A high-performance cathode for the next generation of solid-oxide fuel cells

Abstract

Fuel cells directly and efficiently convert chemical energy to electrical energy1. Of the various fuel cell types, solid-oxide fuel cells (SOFCs) combine the benefits of environmentally benign power generation with fuel flexibility. However, the necessity for high operating temperatures (800–1,000 °C) has resulted in high costs and materials compatibility challenges2. As a consequence, significant effort has been devoted to the development of intermediate-temperature (500–700 °C) SOFCs. A key obstacle to reduced-temperature operation of SOFCs is the poor activity of traditional cathode materials for electrochemical reduction of oxygen in this temperature regime2. Here we present Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF) as a new cathode material for reduced-temperature SOFC operation. BSCF, incorporated into a thin-film doped ceria fuel cell, exhibits high power densities (1,010 mW cm-2 and 402 mW cm-2 at 600 °C and 500 °C, respectively) when operated with humidified hydrogen as the fuel and air as the cathode gas. We further demonstrate that BSCF is ideally suited to ‘single-chamber’ fuel-cell operation, where anode and cathode reactions take place within the same physical chamber3. The high power output of BSCF cathodes results from the high rate of oxygen diffusion through the material. By enabling operation at reduced temperatures, BSCF cathodes may result in widespread practical implementation of SOFCs.

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Figure 1: The area specific resistance (ASR) of the cathode material BSCF under air, measured both with (three-electrode, half cell) and without (two-electrode, symmetric cell) a reference electrode.
Figure 2: Performance obtained from a Ba0.5Sr0.5Co0.8Fe0.2O3-δ ( 20 µm)|Sm0.15Ce0.85O2-δ ( 20 µm)|Ni + Sm0.15Ce0.85O2-δ ( 700 µm) fuel cell.
Figure 3: Cell voltage and power density as functions of current density obtained in single-chamber mode from a Ba0.5Sr0.5Co0.8Fe0.2O3-δ + Sm0.15Ce0.85O2-δ ( 20 µm)|Sm0.15Ce0.85O2-δ ( 20 µm)|Ni + Sm0.15Ce0.85O2-δ ( 700 µm) fuel cell.
Figure 4: Comparison of the catalytic activities of BSCF (Ba0.5Sr0.5Co0.8Fe0.2O3-δ), SSC (Sm0.5Sr0.5CoO3-δ), and LSCF (La0.6Sr0.4Co0.2Fe0.8O3-δ) oxides towards propane oxidation under stoichiometric conditions.

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Acknowledgements

This work was funded by the Defense Advanced Research Projects Agency, Microsystems Technology Office. Additional support was provided by the National Science Foundation through the Caltech Center for the Science and Engineering of Materials. Selected oxygen permeability measurements were carried out in the Laboratory of Reaction Engineering and Energy, Institute of Research on Catalysis, CNRS, France, during the visit of Z.P.S. there, hosted by C. Mirodatos.

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Correspondence to Sossina M. Haile.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Figure 1

The general operation principle of a single-chamber fuel cell using an oxygen ionic conducting electrolyte. (PDF 27 kb)

Supplementary Figure 2

Crystal structure and phase stability of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF). (PDF 51 kb)

Supplementary Figure 3

The performance of silver alone as a cathode for Ce0.85Sm0.15O2-δ (SDC) based fuel cells. (PDF 28 kb)

Supplementary Figure 4

Electrochemical behaviour of an anode supported fuel cell with Sm0.5Sr0.5CoO3-δ + Ce0.85Sm0.15O2-δ (70:30%wt.) as the cathode with 3% H2O + H2 supplied to the anode and air supplied to the cathode. (PDF 53 kb)

Supplementary Figure 5

Analysis of the contributions to the polarization drops across a Ni + SDC (700 µm) | SDC (20 µm) | BSCF (20 µm) fuel cell operated in dual chamber mode. (PDF 36 kb)

Supplementary Figure 6

The difference between fuel cell temperature and furnace temperature in single chamber configuration using propane+oxygen mixture as feed gas. (PDF 19 kb)

Supplementary Figure 7

Oxygen permeability measurement of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) membrane by gas chromatography method. (PDF 24 kb)

Supplementary Figure 8

Measurement of oxygen vacancy diffusion coefficient, DV, and oxygen surface exchange coefficient, ka, from oxygen permeation studies and detailed modelling of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF). (PDF 46 kb)

Supplementary Figure 9

Activation energy for oxygen transportation through Ba0.5Sr0.5Co0.8Fe0.2O3-d dense membranes based simply on oxygen permeation data. (PDF 14 kb)

Supplementary Figure 10

Influence of CO2 and H2O on the area specific resistance of the Ba0.5Sr0.5Co0.8Fe0.2O3-δ cathode. (PDF 42 kb)

Supplementary Figure 11

Influence of cathode thickness and fabrication methods on the area specific resistivity of the Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) cathode. (PDF 25 kb)

Supplementary Figure 12

Long term performance of fuel cells using a Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) based cathode. (PDF 20 kb)

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Shao, Z., Haile, S. A high-performance cathode for the next generation of solid-oxide fuel cells. Nature 431, 170–173 (2004). https://doi.org/10.1038/nature02863

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