectivities and more compact plant. However, a significant barrier to their uptake is the unavailability of membrane systems having the required performance at an acceptable cost. In this paper we will explore the use of one class of membrane that has the potential to deliver high performance at reasonable cost. Ion‐conducting ceramic membranes can be used in a wide range of high temperature applications including fuel cells, advanced reactors and even smart catalytic systems.     

Mechanical aspects of ceramic membrane materials

Interest in ceramic transport membrane materials has increased significantly leading also to questions with respect to mechanical reliability and robustness, hence, requiring knowledge of the mechanical properties. The current review focuses on the mechanical properties of such ceramics, emphasizing in particular relationships between mechanical properties, non-elastic effects, phase changes and materials’ stability. Room and elevated temperature application is considered with a main emphasis on elastic and creep deformation as well as fracture. Consideration is given to dense membranes as well as porous substrate materials for advanced asymmetric concepts. Properties are summarized for selected oxygen and proton conductors. Furthermore, mechanical properties of some selected porous ceramic and metallic substrate materials are given. In addition to the failure probability associated with the Weibull distribution of fracture stresses, creep rupture of dense materials and enhanced creep deformation of porous materials are aspects that need special consideration in the application of these materials in gas separation systems.     

Removal of chlorinated volatile organic contaminants from water by pervaporation using a novel polyurethane urea-poly (methyl methacrylate) interpenetrating network membrane

Polymer membranes are potentially selective for separation of organic compounds from a mixture by pervaporation. A novel crosslinked hydroxyterminated polybutadiene based (HTPB) polyurethane urea (PUU)-poly (methyl methacrylate) (PMMA) interpenetrating network (IPN) membrane has been developed for the selective removal of chlorinated volatile organic compounds (VOCs) such as 1,1,2,2-tetrachloroethane, chloroform, carbon tetrachloride, trichloroethylene present in water in very low concentration by pervaporation. IPNs of different PMMA content and also different crosslink density were used. Since the selective permeation and diffusion of the VOCs through the membrane are dependent on their interaction with the membrane material, their sorption and diffusion behaviors through the membrane were also investigated by swelling the membrane in pure VOCs. The sorption and diffusion behaviors were explained with the help of their solubility parameter data and calculated interaction parameter data of the membrane polymers with the VOCs. From the swelling kinetics data, diffusion coefficients of the VOCs through the membrane were calculated. Diffusion coefficients increased with the increase in crosslink density and PMMA content in the membrane. In pervaporation experiment, concentrations of chlorinated organic compounds in feed were varied from 100 ppm (0.01%) to 1000 ppm (0.1%). All the three IPN membranes showed excellent separation performances of the chlorinated VOCs from water. One IPN containing 26% PMMA (PUU-PMMA-3) produced 88.7% trichloroethylene in permeate, trichloroethylene flux and a separation factor of 7842 from a 0.1% aqueous feed after a pervaporation run of 3 h at . All the three IPN membranes of different compositions have shown the separation performances, viz., flux and separation factor for all the VOCs in the order .     

Synthesis and Characterisation of Sulphonated Poly(arylene sulphone) Terpolymers with Triphenylphosphine Oxide Moieties for Proton Exchange Membrane Fuel Cells

For application in fuel cells, a series of sulphonated poly(phenylene sulphone) terpolymers with triphenylphosphine oxide moieties as constitutional units in the polymer backbone have been prepared. The synthesis of the terpolymers represents a two‐step process including: (i) an aromatic nucleophilic substitution polycondensation of three difluoro monomers with varying ratios, i.e. 3,3′‐disulphonate‐4,4′‐difluorodiphenylsulphone, 4,4′‐difluorodiphenylsulphone and bis(4‐fluorophenyl)phenyl phosphine oxide (BFPPO), with 4,4′‐thiobisbenzenethiol yielding sulphonated poly(phenylene sulphide) terpolymers (sPPSPO) and (ii) their following oxidation with hydrogen peroxide in acidic solution to yield sulphonated poly(phenylene sulphone) terpolymers (sPPSO2PO). The structures and molecular compositions were confirmed by ¹H and ¹³C NMR spectroscopy. The ion exchange capacity (IEC) was adjusted at will choosing the appropriate ratio of sulphonated and unsulphonated monomers. Terpolymers with 1.72 ≤ IEC ≤ 2.32 have been obtained. Sulphonated poly(arylene) ionomers containing only sulphone (–SO₂–) linkages and phosphine oxide (–PO–) units rather than ether or sulphide in the backbone reveal a high thermal and oxidative stability. Membranes were cast either from dimethylformamide (DMF) or from dimethyl sulphoxide (DMSO) solutions. For all terpolymers some general characteristic trends were observed, such as an increase of the proton conductivity with increasing IEC, water uptake and temperature. The series of sPPSO2PO membranes offered high conductivities at high humidification, however, their performance strongly depends on the relative humidity. The mechanical properties of sulphonated poly(phenylene sulphone)s have been considerably improved by means of terpolymerisation with phenylene oxide moieties. Even under high humidification the terpolymers form clear, flexible membranes the stress at break of some membranes exceeds that of Nafion® under the same conditions by 40%.     

Proton conducting materials based on thermoplastic elastomers silica composites

In this research, ionomeric composites based on organophilized silica (SIL) and a thermoplastic elastomer (HSBR), were prepared and characterized from a microstructural and electrical point of view. DSC was used to confirm silica sulfonation and FTIR to characterize the polymer before and after sulfonation reaction. DSC and DMA analysis show that T_g^HPB remains constant in all the samples studied. T_g^PS measured through DMA presents an increase of about 40°C in the sample containing both the sulfonated filler and the sulfonated polymer matrix. The resulting materials can be easily processed to yield thin films (thickness 0.2–0.4 mm) with outstanding proton conducting properties (10^?2 S · cm^?1). The suitability for film formation and good electrical properties is indicative of their potential use as electrolytes in polymer fuel cells. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2715–2720, 2003     

Rhodium supported on thermally enhanced zeolite as catalysts for fuel reformation of jet fuels

Autothermal reformation of military jet fuel (1096 ppmw sulfur) was investigated with rhodium supported on thermally stabilized Y zeolite catalysts. The zeolite catalysts were thermally stabilized by ion exchanging with nitrate solutions of rare-earth metals (La, Ce, Sm, Gd, Dy and Er). Surface area analyses indicated that the exchanged zeolite could maintain its porous structure as high as 950 °C instead of 800 °C for a commercial NaY zeolite. The structure of the exchanged zeolite was characterized by X-ray diffraction (XRD). Rh-SmNaY zeolite reforming catalysts were prepared by incipient wetness and organometallic synthesis. The JP8 reforming experiments were performed in a short contact time adiabatic reactor with a monolithic catalyst with the addition of air and steam at a temperature below 920 °C. The effects of steam and fuel-to-air ratio (C/O ratio) were studied. Hydrogen and carbon monoxide were produced as the main products. Durability tests were performed with Rh/SmNaY-zeolite catalysts. This work shows that zeolite based catalysts can convert transportation fuels such as high sulfur jet fuel (over 1000 ppmw S) to syngas for solid oxide fuel cell applications.     

Microstructural evolution of cobalt-doped barium cerate-zirconate at elevated temperatures under moist reducing conditions

Barium cerates doped with rare earth and transition metal ions are attractive candidate materials for clean-energy applications owing to their catalytic activity combined with mixed ionic-electronic conductivity for electrochemical hydrogen separation. However, the stability of these materials at elevated temperatures in the presence of moisture and CO₂ is not completely understood. In the present work, Co-doped barium cerate-zirconate pellets (BaCe_0.25Zr_0.47Co_0.13O_3−δ) were exposed to a moist reducing environment at 600 °C and 927 °C for 24 h. The as-sintered and reduced pellets were sectioned using FIB and characterized using conventional TEM, STEM and XEDS. The evolution of the microstructure of the material at each step has been reported. The as-sintered material showed a tendency toward Co ex-solution resulting in the formation of a BaO-CoO phase at the grain boundaries. At elevated temperatures, reduction appeared to play a role in the transformation of the material chemistry and microstructure.     

Aqueous pore structure and proton dynamics in solvated Nafion membranes

Molecular dynamics computer simulations of water/Nafion mixtures using an all-atom model were performed as a function of temperature and humidity. The simulations are aimed at investigating processes and structures on the picosecond to nanosecond time scale in the nano-phase-separated material with its technological relevance for low temperature fuel cells. Characteristic differences in aqueous pore structure were observed for systems whose water content was varied between 5 and 10 molecules per acid group in the polymer. As expected, proton transport increases significantly with increasing humidity, its mechanism is dominated by the Grotthus structural diffusion mechanism in accordance with earlier studies in simplified model pores. On the simulated time scale no unambiguous conclusions on the role of polymer dynamics for the transport in dry membranes can be drawn.     

Study of basic biopolymer as proton membrane for fuel cell systems

Up to now, many research groups work to improve the electrical and mechanical properties of membranes with a low cost of production. The biopolymers could be an answer to produce proton membranes at low cost. This work demonstrates that the intrinsic membrane polymer and clays properties can help to develop a novel proton exchange membranes. Biopolymer composites (chitosan-oxide compounds) present conductivity between 10⁻³ and 10⁻² S cm⁻¹. The measurements were calculated by EIS (1 MHz-0.05 Hz) using the two-electrode configuration. Different oxides were used: MgO, CaO, SiO₂, Al₂O₃. The ionic conductivities were compared with Nafion^®'s in the same conditions of P and T. The catalyst layer/membrane ensemble was made during the design with the subsequent demonstration as membrane electrode assemblies and finally the fuel cell was built. Our focus was to increase the compatibility between the proton basic polymer exchange membrane and basic clays as CaO and test a new kind of fuel cell.     

Strength degradation and failure limits of dense and porous ceramic membrane materials

Thin dense membrane layers, mechanically supported by porous substrates, are considered as the most efficient designs for oxygen supply units used in Oxy-fuel processes and membrane reactors. Based on the favorable permeation properties and chemical stability, several materials were suggested as promising membrane and substrate materials: Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ, La_0.6?xSr_0.4Co_0.2Fe_0.8O_3?δ (x = 0, 0.02) and Ce_0.9Gd_0.1O_1.95?δ. Although membranes operate at elevated temperatures, the ends of tubes in certain three-end concepts remain almost at room temperature. The current work concentrates on the failure potential of these membrane parts, where in a complex device also the highest residual stresses should arise due to differences in thermal expansion. In particular, sensitivity of the materials to subcritical crack growth was assessed since the long-term reliability of the component does not only depend on its initial strength, but also on strength degradation effects. The results were subsequently used as a basis for a strength–probability–time lifetime prediction.     

Carbon Nanotubes Based Nafion Composite Membranes for Fuel Cell Applications

Carbon nanotubes (CNTs) containing Nafion composite membranes were prepared via melt‐blending at 250 °C. Using three different types of CNTs such as pure CNTs (pCNTs), oxidised CNTs (oCNTs) and amine functionalised CNTs (fCNTs); the effect of CNTs surface oxidation as well as functionalisation in composite membranes was investigated by focussing on three aspects: thermo‐mechanical stability, thermal degradation and proton conductivity. The oCNTs‐containing Nafion composite membrane exhibited concurrent improvement in most of the properties as compared to that of pure Nafion or other CNTs‐containing Nafion composite membranes.     

Synthesis and characterization of poly(ether sulfone) grafted poly(styrene sulfonic acid) for proton conducting membranes

Two-step synthesis of proton-conducting poly(ether sulfone) (PES) graft copolymer electrolyte membrane is proposed. Fridel Craft alkylation reaction was used to introduce chloromethyl pendant group onto the PES polymer backbone. Later on, atom transfer radical polymerization (ATRP) was applied to synthesize a series of poly(ether sulfone) grafted poly(styrene sulfonic acid) (PES-g-PSSA). Successful chloromethyl substitution and grafting of the pendant group was characterized by the ¹H-NMR and elemental analysis. Electrochemical properties such as ion exchange capacity (IEC), water uptake and proton conductivity increased with increasing PSSA contents. Thermal gravimetric analysis (TGA) showed the thermal stability of membranes up to 270 °C. Proton conductivity for maximum amount of grafting was 0.00297 S/cm.     

导电聚合物复合材料作为超级电容器电极材料

本文综述了基于导电聚合物的复合材料(导电聚合物/碳材料、导电聚合物/金属氧化物材料、导电聚合物/碳材料l金属氧化物材料)作为电极材料在超级电容器中的应用进展,指出将导电聚合物与碳材料或金属氧化物复合,双电层电容与法拉第准电容结合,有机材料与无机材料结合,是超级电容器电极材料研究的重要发展方向.