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Improving the durability of a platinum catalyst is an important step in increasing its utility when incorporated as the anode or cathode of a proton-exchange membrane fuel cell. Using density functional theory, the binding energy between a platinum atom and five graphene surfaces, one pure, and four others singly doped with beryllium, boron, nitrogen, and oxygen, was calculated. The oxygen-doped surface showed the highest binding energy and was calculated to be 7 times higher than the undoped surface. Each dopant modified the surface bonding arrangement within the graphene lattice, which then affected how the surface bonded to the platinum atom. Using molecular orbitals, natural bond orbitals, and the gradient of the electron density, these interactions were explored to explain the strength of the Pt−surface bond, which, in ascending order by dopant, was found to be undoped, nitrogen, boron, beryllium, and oxygen.

The supersonic jet flows of neutral gas from atmospheric to near-vacuum conditions in the interface region of mass-spectrometer systems is investigated by continuum-based (fluid) numerical simulations. An enhanced understanding of the neutral gas transport is of paramount importance to fully understand flows in the interface region of mass spectrometers, for it is the neutral dynamics that governs and drives the ions from the high pressure ion source through the interface orifice towards the ion optics and detector subsystems. The key features and structure of the complex neutral gas flow are examined and the influence of large pressure differences imposed across the interface region, orifice geometry, and gas skimmer configuration used for flow control are assessed. The flow structure is shown to be that of a classical under-expanded free jet for 'skimmer-absent' cases and very good agreement between the numerical predictions and empirical and experimental values is demonstrated. For the 'skimmer-present' cases, the shock structure downstream of the orifice and skimmer is identified and fully described and its influences on the flow skimming and focusing processes are discussed.

A numerical analysis of the neutral dynamics is performed in the case of helium short-gap spark discharges to show the energy memory effect of recurring discharges. The millimetric (4 mm) and submillimetric (0.3 mm) discharges are studied at atmospheric pressure and ambient temperature (293 K). This corresponds to a neutral density of 2.5×1025 m−3. The maximum injected power is either 50 or 3 W with a duration of 1 μs, the relaxation time between the two successive injections is 5 μs. The evolution of the neutral gas is described with the classical transport equations written in a two-dimensional cylindrical geometry with plane electrodes and solved with powerful numerical schemes. The effect of the discharge on the neutral gas is represented by energy and momentum transfers. The neutral gas is no longer considered as an infinite sink dissipating the energy of the electrons and ions acquired from the field. It is shown that the energy and momentum transfer effects initiate and control the variations of temperature, pressure, and neutral population. Concerning the recurring aspect, the neutral memory effect persists during the time lapse between two successive discharges and directly influences the gas dynamics of the following discharge. The specific behavior of the gas dynamics for the shorter gap (0.3 mm) is also discussed in terms of boundary effects. In particular, the influence of the latter on the velocity field is studied.