Synthesis, Conducting Properties And Applications Of BaCe_1-y-xZr_yEr_x O_3-α

BaCeO₃ based ionic conduction ceramic materials as a kind of important functional material have important application value and broad application prospect in hydrogen sensor, steam electrolyzer, separation and purification of hydrogen, hydrogenation and dehydrogenation of some organic compounds, intermediate-temperature solid oxide fuel cells (IT–SOFC), and ammonia synthesis at atmospheric pressure, etc. BaCeO₃ based ionic conduction ceramic materials have higher ion conductivity, but the chemical stability is poor under CO2 and/or water vapor-containing atmospheres which makes the actual application limited. However, BaZrO₃ based ionic conduction ceramic materials have excellent chemical stability and mechanical strength, but the ion conductivity is lower. Since BaCeO₃ and BaZrO₃ easily form solid solutions, it may be possible to achieve a cerate-zirconate solid solution with both high protonic conductivity and good chemical stability through replacing Ce⁴⁺ in BaCeO₃ with Zr⁴⁺.Er–doped BaCeO₃–BaZrO₃ solid solutions have not been reported. So, in this article, this paper prepared series of BaCe_1-y-xZr_yEr_xO_3-α (x = 0.5, 0.1, 0.15, 0.2; y = 0, 0.1, 0.2, 0.3, 0.4) ceramics in which Ce⁴⁺ in BaCeO₃ is substituted by Zr⁴⁺ and Er³⁺, and investigated the conductions in 300―800°C. In addition, we studied the properties of solid oxide fuel cells and ammonia synthesis at atmospheric pressure. Main works and results are as follows:1. The dense ceramic samples BaCe0.9-xZr0.10ErxO₃-α(x = 0.05, 0.10, 0.15, 0.20) were prepared by calcing at 1150°C and sintering at 1550°C the precursor prepared though a microemulsion route. The calcined and sintered temperatures were reduced by 100°C compare with those (1250°C and 1650°C) of traditional solid-state reaction, respectively. The ceramics of BaCe0.9-xZr0.10ErxO₃-α(x = 0.05, 0.10, 0.15,0.20) were almost pure proton conductors in hydrogen atmosphere at 300―800°C, which was confirmed by electrochemical methods including AC impedance spectra, hydrogen concentration cells and electrochemical hydrogen permeation (hydrogen pumping), etc. The sample for x = 0.15 has the highest conductivities.2. Dense ceramic samples BaCe0.85-yZryEr0.15O₃-α(y = 0.0, 0.1, 0.2, 0.30, 0.4) were prepared by calcing at 1150―1200°C and sintering at 1550°C the precursor prepared though a microemulsion route. This paper investigated the chemical stability in 94% N₂ + 3% CO₂ + 3% H₂O atmospheres and the properties of conduction at 300―800°C. It was found that the chemical stability of ceramics decreased and the conductivities increased with the contents of Zr⁴⁺ increasing. Among BaCe0.85-yZryEr0.15O₃-α(y = 0.0, 0.1, 0.2, 0.30, 0.4) ceramics, BaCe_0.65Zr_0.20Er_0.15O_3-α displayed both a high chemical stability in 94% N₂ + 3% CO₂ + 3% H₂O atmosphere and an acceptable conductivity at 300―800°C .3. The properties of conduction in hydrogen atmosphere at 300―800°C were investigated by electrochemical methods including AC impedance spectra, hydrogen concentration cells and electrochemical hydrogen permeation (hydrogen pumping), etc. The results indicated that BaCe_0.65Zr_0.2Er_0.15O_3-α was almost pure ionic conductor which was contributed mainly by proton. The maximum current and power density at 800°C were 360 mAcm^-1 and 90 mWcm^-2, respectively, of hydrogen-air fuel cells using BaCe_0.65Zr_0.20Er_0.15O_3-α an electrolyte (thickness:0.67mm). It indicated that BaCe_0.65Zr_0.20Er_0.15O_3-α is a promising intermediate-temperature solid oxide fuel cell (IT–SOFC) material. And we successfully applied BaCe_0.65Zr_0.20Er_0.15O_3-α to the ammonia synthesis at atmospheric pressure. The peak ammonia formation rate achieved 3.27×10^-9 mols^-1cm^-2 under a direct current of 1.0 mA at 450°C.