Electrochemical behavior of thin-film Sm-doped ceria: insights from the point-contact configuration

The electrochemical behavior of chemical vapor deposition (CVD) grown porous films of Sm-doped ceria (SDC) for hydrogen oxidation has been evaluated by impedance spectroscopy using a point contact geometry at a temperature of 650 °C. Porous SDC films, 950 nm in thickness, were deposited on both sides of single-crystal YSZ(100). Pt paste was applied over the surface of one SDC layer to create a high-activity counter electrode. Ni wire was contacted to the surface of the other SDC layer to create a limited contact-area working electrode. The active area of contact at the working electrode was determined using the Newman equation and the electrolyte constriction impedance. The radius of this area varied from 5 to 18 μm, depending on gas composition and bias. The area-normalized electrode impedance (where the area was that determined as described above) varied from 0.03 to 0.17 Ω cm^2 and generally decreased with cathodic bias and decreasing oxygen partial pressure. From an analysis of the dimensions of the active area with bias, it was found that the majority of the overpotential occurred at the SDC|gas interface rather than the SDC|YSZ interface. Overall, the anode overpotential is found to be extremely small, competitive with the best oxide anodes reported in the literature. Nevertheless, the impedance falls in line with expected values based on extrapolations of the properties of dense, flat SDC model electrodes grown by pulsed laser deposition (Chueh et al., Nat. Mater., 2012). The results demonstrate that, with suitable fabrication approaches, exceptional activity can be achieved with SDC for hydrogen electrooxidation even in the absence of metal–oxide–gas triple phase boundaries

Applicaton of USB Serial Communication to Radon Measuring System

The USB serial communication such as USB-Serial-for PC and USB-Serial-for-Android is studied in order to monitor the measure radon data using a PC screen or a smart phone screen. Through some experimental studies, we believe that the USB serial communication module is useful for checking the data transmitted to a PC from a microcontroller

Zirconia-Based Electrolyte Stability in Direct-Carbon Fuel Cells with Molten Sb Anodes

Direct carbon fuel cells (DCFC) that use zirconia-based electrolytes and molten Sb anodes have much promise for the efficient conversion of carbonaceous solid fuels into electricity. However, etching of the electrolyte, and ultimately cell failure, has been observed during operation. In this study, we have investigated this etching phenomenon as a function of the electrolyte composition and cell operating conditions and demonstrated that it is not electrochemical in nature, but rather results from reaction between the electrolyte and Sb2O3

Proton conductivity of columnar ceria thin-films grown by chemical vapor deposition

Columnar thin films of undoped ceria were grown by metal–organic chemical vapor deposition. The films, deposited on Pt-coated MgO(100) substrates, display a columnar microstructure with nanometer scale grain size and ~30% overall porosity. Through-plane (thickness mode) electrical conductivity was measured by AC impedance spectroscopy. Proton conduction is observed below 350–400 °C, with a magnitude that depends on gas-phase water vapor pressure. The overall behavior suggests proton transport that occurs along exposed grain surfaces and parallel grain boundaries. No impedance due to grain boundaries normal to the direction of transport is observed. The proton conductivity in the temperature range of 200–400 °C is approximately four times greater than that of nanograined bulk ceria, consistent with enhanced transport along aligned grain surfaces in the CVD films

Determination of optical and microstructural parameters of ceria films

Light-matter interactions are of tremendous importance in a wide range of fields from solar energy conversion to photonics. Here the optical dispersion behavior of undoped and 20 mol. % Sm doped ceria thin films, both dense and porous, were evaluated by UV-Vis optical transmission measurements, with the objective of determining both intrinsic and microstructural properties of the films. Films, ranging from 14 to 2300 nm in thickness, were grown on single crystal YSZ(100) and MgO(100) using pulsed laser deposition (both dense and porous films) and chemical vapor deposition (porous films only). The transmittance spectra were analyzed using an in-house developed methodology combining full spectrum fitting and envelope treatment. The index of refraction of ceria was found to fall between 2.65 at a wavelength of 400 nm and 2.25 at 800 nm, typical of literature values, and was relatively unchanged by doping. Reliable determination of film thickness, porosity, and roughness was possible for films with thickness ranging from 500 to 2500 nm. Physically meaningful microstructural parameters were extracted even for films so thin as to show no interference fringes at all

An Investigation of LSF-YSZ Conductive Scaffolds for Infiltrated SOFC Cathodes

Porous compostites of Sr-doped LaFeO3 (LSF and yttria-stabilized zirconia (YSZ) were investigated as conductive scaffolds for infiltrated SOFC cathodes with the goal of producing scaffolds for which only a few perovskite infiltration steps are required to achieve sufficient conductivity. While no new phases form when LSF-YSZ composites are calcined to 1623 K, shifts in the lattice parameters indicate Zr can enter the perovskite phase. Measurements on dense, LSF-YSZ composites show that the level of Zr doping depends on the Sr:La ration. Because conductivity of undoped LSF increases with Sr content while both the iconic and electronic conductivities of Zr-doped LSF decrease with the level of Zr in the perovskite phase, there is an optimum initial Sr content corresponding to La0.9Sr0.1FeO3 (LSF91). Although schaffolds made with 100% LSF had a higher conductivity then scaffolds made with 50:50 LSF-YSZ mixtures, the 50:50 mixture provides the optimal interfacial structure with the electrolyte and sufficient conductivity, providing the best cathode performance upon infiltration of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)

Evidence and model for strain-driven release of metal nano-catalysts from perovskites during exsolution

The authors thank the U.S. National Science Foundation (NSF) and the European Engineering and Physical Sciences Research Council for funding through the Materials World Network Program (grant nos. DMR-1210388 and EP/J018414/1). The authors also thank the NSF MRSEC Center at the University of Pennsylvania (DMR11-20901) for partial support of this work. VBS also acknowledges NSF support through grant CMMI-1363203. Date of Acceptance 07/12/2015The evolution of the surface morphology during exsolution of Ni from the perovskite, La0.4Sr0.4Ti0.97Ni0.03O3-δ, under reducing conditions was determined using atomic force microscopy (AFM). The exsolution process was found to initially induce the formation of a 20-30 nm deep pit on the oxide surface followed by the emergence of a Ni particle at the bottom of the pit. Continued emergence of the particle results in it nearly filling the pit producing a unique structure in which the Ni particle is socketed into the oxide surface. We also show that this morphological evolution can be explained using a simple energy-based model that accounts for the interplay between the surface free energy and the strain energy induced by the included metal nucleate. The unique socketed structure results in strong anchorage between the exsolved particles and the oxide host lattice which imparts both high thermal stability and unique catalytic activity.PostprintPostprintPeer reviewe

Duplexer using microwave photonic band gap structure

We propose a frequency selective duplexer using microwave photonic band gap (PBG) structures. It uses two different PBGs to control the propagation of electromagnetic waves in the microwave region. In this structure, an additional narrow reflection band appears in the transmission spectrum when the PBG structure is not properly located relative to the T junction. By considering multiple reflections, it is proved that this additional reflection band in each PBG structure results from the interference between the input wave and the reflected wave from the other PBG structure. An effective way to prevent this interference effect is also discussed

Linear Wave Reflection by Trench with Various Shapes

author's final versionTwo types of analytical solutions for waves propagating over an asymmetric trench are derived. One is a shallow water wave model and the other is an extended model applicable to deeper water. The water depth inside the trench varies in proportion to a power of distance from the center of the trench (where the center means the deepest water depth point and the origin of -coordinate in this study). The mild-slope equation is transformed into a second order ordinary differential equation with variable coefficients based on the longwave assumption or Hunts (1979) approximate solution for wave dispersion. The analytical solutions are then obtained by using the power series technique. The analytical solutions are compared with the numerical solution of the hyperbolic mild-slope equations. After obtaining the analytical solutions under various conditions, the results are analyzed