Enhanced Performance and Durability of Metal-Supported Fuel Cells by Optimized Cell Processing

Objective: Metal-supported solid oxide fuel cells (MSCs) are preferentially selected for mobile applications, e.g. as auxiliary power unit (APU) in heavy-duty trucks or as range extender for battery electric vehicles. The metallic support material allows the cells to withstand harsh operating conditions like fast thermal cycling, improves the mechanical stability and redox tolerance and offers novel possibilities for the internal reforming of hydrocarbons by catalytic activation. On the other hand the concept offers a potential for reducing the costs for cell production compared to established cell concepts and simplifies the sealing in a fuel cell stack by welding the substrate to the interconnects. The aim of this work was to enhance the Plansee MSC concept, in order to increase power density and avoid severe degradation of the cells.Materials & Methods: To increase performance and long-term stability, new electrode materials, optimized processing routes for anode and cathode and tailored interfaces to the electrolyte and metallic substrate were investigated. Performance improvement was verified by electrochemical cell tests (I-V and EIS). Long-term tests at constant operation conditions enabled to study the durability of the cells. Degradation phenomena were characterized by oxidation test with subsequent microstructure investigations including SEM/EDX.Results: Replacing LSCF by LSC as cathode material in combination with optimization of particle size and sintering regime was found to clearly increase the electrochemical performance, especially at intermediate operation temperature in the range of 600 - 700 °C. For the fuel electrode, introduction of Ni/GDC instead of Ni/YSZ as the functional layer of the anode, accompanied by a stepwise optimization of the microstructure, resulted in another significant increase of cell performance. This effect was mainly based on enlarging the electrochemical active area. Furthermore, lowering the ohmic resistance across the cell by decreasing the electrolyte thickness was enabled by improving the anode surface quality. On the basis of these measures, cell performance could be enhanced from 0.12 A/cm2 to 1.34 A/cm2 at 0.9 V and 700 °C and long term stability was confirmed for up to 1500 h of operation without severe degradation. Moreover, MSC specific degradation phenomena caused by oxidation of the anode and metallic substrate, interdiffusion at the interfaces and Cr based poisoning of the cathodes were identified.Conclusions: The presentation summarizes the main results achieved in the “Christian Doppler Laboratory for Interfaces in Metal-Supported Electrochemical Energy Converters” since 2014 and generally discusses the potential for further increase of cell performance and long-term stability