Evaluation of the Influence of Nickel Addition on LST-CGO Based Solid Oxide Fuel Cell Anodes Performance

Ni/YSZ composite materials have shown the tremendous success over past years for application as SOFC anodes. One of the biggest advantages of Ni/YSZ SOFC anode is its ability of direct utilization of various fuel types, i.e. H₂/H₂O, CO/CO₂ and hydrocarbons. It is, however, well known that operation of those anodes upon various fuels could cause various types of cell degradation. Therefore, the replacement of Ni cermet with alternative ceramic materials is essential to develop long-term operating SOFC technology.

In the present contribution, we combine modeling and experimental study of electrochemical hydrogen oxidation at an alternative perovskite based mixed-conducting SOFC anode with and without an addition of nickel. Composite electrodes were produced by conventional wet ceramic processing (screen printing – spraying) and sintering on YSZ electrolytes (La_0.1Sr_0.9TiO_3-α-Ce_1-xGd_xO_2-α | YSZ) with different compositions and microstructure, and were electrochemically characterized using symmetrical button-cells configuration. An elementary kinetic model was developed and applied to explore the performance of LST based SOFC anode. A detailed multi-step heterogeneous chemical and electrochemical reaction mechanism was established taking into account transport of ions in all ionic phases, and gas transport in channel and porous media. It was found that heterogeneous chemistry at LST surface has capacitive behavior that alters the impedance spectra. In addition, surface charge-transfer reaction, which describes partial oxygen ionization, caused impedance feature and is rate-limiting at high temperature. However, if nickel is added to composite perovskite anodes the impact of LST surface chemistry is diminished leading to an improvement of cell performance.