Synthesis and Electrical Conductivity of LaErO3-based Ceramics
|Keywords||LaErO3 microemulsion proton conductor fuel cell synthesis of ammonia|
High temperature proton conduction has attracted considerable attention due to their increasing importance for potential applications in hydrogen sensors, solid oxides fuel cell (SOFC), water electrolysis, separation and purification of hydrogen, hydrogenation, and dehydrogenation of some organic compounds, synthesis of ammonia at atmospheric pressure, membrane reactors and other high temperature electrochemical devices.Doubly doped LaErO3 ceramics, La0.9Ba0.1Er1-xMgxO3-α(x = 0.05, 0.10, 0.15, 0.20), were synthesized by solid-state reaction and microemulsion method. Gas concentration cells, AC-impedance and electrochemical hydrogen permeation experiments were used to determine and study the conductivities, ionic transference numbers and ionic conduction behavior at 500 ~ 1000℃by using the samples as solid electrolytes and porous platinum as electrodes. And the properties of H2-air fuel cell using the samples by the two methods as solid electrolytes were also studied. Ammonia was synthesized successfully from nitrogen and hydrogen at atmospheric pressure by using La0.9Ba0.1Er0.85Mg0.18O3-αceramic electrolyte.The main results are as follows:(1) The samples are single orthorhombic perovskite-type structure.(2) The pure ion conduction of the ceramics in hydrogen atmosphere was confirmed by a electromotive force method of hydrogen concentration cell, and the observed emf values coincided well with the theoretical ones. Whereas in dry oxygen containing atmosphere, observed emf values of the oxygen concentration cell were far lower than the theoretical ones, indicating that the ceramics were mixed conductors of electron hole and oxide-ion.(3) The conduction of the samples was studied under different oxygen partial pressure range. Under low oxygen partial pressure range (about 10-7 ~ 10-20 atm), the conduction was independent of the oxygen partial pressure, indicating that they were pure ionic conductors, which was consistent with the result by means of hydrogen concentration cell. Whereas at high oxygen partial pressure range (about 10-5 ~ 1 atm), the samples exhibited mixed conductors of ion and electron hole.(4) The electrochemical hydrogen permeation (hydrogen pumping) performances were studied. Under lower current densities, the electrochemical hydrogen permeation (hydrogen pumping) rates determined were in accordance with the theoretical ones calculated from Faraday’s law, which indicated that the ceramics were mainly proton conductors in hydrogen containing atmosphere.(5) The amount of Mg doped at Er sites affected markedly the conductivities of the samples. Under wet hydrogen atmosphere, among the samples, the sample of x = 0.15 showed the highest conductivity (4.3×10-3 S·cm-1 at 1000℃), which was also higher than the conductivity (8.8×10-4 S·cm-1) of La0.9Ba0.1ErO3 at the same conditions.(6) The performances of H2-air fuel cells were almost the same using La0.9Ba0.1Er0.85Mg0.18O3-αas solid electrolyte synthesized by two different methods.(7) Ammonia was synthesized successfully at atmosphere pressure by using La0.9Ba0.1Er0.85Mg0.18O3-αceramics as the solid electrolyte of electrolytic cell, and the rate of ammonia formation is 1.2×10-9 mol·s-1·cm-2.(8) The La0.9Sr0.1Er0.85Mg0.15O3-αceramics was synthesized via solid-state reaction method in this study, and its electrochemical properties were studied by various electrochemical methods. It is found that the conduction properties of the sample were similar to the ones of La0.9Ba0.1Er0.85Mg0.18O3-α.