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Permanent link (DOI): https://doi.org/10.7939/R36W8Q
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Anode materials for sour natrual gas solid oxide fuel cells Open Access
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- Type of item
- Degree grantor
University of Alberta
- Author or creator
- Supervisor and department
Chuang, Karl (Chemical and Materials Engineering)
Luo, Jingli (Chemical and Materials Engineering)
- Examining committee member and department
Etsell, Tom (Chemical and Materials Engineering)
Bergens, Steven (Chemistry)
Vohs, John (Chemical and Biomolecular Engineering, University of Pennsylvania)
Department of Chemical and Materials Engineering
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- Graduation date
Doctor of Philosophy
- Degree level
Novel anode catalysts have been developed for sour natural gas solid oxide fuel cell (SOFC) applications. Sour natural gas comprises light hydrocarbons, and typically also contains H2S. An alternative fuel SOFC that operates directly on sour natural gas would reduce the overall cost of plant construction and operation for fuel cell power generation. The anode for such a fuel cell must have good catalytic and electrocatalytic activity for hydrocarbon conversion, sulfur-tolerance, resistance to coking, and good electronic and ionic conductivity.
The catalytic activity and stability of ABO3 (A= La, Ce and/or Sr, B=Cr and one or more of Ti, V, Cr, Fe, Mn, or Co) perovskites as SOFC anode materials depends on both A and B, and are modiﬁed by substituents. The materials have been prepared by both solid state and wet-chemical methods. The physical and chemical characteristics of the materials have been fully characterized using electron microscopy, XRD, calorimetry, dilatometry, particle size and area, using XPS and TGA-DSC-MS. Electrochemical performance was determined using potentiodynamic and potentiostatic cell testing, electrochemical impedance analysis, and conductivity measurements.
Neither Ce0.9Sr0.1VO3 nor Ce0.9Sr0.1Cr0.5V0.5O3 was an active anode for oxidation of H2 and CH4 fuels. However, active catalysts comprising Ce0.9Sr0.1V(O,S)3 and Ce0.9Sr0.1Cr0.5V0.5(O,S)3 were formed when small concentrations of H2S were present in the fuels. The oxysulﬁdes formed in-situ were very active for conversion of H2S. The maximum performance improved from 50 mW cm−2 to 85 mW cm−2 in 0.5% H2S/CH4 at 850 oC with partial substitution of V by Cr in Ce0.9Sr0.1V(O,S)3 . Selective conversion of H2S offers potential for sweetening of sour gas without affecting the hydrocarbons.
Perovskites La0.75Sr0.25Cr0.5X0.5O3−δ, (henceforth referred to as LSCX, X=Ti, Mn, Fe, Co) are active for conversion of H2, CH4 and 0.5% H2S/CH4. The order of activity in the different fuels depends on the substituent element: CH4, X=Fe>Mn>Ti; H2,X = Fe>Mn>Ti; and 0.5% H2S/CH4, X = Fe>Ti>Mn. The electrocatalytic activity for methane oxidation in a fuel cell correlates with ex-situ temperature programmed catalytic activity. A process is proposed to explain the difference in catalyst order and enhanced activities in H2S/CH4 as fuel compared to CH4 alone. The maximum power density of 250 mW cm−2 was attained using a fuel cell with a composite anode, LSCFe-GDC | YSZ(0.3 mm) | Pt, operated at 850 oC (GDC is Ce0.9Gd0.1O3, a good mixed conductor under reducing conditions).
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