Performance enhancement of SOFC anode through electrochemically induced Ni/YSZ nanostructures

The local morphology of the interface electrolyte/anode of solid oxide fuel cells has a strong effect on the electrochemically active triple-phase boundary length. Therefore, the electrical performance is expected to be enhanced by nanostructuring this interface. This study focuses on the anode functional layer (AFL) of Ni/8YSZ (Ni/8.5 mol % yttria-doped zirconia) composite anodes. A nanometer scaled and nanoporous Ni/YSZ interlayer of about 200 nm thickness was formed after applying a short-time reverse current treatment (RCT) at 700°. Impedance spectroscopy measurements proved a progressive decrease of the overall area specific resistance, when exposing anode supported cells to a series of RCTs. The performance change was attributed purely to the decrease of the polarization resistance in the anode functional layer, which was reduced by 40. Scanning and transmission electron microscopy (TEM) confirmed the formation of a nanocrystalline, porous YSZ matrix containing finely distributed nanosized Ni grains. Energy-filtered TEM yielded the distributions of the cations and oxygen. Furthermore, high-resolution TEM and dark-field TEM imaging identified mainly cubic YSZ including traces of the metastable t"-phase within the nanostructured YSZ. A reaction scheme for the formation of the highly efficient Ni/YSZ structure at the interface electrolyte/anode is proposed.