Performance Enhancement of SOFC Anode Through Electrochemically Induced Ni/YSZ Nanostructures

Abstract

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°C. 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.