Coke and sulfur resistant solid oxide fuel cells: development, test and novel applications

  • Author / Creator
    Yan, Ning
  • Solid oxide fuel cells (SOFC) can be fuelled with external-reformed natural gas or directly with raw natural gas which usually contains significant amount of H2S to reduce the system complexity. The anode catalyst as well as the current collector employed in those environments must have excellent coke and sulfur resistances in addition to the general requirements. The coke-sulfur tolerant SOFC serving as a reactor could co-generate power and value-added chemical products, which promises to drastically minimize the energy waste and increase the efficiency. To address the coking issues in fuel cells fed by syngas or pretreated natural gas, Ni-P coated Ni foam is fabricated via electroless plating as the coke resistant current collector. The coated Ni foam with a surface composition of Ni3P + Ni (P > 6.5 wt%) exhibits excellent coking resistance in 24 h treatment in syngas at 750 oC and an essentially identical current collecting capability during the fuel cells application test. The developed Ni-Sx catalyst obtained through in-situ H2S passivation shows superior balance between high activity and good carbon resistance during 200 h test in dry syngas. The discovered H2 selective oxidation effect using this catalyst has been employed in the novel application of SOFC. To deal with the coking and sulfur deactivation issues in SOFC fuelled directly by sour natural gas with H2S concentration up to 0.5%, a Pd-CeO2/La0.3Sr0.7O3-δ composite anode catalyst has been studied and is applied to the fuel cells via infiltration method. Maximum power densities of 642 mW cm-2 and 274 mW cm-2 have been achieved in H2 and in 0.5% H2S + CH4 at 850 oC, respectively. The Pd particles catalyze the electrochemical conversion of the fuels and are proved to be thermodynamically stable, whereas CeO2 promotes their thermal stability on the electrolyte matrix. The electronically conductive titanate can also serve as the current collecting material in sour natural gas. In the application of the coke/sulfur tolerant fuel cells for the co-generation of electricity and CO from syngas, the developed proton-conduction SOFC is able to reach a maximum power density of 812 mW cm-2 at 750 oC and up to 23.4 % H2 is removed in the stream without oxidizing CO. Novel H2 electrocatalytic selective oxidation in syngas using O-2-conducting SOFC is also studied. The Ni-S anode catalyst shows up to 92% H2 selectivity through selective surface diffusion mechanism in 10% H2 + CO.

  • Subjects / Keywords
  • Graduation date
    Spring 2014
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.