Papers by Keyword: Proton Conductors

Abstract: In³⁺, Gd³⁺ were selected as substitution elements for Ce⁴⁺ in order to increase electrical conductivity and chemical stability of BaCeO₃. A modified sol-gel method was used to fabricate BaCe_0.7In_0.3-xGd_xO_3-δ (x = 0, 0.1, 0.2, 0.3) nanopowders. XRD results indicated that the diffraction angle moved to lower with increase of the Gd^{3 +} doping concentration, so that the interplanar spacing gradually increased. The impedance spectra analysis showed that conductivity first increased (x = 0~0.2) and then decreased with the Gd^{3 +} doping increase. The total conductivities at 800^oC were 3.8 × 10^-3 S·cm^-1 (x = 0), 8.0 × 10^-3 S· cm^-1 (x = 0.1), 2.5 × 10^-2 S· cm^-1 (x = 0.2), 1.36 × 10^-2 S ·cm^-1 (x = 0.3). Chemical stability test in CO₂ show that all samples except for x=0.3 sample calcination at 800^oC for 2h under 100% CO₂ and x=0, 0.1 samples heating in boiling water for 12h kept main perovskite structure. Therefore, x=0.1 sample show better electrical conductivity and chemical stability.

Abstract: Rare-earth-doped BaCeO₃ and BaZrO₃ electrolytes with perovskite structure have been studied extensively in developing proton conducting intermediate temperature SOFC. Acceptor doped alkaline earth cerates and zirconates have been thoroughly studied because of the great interest in their possible applications as solid proton conductors. The perovskite type proton conductor BaCe_0.5Zr_0.35In_0.1Zn_0.05O_3-δwas prepared in the traditional solid state reaction method. The density of the sample obtained about 96% of the theoretical density after sintering at 1350 °C and X-ray diffraction study confirms the pure phase. Rietveld refinement of the neutron and X-ray powder diffraction data shows that this material crystallizes in the orthorhombic symmetry in the space group Pm3m. Particle size measurement shows that the average particle size is about 2.4 μm. The average thermal expansion at 894 °C was 9.49 x 10^-6/°C. Thermogravimetric analysis (TGA) traces obtained for the sample on heating in wet air shows that the maximum proton uptake occurs from 595 °C.

Abstract: Ceramics based on Y-doped BaCeO₃ were prepared by citrate process. The X-ray fluorescence shows that barium stoichiometry deviation is established during calcination step. Through the SEM analysis of fracture surface of sintered samples it was possible to infer that powder highly deficient of barium shows higher diffusion coefficient during sintering than stoichiometric powder promoting grain growth and, consequently, trapping pores into the grains.

Abstract: The effect of irradiation with heavy ions Ne, Ar, and Kr of various energies on the structure and properties of ceramic barium cerate doped with neodymium and annealed in air at 650°C for 7 hours is studied. It is noted that blistering was observed on cerate surface during its irradiation by low energy Ne ions, whereas it was not observed under low-energy Ar and Kr ions irradiation. Irradiation of the cerate with high energy ions caused partial amorphization of the irradiated surface of the material, while the structure of the non-irradiated surface did not change. In addition, the irradiated surface of the cerate endured solid-phase structural changes. Thus, upon high-energy ions irradiation in the range of Ne, Ar, Kr the cerate surface resembled the stages of spherulite formation - nucleation, growth (view of cauliflower), formation of spherulitic crust, respectively. The increase in water molecules release and reduction of molecular oxygen release from the barium cerate, irradiated by high-energy ions is found during vacuum constant rate heating. It is concluded that cerates undergo changes to the distances significantly exceeding the ion ranges in these materials. Features of high-energy ions influence on thermal desorption of carbon dioxide from cerates show, apparently, the formation of weakly bound carbonate compounds on the cerate surface in the irradiation process.

Abstract: The definition and conduction mechanism of high temperature proton conductors is reviewed, its application in prepare hydrogen, fuel cells, chemical sensors, chemical reactors, the homogeneous catalysts are also discussed.

Abstract: The definition and structure of high temperature proton conductors is reviewed. Discusses the high temperature proton conductors of commonly used several preparation methods.

Abstract: This work investigated the possibility of coupling the high conductivity of cerates and the good chemical stability of zirconates as proton conductor electrolytes for solid oxide fuel cells (SOFCs). Two different approaches are discussed: the synthesis of barium cerate and zirconate solid solutions, and the fabrication of a bilayer electrolyte made of a Y-doped barium cerate pellet covered by a thin protecting layer of Y-doped barium zirconate. The chemical stability of the tailored samples was tested exposing them to 100% CO2 atmosphere at 700°C for 3 h. X-ray diffraction (XRD) analysis was used to investigate the phase composition of the specimens before and after the CO2 treatment. Electrochemical impedance spectroscopy (EIS) measurements were carried out in humidified H2. Hydrogen-air breathing fuel cell experiments were carried out at 700°C.