Refractory Cathode Investigation for Single-Step Co-Fired Solid Oxide Fuel Cells (SOFCs)
- PDF / 168,308 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 120 Downloads / 212 Views
0972-AA03-12
Refractory Cathode Investigation for Single-Step Co-Fired Solid Oxide Fuel Cells (SOFCs) Peter A. Zink1, Kyung Joong Yoon1, Wenhua Huang1, Srikanth Gopalan1, Uday B. Pal1, and Donald A. Seccombe, Jr., PE2 1 Manufacturing Engineering, Boston University, 15 Saint Mary's Street, Brookline, MA, 02446 2 BTU International, 23 Esquire Road, North Billerica, MA, 01862
ABSTRACT A single step co-firing process for fabricating planar solid oxide fuel cells (SOFCs) requires refractory electrodes to prevent excessive sintering of the electrode while facilitating full-density sintering of the electrolyte. Single cell current-potential curves and impedance measurements indicate that the majority of the performance losses occur in the cathode and are due to activation polarization. A-site deficient calcium and cerium doped lanthanum ferrite cathode powders were synthesized and investigated as possible refractory cathode materials with low activation polarization losses. Four-probe conductivity measurements indicated that all compositions were suitable as cathodes. However, reactivity with YSZ reduced the conductivity by as much as two orders of magnitude, too low for use as a cathode. These refractory cathode compositions could be effective if a suitable barrier layer is applied to prevent reaction with YSZ. For instance, it is well known that at elevated temperatures, perovskite cathode materials tend to react with YSZ electrolyte and form an insulating phase [1,2]. Future experiments will investigate the applicability of a doped-ceria barrier layer to prevent reaction between the lanthanum ferrite cathode layer and the YSZ electrolyte layer. INTRODUCTION Complete single-cell SOFCs with YSZ and ScSZ electrolytes were manufactured with the single step co-firing process.[3] SOFCs made with either the ScSZ or YSZ electrolyte and Ni-stabilized zirconia cermet anode and lanthanum manganite-based cathode materials showed virtually no difference in electrical performance at intermediate temperatures (600-800°C), as shown in figure 1a. Analytical investigation and cell polarization loss modeling indicated that the limits on cell performance were not due to the electrolyte, but due to polarization resistance in the electrode, as shown in figure 1b. The cathode activation polarization loss contributed significantly to the overall polarization loss.
1.2
0.8
0.8
0.5
0.6
0.4 0.3
0.4 ScSZ electrolyte YSZ electrolyte 0
0.2 0.1 0
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 Current Density (A/cm2)
Figure 1a. Current-potential curves
1 Voltage (V)
0.6 Voltage (V)
Ohmic Loss (Electrolyte) Power Density (W/cm2)
1
0.2
1.2
0.7
Ohmic Loss (Electrode)
0.8
Activation Polarization (Cathode)
0.6
Concentration Polarization (Cathode) Concentration Polarization (Anode)
0.4 0.2 0 0
1
2
3
4
5
Current Density (A/cm2)
Figure 1b. Cell polarization loss model
To lower the activation polarization resistance of the cathode, A-site deficient lanthanum ferrite cathode materials doped with calcium and cerium were synthesized to dete
Data Loading...
