The Application Of Perovskite La_0.8Sr_0.2Cr_0.5Fe_0.5O_3-δ Materials In Solid Oxide Fuel Cells

This thesis focused on the development of new materials with high performance and the improvement of the traditional manufacturing processes for solid oxide fuel cells(SOFCs).Firstly, a series of La0.8Sr0.2Cr1-xFexO3-δ(x=0.1, 0.2, 0.3, 0.4, and 0.5) perovskite oxides, were synthesised and evaluated as potential interconnect materials for SOFCs. “A modified liquid-phase-assisted sintering mechanism” was employed to improve the sintering abilities of La0.8Sr0.2Cr1-xFexO3-δ powders. After sintering in air at 1400 °C for 4 h, relative densities of 94.6 % and 96.6 % were successfully obtained for La0.8Sr0.2Cr0.6Fe0.4O3-δ and La0.8Sr0.2Cr0.5Fe0.5O3-δ, respectively. Furthermore, these compounds were also chemically stable under SOFC operating conditions. The electrical conductivity increased with Fe-doping levels, and the conductivity of La0.8Sr0.2Cr0.5Fe0.5O3-δ was measured to be 21.88 S cm-1 in air and 6.45 S cm-1 in 5 % H2/Ar at 800 °C. Therefore, dense La0.8Sr0.2Cr0.5Fe0.5O3-δ is a promising interconnect alternative for solid oxide fuel cells.Secondly, this paper discusses how to fabricate a dense La0.8Sr0.2Cr0.5Fe0.5O3-δ interconnect membrane on Ni O-YSZ anode substrate for tubular solid oxide fuel cell(SOFC) applications by one-step dip-coating, and co-sintering of the ceramic interconnect with the anode. It can be concluded that after being co-sintered at 1400 °C, a dense La0.8Sr0.2Cr0.5Fe0.5O3-δ ceramic interconnect membrane can be successfully prepared on the anode support of Ni O–YSZ by a dipcoating process.Lastly, an all-perovskite SOFC based on nano La0.8Sr0.2Cr0.5Fe0.5O3-δ anode, La0.9Sr0.1Ga0.8Mg0.2O2.85 electrolyte and nano La Ni0.6Fe0.4O3 cathode was fabricated. The main results are as follows: When the cell was fed with hydrogen, at 700, 750 and 800 °C, the ohmic resistances were 0.23, 0.12 and 0.09 ohm cm2, respectively, the polarization resistances were 0.44, 0.25 and 0.18 ohm cm2, respectively, the maximum power densities were 524, 756 and 846 m W cm-2, respectively. When the fuel was switched from hydrogen to methane, at 800 and 850 °C, the ohmic resistances were 0.19 and 0.17 ohm cm2, respectively, the polarization resistances were 0.75 and 0.44 ohm cm2, respectively, the maximum power densities were 117 and 245 m W cm-2, respectively. The resistances of this cell were lower than the resistances given in the relevant references and the maximum power densities of our cell were compare favorably with the SOFCs with similar structures reported in the literature. What’s more, during a stability test in hydrogen under a current loading of 850 m A cm-2, the power density of the cell could almost stable for over 100 h.