Interaction of a ceria‐based anode functional layer with a stabilized zirconia electrolyte: Considerations from a materials perspective

Abstract

We report on the materials interaction of gadolinium doped ceria (GDC) and yttria stabilized zirconia (YSZ) in the context of high temperature sintering during manufacturing of anode supported solid oxide fuel cells (AS-SOFC). While ceria-based anodes are expected to show superior electrochemical performance and enhanced sulfur and coking tolerance in comparison to zirconia-based anodes, we demonstrate that the incorporation of a Ni-GDC anode into an ASC with YSZ electrolyte decreases the performance of the ASC by approximately 50% compared to the standard Ni-YSZ cell. The performance loss is attributed to interdiffusion of ceria and zirconia during cell fabrication, which is investigated using powder mixtures and demonstrated to be more severe in the presence of NiO. We examine the physical properties of a GDC-YSZ mixed phase under reducing conditions in detail regarding ionic and electronic conductivity as well as reducibility, and discuss the expected impact of cation intermixing between anode and electrolyte.

Rational Design of Superior, Coking‐Resistant, Nickel‐Based Anodes through Tailoring Interfacial Reactions for Solid Oxide Fuel Cells Operated on Methane Fuel

“…Although the addition of LW reduced the specific surface area of the anode, LW showed a better stabilizing effect than that of WO 3 because the specific surface area was almost unchanged after the reoxidation processes, whereas the surface areas of Ni‐YSZ and Ni‐YSZ‐0.42 wt % WO 3 decreased by 53 and 40 %, respectively, after the redox treatment. The elemental contents of the sample surfaces can be semiquantitatively measured by X‐ray photoelectron spectroscopy (XPS) . As shown in Table S1 in the Supporting Information, the atomic ratios of Ni metal were 56.3, 45.0, and 34.0 % for unmodified and 2 and 5 wt % LW modified Ni‐YSZ; this suggested that the addition of LW affected the Ni particle distributions in the anode, which might influence the catalytic activity of fuel electro‐oxidation and reforming reactions.…”

Tuning the Microstructure and Thickness of Ceramic Layers with Advanced Coating Technologies Using Zirconia as an Example

“…[184] Chemically, the diffusion of elements between materials in contact can lead to the formation of new phases and defects in a zone near the interface, which might result in property degradation of the layered system, as shown, for example, in the case of gadolinium-doped ceria in contact with YSZ. [185] Grain growth in YSZ mainly occurs during the final stage of sintering and is strongly dependent on the level of yttrium doping. Grain-boundary mobility in tetragonal zirconia (e.g., 2Y-TZP) is primarily controlled by the space charge segregation of cation solute, and second, by its diffusivity in the lattice.…”

“…[ 184 ] Chemically, the diffusion of elements between materials in contact can lead to the formation of new phases and defects in a zone near the interface, which might result in property degradation of the layered system, as shown, for example, in the case of gadolinium‐doped ceria in contact with YSZ. [ 185 ]…”

Impedance characterization of supported oxygen ion conducting electrolytes

“…[47,48] We recently demonstrated that integrating a NiO-GDC anode into the standard fabrication route of an anode-supported fuel cell with 8YSZ electrolyte leads to a significant loss (> 50%) of performance in cell tests, and explored possible explanations due to interdiffusion between the GDC in the anode and the 8YSZ electrolyte, mainly measured on powder mixtures. [49] Here, we apply impedance analysis of the ionic conductivity of the actual cell to quantify the effect of the interdiffusion on the ionic conductivity of the electrolyte. Figure 8 a) shows a SEM cross-section of the fractured cell after testing, with a yellow line indicating the location of the EDX line scan shown in Figure 8 b).…”

“…In contrast, the interdiffusion zone at the interface to the GDC anode is approximately 6 µm thick (dashed black box in Figure 8 b)), and a substantial amount of Ce can be found in the electrolyte, which can be explained by the high co-sintering temperature during cell manufacturing (1400 °C) and the presence of NiO in the anode, which has been shown to accelerate the interdiffusion of 8YSZ and GDC. [49] This amount of interdiffusion can be assumed to decrease the ionic conductivity of the electrolyte. [49][50][51] In order to quantify the decrease of ionic conductivity and the mechanism behind it, we performed impedance analysis on the cell after it had been tested at SOFC temperatures.…”