Study On Preparation, Characteristics And Application In Hydrogen Sensor Of Proton Conductors

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(Ce_0.5Zr_0.5)_1-xY_xO₃-δhas maximal electrical conductivity and minimal activation energy, which is consistent with results from infrared absoption spectra. The total conductivity of Ba(Ce_0.5Zr_0.5)_0.80Y_0.20O₃-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 BaCe_0.90Y_0.10O₃-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 SrCe_0.95Tm_0.05O₃-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℃.