Browsing by Author "Hao, Chia-Kan"

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Characterization and electrochemical properties of chromium-substituted pyrochlore Y2Ti2-x Cr (x) O7-delta
(2015-11-01)
Hao, Chia-Kan
;
Hung, Hao-En
;
Lee, Chi-Shen
;
應用化學系
;
Department of Applied Chemistry
Pyrochlore oxides Y2Ti2-x Cr (x) O7-delta have been investigated as electrolyte for solid oxide fuel cell. The as-prepared powder was synthesized by sol-gel method and characterized by powder X-ray diffraction, scanning electron microscope/energy-dispersive spectroscopy, inductively coupled plasma atomic emission spectroscopy, temperature-programmed reduction and AC impedance. Y2Ti2-x Cr (x) O7-delta existed in single phase in a range of 0 < x a parts per thousand currency sign 0.8, and the cell parameters decreased as the amount of Cr dopant increased. XPS analyses indicate that the average oxidation state of Cr (n+) ions decreased with the increased Cr content. Measurements of ionic conductivities induced that the optimized performance was observed at x = 0.2 with 0.01 S/cm at 700 A degrees C due to an optimized condition of carrier concentration and carrier mobility. Y2Ti2-x Cr (x) O7-delta existed in single phase in a range of 0 < x a parts per thousand currency sign 0.8 and the optimized performance of ionic conductivity was observed at x = 0.2 with 0.01 S/cm at 700 A degrees C. [GRAPHICS] .
Effect of Ti substitution on the electrochemical properties of LaCr1-x Ti (x) O3+0.5x (x=0-0.15)
(2016-05)
Hao, Chia-Kan
;
Tsai, Chia-Fen
;
Lee, Chi-Shen
;
應用化學系
;
Department of Applied Chemistry
Perovskite compound LaCr1-x Ti (x) O3+0.5x (x = 0-0.15) was synthesized from an EDTA-chelating precursor solution at T < 800 A degrees C, a temperature lower than that of the conventional solid-state method. Structural properties were determined at room temperature using X-ray powder diffraction and the lattice parameter decreased with increasing proportion of Ti. LaCr1-x Ti (x) O3+0.5x was chemically stable under a H-2 atmosphere at 900 A degrees C. Both electrical and ionic conductivity increased with increasing proportion of doped Ti, indicative of a p-type semiconductor. An Arrhenius-like behavior was observed, and the optimized bulk electrical conductivity was 0.107 S cm(-1) for LaCr0.85Ti0.15O3.075 at 850 A degrees C. X-ray photoelectron spectra indicate that the effect of the concentration of charge carrier on conductivity is closely related to the oxidation states of ions. The maximum power density reaches as high as 210 mW cm(-2) at 800 A degrees C for SOFC with LaCr1-x Ti (x) O3+0.5x (x = 0.15) anode. Ti-substituted perovskite materials LaTi (x) Cr1-x O3+0.5x (x = 0-0.15) show enhanced electronic and ionic conductivity with increasing proportion of doped Ti. [GRAPHICS]
Metal-doped Pyrochlore as Novel Electrode Materials For Intermediate Temperature Solid Oxide Fuel Cell
(2013)
Hao, Chia-Kan
;
Lee, Chi-Shen
;
應用化學系
;
Department of Applied Chemistry
In this study, the metal-doped La-2(Zr1-xWx)(2)O-7 (LWZO) pyrochlore phases were synthesized by Pechini sol-gel method and characterized by X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The phase width of tungsten is x = 0.1 - 0.15. Temperature-programmed reduction (TPR) shows that the as-prepared products are stable under hydrogen atmosphere. XPS measurements revealed the valence state of La3+, Zr4+, and W-(5+,W- 6+). The ionic- and electronic-conductivity of the 15% W-doped LWZO is 2.2x10(-3) to 1.9x10(-2) S/cm from 400 to 700 degrees C, which is better than YSZ and GDC over this temperature range. The LWZO is stable up to 1400 degrees C under reduced atmosphere. Bottom cells were fabricated with the LWZO electrolyte and GDC. The results shown that the La-2(Zr1-xWx)(2)O7+delta have a good potential of becoming the electrolyte for IT-SOFCs.
The Stability and Ionic Conductivity in Cr Doped Y2Ti2O7 in the Search for Potential SOFC Electrolyte Materials
(2013)
Hung, Hao-En
;
Hao, Chia-Kan
;
Lee, Chi-Shen
;
應用化學系
;
Department of Applied Chemistry
In this study, a series of Y2Ti2-xCrxO7 were synthesized by sol-gel method and characterized by powder X-ray diffraction (PXRD), scanning electron microscope energy dispersive spectroscopy (SEM-EDS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), temperature-programmed reduction (TPR), and AC-impedance to investigate their properties for the application of intermediate temperature solid oxide fuel cell (IT-SOFC). Y2Ti2-xCrxO7 existed single-phase in a range of 0 < x <= 0.8. The refined cell parameters decreased as the amount of doped Cr concentration increased. In addition, the TPR profiles showed that the as-prepared materials started to react with hydrogen in the temperature range of 350 - 450 degrees C. The analyzed results of XPS suggested that the average oxidation state of Cr decreased with the increased Cr content. Measurements of ionic conductivities induced that the optimized performance was observed at x = 0.2 with 0.01 S/cm at 700 degrees C due to an optimized condition of carrier concentration and carrier mobility. The ionic conductivity dropped under reducing condition, indicative of a p-type semiconductor. The as-prepared Y2Ti1.8Cr0.2O7 exhibits low electrical conductivity (0.0004 S/cm at 700 degrees C) and good ionic conductivity, which is potentially suitable to be utilized as an electrolyte material for IT-SOFC.