Method for the production of a metal foam supported solid oxide fuel cell
Within the scope of the energy revolution, fuel cells play a key role for future energy systems. Solid oxide fuel cells (SOFC) are suitable for the decentralized energy production, as they allow flexible and highly efficient power and heat generation from renewable and conventional energy sources. This invention presents a novel method for the production of a mechanically robust and efficient metal foam supported SOFC (MFS-SOFC), which allows a quick start up, exhibits increased power densities and can be run at lower temperatures.
The core piece of the presented fuel cell is the membrane electrode assembly (MEA), which consists of an anode layer, a cathode layer and an electrolyte membrane, which separates the cathode and anode layers. The different thermal expansion coefficients of the used materials (e.g. metal foam material and the anode material) represent a high demand on an uniform and well-regulated heating process, leading to long start up times in order to avoid severe damage of the SOFC. In addition, high operating temperatures of 600 - 1000°C induce severe stresses on peripheral devices, such as the gas supplies and the cooling unit. Especially the manufacturing process of the membrane stacks and their respective sealing resemble process- and cost-related issues, which makes SOFC sensitive and expensive.
To solve the aforementioned problems, a method for the production of a mechanically robust and energy efficient MFS-SOFC, which can be run at lower temperatures, is presented. The present SOFC is based on a mechanical support structure made of a open-pore metal foam (e.g. nickel foam), onto which the MEA is directly applied via vapour deposition (Fig. 1 A). Thereby, optimal layer thickness can be achieved to make the MEA as efficient as possible. To ensure this, during coating the anode material of the MEA is not infiltrating into the open-pore support structure. The three functional layers of the MEA are then deposited via chemical or physical vapour deposition (CVD or PVD) onto the sealed support structure. The coating process can be achieved by one continuous co-deposition process, so that fluid transitions between the layers can be realized (Fig. 1 B) and the MEA can be produced with an improved tightness. The infiltration material can easily be removed afterwards by thermal or chemical treatment. Finally, another metal foam support structure is added to the cathode layer.
Fig.1: Cross-sectional view of a SOFC. A) The MEA of the SOFC is subdivided into an upper anode layer and a lower cathode layer, separated by an electrolyte membrane. The MEA is embedded into a mechanical support structure in the form of a open-pore metal foam, which is held inside a support frame. For electrical contacting, the MEA stretches through this frame. Through gas in- and outlets (*) fuel or oxidation gases can be injected into the respective chamber of the fuel cell. B) Detailed schematic of the MEA substructure with a diagram of MEA material distribution. Shown is a detailed view of the MEA’s layer structure and the adjacent metal foam support structure (left). Shown is the material distribution within the MEA layers, which is also illustrated in the graph/diagram (right). In the anode layer region, the MEA is composed of yttrium stabilized zirconia (YSZ) with a proportion of nickel (Ni), which concentration decreases towards the core of the MEA, made up by the electrolyte membrane consisting only of YSZ. Towards the cathode layer an increasing amount of platinum (Pt) is codepositioned into the YSZ. (Source: adapted from patent application)
To eliminate the need for additional seals, ideally the single cells of a fuel cell stack can be arranged according to the Janus principle. To achieve this, coating of anode layers onto both sides of a support structure block is performed, so that they resemble deliminations between two neighboring cells. The resulting SOFC structure exhibits excellent mechanical and thermal stability and can thus be started quickly and resist a larger number of temperature cycles (on and off cycles). Hence, it has a better long-term durability and prolonged lifetime. By expanding the three-phase boundary at the MEA region, the electricity yield and power density is increased, resulting in a higher efficiency of the SOFC, which can be run at lower operating temperatures (600°C). Hereby, the thermal stability requirements for peripheral devices (such as gas supplies or the cooling unit) are markedly reduced, resulting in an overall reduction in system costs.
- Increased air-tightness, which results in a higher efficiency
- Higher electricity yield and power density
- Increased mechanical stability (faster start up, longer life cycle)
- Lower operating temperature (reduced stress on peripheral devices)
- Energy generation in power plants
- Combined heat and power units / decentralized energy supply
- Power and hot water or steam production
- Large scale systems for e.g. ships are possible
- Automotive engineering
The production method was successfully tested on the laboratory scale.
German patent application: DE 10 2016 122888 A1
Granted EP-Patent: EP 3 327 848 B1
Technical University Clausthal
Dr. Mirza Mackovic
Patent Manager Technology
Phone: +49 (0) 551 30 724 153