Excellent kinetics of single-phase Gd-doped ceria fuel electrodes in solid oxide cells

Abstract

Ceria containing electrodes offer several advantages compared to state-of-the art nickel-yttria-stabilized zirconia (Ni-YSZ) cermets, such as higher ionic and electronic conductivities, and a high activity for oxygen exchange reactions on the oxide surface. They may also solve current issues like long-term degradation due to microstructural changes and carbon deposition, especially when they are used in dry hydrocarbon fuel, or CO₂ electrolysis mode. For application, compatibility with existing powder-based fabrication methods is of high technological interest. These are the main reasons why ceria containing fuel electrodes can significantly improve cell performance, thus being especially interesting for intermediate temperature and metal-supported cells. In almost all studies so far, the relatively low electron conductivity of ceria-based materials was compensated by addition of a percolating Ni metal phase. Here, we show that anodes with a single phase gadolinia doped ceria (GDC) functional layer perform even better than cermets. The drawback of lower electronic conductivity results in an increased ohmic resistance, which is minimized by a thin functional layer and a current collecting layer on top. By temperature, thickness and atmosphere variations, we can divide the polarization resistance of the GDC anode into an ohmic, electrochemical and gas diffusion contribution. At 800 °C, the electrode arc diameter shrinks to extremely low ∼0.012 Ω cm², even at low H₂ and H₂O pressures and with a significant contribution of gas phase diffusion kinetics.