Rapid and durable oxygen reduction reaction enabled by a perovskite oxide with self-cleaning surface

The growth of electrochemically inert segregation layers on the surface of solid oxide fuel cell cathodes has become a bottleneck restricting the development of perovskite-structured oxygen reduction catalysts.Here,we report a new discovery in which enriched Ba and Fe ions on the near-surface of Nd_(1/2)Ba_(1/2)Co_(1/3)Fe_(1/3)Mn_(1/3)O_(3-δ)spontaneously agglomerate into dispersed Ba_(5)Fe_(2)O_(8) nanoparticles and maintain a highly active and durable perovskite structure on the surface.This unique surface selfcleaning phenomenon is related to the low average potential energy of Ba_(5)Fe_(2)O_(8),which is grown on the near-surface layer.The electrochemically inert Ba_(5)Fe_(2)O_(8) segregation layer on the near-surface of the perovskite catalyst achieves self-cleaning by regulating the formation energy of enriched metal oxides.This self-cleaned perovskite surface exhibits an ultrafast oxygen exchange rate,high catalytic activity for the oxygen reduction reaction,and good adaptability to the actual working conditions of solid oxide fuel cell stacks.This study paves a new way for overcoming the stubborn problem of perovskite catalyst surface deactivation and enriches the scientific knowledge of surface catalysis.

Cobalt(Ⅱ)coordination polymers as anodes for lithium-ion batteries with enhanced capacity and cycling stability

Coordination polymer Co-btca （H4btca = 1,2,4,5-benzenetetracarbo ylic acid） was synthesized using a simply hydrothermal method. In particular, the as-prepared Co-btca was applied as an anode material for lithium-ion battery for the first time. Single crystal X-ray diffraction results indicated that the as- prepared Co-btca displayed unique layer structure, which was beneficial to transport Li ions and electrons. Also, owing to the porous structure and appropriate specific surface area, Co-btca electrode delivered a reversible capacity of 801.3 mA h/g after 50 cycles at a current density of 200 mA/g. The reversible capacity of 773.9 mA h/g was maintained after 200 cycles at a current density of 500 mA/g, exhibiting enhanced cycle stability. It also showed improved rate performance, making it a promising anode material and a new choice for lithium-ion batteries.

Physicochemical properties of proton-conducting SmNiO3 epitaxial films

Proton conducting SmNiO_(3)(SNO)thin films were grown on(001)LaAlO_(3)substrates for systematically investigating the proton transport properties.X-ray Diffraction and Atomic Force Microscopy studies reveal that the as-grown SNO thin films have good single crystallinity and smooth surface morphology.The electrical conductivity measurements in air indicate a peak at 473 K in the temperature dependence of the resistance of the SNO films,probably due to oxygen loss on heating.A Metal-Insulator-Transition occurs at 373 K for the films after annealing at 873 K in air.In a hydrogen atmosphere(3%H_(2)/97%N_(2)),an anomalous peak in the resistance is found at 685 K on the first heating cycle.Electrochemical Impedance Spectroscopy studies as a function of temperature indicate that the SNO films have a high ionic conductivity(0.030 S/cm at 773 K)in a hydrogen atmosphere.The activation energy for proton conductivity was determined to be 0.23 eV at 473-773 K and 0.37 eV at 773e973 K respectively.These findings demonstrate that SNO thin films have good proton conductivity and are good candidate electrolytes for low temperature proton-conducting Solid Oxide Fuel Cells.

Correlation of structural and electrical properties of PrBaCo2O5td thin films at high temperature

Epitaxial PrBaCo_(2)O_(5+δ)(PBCO,0≤δ≤1)thin films were deposited by pulsed laser deposition.The structural and electrical properties of the films were characterized at high temperatures in reduced environments.X-ray diffraction scans at high temperature in reduced environment show potential structural transitions of PBCO as evidenced by both a large(Dl=0.335 nm)expansion of the out-plane(caxis)lattice,due to thermal and chemical expansion,and a step in the expansion of the c-axis lattice parameter.These transitions indicate the presence of oxygen vacancy ordering as the oxygen content in the films is reduced.Resistivity measurements under the same environments also show evidence of sharp transitions related with the structural transformations.This study helps the understanding of the structure-property relationship of PBCO at high temperature and provides important technological information to utilize these materials for solid oxide fuel cell at intermediate temperatures.