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Forschungsgebiete der Abteilung Computergestützte Elektrochemie
Numerical methods and electrochemical impedance simulation
Numerical simulation of such a complex system as a fuel cell requires flexible software packages and powerful mathematical methods. We use a number of commercially available software tools (MATLAB, SIMULINK, STAR-CD, ...) as well as in-house software packages (DENIS). The latter allows the implementation of specialized algorithms, for example for the simulation of electrochemical impedance spectra.
Stack and system level modeling
The modeling and simulation activities on the stack and system level are pursued in the Electrochemical Systems group. They follow several goals: (1) Development of computationally efficient fuel cell stack models for real-time simulations; (2) Development of models for balance-of-plant components (heat exchangers, humidifiers, blowers, fuel processing units etc.) and compilation of component libraries; (3) Analysis of the interaction between the components in order to assess optimum system design and develop control strategies.
The further improvement of energy density, cycleability and safety of batteries requires a detailed understanding of the fundamental physical, chemical, and fluid mechanical processes occurring within the cell. To this goal, multi-scale and multi-physics models as well as modern numerical simulation methods are developed and applied. We have two areas of activities (Fig. 1), commercial lithium-ion batteries and highly energetic next-generation lithium batteries. The work is located at the German Aerospace Center (DLR) in Stuttgart and at the Helmholtz-Institute Ulm for Electrochemical Energy Storage (HIU).
Polymer electrolyte fuel cell (PEFC) and direct methanol fuel cell (DMFC) electrode and cell level modeling
The PEFC or DMFC single cell is a complex arrangement of multiple functional layers, including the polymer membrane, catalyst layers, microporous layers, and gas diffusion layers. A central task of the modeling activities is to describe, understand and optimize the functionalities of these layers. Typically, multiple different phases and materials are involved, that is, solid membrane, solid catalyst, solid diffusion layer, liquid aqueous phase, and gas phase (Fig. 1), all of which have different transport and chemical properties that need to be included in the model.
Solid oxide cells (SOFC&SOEC) electrode and cell level modeling
The Solid Oxide Fuel Cell (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, nickel oxide formation, cell aging etc. are addressed.
Multi-scale and multi-physics modeling
The fuel cell is an outstanding example for a multi-scale system. This situation is shown schematically in Figure 1. Chemical and electrochemical reactivity takes place on a nanometer scale; it is strongly dependent on nano- and microstructural properties. Mass, charge and heat transport takes place from a micrometer over millimeter up to decimeter scale. Time scales vary from sub-nanoseconds (electrochemical and chemical reactions) over seconds (transport) up to days or even months (structural and functional degradation). All process are strongly, and often nonlinearly, coupled over the various scales. Processes on the microscale can therefore dominantly influence macroscopic behavior.
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