Influence of microporous layer on corrosion of metallic bipolar plates in fuel cells

The effect of the presence of a microporous layer on the propensity for corrosion of metallic bipolar plates in an operating polymer electrolyte membrane fuel cell is investigated using an in situ reference electrode array. The local potential at the surface of the cathode bipolar plate is significantly more negative in the presence of the microporous layer, which is attributed to the higher ionic resistance of the aqueous phase in the reactant transport layer associated with more effective removal of water from the catalyst layer/reactant transport layer interface. As a result the bipolar plate is effectively shielded from elevated potentials that may be present at the cathode electrode, even during start-up and shutdown of the cell. Revision of ex situ test protocols for candidate bipolar plate materials, surface treatments and coatings is recommended to reduce unnecessary conservatism in testing

Fragmentation of H2^2+ ions following double electron capture in slow Xe23+ and O5+ + H2 collisions

International audienceThe energy distributions of H+ fragments produced in 345 keV Xe23+ + H2 and 75 keV O5+ + H2 collisions have been investigated experimentally as a function of the detection angle. For both systems, the experiment shows strong deviations from the molecular Coulomb explosion. Two- and three-body model calculations have also been performed to understand the energy spectra. In the collisions involving the heaviest projectile Xe23+ , the two-body calculations reproduce the experimental data satisfactorily, indicating that the recoil energy transferred to the target plays an important role in the fragment-energy distributions. On the other hand, for the system O5+ + H2, the deviations between calculations and experiment suggest that the interaction between the outgoing projectile and each fragment plays the major role

Simple and Validated Quantitative H-1 NMR Method for the Determination of Methylation, Acetylation, and Feruloylation Degree of Pectin

The knowledge of pectin esterification degree is of primary importance to predict gelling and other properties of pectin from different sources. This paper reports the development of a simple and rapid H-1 NMR-based method for the simultaneous quantitative determination of methylation, acetylation, and feruloylation degree of pectin isolated from various food sources. Pectin esters are hydrolyzed in NaOH/D2O, and the obtained methanol, acetic acid, and ferulic acid are directly measured by H-1 NMR. High accuracy, repeatability, and reproducibility of the method were obtained, and the analysis time is reduced as compared to conventional chromatography- or titration-based methods

MICROSCOPE Mission: Final Results of the Test of the Equivalence Principle

International audienceThe MICROSCOPE mission was designed to test the weak equivalence principle (WEP), stating the equality between the inertial and the gravitational masses, with a precision of 10-15 in terms of the Eötvös ratio η. Its experimental test consisted of comparing the accelerations undergone by two collocated test masses of different compositions as they orbited the Earth, by measuring the electrostatic forces required to keep them in equilibrium. This was done with ultrasensitive differential electrostatic accelerometers onboard a drag-free satellite. The mission lasted two and a half years, cumulating five months worth of science free-fall data, two-thirds with a pair of test masses of different compositions—titanium and platinum alloys—and the last third with a reference pair of test masses of the same composition—platinum. We summarize the data analysis, with an emphasis on the characterization of the systematic uncertainties due to thermal instabilities and on the correction of short-lived events which could mimic a WEP violation signal. We found no violation of the WEP, with the Eötvös parameter of the titanium and platinum pair constrained to η(Ti,Pt)=[-1.5±2.3(stat)±1.5(syst)]×10-15 at 1σ in statistical errors