Near-Ambient-Pressure X-ray Photoelectron Spectroscopy Study of Methane-Induced Carbon Deposition on Clean and Copper-Modified Polycrystalline Nickel Materials

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• 作者：Raffael Rameshan ; Lukas Mayr ; Bernhard Kl枚tzer ; Dominik Eder ; Axel Knop-Gericke ; Michael H盲vecker ; Raoul Blume ; Robert Schl枚gl ; Dmitry Y. Zemlyanov ; Simon Penner
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：December 3, 2015
• 年：2015
• 卷：119
• 期：48
• 页码：26948-26958
• 全文大小：714K
• ISSN：1932-7455

文摘

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 掳C. Two complementary polycrystalline Ni samples were used, namely, Ni foam鈥攕erving as a model structure for bulk Ni in cermet materials such as Ni/YSZ鈥攁nd 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 鈥渋ncubation鈥?period of the Ni foam in methane at 0.2 mbar and temperatures around 400 掳C, cooling down to 鈭?50 掳C, and keeping the sample at this temperature for 50鈥?0 min, initial formation of a near-surface carbide phase was observed, which exhibited the same spectroscopic fingerprint as the C₂H₄ induced 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 掳C, decomposition/bulk dissolution of the graphene/graphite phase was observed on the rather 鈥渙pen鈥?surface of the Ni foam. In contrast, Ni foil showed鈥攗nder otherwise identical conditions鈥攑redominant formation of unreactive amorphous carbon, which can only be removed at 鈮?00 掳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.