CO Oxidation at the SOFC Ni/YSZ Anode: Langmuir- Hinshelwood and Mars-van-Krevelen versus Eley-Rideal Reaction Pathways

摘要

In technical solid oxide fuel cell (SOFC) systems practically relevant fuels are reformate gases and hydrocarbons where carbon monoxide (CO) is either used directly or is formed in situ. The oxidation of CO can take place via heterogeneously catalyzed reactions at the triple phase boundary (TPB) of gas-phase, Ni electrode and YSZ electrolyte. In the field of heterogeneous catalysis, CO oxidation on metal and metal oxide surfaces is generally believed to occur via Langmuir-Hinshelwood (LH) and Mars-van-Krevelen (MvK) elementary reaction mechanisms, respectively. In a recent experimental and theoretical investigation of Ni, CO-CO2|YSZ SOFC model anode systems, however, evidence for the occurrence of Eley-Rideal (ER) type heterogeneous thermal CO oxidation reaction steps on both the Ni anode material and the YSZ electrolyte was found [1]. In the present contribution, results of comprehensive quantum chemical calculations, performed in the framework of Density-Functional Theory (DFT), are presented, in which the energetics of CO adsorption and CO oxidation kinetics via the above mentioned reaction pathways over Ni and YSZ surfaces were investigated. The results allow assessing the relative importance of these three mechanisms and their influence on the overall CO oxidation kinetics over Ni, CO-CO2|YSZ SOFC model anodes.