TAILIEUCHUNG - Materials for the Hydrogen Economy (2009) Part 9

Tham khảo tài liệu 'materials for the hydrogen economy (2009) part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 216 Materials for the Hydrogen Economy The stability of Bi2O3 was reported to improve by forming solid solution with vanadium which can be partially substituted with Co Ni or Cu. A so-called BIMEVOX bismuth metal-ion vanadium oxide consists of oxygen vacancies in a perovskite-like V-O layer which possesses extremely high oxygen ion conductivity. For instance ionic conductivity reaches 3 X 10-3 S cm at 300 C which is nearly two orders higher than any other oxygen ion conductors. The high reactivity and instability however hinder its further application in fuel cells as an electrolyte. PEROVSKITES LaGaO3 The perovskite structure is basically cubic with the general formula of ABO3 in which A the large cation site is an alkali alkaline earth or rare earth ion and B the small cation site is a transition metal cation. The large cations are in 12-fold coordination with oxygen while the small cations fit into octahedral positions. The occupancy of these sites by different cations is determined primarily by ionic radius rather than the valence. This opens the door for the materials scientists to substitute selectively for either the A or B ion by introducing isovalent or aliovalent cations. An oxygen ion conductor can be tailored because of the geometrical and chemical flexibility of the perovskite structure. This is borne out by La Sr Mg Ga O3 LSMG 47-51 which has attracted great attention since its There exist however two drawbacks for LSMG electrolytes 1 the uncertainty in the cost of Ga sources and 2 the chemical and mechanical stability of LSMG. It is apparent that ordering occurs sometimes at specific temperatures that significantly decreases the oxygen ionic conductivity because of lower defect mobility and reduced effective vacancy concentration. Stevenson et al. studied the role of microstructure and nonstoichiometry on ionic conductivity of The electrical conductivity of sintered LSGM tends to decrease with increasing A B cation

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