A Field Effect Based Hydrogen Sensor for Low and High Concentrations

The kinetics of hydrogenolysis of methylamine to methane and ammonia on a rhodium catalyst were investigated at hydrogen partial pressures in the range of 2–10 atm at temperatures of 368, 383, and 408 K. At a fixed methylamine partial pressure, the rate decreased with increasing hydrogen partial pressure. When the hydrogen pressure was held constant, the rate increased with increasing methylamine pressure. Results of a previous investigation by our group at lower hydrogen partial pressures (0.01–1 atm) indicated that the hydrogenolysis rate passed through a maximum with increasing hydrogen pressure. Moreover, at the lower hydrogen pressures, there was an inverse rather than positive dependence of the rate on methylamine partial pressure. With the aid of the present results, there is a much clearer definition of the maximum in the experimental data relating the reaction rate to hydrogen partial pressure. The inversion of the effect of methylamine pressure on the rate as the hydrogen pressure is varied over a sufficiently wide range is also firmly established. With regard to the interpretation of the many interesting features of the kinetics, we retain the suggestion from our earlier work that the rate limiting step at the highest hydrogen pressures is the scission of the carbon-nitrogen bond in a partially dehydrogenated methylamine intermediate chemisorbed on the rhodium, with no direct participation of hydrogen as a reactant in this step. At the lowest hydrogen pressures, however, there is a different rate limiting step in which hydrogen does participate directly as a reactant.

Electron beam-induced degradation of zinc sulfide-based phosphors

Solid oxide fuel cell (SOFC) has excellent fuel flexibility for various fuels. Despite some drawbacks like storage and transportation, hydrogen stands up as the best fuel for SOFC. Hydrogen fuel is diluted non-reactive gas species before it is supplied to the SOFC. In this study, a quasi-three-dimensional SOFC model with real microstructure is used to analyse the effect of the diluted fuel mixture. The hydrogen fuel is diluted with nitrogen and a small amount of steam. The mole amount of hydrogen within fuel mixtures is kept constant. On the other hand, the air that is supplied to the air channel of the SOFC remains unchanged. It is found that the cell that is supplied with the highest concentration of hydrogen has the highest performance due to its high partial pressure of hydrogen within the fuel mixture. Such a high partial pressure promotes a low anode concentration loss. Also, the cell that is supplied with a low hydrogen concentration is unable to benefit from its high average cell temperature as its performance is drained by the low partial pressure of hydrogen within the fuel mixture.

Can hydrogen trapped within the lattice of copper film produce irreversible effects on the electrical resistivities of copper film at room temperature? In order to answer this question, copper films were sputtered in the presence of hydrogen and resistivities were measured in vacuum at room temperature. A series of sputtering depositions were carried out at different hydrogen partial pressures to confirm irreversible hydrogen effects. Films sputtered in argon only, were used as controls. The electrical resistivities of copper films were measured as a function of hydrogen partial pressure. Saturation is reached for the electrical resistivity in high hydrogen partial pressures. The saturation is at around 5.0% hydrogen partial pressure of total sputtering pressure. The electrical resistivities of copper films are lowered irreversibly by hydrogen, because the films were sputtered in the gas mixtures of argon and hydrogen and the electrical resistivities of films were measured in the air. The sputtering rate decreases as the hydrogen partial pressure increases. The sputtering rate is found to be proportional to the average mass of the incident ion.

<p>One of the major challenges to be overcome before hydrogen fuelled vehicles can become commonplace is to store hydrogen with sufficient storage density to be practical. One approach to overcoming this challenge involves converting the hydrogen into a secondary fuel that can be stored more easily, such as ammonia. This introduces the challenge of efficiently retrieving the hydrogen from the secondary fuel with sufficient purity to be used in a polymer electrolyte membrane fuel cell. Putting the hydrogen producing reaction inside a membrane which is capable of filtering out hydrogen creates a membrane reactor which can increase hydrogen purity and can accelerate the reaction both kinetically and thermodynamically. The most effective materials currently known for hydrogen membranes are high palladium alloys of copper and silver. These are able to absorb hydrogen on the side with high hydrogen partial pressure and desorb that hydrogen on the side with low hydrogen pressure. Palladium metal is also able to interact with some catalysts by hydrogen spillover. Hydrogen is transported from the surface of the catalyst to the palladium surface more quickly than the hydrogen can desorb from the catalyst, this potentially accelerates both the catalysis and the hydrogen filtration. This research aimed to create a catalytic spillover membrane to extend the possibility of ammonia as a secondary fuel for hydrogen transport. In this research, several methods to produce a nickel catalyst on the surface of the palladium were explored: electrodeposition with and without a lithographic template; spray coating with nanoparticles; and preshaped nickel mesh and nickel foam. These potential catalysts were tested for ammonia decomposition. Templated electrodeposition created the most effective catalyst, but the nickel foam was most easily applied to the next stage of the research. The nickel foam catalyst was subsequently retested for ammonia decomposition in three scenarios: in contact with palladium foil; in a reactor with a palladium membrane; and in contact with a palladium membrane. The presence of a palladium membrane improved decomposition more than spillover contact between nickel foam catalyst and palladium, however, the combination of spillover contact with a palladium membrane increased the ammonia decomposition further. The rate of hydrogen flux through the palladium membranes was calculated for the experimental results. These were compared to flux values predicted by a model equation. The results showed that spillover contact between nickel catalyst and palladium membrane increased the hydrogen flux through the membrane.. The research outcomes have generated new knowledge and improved understanding of the morphology and role of nickel catalysts in accelerating ammonia decomposition. The research highlights the complex relationship between reactor design, gas flow paths, catalyst presentation and catalysis chemistry, suggesting promising areas for future research.</p>

At low partial pressures of hydrogen (less than 0.1 MPa), hydrogen interacts with the metal and lowers the cohesive strength of the lattice (Oriani and Josephic, 1977). The decohesion theory postulates that regions exist near the crack tip with hydrogen concentrations, which are several orders of magnitude larger than the lattice concentration of hydrogen. The microstructure strongly influences the embrittlement process and the crack growth kinetics. (Kumnick and Johnson, 1980). Thus it can be expected, that the experimental study of the mechanism of gaseous hydrogen embrittlement is facilitated by studying the process at the crack tip in its simplest form under the most simple boundary conditions. For these reasons FeSi-single crystals are used, since the micro-processes for ductile and brittle fracture are well known in this alloy (Vehoff and Neumann, 1979, 1980). Tests are carried out at different temperatures, hydrogen pressures and plastic crack tip opening rates in order to investigate the influence of the hydrogen concentration at the crack tip on the brittleness of the fracture process (Wei and co-workers, 1980).

Self-reduction process of Eu3+ to Eu2+ in Eu-doped SrLaMgTaO6 double perovskite thin films and its photoluminescence properties

Samples of annealed and severely cold-rolled vanadium were bombarded at room temperature with 150-keV H+ ions at fluxes from 1.2×1015 to 1.2×1016 H+/cm2 sec to doses of from 3.6×1017 to 3.2×1019 H+/cm2. All samples irradiated to doses greater than 1.1×1019 H+/cm2 exhibited blistering in spite of the fact that temperatures never exceeded the peak miscibility gap temperatures below which vanadium hydride is stable with respect to gaseous hydrogen even at low hydrogen partial pressures. Niobium also blistered under similar conditions. This unexpected observation must be reconciled by any acceptable theory of radiation blistering.

Process economics studies of the fuel oil mode of operation at lowered hydrogen partial pressure indicated that the potential capital saving of reduced pressure design outweighs the cost of increased catalyst usage needed to maintain product yield and quality. Because the yields, product properties and catalyst deactivation rates were an extrapolation of the existing data base, it was recommended that experimental work be done to verify this observation. On the basis of an experimental program conducted at the HRI R and D Center, the following conclusions were reached: lower pressure operation can yield an economic, as well as mechanical, benefit (1140 psi vs 1800 psi hydrogen partial pressure at the reactor outlet); test results from this bench run support most of the findings of an engineering study on a commercial design case at a lower hydrogen partial pressure (1200 psi). The experimental yields and predicted yields agree with each other within 2%, while the experimental data show a lower sulfur content and lower apparent viscosity than predicted; the spent catalyst from the low pressure run had a higher carbon content, by 4 W% (16.3 vs 11.6 W%), than the spent catalyst from a standard pressure run. Recovery of pore volume on ignition was equivalent for each (93%).

Microstructures in (Y0.95Ca0.05)Ba2Cu4O8 prepared by low and high oxygen partial pressure techniques

Ozone soundings performed since 1988 on the Antarctic Peninsula at Marambio (64.2°S, 57.7°W) and in the European Arctic at Sodankyla (67.4°N, 26.6°E), Bear Island (74.5°N, 19.0°E) and Ny Alesund (78.9°N, 11.9°E) have been studied. Regular ozone soundings have never been made at these locations. A comparison of monthly mean tropospheric ozone profiles at high southern and northern latitudes has been made. In midwinter, differences between the monthly means in the northern and southern hemispheres are small, i.e. < 1 mPa. The general photochemical activation in springtime leads to larger differences: the partial pressures decrease in Antarctica whereas in the Arctic, pronounced production of ozone is seen. In spring and summer, the hemispheric differences are about 3 mPa. Exceptionally high and low partial pressures at Sodankyla and Marambio have been studied using 3-dimensional trajectories based on the ECMWF analyses. Episodes of upper tropospheric ozone loss at Marambio have been observed during the stratospheric ozone depletion period in spring. The only cause for especially high tropospheric ozone concentrations in Antarctica has been stratospheric intrusions. Low partial pressures in the boundary layer have been connected with advection of marine airmasses to Marambio. At Sodankyla, low boundary layer values have been observed during an advection from the Northern sea areas and also during the transport of airmasses from industrial source areas of Eastern Europe. Especially strong stratospheric ozone intrusion into the middle troposphere was observed at Sodankyla in September 1989. Partial pressures exceeding 7 mPa in the lower troposphere have been observed at Sodankyla during the summer in connection with the long-range transport of NO x /HC-containing air from Western Europe to Northern Scandinavia. DOI: 10.1034/j.1600-0889.1993.t01-1-00003.x

Insights into microbial metabolic coordination under driving force of different conductive materials-mediated direct interspecies electron transfer during anaerobic digestion

New insights into the mechanisms underlying biochar-assisted sustained high-efficient co-digestion: Reducing thermodynamic constraints and enhancing extracellular electron transfer flux

Nitric oxide (NO) reduction pathways are systematically studied on a (111) facet of the octahedral nickel (Ni85) nanocluster in the presence/absence of hydrogen. Thermodynamic (reaction free energies) and kinetic (free energy barriers, and temperature dependent reaction rates) parameters are investigated to find out the most favoured reduction pathway for NO reduction. The catalytic activity of the Ni-nanocluster is investigated in greater detail toward the product selectivity (N2 vs. N2O vs. NH3). The previous theoretical (catalyzed by Pt, Pd, Rh and Ir) and experimental reports (catalyzed by Pt, Ag, Pd) show that direct N-O bond dissociation is very much unlikely due to the high-energy barrier but our study shows that the reaction is thermodynamically and kinetically favourable when catalysed by the octahedral Ni-nanocluster. The catalytic activity of the Ni-nanocluster toward NO reduction reaction is very much efficient and selective toward N2 formation even in the presence of hydrogen. However, N2O (one of the major by-products) formation is very much unlikely due to the high activation barrier. Our microkinetic analysis shows that even at high hydrogen partial pressures, the catalyst is very much selective toward N2 formation over NH3.

Elucidating the field influence on the energetics of the methane steam reforming reaction: A density functional theory study