Abstract
This paper addresses the damage behaviour of a nickel/yttria-stabilised zirconia (Ni-YSZ) anode, in order to understand microstructural degradation processes of Solid Oxide Fuel Cells (SOFCs) during long-term operation. Numerical investigations are carried out to analyse the failure mechanisms in detail. For this purpose, finite element (FE) models are generated from focused ion beam-scanning electron microscopy 3D image data, representing the anode microstructure with varying phase compositions. A brittle model and a ductile material model were assigned to the YSZ phase and the nickel phase, respectively. The porosity is found to affect the strength of the microstructure significantly, leading to low compressive strength results. A high Ni content generally increases the toughness of the overall structure. However, the orientation and the geometry of the nickel phase is essential. When the Ni phase is aligned parallel to the loading direction, a supporting effect on the microstructure is observed, resulting in a significant high toughness. On the contrary, a rapid failure of the sample occurs when the Ni phase is oriented perpendicular to the loading direction. Two main failure mechanisms are identified: (i) cracking at the Ni/YSZ interface and (ii) cracking of struts at the location of the smallest diameter.
Highlights
Solid Oxide Fuel Cells (SOFCs) directly convert the chemical energy stored in fuels, such as hydrogen or gaseous hydrocarbons, into electrical power and thermal energy through electrochemical reactions
The five presented models were examined in the x, y, and z directions by compression tests to verify if effective anisotropic material behaviour exists
In order to investigate the damage of the Ni/YSZ ratio of 40:60 (Ni) and yttria-stabilised zirconia (YSZ) phase and the corresponding influence of the microstructure morphology, the shape of the stress–strain curves of models tested in the x direction is correlated to single events during testing
Summary
Solid Oxide Fuel Cells (SOFCs) directly convert the chemical energy stored in fuels, such as hydrogen or gaseous hydrocarbons, into electrical power and thermal energy through electrochemical reactions. In terms of energy conversion, fuel flexibility, and low CO2 emissions, when running on hydrocarbons, represent key benefits of an SOFC for mobile or stationary applications. A planar SOFC consists of two porous ceramic electrodes providing a large inner surface with a huge amount of reactive sites for the fuel and the oxygen, separated by a gas-tight solid oxide electrolyte layer. At the interface of the electrolyte and anode layer, the TEC difference results in residual stresses, which can lead to low reliability during cell operation and can cause cell failure [1,2]
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