Nanostructured Ni/YSZ Anodes: Fabrication and Performance Analysis

The design state of the art SOFC anodes limit the electrooxidation reaction inherently by its µm-scaled microstructure. An increase in cell performance of anode supported SOFCs (ASC) is achieved by a method, which induces the formation of an additional nanostructured Ni/YSZ layer in the electrochemically active region of the anode. This in-operando technique is based on a short-time application of a high current in reverse direction (reverse current treatment - RCT). In this contribution we investigate the nanostructured layer in a new model anode setup on a single crystalline YSZ substrate. This new setup guarantees homogenous experimental conditions due to simplified cell geometry. It is possible to control the RCT parameters and fabricate nanostructured layer with thicknesses up to 1100 nm and grain sizes between 10...20 nm. After conducting the RCT, a dense ~200 nm thin Ni film is still remaining, covering the whole nanostructured layer. Gas impermeability of the Ni film inhibits at first sufficient fuel gas access to the electrochemically active region in the nanostructured layer. Open porosity in the dense Ni film is thus necessary to characterize the electrochemical performance of the nanostructured model anode by means of impedance spectroscopy. Therefore an oxidation-reduction cycle is introduced leading to an impressively low anode polarization resistance compared to technical SOFC anodes. Furthermore, TEM analysis provides new information of the serve interaction of YSZ with the adjacent Ni phase during RCT, which is essential for a controlling and optimizing the fabrication process.