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In anode‐supported solid oxide fuel cells (SOFCs), air break‐in on the anode side can result in reoxidation of metallic nickel. The volume expansion caused by Ni oxidation generates stresses within the substrate, the anode and the electrolyte. Those stresses exceed the stability of the components, potentially promoting crack growth. Therefore, either the SOFC degrades continuously after each redox‐cycle or the membrane electrode assembly (MEA) fails completely if the electrolyte cracks. The influence of several reoxidation parameters on the mechanical integrity of Ni–YSZ‐anodes after reoxidation was investigated using different types of samples. All samples were SFEs (substrate–functional layer–electrolytes), consisting of Ni–YSZ‐substrate, Ni–YSZ‐anode and YSZ‐electrolyte. Investigations were carried out on freestanding SFEs and SFEs attached to steel plates (Crofer22APU, Thyssen Krupp V. D. M., Material Data Sheet No. 4046, Edition of December 2006) with a glass sealing. The results show a big influence of the degree of oxidation, homogeneity of oxidation, the operating temperature and the incident flow on the behaviour and the mechanical integrity of the reoxidised SFEs. The time of oxidation and the gas flow rate were influencing parameters, whereas the influence of the porosity was insignificant. The behaviour of the SFEs upon reoxidation also changes dramatically when comparing freestanding samples with attached samples.

The main function of the solid oxide fuel cell (SOFC) anode is to provide the reaction sites for the electrochemical oxidation of the fuel gas. Thus, the anode material must be stable in the reducing environment and have sufficient electronic conductivity and catalytic activity for the fuel/gas reaction under operating conditions. A porous cermet made of Ni and yttria-stabilized zirconia (YSZ) is widely used as anode material. The network of Ni particles has a large catalytic activity and is responsible for the transportation of electrons from the electrode reaction site to the current collector. Open porosity is required for the electrode to supply fuel as well as for removal of the reaction products. The addition of YSZ is necessary to support the Ni particles, to inhibit nickel grain coarsening at the usual operating temperatures and to give the cermet a thermal expansion coefficient acceptably close to that of the other cell components. [1] The presence of YSZ in the anode is considered to be inactive for the electrode reaction. [1] An alternative approach is for the YSZ component to extend the active area of the electrode reaction into the bulk of the electrode. [2] Although sinterability of Ni is reduced with increasing YSZ content, increasing YSZ content also raises the internal resistance (IR) of the SOFC. The particle size and ratio of Ni/YSZ are critical for the performance of the Ni/YSZ cermet anode. [3,4] Deposition of a thin anode interlayer on the anode substrate with finer particles reduces ADVANCED

Since the mid-nineties several generations of SOFC stacks have been designed and tested incorporating the anode substrate-type cells developed in Jülich. The 6 th generation, the so-called F-design stacks, with metallic interconnect has been the 'work horse' used for testing materials, cells and manufacturing processes in cell and stack development since its introduction in the year 2001. Stacks with up to 60 layers have been operated in recent years, delivering up to 13 kW of electric power. The ferritic parts are made of the commercial steel type CroFer22APU. This paper summarises the current developments at FZJ and presents some recent results obtained with new materials.