Novel ETFE based radiation grafted poly(styrene sulfonic acid-co-methacrylonitrile) proton conducting membranes with increased stability

Styrene radiation grafted ETFE based proton conducting membranes are subject to degradation under fuel cell operating conditions and show a poor stability. Lifetimes exceeding 250 h can only be achieved with crosslinked membranes. In this study, a novel approach based on the increase of the intrinsic oxidative stability of uncrosslinked membranes is reported. Hence, the co-grafting of styrene with methacrylonitrile (MAN), which possesses a protected α-position and strong dipolar pendant nitrile group, onto 25 μm ETFE base film was investigated. Styrene/MAN co-grafted membranes were compared to a styrene based membrane in durability tests in single H2/O2 fuel cells. It is shown that the incorporation of MAN considerably improves the chemical stability, yielding fuel cell lifetimes exceeding 1000 h. The membrane preparation based on the co-grafting of styrene and MAN offers the prospect of tuning the MAN content and introduction of a crosslinker to enhance the oxidative stability of the resulting fuel cell membranes

Cross-linker effect in ETFE-based radiation-grafted proton-conducting membranes II. Extended fuel cell operation and degradation analysis

In this study the effect of crosslinker (divinylbenzene (DVB)) content on the chemical stability of poly(ethylene-alt-tetrafluoroethylene) (ETFE) based membranes using an H2O2 solution was carried out. Furthermore, the first long term-testing of single H2/O2 cell over 2180h of an MEA assembled using an optimized ETFE-based membrane prepared by radiation-induced grafting of styrene / DVB and subsequent sulfonation with a graft level of 25 % was carried out. The in situ MEA properties were characterized over the testing period using auxiliary current-pulse resistance, electrochemical impedance spectroscopy, polarization and H2 permeation. It is shown that the crosslinking dramatically improves the ex situ chemical stability, while no significant trend with the crosslinker content was observed. The performance of the tested MEA exhibits a decay rate of 13 μV.h-1 in voltage over the testing time at 500 mA.cm-2 at 80°C, while the hydrogen permeation shows a steady increase over time. This indicates clearly that to some extent changes in the membrane morphology occur over the operating time. The local post mortem analysis of the tested membrane reveals that high degradation was observed in areas adjacent to the O2 inlet and in other areas nearb

Power saving MAC protocols in wireless sensor networks: a survey

In a wireless sensor network, energy is almost always the greatest limitation. Energy sources are restricted in many of the environments where nodes are deployed, limiting them to the use of batteries for power. Therefore, conserving energy is supremely important, however, such a task poses many challenges to hardware and protocol design. One of the greatest problems faced is reducing the energy consumption of the communications systems, which represents a substantial amount of the total consumption. This paper surveys the most recent schemes designed to reduce the communications module energy consumption with a focus on novel MAC protocols for ad-hoc wireless sensor networks. It initially describes the many challenges involved, then it analyses each protocol individually. Finally, the presented protocols are compared and the issues that remain open are raised for further research

Investigation of the Dimensional Variation of Microstructures Through the μMIM Process

The mass production of components with dimensions in the micron and sub-micron range is anticipated to be one of the leading technology areas for the present century and to be of high market potential. Micro metal injection molding (μMIM) has the potential to be an important contributor to this industry as it can produce precise metallic microstructures in large quantities at a relatively low production cost. The μMIM process is a miniaturization of metal injection molding (MIM) methods. The process comprises of four main steps: mixing, injection molding, debinding and sintering. A metallic powder is mixed with a binder system to form the feedstock. The feedstock is then injection molded into the required shape and the binder removed via thermal or other means. The final microstructures are obtained by sintering the remaining powder in a controlled environment. In this work, the dimensional variation of the microstructures, in particular the warpage, roughness and volume variation, at each stage of the μMIM process was quantified and compared. The results of a preliminary study of the sensitivity of warpage of the microstructures to the packing pressure are also reported.Singapore-MIT Alliance (SMA

Radiation Tolerance of CMOS Monolithic Active Pixel Sensors with Self-Biased Pixels

CMOS Monolithic Active Pixel Sensors (MAPS) are proposed as a technology for various vertex detectors in nuclear and particle physics. We discuss the mechanisms of ionizing radiation damage on MAPS hosting the the dead time free, so-called self bias pixel. Moreover, we discuss radiation hardened sensor designs which allow operating detectors after exposing them to irradiation doses above 1 Mra

Variable coordination of amine functionalised N-heterocyclic carbene ligands to Ru, Rh and Rr: C-H and N-H activation and catalytic transfer hydrogenation

Chelating amine and amido complexes of late transition metals are highly valuable bifunctional catalysts in organic synthesis, but complexes of bidentate amine–NHC and amido–NHC ligands are scarce. Hence, we report the reactions of a secondary-amine functionalised imidazolium salt 2a and a primary-amine functionalised imidazolium salt 2b with [( p -cymene)RuCl 2 ] 2 and [Cp*MCl 2 ] 2 (M = Rh, Ir). Treating 2a with [Cp*MCl 2 ] 2 and NaOAc gave the cyclometallated compounds Cp*M(C,C)I (M = Rh, 3 ;M = Ir, 4 ), resulting from aromatic C–H activation. In contrast, treating 2b with [( p -cymene)RuCl 2 ] 2 ,Ag 2 O and KI gave the amine–NHC complex [( p -cymene)Ru(C,NH 2 )I]I ( 5 ). The reaction of 2b with [Cp*MCl 2 ] 2 (M = Rh, Ir), NaO t Bu and KI gave the amine–NHC complex [Cp*Rh(NH 2 )I]I ( 6 ) or the amido–NHC complex Cp*Ir(C,NH)I ( 7 ); both protonation states of the Ir complex could be accessed: treating 7 with trifluoroacetic acid gave the amine–NHC complex [Cp*Ir(C,NH 2 )I][CF 3 CO 2 ]( 8 ). These are the first primary amine– or amido–NHC complexes of Rh and Ir. Solid-state structures of the complexes 3–8 have been determined by single crystal X-ray diffraction. Complexes 5 , 6 and 7 are pre-catalysts for the catalytic transfer hydrogenation of acetophenone to 1-phenylethanol, with ruthenium complex 5 demonstrating especially high reactivity

Preparation of anti-vicinal amino alcohols: asymmetric synthesis of D-erythro-Sphinganine, (+)-spisulosine and D-ribo-phytosphingosine

Two variations of the Overman rearrangement have been developed for the highly selective synthesis of anti-vicinal amino alcohol natural products. A MOM-ether directed palladium(II)-catalyzed rearrangement of an allylic trichloroacetimidate was used as the key step for the preparation of the protein kinase C inhibitor D-erythro-sphinganine and the antitumor agent (+)-spisulosine, while the Overman rearrangement of chiral allylic trichloroacetimidates generated by asymmetric reduction of an alpha,beta-unsaturated methyl ketone allowed rapid access to both D-ribo-phytosphingosine and L-arabino-phytosphingosine

Improved control strategy of DFIG-based wind turbines using direct torque and direct power control techniques

This paper presents different control strategies for a variable-speed wind energy conversion system (WECS), based on a doubly fed induction generator. Direct Torque Control (DTC) with Space-Vector Modulation is used on the rotor side converter. This control method is known to reduce the fluctuations of the torque and flux at low speeds in contrast to the classical DTC, where the frequency of switching is uncontrollable. The reference for torque is obtained from the maximum power point tracking technique of the wind turbine. For the grid-side converter, a fuzzy direct power control is proposed for the control of the instantaneous active and reactive power. Simulation results of the WECS are presented to compare the performance of the proposed and classical control approaches.Peer reviewedFinal Accepted Versio