title: Near-Ambient-Pressure X-ray Photoelectron Spectroscopy Study of Methane-Induced Carbon Deposition on Clean and Copper-Modified Polycrystalline Nickel Materials.
abstract: In order to simulate solid-oxide fuel cell (SOFC)-related coking mechanisms of Ni, methane-induced surface carbide and carbon growth was studied under close-to-real conditions by synchrotron-based near-ambient-pressure (NAP) X-ray photoelectron spectroscopy (XPS) in the temperature region between 250 and 600 °C. Two complementary polycrystalline Ni samples were used, namely, Ni foam-serving as a model structure for bulk Ni in cermet materials such as Ni/YSZ-and Ni foil. The growth mechanism of graphene/graphite species was found to be closely related to that previously described for ethylene-induced graphene growth on Ni(111). After a sufficiently long "incubation" period of the Ni foam in methane at 0.2 mbar and temperatures around 400 °C, cooling down to ∼250 °C, and keeping the sample at this temperature for 50-60 min, initial formation of a near-surface carbide phase was observed, which exhibited the same spectroscopic fingerprint as the C2H4induced Ni2C phase on Ni(111). Only in the presence of this carbidic species, subsequent graphene/graphite nucleation and growth was observed. Vice versa, the absence of this species excluded further graphene/graphite formation. At temperatures above 400 °C, decomposition/bulk dissolution of the graphene/graphite phase was observed on the rather "open" surface of the Ni foam. In contrast, Ni foil showed-under otherwise identical conditions-predominant formation of unreactive amorphous carbon, which can only be removed at ≥500 °C by oxidative clean-off. Moreover, the complete suppression of carbide and subsequent graphene/graphite formation by Cu-alloying of the Ni foam and by addition of water to the methane atmosphere was verified.
authors.affiliation: Institute of Physical Chemistry, University of Innsbruck , Innrain 80-82, A-6020 Innsbruck, Austria ; Department of Inorganic Chemistry, Fritz-Haber-Institute of the Max-Planck-Society , Faradayweg 4-6, D-14195 Berlin, Germany.
authors.forename: Raffael
authors.initials: R
authors.lastname: Rameshan
authors.affiliation: Institute of Physical Chemistry, University of Innsbruck , Innrain 80-82, A-6020 Innsbruck, Austria.
authors.forename: Lukas
authors.initials: L
authors.lastname: Mayr
authors.affiliation: Institute of Physical Chemistry, University of Innsbruck , Innrain 80-82, A-6020 Innsbruck, Austria.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Klötzer
authors.affiliation: Institute of Physical Chemistry, University of Münster , Corrensstrasse 28/30, D-48149 Münster, Germany.
authors.forename: Dominik
authors.initials: D
authors.lastname: Eder
authors.affiliation: Department of Inorganic Chemistry, Fritz-Haber-Institute of the Max-Planck-Society , Faradayweg 4-6, D-14195 Berlin, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Knop-Gericke
authors.affiliation: Department of Inorganic Chemistry, Fritz-Haber-Institute of the Max-Planck-Society , Faradayweg 4-6, D-14195 Berlin, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Hävecker
authors.affiliation: Department of Inorganic Chemistry, Fritz-Haber-Institute of the Max-Planck-Society , Faradayweg 4-6, D-14195 Berlin, Germany.
authors.forename: Raoul
authors.initials: R
authors.lastname: Blume
authors.affiliation: Department of Inorganic Chemistry, Fritz-Haber-Institute of the Max-Planck-Society , Faradayweg 4-6, D-14195 Berlin, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Schlögl
authors.affiliation: Birck Nanotechnology Center, Purdue University , 1205 West State Street, West Lafayette, Indiana 47907-2057, United States.
authors.forename: Dmitry Y
authors.initials: DY
authors.lastname: Zemlyanov
authors.affiliation: Institute of Physical Chemistry, University of Innsbruck , Innrain 80-82, A-6020 Innsbruck, Austria.
authors.forename: Simon
authors.initials: S
authors.lastname: Penner