Properties of B-site substituted La0.5Sr0.5FeO3−δ{\mathbf{La}}_{{0.5}} {\mathbf{Sr}}_{{0.5}} {\mathbf{FeO}}_{{3 - {\mathbf{\delta }}}} perovskites for application in oxygen separation membranes

Mixed ionic-electronic conducting $$La_{0.5} Sr_{0.5} Fe_{1 - x} B_x O_{3 - \delta }$$ (B: Al, Cr, Zr, Ga, Ti, Sn, Ta, V, Mg, and In with x = 0, 0.1, 0.2) perovskite materials were produced via solid-state synthesis. In order to study the effect of B-site substitution on the expansion behavior of these materials, their thermal expansion in air up to 900°C and isothermal expansion at the same temperature from air to Ar were measured by dilatometry. Ti and Ta were found to be the most effective substitutions in suppressing the isothermal expansion. The isothermal expansion at 900°C from air to Ar was reduced by 50% by substitution of 20% Ti or 10% Ta. Therefore, these compositions were further characterized by 4-probe total DC conductivity and permeation measurements under air/Ar gradient. The total conductivity of $$La_{0.5} Sr_{0.5} FeO_{3 - \delta }$$ was decreased by more than one order of magnitude at low temperatures and from 430S/cm, which is the maximum, to around 100S/cm at 500°C with the addition of Ti and Ta. The normalized oxygen permeation of LSF at 900°C decreased from 0.18 to 0.05μmol/cm2s and 0.07μmol/cm2s with the substitution of 20% Ti and 10% Ta, respectivel

Oxygen transport in La0.5Sr0.5Fe1−yTiyO3− δ ( y =0.0, 0.2) membranes

The influence of partial substitution of Fe with Ti on the oxygen transport properties of La1−x Sr x FeO3 membranes was investigated in view of their application for oxygen separation. Samples of composition $$La_{{0.5}} Sr_{{0.5}} {\text{Fe}}_{{1 - y}} {\text{Ti}}_{y} {\text{O}}_{{3 - \delta }}$$ (y=0, 0.2) were prepared and their oxygen transport properties characterised by potential step relaxation and by oxygen permeation measurement in an air/argon gradient. With the first technique, chemical diffusion $${( {\widetilde{D}} )}$$ and surface exchange (k S) coefficients were obtained by fitting of the current relaxation data to a single expression valid over the complete time range. The Ti-substituted composition gave slightly larger values of $${\widetilde{D}}$$ and k S. The trend was opposite for the measured oxygen permeation flux. In the latter experience, ordering of oxygen vacancies was observed at lower temperature, reducing significantly the performance of the materia

Ethanol internal steam reforming in intermediate temperature solid oxide fuel cell

This study investigates the performance of a standard Ni-YSZ anode supported cell under ethanol steam reforming operating conditions. Therefore, the fuel cell was directly operated with a steam/ethanol mixture (3 to 1 molar). Other gas mixtures were also used for comparison to check the conversion of ethanol and of reformate gases (H2, CO) in the fuel cell. The electrochemical properties of the fuel cell fed with 4 different fuel compositions were characterized between 710 and 860°C by I-V and EIS measurements at OCV and under polarization. In order to elucidate the limiting processes, impedance spectra obtained with different gas compositions were compared using the derivative of the real part of the impedance with respect of the natural logarithm of the frequency. Results show that internal steam reforming of ethanol takes place significantly on Ni-YSZ anode only above 760°C. Comparisons of results obtained with reformate gas showed that the electrochemical cell performance is dominated by the conversion of hydrogen. The conversion of CO also occurs either directly or indirectly through the water-gas shift reaction but has a significant impact on the electrochemical performance only above 760°C

In-situ experimental benchmarking of solid oxide fuel cell metal interconnect solutions

The progress in the diffusion of solid oxide fuel cell (SOFC) as commercial devices is not paired by literature production. Articles describing the behaviour of SOFC stacks are rare because of confidentiality reasons for commercial suppliers while research centres prefer to focus on single components or low technology readiness level research. This article aim to fill this gap presenting the analysis of three short stacks run in operative conditions for 10 000 h each. The stacks are characterized through voltage vs time curves, electron microscopy, and electrochemical impedance spectroscopy. Focus is given on the interconnect; notably on the different types of coatings, varying for composition (MnCo2O4, MnCo1.8Fe0.2O4) and deposition technique (atmospheric plasma spray-APS, physical vapour deposition-PVD, wet powder spraying-WPS). Nitriding of the steel substrate as a solution to improve the chromium retention properties is tested as well

Oxygen transport and nonstoichiometry in SrFeO3-delta

Chemical diffusion (D) and surface exchange (k) coefficients for SrFeO3-delta were measured using an electrochemical cell combined with electrochemical impedance spectroscopy (EIS) and potential step technique (PS) in the temperature range of 850-915°C. A value of ~ 4x10-5 cm2/s and a k value of ~ 8x10-5 cm/s were obtained at 900°C. Slow scan (0.5-3 microV/s) cyclic voltametry (CV) was performed in the same temperature range, using the same electrochemical cell to obtain oxygen nonstoichiometry data. The oxygen nonstoichiometry (delta) at 900°C in air was determined as 0.4. A plateau corresponding to delta = 0.5 was observed below an oxygen partial pressure (pO2) of 10-6 atm. These results were shown to be consistent with the literature data. Nonstoichiometry data were further analysed using the existing defect models, and the limits of the independent point defect approximation and the necessity of considering interactions between point defects and clusters were established. Keywords: Strontium Ferrate/Ferrite; Oxygen transport; Oxygen nonstoichiometry

Modeling of Local Cell Degradation in Solid Oxide Fuel Cells: Cumulative Effect of Critical Operating Points

A CFD model was developed to predict with accuracy the local electrochemical performance in an operating solid oxide fuel cell. A particular focus was given on the study of performance limitations and degradation sources caused by the design of the fuel cell, by the choice of materials and components, or by improper operating points. The model is used to understand typical degradation effects observed on stacks tested in collaboration with HTCeramix - SOFCpower. The model is able to predict several degradation effects caused by the use of compressive seal materials with remaining open porosity. Diffusion across seals is modeled, as well as the resulting parasitic combustion of air and fuel. The risk of local redox-cycling for the anode supported cell is evaluated locally, as well as an eventual local reduction of the cathode layers. The cracking of electrolyte caused by redox cycles is modeled locally, with increasing gas leakage at each cycle, allowing to model the cumulative effect of successive critical operating points. The results are compared with experiments, showing an overall good agreement

Towards the Next-Generation of Solid Oxide Fuel Cell Systems

To improve the industry benchmark of solid oxide fuel cell systems (SOFC), we consider anode off-gas recirculation using a blower as an add-on to our next-generation SOFC system. Evolutionary algorithms compare the different design alternatives, i.e. co-flow or counter-flow stack operation with hot or cold recirculation. The system performance is evaluated through multiobjective optimization criteria, i.e. maximization of electrical efficiency and cogeneration efficiency. The results obtained suggest that improvements to the best SOFC systems, in terms of net electrical efficiency, are achievable

Avifauna e uso da terra: o caso do Parque Natural de Montesinho

Apresenta-se uma possível utilização da informação dos atlas de avifauna como instrumentos de apoio à gestão de áreas de alta diversidade biológica. O atlas de avifauna do Parque Natural de Montesinho recolhe a informação relativa a um total de 119 espécies, de aves referenciadas, em 48 quadrículas de 5 por 5 quilómetros. A relação entre a avifauna e os sistemas de utilização da terra que a sustenta estimou-se por correlações canónicas (CCA - ter Braak, 1986). Uma análise de classificação (TWINSPAN- Hill, 1979) permitiu discriminar os sectores representativos do PNM. A amplitude de nicho das espécies em relação aos usos da terra, assim como a sua capacidade descritiva e discriminante, avaliam-se, mediante índices de informação (Shannon e Weaver, 1949). Os três eixos gerados pelas CCA avaliaram em 0,594, 0,689 e 0,633 a correlação (Kendall) da avifauna e os usos da terra considerados. Os seus resultados classificam o território do PNM em duas grandes unidades separadas pelo Rio Sabor, o sector ocidental evidencia gradientes climáticos e o oriental gradientes fisiográficos. São fundamentalmente passariformes residentes e biogeografia paleártica (Alauda arvensis, Pica pica, Passer montanus, etc.) as espécies mais envolvidas na dinâmica do território, apresentando os mais elevados valores de entropia. Os usos da terra apresentam distintas relações com o valor informativo das variáveis avifaunísticas. Destacam-se as relações positivas com os secadais, soutos e carvalhais, as neutras com as culturas de regadio e as negativas com os pinhais. A preponderância dos passeriformes residentes na discriminação do território destaca a escala de trabalho, para as quais o uso da terra têm uma importância acrescida na determinação do habitat dessas espécies. As relações com o uso da terra parecem manifestar uma adaptação da avifauna aos sistemas agrários tradicionais ( dos carvalhais aos lameiros e soutos), o que não ocorrerá em relação às formas mais modernas de utilização da terra (regadio e pinhais).Reitoria da Universidade de Coimbra, Fundação Calouste Gulbenkian, Fundação para a Ciência e Tecnologia, Fundação Luso-Americana para o Desenvolvimento, Câmara Municipal de Coimbra, Região de Turismo do Centro, Banco do Comércio e Indústria, SA, Cafés Delt

Geospatial Information Research: State of the Art, Case Studies and Future Perspectives

Geospatial information science (GI science) is concerned with the development and application of geodetic and information science methods for modeling, acquiring, sharing, managing, exploring, analyzing, synthesizing, visualizing, and evaluating data on spatio-temporal phenomena related to the Earth. As an interdisciplinary scientific discipline, it focuses on developing and adapting information technologies to understand processes on the Earth and human-place interactions, to detect and predict trends and patterns in the observed data, and to support decision making. The authors – members of DGK, the Geoinformatics division, as part of the Committee on Geodesy of the Bavarian Academy of Sciences and Humanities, representing geodetic research and university teaching in Germany – have prepared this paper as a means to point out future research questions and directions in geospatial information science. For the different facets of geospatial information science, the state of art is presented and underlined with mostly own case studies. The paper thus illustrates which contributions the German GI community makes and which research perspectives arise in geospatial information science. The paper further demonstrates that GI science, with its expertise in data acquisition and interpretation, information modeling and management, integration, decision support, visualization, and dissemination, can help solve many of the grand challenges facing society today and in the future