The evolution of the Mn charge state, chemical composition, and electronic structure of La 0.8 Sr 0.2 MnO 3 ͑LSMO͒ cathodes during the catalytic activation of solid oxide fuel cell ͑SOFC͒ has been studies using X-ray spectroscopy of as-processed, exposed, and activated dense thin LSMO films. Comparison of O K-edge and Mn L 3,2 -edge X-ray absorption spectra from the different stages of LSMO cathodes revealed that the largest change after the activation occurred in the Mn charge state with little change in the oxygen environment. Core-level X-ray photoemission spectroscopy and Mn L 3 resonant photoemission spectroscopy studies of exposed and as-processed LSMO determined that the SOFC environment ͑800°C ambient pressure of O 2 ͒ alone results in La deficiency ͑severest near the surface with Sr doping Ͼ0.55͒ and a stronger Mn 4+ contribution, leading to the increased insulating character of the cathode prior to activation. Meanwhile, O K-edge X-ray absorption measurements support Sr/La enrichment nearer the surface, along with the formation of mixed Sr x Mn y O z and/or passive MnO x and SrO species.

Micro unmanned underwater vehicles (UUVs) need to house propulsion mechanisms that are small in size but sufficiently powerful to deliver on-demand acceleration for tight radius turns, burst-driven docking maneuvers, and low-speed course corrections. Recently, small-scale hydrogen peroxide (H2O2) propulsion mechanisms have shown great promise in delivering pulsatile thrust for such acceleration needs. However, the need for robust, high surface area nanocatalysts that can be manufactured on a large scale for integration into micro UUV reaction chambers is still needed. In this report, a thermal/electrical insulator, silicon oxide (SiO2) microfibers, is used as a support for platinum nanoparticle (PtNP) catalysts. The mercapto-silanization of the SiO2 microfibers enables strong covalent attachment with PtNPs, and the resultant PtNP–SiO2 fibers act as a robust, high surface area catalyst for H2O2 decomposition. The PtNP–SiO2 catalysts are fitted inside a micro UUV reaction chamber for vehicular propulsion; the catalysts can propel a micro UUV for 5.9 m at a velocity of 1.18 m/s with 50 mL of 50% (w/w) H2O2. The concomitance of facile fabrication, economic and scalable processing, and high performanceincluding a reduction in H2O2 decomposition activation energy of 40–50% over conventional material catalystspaves the way for using these nanostructured microfibers in modern, small-scale underwater vehicle propulsion systems.

No abstract

Patterned cathodes with composition (La 0.87 Ca 0.13 ) 0.95 MnO 3 (LCM) were fabricated by rf-magnetron sputter deposition on 8 mol% yttria-doped zirconia (YSZ) substrates to have a constant LCM/YSZ contact area of 0.8 cm 2 , but have triple phase boundary (TPB) lengths ranging from 450-1600 cm cm −2 . Electrochemical impedance spectroscopy (EIS) spectra were collected over a temperature and pO 2 range of 600-800 • C and 10 −3 -1.0 atm, respectively, with no applied bias. The resultant spectra were analyzed using a statespace modeling (SSM) approach to understand the oxygen reduction reaction (ORR) kinetics. The SSM model chosen accounts for dissociative adsorption in parallel with surface diffusion to the TPB where full reduction and incorporation into the electrolyte occur. The model explains the observed trends in the experimental data, and enabled extraction of parameters. Of particular significance, the surface diffusivity, D S , was found to be 1.4 × 10 −5 cm 2 s −1 at 700 • C, with an Arrhenius activation energy of 248 kJ mol −1 . The enthalpy of adsorption was found to be −83 kJ mol −1 and almost independent of surface coverage. From the model it was determined that, in air, charge transfer resistance accounts for 40% of the total polarization resistance at 800 • C whereas at 600 • C it accounts for only 3%. Over much of the measured operating conditions, surface diffusivity accounts for the majority of the total polarization resistance.

The ultra-high vacuum surface preparation of heteroepitaxial lanthanum strontium cobalt ferrite thin films has been studied using soft x-ray photoelectron spectroscopy. Specifically, the effect of annealing the films at low temperatures in low partial pressures of oxygen and argon has been investigated. We find that atmospheric surface carbon contamination of the films can be removed in select anneal temperature regimes in argon, but remains bound to the surface with oxygen annealing at any temperature. Irrespective of the gas used, an insulating phase transition occurs near 300 • C due to strontium segregation at the surface. The surface develops more insulating character if annealed with oxygen. Different species are proposed to be responsible for the discrepancy in insulating character.