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Research Papers

Evaluation of Bi2V0.9Cu0.1O5.35—an Aurivillius-Type Conducting Oxide—as a Cathode Material for Single-Chamber Solid-Oxide Fuel Cells

[+] Author and Article Information
Zongping Shao1

Materials Science, California Institute of Technology, Pasadena, CA 91125

Jennifer Mederos

Materials Science, California Institute of Technology, Pasadena, CA 91125

Chan Kwak2

Materials Science, California Institute of Technology, Pasadena, CA 91125

Sossina M. Haile3

Materials Science, California Institute of Technology, Pasadena, CA 91125smhaile@caltech.edu

1

Present address: College of Chemistry and Chemical Engineering, Nanjing University of Technology, PR China.

2

Present address: Samsung SDI, Corp. R&D, Shin Dong 575, Gyeonggi Do 443731, South Korea.

3

Corresponding author.

J. Fuel Cell Sci. Technol 7(2), 021016 (Jan 12, 2010) (8 pages) doi:10.1115/1.3182729 History: Received May 08, 2008; Revised February 03, 2009; Published January 12, 2010; Online January 12, 2010

The compound Bi2V0.9Cu0.1O5.35, a typical Aurivillius-type fast oxygen ion conductor, was evaluated as a possible cathode material for single-chamber solid-oxide fuel cells operated under mixed propane and oxygen. The material was found to be structurally stable under various C3H8+O2 environments over a wide temperature range and furthermore displayed low catalytic activity for propane oxidation. However, at temperatures above 650°C, detrimental reactions between the cathode and the ceria electrolyte occurred, producing low conductivity interfacial phases. At these high temperatures the cathode additionally underwent extensive sintering and loss of porosity and, thus, stable fuel cell operation was limited to furnace temperatures of <600°C. Even under such conditions, however, the partial oxidation occurring at the anode (a ceria nickel cermet) resulted in cell temperatures as much as 70110°C higher than the gas-phase temperature. This explains the sharp decrease in fuel cell performance with time during operation at a furnace temperature of 586°C. Under optimized conditions, a peak power density of 60mW/cm2 was obtained, which does not compete with recent values obtained from higher activity cathodes. Thus, the poor electrochemical activity of Bi2V0.9Cu0.1O5.35, combined with its chemical instability at higher temperatures, discourages further consideration of this material as a cathode in single-chamber fuel cells.

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Figures

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Figure 1

X-ray diffraction patterns of Bi2V0.9Cu0.1O5.35 oxide (obtained from the EDTA-complexing method) after treatment under various conditions: (a) after calcination at 700°C for 6 h in air; (b) powder (a) after 6 h exposure to 10 ml/min C3H8+30 ml/min O2+120 ml/min He at the temperatures indicated; (c) powder (a) after 6 h exposure at 700°C to a gas stream with the propane-to-oxygen ratio as indicated and fixed propane and helium flow rates of 10 ml/min and 120 ml/min, respectively; and (d) mixtures of 50 wt % SDC+50 wt %Bi2V0.9Cu0.1O5.35 after a 6 h anneal under air at the temperatures indicated

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Figure 2

The temperature dependence of the catalytic activity of Bi2V0.9Cu0.1O5.35 for propane oxidation, as measured using 0.3 g of catalyst under C3H8:1 ml/min, O2:5 ml/min, He:120 ml/min: (a) propane and oxygen conversion with and without the catalyst, (b) yield of carbon based products obtained over the catalyst, and (c) without the catalyst

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Figure 3

Scanning electron micrographs showing (a) the cross section of the as-fabricated complete fuel cell (fired at 600°C, 6 h) and the surface morphologies of the cathode after firing for 6 h at (b) 600°C, (c) 650°C, (d) 700°C, and (e) 800°C

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Figure 4

Fuel cell performance as function of time for a gas stream temperature of 587°C under a gas stream of C3H8:10 ml/min, O2:40 ml/min, and He:120 ml/min

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Figure 5

The fuel cell performance at a gas-phase temperature of 514°C and a propane flow rate of C3H8:10 ml/min, an O2 flow rate as indicated (24–36 ml/min), and a He flow rate five times that of the oxygen flow rate (120–180 ml/min): (a) polarization curves and (b) open circuit voltage and peak power density as functions of the oxygen flow rate

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Figure 6

Temperature dependence (gas-phase temperature) of the optimal oxygen-to-propane ratio at a constant propane flow rate of 10 ml/min and a helium flow rate five times that of the oxygen flow rate

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Figure 7

Cell temperature (at open circuit) as a function of oxygen-to-propane molar ratio at selected gas stream temperatures. Propane flow rate fixed at 10 ml/min, oxygen flow rate varied from 24 ml/min to 36 ml/min, and helium flow rate set to five times that of the oxygen.

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Figure 8

Expected carbon yields under thermodynamic equilibrium for indicated oxygen-to-propane ratios in the feed gas

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