300 eV Helium implantation process into tungsten at 300 K has been studied with molecular dynamic simulations (MD). Predicted retention doses were compared to that obtained from experiments performed in equivalent conditions. A saturation phenomenon of the helium retention was evidenced for a number of impinging He atoms and a retention dose similar in both, experiments and simulations. From MD simulations it is learnt that observed Helium diffusion, formation and coalescence of clusters are the phenomena leading to the flaking of the substrate. These processes could explain the saturation of the Helium retention observed experimentally at low energies.
PdPt catalysts with different morphologies and atomic ratios have been synthesized on native SiO2/Si and on proton exchange membrane. The combination of the gas-aggregation source and of the magnetron sputtering techniques allows the formation of quasi core-shell Pd0.97Pt0.03@Pt nanoclusters. Transmission electron microscopy and grazing incidence wide angle X-ray scattering measurements on Pd-rich core reveal a mean diameter of 4 nm and a fcc structure. The Pt shell around the half of the Pd-rich core is formed by magnetron sputtering which leads to the increase of nanocluster diameter (up to 10 nm) and of the overall Pt content (up to 85%). The membranes coated by PdPt core catalyst and PdPt@Pt catalyst (resulting in the formation of catalyst coated membrane) are incorporated into fuel cells and their electrical characteristics are measured. The association of the two deposition techniques resulting in the formation of quasi core-shell PdPt@Pt nanoclusters improves the startup step of the fuel cell.
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