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Research Papers

# Curvature and Strength of Ni-YSZ Solid Oxide Half-Cells After Redox Treatments

[+] Author and Article Information
Antonin Faes

Laboratory of Industrial Energy Systems (LENI) and Interdisciplinary, Centre for Electron Microscopy (CIME), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland

Henrik Lund Frandsen, Mikko Pihlatie, Andreas Kaiser

Department of Fuel Cells and Solid State Chemistry, Risø National Laboratory, Technical University of Denmark, DK-4000 Roskilde, Denmark

Darlene R. Goldstein

Institut de Mathématiques (IMA), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland

J. Fuel Cell Sci. Technol 7(5), 051011 (Jul 19, 2010) (7 pages) doi:10.1115/1.4001019 History: Received August 14, 2009; Revised November 12, 2009; Published July 19, 2010; Online July 19, 2010

## Abstract

One of the main drawbacks of anode-supported solid oxide fuel cell technology is the limited capability to withstand reduction and oxidation (“RedOx”) of the Ni phase. This study compares the effect of RedOx cycles on curvature and strength of half-cells, composed of a nickel-yttria-stabilized-zirconia (Ni-YSZ) support, a Ni-YSZ anode, and an 8YSZ electrolyte. Five different treatments are studied: (i) reduction at $600°C$, (ii) reduction at $1000°C$, (iii) 1RedOx cycle at $750°C$, (iv) 5RedOx cycles at $750°C$, and (v) 5RedOx cycles at $600°C$. The strength is measured by the ball-on-ring method, where it is calculated analytically from the force. In this calculation the thermal stresses are estimated from the curvature of the half-cell. For each treatment, more than 30 samples are tested. About 20 ball-on-ring samples are laser cut from one original $12×12 cm2$ half-cell. Curvature and porosity are measured for each sample before and after RedOx treatments. The first observations show that increasing the reduction temperature enhance strength but does not influence the curvature, whereas 1RedOx cycle at $750°C$ increases the curvature without changing the strength. Consecutive RedOx cycles seem to decrease anode-supported cell strength but this is coupled to lower porosity of the tested samples.

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## Figures

Figure 1

Ball-on-ring setup with a sample (a) picture of the setup (without the testing machine) and (b) dimension of the setup (F is the load, a is the radius of the ring, b is the radius of the ball and R is the radius of the disk, and σr and σθ are the radial and tangential stresses, respectively)

Figure 2

Total porosity of sample in the as-sintered and reduced state for the different cells and different treatments

Figure 3

Scheme of cell curvature (curvature: κ=R−1)

Figure 4

Curvature measurements for the samples in the as-sintered state and after treatments for the different cells and different treatments

Figure 5

Weibull distribution for the different treatments (21)

Figure 6

Strength measurements for the samples after treatments for the different cells and different treatments

Figure 7

Variation in cell curvature and anode bottom stress for a load of 35 N depending on (a) the reference temperature (Tref), (b) the electrolyte thickness (he), and (c) the anode support Young’s modulus (Ea)

Figure 8

Qualitative curvature variation between Cell2 (left) and Cell8 after 5RedOx cycles at 750°C (electrolyte down)

Figure 9

Electrolyte of half-cell after 5RedOx cycles at 750°C at same magnification from (a) Cell2 and (b) Cell8; marker length is 1 mm

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