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An impedimetric NO[subscript x] dosimeter based on the NO[subscript x] sorption material KMnO[subscript 4] is proposed. In addition to its application as a low level NO[subscript x] dosimeter, KMnO[subscript 4] shows potential as a precious metal free lean NO[subscript x] trap material (LNT) for NO[subscript x] storage catalysts (NSC) enabling electrical in-situ diagnostics. With this dosimeter, low levels of NO and NO[subscript 2] exposure can be detected electrically as instantaneous values at 380 °C by progressive NO[subscript x] accumulation in the KMnO[subscript 4] based sensitive layer. The linear NO[subscript x] sensing characteristics are recovered periodically by heating to 650 °C or switching to rich atmospheres. Further insight into the NO[subscript x] sorption-dependent conductivity of the KMnO[subscript 4]-based material is obtained by the novel eTPD method that combines electrical characterization with classical temperature programmed desorption (TPD). The NO[subscript x] loading amount increases proportionally to the NO[subscript x] exposure time at sorption temperature. The cumulated NO[subscript x] exposure, as well as the corresponding NO[subscript x] loading state, can be detected linearly by electrical means in two modes: (1) time-continuously during the sorption interval including NO[subscript x] concentration information from the signal derivative or (2) during the short-term thermal NO[subscript x] release., National Science Foundation (U.S.). Division of Materials Research (Material World Network DMR-0908627)

The correlation between the surface chemistry and electronic structure is studied for SrTi[subscript 1−x]Fe[subscript x]O[subscript 3] (STF), as a model perovskite system, to explain the impact of Sr segregation on the oxygen reduction activity of cathodes in solid oxide fuel cells. Dense thin films of SrTi[subscript 0.95]Fe[subscript 0.05]O[subscript 3] (STF5), SrTi[subscript 0.65]Fe[subscript 0.35]O[subscript 3] (STF35) and SrFeO[subscript 3] (STF100) were investigated using a coordinated combination of surface probes. Composition, chemical binding, and valence band structure analysis using angle-resolved X-ray photoelectron spectroscopy showed that Sr enrichment increases on the STF film surfaces with increasing Fe content. In situ scanning tunnelling microscopy/spectroscopy results proved the important and detrimental impact of this cation segregation on the surface electronic structure at high temperature and in an oxygen environment. While no apparent band gap was found on the STF5 surface due to defect states at 345 °C and 10[superscript −3] mbar of oxygen, the surface band gap increased with Fe content, 2.5 ± 0.5 eV for STF35 and 3.6 ± 0.6 eV for STF100, driven by a down-shift in energy of the valence band. This trend is opposite to the dependence of the bulk STF band gap on the Fe fraction, and is attributed to the formation of a Sr-rich surface phase in the form of SrO[subscript x] on the basis of the measured surface band structure. The results demonstrate that Sr segregation on STF can deteriorate oxygen reduction kinetics through two mechanisms – inhibition of electron transfer from bulk STF to oxygen species adsorbing onto the surface and the smaller concentration of oxygen vacancies available on the surface for incorporating oxygen into the lattice., United States. Dept. of Energy. Office of Basic Energy Sciences (Contract DE-SC0002633)

Author Manuscript date May 20, 2011, In this paper we present the parameterization of a new interionic potential for stoichiometric, reduced and doped CeO[subscript 2]. We use a dipole polarizable potential (DIPPIM: the dipole polarizable ion model) and optimize its parameters by fitting them to a series of density functional theory calculations. The resulting potential was tested by calculating a series of fundamental properties for CeO[subscript 2] and by comparing them against experimental values. The values for all the calculated properties (thermal and chemical expansion coefficients, lattice parameters, oxygen migration energies, local crystalline structure and elastic constants) are within 10–15% of the experimental ones, an accuracy comparable to that of ab initio calculations. This result suggests the use of this new potential for reliably predicting atomic scale properties of CeO[subscript 2] in problems where ab initio calculations are not feasible due to their size limitations., Schlumberger-Doll Research Center, National Science Foundation (U.S.) (TeraGrid Research Allocation TG-DMR110004), National Science Foundation (U.S.) (TeraGrid Advanced Support Programme Start-Up Allocation TG-DMR100098), National Science Foundation (U.S.) (TeraGrid Advanced Support Programme Research Allocation TG-DMR110004)

While SOFC perovskite oxide cathodes have been the subject of numerous studies, the critical factors governing their kinetic behavior have remained poorly understood. This has been due to a number of factors including the morphological complexity of the electrode and the electrode- electrolyte interface as well as the evolution of the surface chemistry with varying operating conditions. In this work, the surface chemical composition of dense thin film SrTi_(1−x)Fe_xO_(3-δ) electrodes, with considerably simplified and well-defined electrode geometry, was investigated by means of XPS, focusing on surface cation segregation. An appreciable degree of Sr-excess was found at the surface of STF specimens over the wide composition range studied. The detailed nature of the Sr-excess is discussed by means of depth and take-off angle dependent XPS spectra, in combination with chemical and thermal treatments. Furthermore, the degree of surface segregation was successfully controlled by etching the films, and/or preparing intentionally Sr deficient films. Electrochemical Impedance Spectroscopy studies, under circumstances where surface chemistry was controlled, were used to examine and characterize the blocking effect of Sr segregation on the surface oxygen exchange rate.

In this paper we present the parameterization of a new interionic potential for stoichiometric, reduced and doped CeO$_2$. We use a dipole-polarizable potential (DIPPIM) and optimize its parameters by fitting them to a series of DFT calculations. The resulting potential was tested by calculating a series of fundamental properties for CeO$_2$ and by comparing them to experimental values. The agreement for all the calculated properties (thermal and chemical expansion coefficients, lattice parameters, oxygen migration energies, local crystalline structure and elastic constants) is within 10-15% of the experimental one, an accuracy comparable to that of ab initio calculations. This result suggests the use of this new potential for reliably predicting atomic-scale properties of CeO$_2$ in problems where ab initio calculations are not feasible due to their size-limitations., 12 pages, 6 figures and 5 tables. Accepted on Journal of Physics: Condensed Matter

To understand the kinetics controlling the SOFC cathode processes, a model mixed conducting perovskite materials system, SrTi_(1-x)Fe_xO_(3-δ), was selected, offering the ability to systematically control both the levels of electronic and ionic electrical conductivity as well as the energy band structure. This, in combination with considerably simplified electrode geometry, served to demonstrate that the rate of oxygen exchange at the surface of SrTi_(1-x)Fe_xO_(3-δ) is only weakly correlated with either high electronic or ionic conductivity, in apparent contradiction with common expectations. On the other hand, evidence was found suggesting the importance of minority electronic species in determining the rate of oxygen exchange. Furthermore, the enrichment of Sr to the surface of the electrodes was found to reduce the oxygen exchange rate constant; this effect becoming more evident with increasing values of x. The observed trends are discussed in relation to the cathodic behavior of MIEC electrodes.