Mikrostrukturen für die katalytische Wasserstofferzeugung aus Ethanol

Hydrogen for fuel cell applications has been generated by catalytic steam reforming of ethanol in microstructures. The influence of reaction temperature, contact time and molar ratio steam to carbon (S/C) on the reaction has been investigated. The Co/ZnO catalyst coated on the microstructure showed high activity and selectivity. The hydrogen yield obtained was up to 5.2 mol mol^–1 ethanol. Ethanol has been completely converted at short contact time (W/F 25 g min mol^–1) and 600 °C at S/C ratio between 4.9 and 6.5.     

Verbesserte Simulation der Temperaturentwicklung von HT‐PEM‐Brennstoffzellen zur Effizienzsteigerung

Identification and prevention of large temperature gradients can extend the lifespan of fuel cells. Estimating the temperature distribution during operation is difficult because of the complex processes in the cell. Therefore, even with large computational power only small and simple flow field geometries can be calculated yet. The integration of a new mathematical formulation in commercial simulation software allows calculation and assessment of complex geometries in order to increase their efficiency and lifespan.     

Low‐Cost‐Membranen für die Vanadium‐Redox‐Flow‐Batterie

Vanadium redox‐flow batteries are a technology that can be used to store fluctuating energies from solar and wind power. In order to reduce the manufacturing costs of the batteries, e.g., cheaper raw materials can be used. By using polystyrene‐based polymers for membrane production, conductivities comparable to perfluorosulfonic acid membranes can be achieved. A way to produce these heterogeneous membranes consisting of disperse and continuous phase is shown.     

Protonenleitende Komposit‐Membranen für zukunftsorientierte Anwendungen in Brennstoffzellen,Entsalzungsanlagen und in der Photokatalyse

Inorganic filler materials are often incorporated into polymer membranes to improve their mechanical, thermal and chemical stabilities. In case of proton‐conducting polymers, however, it is necessary to support or at least not to disturb the proton‐conducting matrix. By suitable combination of polymer and filler, effective and highly conductive composite membranes can be prepared. This article gives an overview of the possible applications of a special kind of such proton‐conducting composite membranes containing functionalized SiO₂ particles with ordered mesoporosity in fuel cell, in desalination and in photocatalysis.     

Defektfreie Mixed‐Matrix‐Membranen aus Matrimid® und Aktivkohle für die Gastrennung

In this work the fabrication of new mixed‐matrix membranes (MMMs) of Matrimid® and activated carbon (AC) for gas separation is reported. The aim is the fabrication of membranes that have better gas permeation properties compared to the pristine Matrimid® membranes. The membranes were thermally and morphologically characterized, and the gas transport properties of single gases were estimated by a variety of methods. It has been found that with an increase of the AC content the selectivity remained stable for the different gases despite the marked increase in the effective permeability of the pure gases.     

An empirical fuel cell polarization curve fitting equation for small current densities and no-load operation

A logarithmic term is applied to account for the charge transfer overvoltage with most empirical polarization curve fitting equations for polymer electrolyte membrane fuel cells. The logarithmic term applied with state-of-the-art fitting equations is proportional to the logarithm of the cell output current density. This provides good fitting characteristics with large current densities, but results in significant deviations from measured current/voltage characteristics if small current densities or no-load operation are investigated. A modified logarithmic charge transfer overvoltage term utilising the exchange current density and an internal cell current density is therefore introduced to provide accurate fitting characteristics with small current densities and no-load operation. Fitting characteristics of this modified polarization curve fitting equation are investigated and compared to standard fitting equations.     

Statistische Analyse des lokalen Wassertransportes einer Polymer‐Elektrolyt‐Brennstoffzelle

The water transport in the gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC) was simulated using the Lattice Boltzmann method. By means of a stochastic geometry model an ensemble of microstructures was generated, all of them stochastically equivalent to the real structure of a GDL. The rough surface of the GDL defines the interface between the GDL and air channel of a PEFC. The water droplets emerging from the GDL were analyzed statistically regarding their contact angles. A short insight to the dynamics is given.     

Cation exchange membranes by radiation‐induced graft copolymerization of styrene onto PFA copolymer films. III. Thermal stability of the membranes

Thermal stability of cation exchange, PFA‐g‐polystyrene sulfonic acid membranes prepared by radiation‐induced graft copolymerization of styrene onto PFA films followed by sulfonation was studied by thermal gravimetric analysis (TGA) and oven heat treatment. The tested samples included original and grafted PFA films as reference materials. All the membranes showed multistep decomposition patterns due to dehydration, desulfonation, dearomatization, and decomposition of the PFA matrix. Investigations of the individual decomposition behaviors showed that the weight loss strongly depends upon the degree of grafting. However, the decomposition temperatures were found to be independent of the degree of grafting. The loss in some selected membrane properties such as ion exchange capacity and water uptake was found to be function of the degree of grafting, temperature, and the time of heat treatment. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1877–1885, 2000     

Cation exchange membranes by radiation‐induced graft copolymerization of styrene onto PFA copolymer films. II. Characterization of sulfonated graft copolymer membranes

PFA‐g‐polystyrene sulfonic acid membranes were prepared by simultaneous radiation‐induced graft copolymerization of styrene onto poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA) film followed by sulfonation. The membrane physico‐chemical properties such as swelling behavior, ion exchange capacity, hydration number, and ionic conductivity were studied as a function of the degree of grafting. Thermal as well as chemical stability of the membranes was also investigated. The membrane properties were found to be mainly dependent upon the degree of grafting. The water uptake, ion exchange capacity, hydration number, and ionic conductivity of the membranes were increased, whereas the chemical stability decreased as the degree of grafting increased. The membranes showed reasonable physico‐chemical properties compared to Nafion 117 membranes. However, their chemical stability has to be further improved to make them acceptable for practical use in electrochemical applications. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1–11, 2000     

Single Radiation‐Induced Grafting Method for the Preparation of Two Proton‐ and Lithium Ion‐Conducting Membranes

Summary: Two distinct types of polymer electrolyte membranes for conducting protons and lithium ions have been prepared by a radiation‐induced grafting method. The polymer electrolyte precursor (PVDF‐g‐PS) is obtained by the simultaneous grafting of styrene onto poly(vinylidene fluoride) (PVDF) followed by one of two specific treatments. This includes sulfonation with a chlorosulfonic acid/dichloromethane mixture to obtain proton (H⁺)‐conducting membranes, or activation with LiPF₆/EC/DC liquid electrolyte to obtain lithium ion (Li⁺)‐conducting membranes. The chemical structure of the obtained electrolyte membranes is verified by FT‐IR spectroscopy. Differential scanning calorimetry is used to examine the changes in the crystallinity and the thermal properties of both electrolyte membranes during the preparation process. The thermal stability of both electrolyte membranes is also evaluated using thermal gravimetrical analysis. The obtained polymer electrolyte membranes achieve superior conductivity values: 1.61 × 10^?3 S · cm^?1 for Li⁺ and 5.95 × 10^?2 S · cm^?1 for H⁺ at room temperature at a polystyrene content of 50%. The results of this work suggest that high quality H⁺‐ and Li⁺‐conducting membranes can be obtained using a single radiation‐induced grafting method.

Schematic representation of the single root for preparation of Li⁺‐ and H⁺‐conducting membranes started by radiation‐induced grafting of styrene onto a PVDF film followed by chemical treatment.     

Adsorption of Pb2+ and Pd2+ on polyethylene membrane with amino group modified by radiation‐induced graft copolymerization

Six chelating hollow fiber membranes were prepared by radiation‐induced grafting of glycidyl methacrylate onto a polyethylene hollow fiber membrane and its subsequent amination. The adsorption characteristics of Pb²⁺ and Pd²⁺ for the chelating hollow fiber membranes were presented when the solution of Pb²⁺ and Pd²⁺ permeates across the chelating membrane, respectively. The degree of grafting for glycidyl methacrylate increases with increasing monomer concentration, reaction temperature, and preirradiation dose. The adsorption of Pd²⁺ by chelating hollow fiber membranes modified with five kinds of amines was in the following order: diethylene triamine > hexamethyl diamine > ethylene diamine > dimethyl amine > trimethyl amine. The chelating hollow fiber membrane modified with iminodiacetic acid adsorbed Pb²⁺ ions much more than Pd²⁺. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 643–650, 1999     

A pH‐sensitive porous chitosan membrane prepared via surface grafting copolymerization in supercritical carbon dioxide

We report the successful grafting copolymerization of acrylic acid (AA) on a crosslinked porous chitosan membrane in supercritical carbon dioxide at pressures ranging from 13 to 25 MPa with the use of benzyl peroxide (BPO) as the reduction–oxidation free radical initiator. The effects of reaction pressure, initiator concentration, monomer concentration, reaction temperature and reaction time on grafting yield (GY) were investigated. GY initially increases and then decreases with increasing polymerization temperature and AA and BPO concentrations. The optimum grafting conditions to obtain maximum GY are as follows: 8 h reaction time, 80 °C reaction temperature, 3.05 × 10^?2 g mL^?1 AA concentration, 3 × 10^?3 g mL^?1 BPO concentration and 16 MPa reaction pressure. The water flux of the grafted chitosan membranes decreases with pH from 2 to 7, even at considerably low GY (0.95 wt%). A novel and green modification method has been developed for the preparation of biopolymer‐based membranes. © 2014 Society of Chemical Industry     

Cation exchange membranes by radiation‐induced graft copolymerization of styrene onto PFA copolymer films. IV. Morphological investigations using X‐ray photoelectron spectroscopy

Morphological investigations of poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA)‐g‐polystyrene sulfonic acid membranes prepared by radiation‐induced graft copolymerization of styrene onto PFA films followed by sulfonation were performed by X‐ray photoelectron spectroscopy. The analyzed materials included grafted film and sulfonated membrane samples having various degrees of grafting. Original PFA film was used as a reference material. The results of the X‐ray photoelectron spectral analysis show that PFA film undergoes changes in terms of chemical compositions and binding energies of its basic elemental components under the influence of membrane preparation procedure, i.e., grafting and sulfonation. The chemical compositions of the surfaces of the membranes were found to be dependent on the degree of grafting unlike the binding energies of their elemental components (C, F, O, and S), which were found to be independent of the degree of grafting. The atomic ratio of F/C was found to decrease drastically with the increase in the degree of grafting and the membranes were found to have almost pure hydrocarbon structure at the layers close to their surfaces where degradation is suggested to be concentrated. The results of these investigations suggest that the morphology of the membranes plays an important role in the chemical degradation of the membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2455–2463, 2000     

Adsorption of Co2+ and Cs1+ by polyethylene membrane with iminodiacetic acid and sulfonic acid modified by radiation‐induced graft copolymerization

Two modified hollow fiber membranes, the chelating hollow fiber membrane with iminodiacetic acid and the cation‐exchange hollow fiber membrane with sulfonic acid group ( SO₃H), were prepared by radiation‐induced grafting of glycidyl methacrylate onto polyethylene hollow fiber membrane and its subsequent iminodiacetation and sulfonation. The adsorption characteristics of Co²⁺ and Cs¹⁺ for the 2 hollow fiber membranes were examined when the solutions of Co²⁺ and Cs¹⁺ permeate across the 2 membranes, respectively. Without regard to the chelating membrane with iminodiacetic acid group and the cation‐exchange membrane with sulfonic acid group ( SO₃H), 2 membranes were observed to adsorb Co²⁺ higher than Cs¹⁺. The adsorption curves of Co²⁺ by IDA group‐chelating fiber membrane in the presence of Na¹⁺ and Ca²⁺ showed that the chelating hollow was found to have a very high selectivity for Co²⁺, even though there is a high concentration of Na¹⁺ and Ca²⁺ in the inlet solution. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 999–1006, 1999     

Energetische Evaluierung von Kältespeichern und Abwärmenutzung für Kühl‐ und Gefrieranwendungen

A thermodynamic analysis of cold storage systems and waste heat usage for refrigeration and freezing applications is presented. The focus is set mainly on the energetic efficiency of the systems. The environment is considered as an infinite heat sink to which the heat from the refrigeration compartment can be transported directly. Five different concepts are presented and evaluated based on the annual electric energy and primary energy demand.     

A Bioelectrochemically‐Assisted Membrane Bioreactor for Simultaneous Wastewater Treatment and Energy Production

A bioelectrochemically‐assisted membrane bioreactor (BEAMBR), integrating a microbial fuel cell with a membrane bioreactor, was developed for energy recovery and efficient wastewater treatment. The stainless‐steel membrane module with biofilm, served not only as dynamic membrane separation device but also as biocathode. The effluent turbidity reached 0.8 NTU after stable operation, and particle with average size larger than 1.14 μm were effectively rejected from the mixed liquor by the dynamic membrane. The BEAMBR successfully removed the chemical oxygen demand and ammonium. With increasing hydraulic retention time and decreasing volumetric organic loading rate, the power production in this reactor was enhanced. The results showed that the BEAMBR is a promising process for efficient energy recovery and wastewater treatment.     

Preparation and properties of bisphenol A‐based sulfonated poly(arylene ether sulfone) proton exchange membranes for direct methanol fuel cell

Novel bisphenol A‐based sulfonated poly(arylene ether sulfone) (bi A‐SPAES) copolymers were successfully synthesized via direct copolymerization of disodium 3,3′‐disulfonate‐4,4′‐dichlorodiphenylsulfone, 4,4′‐dichlorodiphenylsulfone, and bisphenol A. The copolymer structure was confirmed by Fourier transform infrared spectra and ¹H NMR analysis. The series of sulfonated copolymers based membranes were prepared and evaluated for proton exchange membranes (PEM). The membranes showed good thermal stability and mechanical property. Transmission electron microscopy was used to obtain the microstructures of the synthesized polymers. The membranes exhibit increased water uptake from 8% to 66%, ion exchange capacities from 0.41 to 2.18 meq/g and proton conductivities (25°C) from 0.012 to 0.102 S/cm with the degree of sulfonation increasing. The proton conductivities of bi A‐SPAES‐6 membrane (0.10–0.15 S/cm) with high‐sulfonated degree are higher than that of Nafion 117 membrane (0.095–0.117 S/cm) at all temperatures (20–100°C). Especially, the methanol diffusion coefficients of membranes (1.7 × 10^?8 cm²/s–8.5 × 10^?7 cm²/s) are much lower than that of Nafion 117 membrane (2.1 × 10^?6 cm²/s). The new synthesized copolymer was therefore proposed as a candidate of material for PEM in direct methanol fuel cell. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Critical analysis of aqueous tape casting,sintering, and characterization of planar Yttria‐Stabilized Zirconia electrolytes for SOFC

Tape casting is an established forming technique for several industries, however, researches focus more on slurry composition. In this work, the combined use of design of experiment and materials characterization techniques showed tape casting process parameters have great influence on the microstructure and mechanical properties of green tapes. Formulation and processing optimization allowed obtaining YSZ green tapes with good mechanical characteristics and homogeneous microstructure without laminating step. The optimized sintering schedule and sintering load allowed obtaining planar electrolytes with high density, tensile strength, and electrical conductivity. This work provides an environmental friendly procedure for large‐scale production of SOFCs planar electrolytes.     

Enhancing the stability of power generation of single‐chamber microbial fuel cells using an anion exchange membrane

BACKGROUD: A decreased power density could be observed in a single‐chamber microbial fuel cell (MFC) with a cation exchange membrane (CEM), as a result of pH‐associated problem and a precipitated salt‐associated problem, due to the transport of cations other than protons through the membrane to the cathode. To inhibit cation transport and enhance the stability of power generation, an anion exchange membranes (AEM) was applied in a single‐chamber MFC. RESULTS: After 70 days' operation, the power density dropped 29% in the MFC with an AEM (AMFC), smaller than 48% in the MFC with a cation exchange membrane (CMFC). The reason for this difference lay in internal resistance development. Membrane resistance in the AMFC remained the same but that in the CMFC was increased by 67 Ω, and the cathode resistance increase in the AMFC was 54 Ω, while that in the CMFC was 123 Ω. The precipitated cations on the cathode catalyst surface in the CMFC, which accounted for the resistance increase, were up to 84 times larger than that in the AMFC. CONCLUSION: Because of its capacity for inhibiting cations, the AMFC possessed more stable membrane and cathode resistances; thus an enhanced power generation was obtained. Copyright © 2009 Society of Chemical Industry