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Research Papers

Impact of Cofiring Ceria in Ni/YSZ SOFC Anodes for Operation With Syngas and n-Butane

[+] Author and Article Information
Siddharth Patel, Paul F. Jawlik, Lei Wang

Department of Mechanical Engineering,  University of Maryland, College Park, MD 20742

Gregory S. Jackson1

Department of Mechanical Engineering,  University of Maryland, College Park, MD 20742gsjackso@umd.edu

Ali Almansoori

Department of Chemical Engineering,  The Petroleum Institute, Abu Dhabi, United Arab Emirates

1

Corresponding author.

J. Fuel Cell Sci. Technol 9(4), 041002 (Jun 14, 2012) (7 pages) doi:10.1115/1.4006823 History: Received November 27, 2011; Revised May 03, 2012; Published June 14, 2012; Online June 14, 2012

This study explores cofiring ceria (CeO2 ) with NiO and 8 mol% yttria-stabilized zirconia (YSZ) to form Ni-based cermet anodes for high-temperature solid oxide fuel cells (SOFCs) operating on syngas and n-butane/steam fuel feeds. Particular attention is paid to the suppression of carbon deposit growth in Ni-based anodes with carbonaceous fuel feeds. CeO2 was cofired with NiO and YSZ to form a porous Ni cermet anode support layer after reduction in H2 at 800°C. The porous anode support layer (1 mm thick) was combined with a Ni/YSZ functional layer (∼25 μm thick), a dense YSZ electrolyte (10–20 μm thick), and porous La0.8 Sr0.2 MnO3−x (LSM)/YSZ cathodes (∼50 μm thick) to form anode-supported button cells for electrochemical characterization. The button cells were tested from 700 °C to 800 °C on various fuels including syngas and n-butane/H2 O mixtures at steam-to-carbon (S/C) ratios of 1.0 and 1.5. Electrochemical testing revealed that CeO2 addition provided stable performance at 800 °C without compromising power densities—up to 0.6 W/cm2 on syngas and 0.35 W/cm2 on direct butane feeds. Furthermore, the addition of CeO2 suppressed significant carbon deposition as observed for Ni/YSZ anode support layers without CeO2 . Testing with syngas at different H2 and CO partial pressures indicated that high power densities can be maintained along an anode channel for up to 50% fuel conversion. The results indicate that cofiring CeO2 in Ni/YSZ anode support layers presents a viable option for stable SOFC operation on either prereformed or internally reformed light-hydrocarbon fuel feeds.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Post-testing SEM images of microstructure for an MEA operated on hydrogen, syngas, and butane: (a) anode/electrolyte interface with Ni/YSZ functional layer and Ni/CeO2 /YSZ support layer (entire 1 mm thickness not shown) and (b) cathode/electrolyte interface with LSM/YSZ functional layer and LSM current collecting layer

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Figure 2

XRD pattern obtained at 25 °C from the anode support layer for Ni/CeO2 /YSZ cell after sintering it at 1450 °C

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Figure 3

Voltage and power density versus current density curves for Ni/CeO2 /YSZ anode-supported thin-electrolyte MEAs (a) operating on 0% conversion syngas for a range of Tcell and (b) operating at Tcell  = 800 °C for a range of syngas conversions (as indicated in Table 1)

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Figure 4

Comparison of voltage and power density versus current density curves for Ni/CeO2 /YSZ and Ni/YSZ anode-supported MEAs with 20 μm thick electrolytes—operating on 0% conversion syngas at Tcell  = 800 °C

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Figure 5

Electrochemical impedance spectra at 300 mV total cell overpotential for the following tests: a Ni/YSZ cell with syngas feed at 0% conversion, a Ni/CeO2 /YSZ cell operating on syngas at 0% conversion, and a Ni/CeO2 /YSZ cell operating on n-butane with a steam-to-carbon ratio of 1.5. Points at frequencies of 500 Hz and 10 Hz for both fuel types are indicated by arrows on the plot. Electrolytes for both cells were approximately 20 μm thick.

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Figure 6

Voltage and power density versus current density curves for Ni/CeO2 /YSZ anode-supported thin-electrolyte MEA operating at two Tcell on an n-butane feed with a steam-to-carbon ratio of 1.5

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Figure 7

Voltage and power density versus current density for Ni/CeO2 /YSZ and Ni/YSZ anode-supported MEAs with electrolyte thicknesses of ∼20 μm. Testing was performed with n-butane feeds at (a) Tcell  = 800 °C and S/C = 1.0 and (b) Tcell  = 800 °C and S/C = 1.5.

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Figure 8

Cyclic ramping of Ni/CeO2 /YSZ MEA with 20 μm thick electrolyte operating at Tcell  = 800 °C on an n-butane feed with a S/C = 1.5

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Figure 9

Photographic images of Ni/CeO2 /YSZ and Ni/YSZ anode support layer after exposing the cells for over 45 h (Ni/CeO2 /YSZ) and over 20 h (Ni/YSZ) under steam reformed butane at S/C = 1.5

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Figure 10

EDX line scan for C, Ni, and Y for outermost 200 μm of anode functional layer in a Ni/CeO2 /YSZ after testing for several days at Tcell  = 800 °C on syngas and on an n-butane feed with a S/C = 1.5

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