First principles calculations of oxygen reduction reaction at fuel cell cathodes

The efficiency of solid oxide fuel cells (SOFC) depends critically on materials, in particular for the cathode where the oxygen reduction reaction (ORR) occurs. Typically, mixed conducting perovskite ABO₃-type materials are used for this purpose. The dominating surface terminations are (001) AO and BO₂, with the relative fractions depending on materials composition and ambient conditions.Here, results of recent large-scale first principles (ab initio) calculations for the two alternative polar (La,Sr)O and MnO₂ (001) terminations of (La,Sr)MnO₃ cathode materials are discussed. The surface oxygen vacancy concentration for the (La,Sr)O termination is more than 5 orders of magnitude smaller compared to MnO₂, which leads to drastically decreased estimated ORR rates. Thus, it is predicted for prototypical SOFC cathode materials that the BO₂ termination largely determines the ORR kinetics, although with Sr surface segregation (long-term degradation) its fraction of the total surface area decreases, which slows down cathode kinetics.     

Detonatability of high-energy-density heterocyclic compounds

The detonatability of 3,4-dinitrofurazanfuroxan (DNTF) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (?-polymorph, CL-20) and mixtures thereof with polydimethylsiloxane rubber was studied. The dependences of the critical detonation diameter for the mixtures on the HE content and of pure DNTF and CL-20 on their specific surface area within 400–8000 cm²/g were examined. It was established that the detonatabilities of DNTF and CL-20 are close to those of PETN and HMX, respectively.     

Viscosity and temperature transitions in dimethylacetamide solutions of polyamidobenzimidazole and its blends with polysulfone

The rheological properties of 5% solutions of a fiber-forming polyamidobenzimidazole in DMAA containing LiCl additives and polyamidobenzimidazole-polysulfone blends in the same solvent have been studied. The total concentration of polymer blends with various component ratios is 5 wt %. At temperatures below ∼110°C, the systems under study behave as non-Newtonian fluids and their viscosity decreases with temperature. At T > 110°C, the temperature dependence of viscosity passes through a minimum. The position of the minimum on the temperature scale decreases with the concentration of polyamidobenzimidazole. This character of a change in viscosity is associated with the phase separation of polyamidobenzimidazole solution that leads to its gelation. The temperature corresponding to the minimum viscosity coincides with the onset temperature of a sharp turbidity of solution during heating. It is suggested that solutions containing up to 5% polyamidobenzimidazole possess an LCST. The addition of up to 50% polysulfone has almost no effect on the temperature of transition but brings about a marked decline in the viscosity of the system.