Browsing by Author "Tsai, Yen-Chang"

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Chemical stability and electrical conductivity of BaCe0.4Zr0.4Gd0.1Dy0.1O3-delta perovskite
(2015-11-01)
Tsai, Yen-Chang
;
Chen, San-Yuan
;
Wang, Jeng-Han
;
Wu, Pu-Wei
;
Chen, Po-Chun
A proton-conducting BaCe0.4Zr0.4Gd0.1Dy0.1O3-delta (BCZGD) perovskite is fabricated via a wet chemical route using precursors including Ba(NO3)(2), Ce(NO3)(3)center dot 6H(2)O, ZrO(NO3)(4)center dot 6H(2)O, Gd(NO3)(3)center dot 6H(2)O, and Dy(NO3)(3)center dot 5H(2)O. The synthesis process involves the dissolution of relevant precursors and glycine in deionized water at proper molar ratios. Subsequently, the mixture undergoes a heat treatment at 1300 degrees C for 10 h in air to form the perovskite powders. The as-synthesized BCZGD powders are filtered and pressed at 440 MPa, following by a sintering at 1450 degrees C for 24 h in air to render a free-standing proton-conductive disk with a thickness of 850 mu m. Material characterization including scanning electron microscopy (SEM), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), and electrical conductivity measurements are performed. The electrical conductivity of the BCZGD sample is recorded at 1.93 x 10(-3) S cm(-1) at 700 degrees C in a humid hydrogen atmosphere with an activation energy of 0.41 eV. TGA results confirm chemical stability of the BCZGD against carbon dioxide without any decomposition. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Palladium based cermet composite for hydrogen separation at elevated temperature
(2015-01-15)
Tsai, Yen-Chang
;
Lin, Chien-Cheng
;
Lin, Wei-Lin
;
Wang, Jeng-Han
;
Chen, San-Yuan
A cermet composite consisting of palladium and BaCe0.4Zr0.4Gd0.1DY0.1O3-x (BCZGD) is fabricated by mixing palladium and BCZGD powders in a ball mill, followed by pressing and sintering at 1450 degrees C for 24 h in air. The Pd-BCZGD cermet demonstrates impressive hydrogen permeation flux in a mixture of hydrogen and carbon dioxide at elevated temperature, in which the palladium plays the predominant role of facile transport in the hydrogen atoms whereas the BCZGD provides channels for proton conduction. Material characterization including scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermo-gravimetric analysis (TGA) are performed. XRD patterns indicate pure phases of fcc palladium and perovskite BCZGD. SEM images and element mapping suggest a homogeneous mixture of cermet without noticeable defect and phase segregation. TGA results confirm stability of the cermet against carbon dioxide without chemical decomposition. The hydrogen permeation flux is determined via a gas chromatography from 400 to 700 degrees C at various hydrogen concentration gradients. We record a hydrogen flux of 1.25 cm(3) min(-1) cm(-2) in 50% hydrogen and 50% carbon dioxide at 700 degrees C, with a selectivity of H-2/CO2 approaching infinity. (C) 2014 Elsevier B.V. All rights reserved.