Performance of metal alloys as hydrogen evolution reaction catalysts in a microbial electrolysis cell

H₂ can be produced from organic matter with a microbial electrolysis cell (MEC). To decrease the energy input and increase the H₂ production rate of an MEC, a catalyst is used at the cathode. Platinum is an effective catalyst, but its high costs stimulate searching for alternatives, such as non-noble metal alloys. This study demonstrates that copper sheet coated with nickel-molybdenum, nickel-iron-molybdenum or cobalt-molybdenum alloys have a higher catalytic activity for the hydrogen evolution reaction than nickel cathodes, measured near neutral pH. However, the catalytic activity cannot be fully exploited near neutral pH because of mass transport limitation. The catalytic activity is best exploited at alkaline pH where mass transport is not limiting. This was demonstrated in an MEC with a cobalt-molybdenum coated cathode and anion exchange membrane, which produced 50 m³ H₂ m⁻³ MEC d⁻¹ (at standard temperature and pressure) at an electricity input of 2.5 kWh m⁻³ H₂.     

Latex derived blends of poly(vinyl acetate) and natural rubber: thermal and mechanical properties

Poly(vinyl acetate) (PVAc) and natural rubber blends (NR) were prepared by low shear blending of the corresponding lattices. Thin films were cast using a doctor blade technique. SEM and DMA confirmed the essential immiscibility of the two polymers. Even when the poly(vinyl acetate) forms the matrix phase, it still contains domains encapsulated by a rubber phase where particles that resemble the original latex are visible. This incomplete droplet coalescence of the poly(vinyl acetate) is attributed to the fact that the rubber latex droplets were an order of magnitude smaller than the poly(vinyl acetate) latex droplets. Tensile testing revealed a nonlinear dependence of tensile strength and elongation on blend composition. Surprisingly good tensile yield strengths were obtained at intermediate to high PVAc contents. Thermogravimetric analysis of degradation in air and nitrogen atmospheres indicated independent degradation of the parent polymers.     

Computer Aided Tolerance Analysis and Synthesis in Micro Systems (μ-ToAST)

The large variety of the technologies and physical, chemical or biochemical effects united in micro systems requires a new generation of quality assurance. An appropriate quality management should check all conceivable influences on the product and perform a complete tolerance synthesis based on its function and with regard to manufacturing and cost optimization. In the following a new approach to function-oriented tolerance analysis and synthesis is presented.The authors have developed a computer program which assists Design Engineers in tolerance analysis and synthesis in micro technology. This contribution presents the theoretical background and the basic functionality of this software. For a better understanding a short MEMS example is shown.     

Effect of alkali treatment on the flexural properties of Hildegardia fabric composites

A uniaxial natural fabric of Hildegardia populifolia was treated with 5% sodium hydroxide solution for 1 h, and the resulting changes were analyzed by polarized and scanning electron microscopic techniques. The untreated and treated H. populifolia fabric was reinforced in epoxy and toughened with 10% polycarbonate. The variation of the flexural strength and flexural modulus with different fabric contents and fiber orienrations was studied. The effect of sodium hydroxide and a silane coupling agent on the flexural properties of the composite was also studied. It was observed that the flexural properties increased on alkali treatment and when the coupling agent was used. The morphology of the cryogenically fractured surfaces indicated good bonding between the matrix and the reinforcement when a coupling agent was used. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1297–1302, 2006     

Relationship between magnetic field strength and magnetic-resonance-related acoustic noise levels

The need for better signal-to-noise ratios and resolution has pushed magnetic resonance imaging (MRI) towards high-field MR-scanners for which only little data on MR-related acoustic noise production have been published. The purpose of this study was to validate the theoretical relationship of sound pressure level (SPL) and static magnetic field strength. This is relevant for allowing adequate comparisons of acoustic data of MR systems at various magnetic field strengths. Acoustic data were acquired during various pulse sequences at field strengths of 0.5, 1.0, 1.5 and 2.0 Tesla using the same MRI unit by means of a Helicon rampable magnet. Continuous-equivalent, i.e. time-averaged, linear SPLs and 1/3-octave band frequencies were recorded. Ramping from 0.5 to 1.0 Tesla and from 1.0 to 2.0 Tesla resulted in an SPL increase of 5.7 and 5.2 dB(L), respectively, when averaged over the various pulse sequences. Most of the acoustic energy was in the 1-kHz frequency band, irrespective of magnetic field strength. The relation between field strength and SPL was slightly non-linear, i.e. a slightly less increase at higher field strengths, presumably caused by the elastic properties of the gradient coil encasings. Electronic Publication     

Clotting Phenomena at the Blood-Polymer Interface and Development of Blood Compatible Polymeric Surfaces

In the past two decades many attempts have been made to relate surface and interfacial parameters with the blood compatibility of polymeric surfaces. It is however doubtful if by a single parameter the behaviour of blood on a surface can be predicted. Two major aspects of blood compatibility—the prevention of platelet adhesion and the deactivation of the intrinsic coagulation system are determined by the measure and nature of competitive blood protein adsorption on the foreign surface. The adhesion of blood platelets is promoted by adsorbed fibrinogen and gamma globulin, while adsorbed albumin inhibits platelet adhesion. Heparinised surfaces do not adsorb fibrin and consequently no adhesion of platelets takes place. Other surfaces with low platelet adhesion are the hydrogels, certain block copolyetherurethanes, polyelectrolyte complexes and biolised proteins. Heparinised surfaces of the cationically bonded type inhibit the intrinsic coagulation as well, however this may be due to unstable coatings and heparin leakage. In the authors laboratory a synthetic heparinoid was prepared with the structure - [CH₂ - C(CH₃ NHSO₃ Na - C(H) COONa - CH₂ -] x? with M?_w = (7.5 /pm 1.0) × 10⁵ and an in vivo anticoagulant activity of 50% of heparin. Its coatings on PVC, using tridodecylmethyl-ammonium chloride as a coupling agent, are stable in plasma and salt solutions and provide surfaces which show negligible platelet adhesion and a strong inhibition of the intrinsic coagulation on contact with blood. Similar results were found with polydimethylsiloxane surfaces coated with this heparinoid.     

Thermal and dynamic mechanical properties of bio-based poly(furfuryl alcohol)/sisal whiskers nanocomposites

In this study, bio-based nanocomposites of sisal whiskers-reinforced poly(furfuryl alcohol) (PFA) were prepared using an in situ polymerization method. Furfuryl alcohol (FA), which is a derived renewable monomer, was used to serve first as a solvent to disperse the whiskers and later as a monomeric precursor to produce PFA. Sisal whiskers were prepared via acid hydrolysis, which was followed by freeze-drying and re-dispersion of the dried whiskers in FA by sonication for 20 min. The polymerization process was catalysed using citric acid, which is also a renewable carboxylic acid found in citrus fruits. The effect of increased sisal whiskers loading on the thermal and dynamic mechanical properties of the nanocomposites was investigated using thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The TGA results showed slightly higher thermal stability for the nanocomposite samples compared to neat PFA. The DMA results showed that the incorporation of sisal whiskers imparts significant enhancement in the storage modulus of the PFA matrix. Moreover, the intensity of the tan δ peak at ~75 °C for the nanocomposites was remarkably reduced compared to that of neat PFA.     

30,000 h operation of a 70 kW stationary PEM fuel cell system using hydrogen from a chlorine factory

A pilot PEM Power Plant is described utilizing by-product hydrogen from the electrolysis of brine in the Akzo Nobel chlor-alkali plant at Delfzijl, the Netherlands. The performance of this 70 kW fuel cell unit is reported for a period of five and a half years, starting in April 2007. Results of measurements of cell voltages on PEM fuel cells with different types of Membrane Electrode Assemblies are reported for an operational period of 30,000 h. Stack performance is highly dependent on the MEA it contains, leading to a wide variety in reversible and irreversible voltage decay rates. Best performing MEAs enable stack operation of more than 16,000 h of power generation, with an average voltage decay rate of 2.5 μV/h. The reversible decay is linked to contaminants, primarily at the anode.