S.N. Savvin

Engineering of materials for solid oxide fuel cells and other energy and environmental applications

The search for cleaner environmentally friendly power sources has been one of the hot topics in research over the past few years. Solid oxide fuel cells can be considered a promising option for the production of clean energy and one of the simplest routes to improve the efficiency of these devices is the microstructural engineering of component materials. In this work, an insight is provided into several cost-effective procedures of microstructural control of SOFC materials, ranging from an “eye-scale” down to the micrometre scale. The proposed procedures may be considered general and as such they can be used to optimise various materials for energy and environmentally related areas.

Proton Conduction and Long-Range Ferrimagnetic Ordering in Two Isostructural Copper(II) Mesoxalate Metal–Organic Frameworks

Two compounds of formula {(H3O)[Cu7(Hmesox)5(H2O)7]·9H2O}n (1a) and {(NH4)0.6(H3O)0.4[Cu7(Hmesox)5(H2O)7]·11H2O}n (1b) were prepared and structurally characterized by single-crystal X-ray diffraction (H4mesox = mesoxalic acid, 2-dihydroxymalonic acid). The compounds are crystalline functional metal-organic frameworks exhibiting proton conduction and magnetic ordering. Variable-temperature magnetic susceptibility measurements reveal that the copper(II) ions are strongly ferro- and antiferromagnetically coupled by the alkoxide and carboxylate bridges of the mesoxalate linker to yield long-range magnetic ordering with a Tc of 17.6 K, which is reached by a rare mechanism known as topologic ferrimagnetism. Electric conductivity, measured by impedance methods, shows values as high as 6.5 × 10(-5) S cm(-1) and occurs by proton exchange among the hydronium/ammonium and water molecules of crystallization, which fill the voids left by the three-dimensional copper(II) mesoxalate anionic network.

Electrical conductivity of Ln6–xZrxMoO12 + δ (Ln = La, Nd, Sm; x = 0.2, 0.6) ceramics during thermal cycling

In this paper, we analyze the relationship between the microstructure of new polycrystalline electron–proton conductors, Ln6–xZrxMoO12 + δ (Ln = La, Nd, Sm; x = 0.2, 0.6), and the reduction and hydration processes in these materials in humid atmospheres (air and argon). The La5.8Zr0.2MoO12.1 solid solution with a rhombohedral structure possesses not only the highest electrical conductivity among the materials studied here but also high stability in various dry and humid, oxidizing (air) and reducing atmospheres. La5.8Zr0.2MoO12.1 ceramic grains have a twin microstructure, and the conductivity of this material along the grain boundaries, consisting of ordered domains, differs little from its bulk conductivity. It seems likely that we observe a “domain wall” effect, typical of La0.95Sr0.05Ga0.9Mg0.1O3–δ (LSGM) oxygen ion conductors [1]. In studies of Ln6–xZrxMoO12 + δ (Ln = Nd, Sm; x = 0.2, 0.6) ceramics in humid atmospheres, we detected a grain-boundary contribution, which limited the total conductivity, like in perovskite BaZr0.8Y0.2O3–δ. We believe that such conditions lead to a reduction process in these materials and that Mo6+ is reduced before Nd3+ and Sm3+. The process first occurs on grain boundaries.