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Research Papers

Performances and Degradation Phenomena of Solid Oxide Anode Supported Cells With LSM and LSCF Cathodes: An Experimental Assessment

[+] Author and Article Information
A. Lanzini, P. Leone, M. Santarelli, P. Asinari, M. Calì, R. Borchiellini

Dipartimento di Energetica, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy

J. Fuel Cell Sci. Technol 6(1), 011020 (Nov 25, 2008) (14 pages) doi:10.1115/1.2971128 History: Received June 14, 2007; Revised April 17, 2008; Published November 25, 2008

Abstract

The performance of solid oxide fuel cells is affected by various polarization losses, usually grouped in Ohmic, activation, and concentration polarizations. Under typical operating conditions, these polarization losses are largely dependent on cell materials, electrode microstructures, and cell geometry: as an example, the performance of a tubular cell is strongly limited by the Ohmic polarization due to the long current path of electrons, while in a planar cell each of these losses has a comparable effect. It is therefore of interest, in the case of planar geometry, to investigate the main performance limiting factors. In this paper, a performance evaluation of planar circular-shaped seal-less SOFC cells was performed. Two different designs of planar cells are considered. Both have a porous NiO-YSZ (yttria stabilized zirconia) anode as mechanical support, a NiO-YSZ anode active layer, and an YSZ electrolyte, and they only differ in the cathode design: (1) strontium doped lanthanum manganate (LSM)-YSZ cathode functional layer and LSM cathode current collector layer; (2) yttria doped ceria blocking layer and lanthanum strontium cobalt ferrite oxide (LSCF) functional layer. The characterization was performed by taking $V-I$ measurements over a range of temperatures between $650°C$ and $840°C$ with hydrogen as fuel and air as oxidant. The experimental data analysis consisted in the analysis of some typical performance indicators (maximum power density (MPD); current density at $0.7V$). The dependence of the cell performance on the various polarization contributions was rationalized on the basis of an analytical model—through a parameter estimation of the experimental data—devoted to the determination of the main polarization losses. Based on the results of the investigation, it is concluded that LSCF cathodes are really effective in decreasing the cathode activation polarization, allowing the reduction in operating temperature.

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Figures

Figure 1

Picture of the single-cell SOFC laboratory in Torino

Figure 2

Microscopic morphology of the ASC1 cell by means of optical microscopy

Figure 3

Microscopic morphology of the ASC2 cell by means of optical microscopy

Figure 4

Power-generating characteristics of unit-cells; anode supported cell with the YSZ/LSM cathode (ASC1) at 740°C

Figure 5

Power-generating characteristics of unit-cells; anode supported cell with the YSZ/LSM cathode (ASC1) at 800°C

Figure 6

Power-generating characteristics of unit-cells; anode supported cell with the YSZ/LSM cathode (ASC1) at 840°C

Figure 7

Power-generating characteristics of unit-cells; anode supported cell with the YDC/LSCFs cathode (ASC2) at 650°C

Figure 8

Power-generating characteristics of unit-cells; anode supported cell with the YDC/LSCF cathode (ASC2) at 740°C

Figure 9

Power-generating characteristics of unit-cells; anode supported cell with the YDC/LSCF cathode (ASC2) at 800°C

Figure 10

Power-generating characteristics of unit-cells; anode supported cell with the YDC/LSCF cathode (ASC2) at 840°C

Figure 11

Polarization curves of ASC2 after thermal cycling

Figure 12

Apparatus load to estimate Young’s modulus of anode supported cell

Figure 13

Comparison of deformation curves between unreduced and reduced ASC2 cells

Figure 14

Optical cross-sectional view of a reduced ASC2 anode (white: Ni, gray: YSZ, black: pores)

Figure 15

SEM images relative to the delamination of the cathode electrode from the YDC protective layer (SE image); from left to right: LSCF cathode, YDC interlayer, YSZ electrolyte, and Ni-YSZ anode

Figure 16

Experimental versus model behavior of anode supported cells ASC1 and ASC2

Figure 17

Comparison of ASC1 and ASC2 performances

Figure 18

Comparison of cell performances in terms of temperature effect and fuel utilization effect

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