Effect of A/B‐Site Non‐stoichiometry on the Structure and Properties of La_0.9Sr_0.1Ga_0.9Mg_0.1O_3−δ Solid Electrolyte in Intermediate‐Temperature Solid Oxide Fuel Cells

Abstract

La 0.9 Sr 0.1 ) x (Ga 0.9 Mg 0.1 ) y O 3-d [(LS) x (GM) y ] (x = 0.97, 1.00, 1.03; y = 1.00 and x = 1.00; y = 0.97, 1.00, 1.03) electrolyte is prepared through a sol-gel method followed by sintering at 1300 8C for 10 h. The microstructures of the samples are characterized by using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The electrical and thermal stability properties are measured by means of electrochemical impedance spectroscopy (EIS) and thermal expansion coefficient (TEC), respectively. It is shown that phase purity could improve by adjusting the non-stoichiometry of A/B-site. This, in turn, affects the conductivity and thermal expansion of the solid electrolyte. The samples with B-site defects [LS(GM) 0.97 ] are found to exhibit the best phase purity and density with minimal grain boundary/total resistances, and superior thermal stability. The conductivity of LS(GM) 0.97 is 1.56 time higher than that of LSGM. The average thermal expansion coefficient of LS(GM) 0.97 at 50-850 8C is 4.13 % lower than that of LSGM. The maximum power density of single cells containing LS(GM) 0.97 electrolyte could reach 0.54 W cm À1 at 800 8C, which is 16.7 % higher than that of cells containing LSGM electrolyte. The stability test for over 120 h at 800 8C indicates a slight decrease in performances during the first 10 h, but no significant differences in electrode polarization are observed even after long-term operation. These findings suggest the potential applications of LS(GM) 0.97 as a novel electrolyte for intermediate-temperature solid oxide fuel cells.[a] J.

Recent Progress in the Design, Characterisation and Application of LaAlO3- and LaGaO3-Based Solid Oxide Fuel Cell Electrolytes

“…These data testify that enhanced power densities were achieved for electrolyte-supported SOFCs when the LSGM electrolyte thickness was in a range of 100-300 µm. Buffer layers of doped ceria were used between the electrolyte and anode: Ce 0.8 Sm 0.2 O 2−δ [144,145,149,155,160,167], Ce 0.8 Gd 0.2 O 2−δ [170] and Ce 0.6 La 0.4 O 2−δ [171,172]. Considering the details in Figure A3, one can see that the SOFCs' power density tends to increase with a decrease in the electrolyte's thickness (due to a corresponding decline in the ohmic resistance) despite the existence/absence of CeO 2 -based buffer layers.…”

“…This LSGM-supported cell yielded up to 2200 and 1350 mW cm −2 at 850 and 800 • C, respectively. The typical I-V curve and power densities at different temperatures for the LSGM-supported cell are shown in Figure 8b, which is based on the Ni-Ce 0.8 Gd 0.2 O 2−δ /Ce 0.8 Gd 0.2 O 2−δ /(La 0.9 Sr 0.1 ) 0.97 Ga 0.9 Mg 0.1 O 3−δ /La 0.6 Sr 0.4 Fe 0.8 Co 0.2 O 3−δ cell tested in [170]. The maximum power density of the aforementioned cell reached 540 mW cm −2 at 800 • C, while the maximum power density of a cell containing a La 0.9 Sr 0.1 Ga 0.9 Mg 0.1 O 2.9 electrolyte reached 450 mW cm −2 at 800 • C. The electrode polarization resistance values of the La 0.9 Sr 0.1 Ga 0.9 Mg 0.1 O 3−δ and (La 0.9 Sr 0.1 ) 0.97 Ga 0.9 Mg 0.1 O 3−δ based cells were equal to 0.34 and 0.30 Ω cm 2 at 800 • C, respectively.…”

“….8Gd0.2O2−δ/Ce0.8Gd0.2O2−δ/(La0.9Sr0.1)0.97Ga0.9Mg0.1O3−δ/ La0.6Sr0.4Fe0.8Co0.2O3−δ cell tested in[170]. The maximum power density of the aforementioned cell reached 540 mW cm −2 at 800 °C, while the maximum power density of a cell containing a La0.9Sr0.1Ga0.9Mg0.1O2.9 electrolyte reached 450 mW cm −2 at 800 °C.…”