For cell development and optimization of operating strategies, a quantitative description of the occurring transport mechanisms (heat, mass and charge transport) in SOFCs is relevant. Due to the very limited possibility to measure local transport processes in situ, a simulation of these molecular transport mechanisms is of great importance. A suitable approach to describe transport mechanisms in nonequilibrium systems is the thermodynamics of irreversible processes (TiP). This modeling approach considers from the outset the possible coupling of transport processes. In this theory, the flux of an extensive thermodynamic state variable depends on several driving ,,thermodynamic forces," i.e., gradients of intensive state variables. Since the phenomenological coefficients necessary for TiP modeling are not sufficiently known, empirical approaches, which provide only one thermodynamic force at a time to describe fluxes, currently dominate in the modeling of electrochemical systems. The focus of this project is therefore to provide these phenomenological coefficients for the electrolyte, in which a coupling between the heat flux density and the electric current density is assumed here (see Fig. 1). From the corresponding fluxes and forces, the local entropy production due to the transport process can be determined. Local entropy production rates can be identified as loss mechanisms and quantified as exergy losses. Since these represent a local heat source, these dissipative fractions affect the temperature field.
Under certain assumptions, a connection can be established between the phenomenological coefficients and the classical empirical coefficients, so that the determination of the phenomenological coefficients is carried out via the experimental determination of the empirical coefficients. The measurement of these respective coefficients first requires the specific exclusion of all forces except for the one driving force considered in each case. By observing the necessary boundary conditions and the equipment of the institute (see Fig. 2), it is possible to determine the thermal conductivity, the ionic conductivity and the Peltier coefficient.
In order to verify the experimental setup and validate the envisaged measurement methods, the empirical transport coefficients and for the sufficiently investigated material 8YSZ are first determined and compared with data from the literature. After this validation, the mentioned empirical coefficients will be measured in the system 10Sc1CeSZ and the phenomenological coefficients will be derived from them. The electrolyte material 10Sc1CeSZ is a novel and promising electrolyte material for SOFC and SOEC applications.
Processing
30823 Garbsen
