Fabrication and Electrochemical Performance Characterization of Nickel-based Thin-film Anodes for Low-temperature Solid Oxide Fuel Cells

Abstract

In this study, various types of pure nickel (Ni) and Ni-based cermet anodes were fabricated onto nanoporous substrates and applied to thin-film solid oxide fuel cells (SOFCs) for low temperature operation. Sputtering technique was utilized to fabricate the experimental fuel cells by sequential deposition of anodes, electrolytes, and cathodes on the substrate materials. Depending on its nanostructure, the pure Ni anodes exhibited comparable performance to the optimized platinum (Pt) anode at 500 ℃. However, compared to the optimized Pt anode cell, the polarization resistances of the pure Ni anode cells were significantly larger. In order to reduce the polarization resistance of Ni-based anodes and obtain better electrochemical characteristics, a Ni/Ni-based cermet bilayer anode structure was introduced. For optimization of the Ni-based cermet, five types of Ni-yttria stabilized zirconia (Ni-YSZ) composite films were fabricated via co-sputtering method and electrochemically investigated. As a result, a Ni-YSZ film fabricated by co-sputtering method with 50 W DC and 100 W RF powers showed the lowest polarization resistance. Therefore, this Ni-YSZ film was selected as Ni-YSZ layer of the Ni/Ni-YSZ bilayer anode. For Ni layer, a 150 nm-thick pure Ni anode, which showed the best performance among the fabricated pure Ni films, was employed. This 150 nm-thick pure Ni film was sputtered with DC 200 W under 5 mTorr argon (Ar) atmosphere. On the nanoporous substrate, the Ni-based bilayer anode, YSZ electrolyte, and Pt cathode was sequentially deposited to fabricate a full cell. At 500 ℃, the peak power density of the full cell was about 37 % higher (282 mW/cm2) than that of the optimized Pt anode cell (205 mW/cm2). Moreover, the Ni-based bilayer anode cell exhibited much lower ohmic and polarization resistances compared to other fabricated cells. This shows the acceptability of non-noble metal anode for low-temperature SOFCs.