Goal

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The central goal of the sub-project is to better understand the mechanisms of a series of  surface/interface reactions near the anode three-phase boundary at the fundamental atomic level, namely with respect to both the geometric and the electronic structure of the involved active sites.

We regard a more fundamental understanding of these sites and the mechanism of the "at-site" reactions as an important and necessary contribution to further directional development of anode materials and in particular of their optimum combinations.

The following catalytic reactions leading to H2 and CO at/near the anode three phase boundary are in the focus of our project:

CH4 → C + 2H2 methane dissociation reaction

C + H2O → CO + H2 water gas reaction

C + CO2 → 2 CO Boudouard reaction

CO + H2O → CO2 + H2 water gas shift reaction

These four "basic" reactions finally sum up (with catalyst-specific degrees) to:

CH4 + H2O → CO + 3H2 methane steam reforming I

CH4 + 2 H2O → CO2 + 4H2 methane steam reforming II

CH4 + CO2 → 2CO + 2H2 methane dry reforming

At the high temperatures of SOFC operation, reaction mechanisms involving higher-molecular intermediates are highly underrepresented or absent at all. C is the most important intermediate and thus the way how fast (and in which form) carbon is formed and further reacted defines the main mechanistic questions. We will study the respective initial elementary reaction steps (activation of water, methane, CO and CO2, with specific interest in rate limiting processes), the intermediate reactions and finally the full reforming reactions both on the respective "inverse" model systems (e.g. thin oxide islands grown on (bi)metallic surfaces) and on our epitaxial nanoparticle model catalysts (epitaxially grown (bi)metallic nanoparticles embedded in thin oxide film supports), using a broad choice of ex-situ and in-situ spectroscopies, structural analysis methods and microscopic techniques. We will separately assess the role of the (bi)metallic surfaces and of the individual (reduced) oxide surfaces for "carbon management" and the activation of the involved reactant molecules (in particular of water), before tackling potential promoting effects of oxide-(bi)metal interfaces for reactant activation and the choice of the above-mentioned reactions. By firstly looking at the individual actions of the (bi)metallic and oxidic (nano)phases governed by electronic, ensemble, particle size and defect chemistry, potential catalytic synergisms located at the (bi)metal-oxide or oxide-oxide phase boundary can be extracted.