Oxides with polyatomic anions considered as new electrolyte materials for solid oxide fuel cells (SOFCs)

Hasdinor Bin Hassan, Oskar

Dissertation / PhD Thesis/Book

Oxides with polyatomic anions considered as new electrolyte materials for solid oxide fuel cells (SOFCs)

Hasdinor Bin Hassan, O. (Corresponding author)FZJ*

2010
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-89336-633-0

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich : Energie & Umwelt / Energy & Environment 68, VII, 121 S. (2010) = Ruhr-Univ. Bochum, Diss., 2010

Please use a persistent id in citations: http://hdl.handle.net/2128/3778

Abstract: Materials with Polyatomic anions of [Al$_{2}$O$_{7}]^{-8}$, [Ti$_{2}$O$_{8}]^{-8}$ and [P$_{2}$O$_{7}]^{-4}$ were investigated with respect to their ionic conductivity properties as well as its thermal expansion properties with the aim to use them as SOFCs electrolytes. The polyatomic anion groups selected from the oxy-cuspidine family of Gd$_{4}$Al$_{2}$O$_{9}$ and Gd$_{4}$Ti$_{2}$O$_{10}$ as well as from pyrophosphate SnP$_{2}$O$_{7}$. The pure oxy-cuspidine Gd$_{4}$Al$_{2}$O$_{9}$, the series of Gd$_{4}$Al$_{2-x}$Mg$_{x}$O$_{9-x/2}$ with x = 0.10–1.0 and Gd$_{4-x}$M$_{x}$Al$_{2}$O$_{9-x/2}$ (M=Ca, Sr) with x = 0.05–0.5 were prepared successfully by the citrate complexation method. All samples showed the crystal structure of monoclinic oxycuspidine structure with space group of P2$_{1}$/c and Z=4. No solid solution was observed for Gd$_{4}$Al$_{2-x}$Mg$_{x}$O$_{9-x/2}$ where additional phases of Gd$_{2}$O$_{3}$ and MgO were presence. XRD semiquantitative analysis together with SEM-EDX analysis revealed that Mg$^{2+}$ was not able to substitute the Al$^{3+}$ ions even at low Mg$^{2+}$ concentration. The solid solution limit of Gd$_{4-x}$Ca$_{x}$Al$_{2}$O$_{9-x/2}$ and Gd$_{4-x}$Sr$_{x}$Al$_{2}$O$_{9-x/2}$ was determined between 0.05-0.10 and 0.01-0.05 mol for Ca and Sr, respectively. Beyond the substitution limit Gd$_{4}$Al$_{2}$O$_{9}$, GdAlO$_{3}$ and SrGd$_{2}$Al$_{2}$O$_{7}$ appeared as additional phases. The highest electrical conductivity obtained at 900 °C yielded $\sigma$ = 1.49 x 10$^{-4}$ Scm$^{-1}$ for Gd$_{3.95}$Ca$_{0.05}$Al$_{2}$O$_{8.98}$. In comparison, the conductivity of pure Gd$_{4}$Al$_{2}$O$_{9}$ was $\sigma$ = 1.73 x 10$^{-5}$ Scm$^{-1}$. The conductivities determined were in a similar range as those of other cuspidine materials investigated previously. The thermal expansion coefficient of Gd$_{4}$Al$_{2}$O$_{9}$ at 1000 °C was 7.4 x 10$^{-6}$ K$^{-1}$. The earlier reported phase transition between 1100 and 1200 °C changed with increasing substitution of Ca and Sr. Consequently, the analogue materials of pure oxy-cuspidine Gd$_{4}$Ti$_{2}$O$_{10}$, the series of Gd$_{4}$Ti$_{2-x}$Mg$_{x}$O$_{10-x/2}$ with x=0.05 - 0.50 and the series Gd$_{4-x}$M$_{x}$Ti$_{2}$O$_{10-x/2}$ (M=Ca, Sr) with x=0.05 - 0.50 were prepared successfully also by the citrate complexation method. All samples show the crystal structure of orthorhombic oxy-cuspidine structure with space group of Pnma and Z=4. No solid solution was observed for Gd$_{4}$Ti$_{2-x}$Mg$_{x}$O$_{10-x/2}$ where additionally phase of monoclinic Gd$_{2}$O$_{3}$ was present. The solid solution limit of Gd$_{4-x}$Ca$_{x}$Ti$_{2}$O$_{10-x/2}$ and Gd$_{4-x}$Sr$_{x}$Ti$_{2}$O$_{10-x/2}$ was determined between 0.20-0.30 and 0.05-0.10 mol for Ca and Sr, respectively. Beyond the substitution limit, GdTiO$_{3}$ and SrTiO$_{3}$ appeared as additional phases, respectively. The highest electrical conductivity obtained at 900 °C yielded $\sigma$ = 2.50 x 10$^{-4}$ Scm$^{-1}$ for Gd$_{3.80}$Ca$_{0.20}$Ti$_{2}$O$_{9.90}$. In comparison, the conductivity of pure Gd$_{4}$Ti$_{2}$O$_{10}$ was $\sigma$ = 3.10 x 10$^{-5}$ Scm$^{-1}$. Again the conductivities determined were in a similar range as those of other cuspidine materials investigated previously. The thermal [...]

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