Anode materials for H2S containing feeds in a solid oxide fuel cell

• Author / Creator

  Roushanafshar, Milad

• SOFCs which can directly operate under high concentration of H2S would be economically beneficial as this reduces the cost of gas purification. H2S is highly reactive gas specie which can poison most of the conventional catalysts. As a result, developing anode materials which can tolerate high concentrations of H2S and also display high activity toward electrochemical oxidation of feed is crucial and challenging for this application. The performance of La0.4Sr0.6TiO3±δ-Y0.2Ce0.8O2-δ (LST-YDC) composite anodes in solid oxide fuel cells significantly improved when 0.5% H2S was present in syngas (40% H2, 60% CO) or hydrogen. Gas chromatography and mass spectrometry analyses revealed that the rate of electrochemical oxidation of all fuel components improved when H2S containing syngas was present in the fuel. Electrochemical stability tests performed under potentiostatic condition showed that there was no power degradation for different feeds, and that there was power enhancement when 0.5% H2S was present in various feeds. The mechanism of performance improvement by H2S was discussed. Active anodes were synthesized via wet chemical impregnation of different amounts of La0.4Ce0.6O1.8 (LDC) and La0.4Sr0.6TiO3 (L4ST) into porous yttria-stabilized zirconia (YSZ). Co-impregnation of LDC with LS4T significantly improved the performance of the cell from 48 mW.cm-2 (L4ST) to 161 mW.cm-2 (LDC-L4ST) using hydrogen as fuel at 900 °C. The contribution of LDC to this improvement was investigated using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM). EIS measurements using symmetrical cells showed that the polarization resistance decreased from 3.1 Ω.cm2 to 0.5 Ω.cm2 when LDC was co-impregnated with LST, characterized in humidified H2 (3% H2O) at 900 °C. In addition, the microstructure of the cell was modified when LDC was impregnated prior to L4ST into the porous YSZ. TEM and SEM results showed that the L4ST particles were finely distributed into the anode structure in the presence of LDC when compared to the L4ST alone. The rate of electrochemical oxidation of H2 and CH4 feeds over L0.4Sr0.6TiO3±δ and La0.4Ce0.6O1.8-La0.4Sr0.6TiO3±δ impregnated solid oxide fuel cell anodes increased significantly when H2S (0.5%) was present. There was recovery of the fuel cell under galvanostatic conditions at 40 mA.cm-2 and 800 °C in both H2S (0.5%)-H2 and H2S (0.5%)-CH4 after switching to H2 as fuel. Mass spectrometry analysis revealed the effect of H2S (0.5%) on the enhancement of CH4 electrochemical oxidation.

• Subjects / Keywords

  • Solid oxide fuel cells
  • Impregnation
  • Methane
  • Syngas
  • Hydrogen sulfide
  • Anode materials

• Graduation date

  Spring 2013

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3HW6R

• 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.