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Study on Preparation, Characteristics and Application in Hydrogen Sensor of Proton Conductors

Author: LvJingDe
Tutor: WangLing
School: Hebei University of Technology
Course: Chemical processes
Keywords: proton conductor perovskite chemical stability electrical conductivity mixed conductor hydrogen sensor
CLC: TP212.2
Type: Master's thesis
Year: 2008
Downloads: 17
Quote: 0
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Abstract


Perovskite-type high temperature proton conductors （HTPC） have been paid more attention in recent years due to their potential applications in separation of hydrogen, fuel cells, membrane reactors, hydrogen sensors.The sintering, chemical stability and electrical characteristic of HTPC were investigated. A type of limiting current hydrogen sensor using proton conductor as an electrolyte and mixed proton-electron conductor as dense diffusion barrier was constructed. The crystalline phase, microstructure and electrical conductivity of proton conductors were investigated by XRD, SEM and EIS, respectively. In addition, their chemical stability against CO2 and boiling water was also examined. Hydrogen sensing properties of the sensor were conducted.The effect of sintering temperature, doped ion, dopant concentration on the structure and properties of BaCeO3-BaZrO3 solid solutions was investigated. Proton conductors sintered at 1600℃have the dense and single phase perovskite structure. The sintered samples at the temperature have the highest conductivity. The dopant ionic radius matching with that of Ce4+ is beneficial for conductivity while matching with that of Zr4+ is beneficial with respect to chemical stability. The sample with x=0.20 for the series of Ba(Ce0.5Zr0.5)1-xYxO3-δhas maximal electrical conductivity and minimal activation energy, which is consistent with results from infrared absoption spectra. The total conductivity of Ba(Ce0.5Zr0.5)0.80Y0.20O3-δproton conductor in air is 2.07×10-2 S·cm-1 at 800℃, and activation energy is 72.34 kJ·mol-1.By comparing with the chemical stability between Y doped BaCeO3-BaZrO3 solid solutions and BaCe0.90Y0.10O3-δ, it is found that introduction of Zr greatly enhances their chemical stability against CO2 and boiling water, which is in agreement with the result of thermodynamic calculation.The atmospheres （Air, 4%H2, Ar） have low effect on bulk conductivity of mixed proton-electron conductor SrCe0.95Tm0.05O3-δ, while grain boundary and total conductivity are obviously influenced by atmospheres. The electronic conduction of mixed conductor results from the charge transfer between Tm2+ and Tm3+. There is a close bonding between proton conductor and mixed conductor as barrier layer in limiting current hydrogen sensor and the interface is clear. Good limiting current plateaus in I-V curves are observed at a hydrogen concentration in the range of 017700ppm from 600 to 800℃. There is an excellent linear relationship between hydrogen concentration and limiting current. The sensitivity to hydrogen increases with temperature and it is 1.30μA·ppm-1 at 800℃.

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