Synthesis, Conducting Properties and Applications of BaCe1-y-xZryErx O3-α
|Keywords||BaCeO3 BaZrO3 Protonic conductor Solid Oxide Fuel Cells Ammonia synthesis at atmospheric pressure|
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 BaCe1-y-xZryErxO3-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, BaCe0.65Zr0.20Er0.15O3-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 BaCe0.65Zr0.2Er0.15O3-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 BaCe0.65Zr0.20Er0.15O3-α an electrolyte （thickness:0.67mm）. It indicated that BaCe0.65Zr0.20Er0.15O3-α is a promising intermediate-temperature solid oxide fuel cell （IT–SOFC） material. And we successfully applied BaCe0.65Zr0.20Er0.15O3-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.