Solid oxide fuel cell (SOFC) electrode and cell level modeling
The SOFC is characterized by high operating temperatures (600-900°C). Within an SOFC electrode, fundamental physicochemical processes involve heterogeneous catalytic chemistry and electrochemistry, which are coupled to transport processes in the porous electrode structures. The complex interaction between these processes requires models with detailed kinetic mechanisms and transport on a microscopic level. A number of crucial issues concerning the influence of catalyst structure and composition, reforming chemistry and direct oxidation, carbon deposition, cell aging etc. are addressed.
An example for the research activities on the surface and electrode level is the investigation of electrocatalysis at the three-phase boundary of an SOFC anode (Fig. 1). This is the region where the gas phase and the two solid phases of electrode (Nickel, Ni) and electrolyte (yttria-stabilized zirconia, YSZ) meet. Here, effects such as surface reaction, surface diffusion and surface phase transitions due to spillover between the two solid phases are simulated. Proposed reaction mechanisms vary not only in the degree of simplification, but also in the fundamental pathway. The goal of the work in this field is the elucidation of the elementary electrochemical reaction mechanism in the SOFC.
Activities on the cell level include the investigation of the coupling of detailed kinetics with macroscopic transport processes, needed for the prediction of spatially resolved electrochemical properties (Fig. 2). Depending on the boundary conditions (fixed or periodic), situations in either a single cell or a stack repeat element can be modeled. Furthermore, full 3D simulations of transport processes in realistic cell geometries are carried out (Fig. 3). A specific interest here is the assessment of temperature distributions, as inhomogeneous temperatures can strongly contribute to thermomechanical stress and degradation.