Formation, Performance, and Long-Term Stability of Nanostructured Ni-YSZ Thin Film Electrodes

Nickel and yttria-stabilized zirconia (YSZ) composite anodes were fabricated by a powder-free, polymeric precursor-based process, in which Ni, Y, and Zr cations are redistributed by phase separation at the nanoscale, forming YSZ and Ni(O). Transmission electron microscopy/energy-dispersive X-ray spectroscopy analyses revealed for the first-time in the literature that the nanocomposite thin film Ni-YSZ anodes had microstructures consisting of alternating Ni and YSZ nanolayers. A pre-calcination step applied in the oxidized state enhanced the interconnectivity of the Ni and YSZ phases after reduction, which improved the electrochemical performance. Electrochemical and microstructural analyses showed that performance degradation upon long-term exposure to dilute hydrogen at 600 °C was closely related to Ni coarsening in general. Evidently, the pre-calcination step enhanced the performance stability of the anodes by strengthening the YSZ network and thus inhibiting Ni agglomeration. In addition, the deposition of a thin, electronically conductive CeO2 overlayer on top of the Ni-YSZ anode inhibited the excessive agglomeration of Ni at the top surface. Our experiments showed that the pre-calcination of Ni-YSZ anodes in the oxidized state with a CeO2 overlayer gave the highest electrocatalytic performance, i.e., a polarization resistance of 0.72 Ω·cm2 at 600 °C, in dilute hydrogen, as well as the highest long-term performance stability.