Lanthanum Nickelate Infiltration into Porous Gd-Doped Ceria As Cathode for Solid Oxide Fuel Cells

To increase Solid Oxide Fuel Cells performances, the optimization of the oxygen electrode is mandatory as its activation overpotential is higher than the one of the hydrogen electrode. One way to increase the cathode electrocatalytic properties and to decrease its polarization resistance is to increase the Triple Phase Boundaries zone, where the oxygen is reduced. A promising solution to achieve this goal is to disperse an oxygen reduction catalyst on the surface of a porous ionic conductor. The lanthanum nickelate La₂NiO_4+δ (LNO) has remarkable surface exchange reaction rate and oxygen diffusion coefficient. However, when the electrode is shaped by classical screen printing technique, it displays higher polarization resistance (≈ 1 Ω.cm²) than the standard lanthanum cobaltite-based materials (≈ 0.1 Ω.cm² for La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ).

In this study, cathodes were prepared by infiltration of lanthanum nickelate into a Gd-doped ceria (GDC) backbone sintered on 8YSZ electrolyte pellets. The influence of the preparation parameters of the composite electrodes on their electrochemical activity will be presented. The optimization of the preparation parameters led to a large decrease of the polarization resistance, down to 0.1 Ω·cm² at 600 °C. Using the Adler-Lane-Steele model, the impedance diagrams were fitted, allowing the determination of the surface exchange rate and ionic conductivity of the electrode: the obtained values well agree with those previously reported in the literature. Using this infiltration process, single cells were made starting from commercial half cells (Ni cermet/8YSZ), the cathode being the composite LNO/GDC. Voltammetry measurements showed power density higher than 1 W.cm^-2 at 800°C.