Influence of synthetic method on the properties of La0.5Ba0.5FeO3 SOFC cathode

Power Point presentado en The Energy and Materials Research Conference - EMR2015 celebrado en Madrid (España) entre el 25-27 de febrero de 2015Perovskite type (ABO3) oxides have been widely studied as SOFC cathode materials at high temperatures. Given that several of the challenges hindering SOFC technology are consequence of the high operation temperature (about 1000ºC) [1,2], an important goal is to reduce it to 600-800ºC. To minimize this effect new perovskite-type mixed ionic-electronic conducting oxides have been widely studied as promising IT-SOFC cathodes. Among them, iron perovskites (LSF) seem to be good candidates mainly for their appropriate thermal expansion match with YSZ electrolytes and their good catalytic activity for the oxygen reduction [3,4]. The properties of these compounds and thus their cell performance depends on several factors: the right choice of A and B elements, the amount of doping cations (A1-xAx) and some structural parameters such as the tolerance factor [5], the average size of the A-site cations () and the A cation size disorder (σ2(rA)). Studies on the influence of the hole-doping (x) in the A-site of LSF perovskites have shown good cathode performances in compounds with intermediate doping levels [6]. The change of and σ2(rA) indicate that better performances are observed for highest and lowest σ2(rA) [7]. External parameters, such as the synthetic method, are also important factors that influence the final properties [8]. In this sense it has been observed that porosity, grain size and morphology of the compounds strongly depend on the sample preparation techniques. In this research, a La0.5Ba0.5FeO3 perovskite has been synthesized by two different methods (ceramic and glycine-nitrate routes) in order to study the synthetic method influence on the properties of this compound as IT-SOFC cathode material. This composition has been chosen due to its intermediate hole doping level (0.5) and high average size of the A-site cations ( = 1.48 Å, when rA are standard 12-coordinate ionic radii), these parameters, according with previous studies should show interesting properties for its use as SOFC cathode. It has been observed that the two La0.5Ba0.5FeO3 compounds show different room temperature crystal structure depending on the synthesis route. The sample obtained by the ceramic method has higher oxygen vacancy content, but in the other hand the SEM micrographs show that glycine-nitrate process leads to a compound with porous structure and particles with nanometric grain sizes. At 700 or 800ºC the electrical conductivity of both samples is similar but the sample obtained by glycine-nitrate route shows better electrochemical performance. The ceramic sample has lower adherence than the glycine counterpart and this derivates in higher values of polarization resistance. It is believed that this is a consequence of the heterogenous morphology of this sample. Therefore, it seems that the glycine-nitrate synthetic method is a more appropriate technique for preparing perovskite cathodes

Optimization of the large scale synthesis of the LSF-20 cathode material for SOFCs

Póster presentado en: 21st World Hydrogen Energy Conference 2016. Zaragoza, Spain. 13-16th June, 2016Solid oxide fuel cells (SOFCs) have the potential to be one of the cleanest and most efficient energy technologies for direct conversion of chemical fuels to electricity. Economically competitive SOFC systems appear poised for commercialization, but widespread market penetration will require continuous innovation of materials and fabrication processes to enhance system lifetime and reduce cost. Additional requirements arise for the technologies for synthesis of SOFC materials. These requirements originate from the demands for large scale SOFC industrial production. In this sense, solution combustion synthesis (SCS) is a simple and reproducible method used to obtain several types of ceramic oxides for a variety of applications. A typical SCS procedure utilizes a self-sustained exothermic reaction among well-mixed reactants to achieve the rapid and economical synthesis of particulate products. Up to 2008, SCS method has been adopted to fabricate more than 1000 kinds of oxide powders over more than 65 countries [1]. The properties of the resulting powders (crystalline structure, amorphous structure, crystallite size, purity, specific surface area and particle agglomeration) depend heavily on the adopted processing parameters [2,3]. The objective of this work is to obtain, on a large scale, the perovskite-type oxide La0.8Sr0.2FeO3 that shows promising properties as cathode for SOFC applications. In this study, the optimization of the large scale synthesis has been realized by the glycine-nitrate combustion method (Figure 1). In this sense, first of all, the effect of some parameters such as temperature, glycine/nitrate ratio and times and cooling rates used in the temperature treatments, that play a key role in the final properties of the obtained materials, has been analyzed. The characterization has been realized by ICP (inductively coupled plasma atomic emission spectroscopy) XRD (X Ray diffraction), SEM (scanning electron microscopy) and dilatometry.This research has been funded by the Ministerio de Economía y Competitividad (MAT2013-42092-R) with co-financing FEDER-EU) and Dpto. Educación, Política Lingüística y Cultura of the Basque Goverment (IT-630-13). The authors thank SGIker (UPV/EHU) technical support

Effect of the A cation size disorder and synthesis conditions on the properties of an iron perovskite series

Póster presentado en The Energy and Materials Research Conference - EMR2015 celebrado en Madrid (España) entre el 25-27 de febrero de 2015Solid state chemistry thrives on a rich variety of solids that can be synthesized using a wide range of techniques. It is well known that the preparative route plays a critical role on the physical and chemical properties of the reaction products, controlling the structure, morphology, grain size and surface area of the obtained materials. This is particularly important in the area of ABO3 perovskite compounds given that they have for long been at the heart of important applications [1]. Particularly, perovskite systems such as La1-xSrxFeO3 (LSF) are now receiving researchers attention for their interesting applications [2-4] such as ceramic membranes (CMs) for oxygen separation, solid oxide fuel cells (SOFCs) electrodes for efficient power generation, catalysts for complete oxidation of CO in vehicle engines, etc. In order to develop these advanced materials, combustion methods (glycine-nitrate, urea based, and other modifications) have been proposed as one of the most promising methods for their synthesis [5,6]. This method consists of a highly exothermic self-combustion reaction between the fuel (usually glycine, urea or alanine) and the oxidant (metal nitrates), that produces enough heat to obtain the ceramic powders. The characteristics (including purity, structure and size) of the combustion synthesis oxide powders are typically determined by several synthetic parameters, such as the species of fuel and oxidizer reactants, the fuel/oxidizer ratio, and the subsequent sintering treatment after combustion process [7]. In the other hand, physical properties of these perovskite materials are very sensitive to changes in the doping level (x), the average size of the A cations (), and the effects of A cation size disorder (σ2(rA)) quantified as σ2(rA) = – 2 [8]. Our searching approach to find the optimum synthetic conditions for new materials within the LSF system has been based on the study of only one of the indicated parameters isolated from the rest. In this sense, this study is focused on the effect of the variation of the cation size disorder, calcination temperature and the fuel/oxidizer ratio of glycine/nitrate on the structural, morphological, electrical and catalytic properties of a series of Ln0.5M0.5FeO3-δ perovskites (Ln = La, Sm; M = Ba, Sr)

Scalable synthetic method for SOFC compounds

Although economically competitive SOFC systems seems to be ready for commercialization, a broad inventory of key starting materials and fabrication processes are needed to enhance systems and reduce costs. These necessities are raised by the demands for large scale SOFC industrial production. Taking into account these reasons, we have synthesized the mean components of a fuel cell, on a large scale, by the glycine nitrate combustion method. The synthesized different components of SOFC have been the interconnector protective coating (MnCo1.9Fe0.1O4), contact layer (LaNi0.6Fe0.4O3), cathode (La0.6Sr0.4FeO3), interlayer (Sm0.2Ce0.8O1.9), electrolyte (ZrO2)0.92(Y2O3)0.08 and anode (Ni0.3O-(ZrO2)0.92(Y2O3)0.08) material, obtaining reproducible pure samples and amounts up to 12 g for each batch, being able to increase easily this amount to lots of hundred of grams. The obtained materials have been characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray fluorescence (XRF), X-ray diffraction (XRD), dilatometry, scanning electron microscopy (SEM), particle size distribution and conductivity measurements.Ministerio de Economía, Industria y Competitividad (MAT2016-76739-R) (AEI/FEDER, UE) and (MAT2015-2015-86078-R) Dpto. Educación del Gobierno Vasco (IT-630-13) European Regional Development Fund (ERDF). Ministerio de Economía y Competitividad (BES-2014-068433

Scalable synthetic method for SOFC compounds

Although economically competitive SOFC systems seems to be ready for commercialization, a broad inventory of key starting materials and fabrication processes are needed to enhance systems and reduce costs. These necessities are raised by the demands for large scale SOFC industrial production. Taking into account these reasons, we have synthesized the mean components of a fuel cell, on a large scale, by the glycine nitrate combustion method. The synthesized different components of SOFC have been the interconnector protective coating (MnCo1.9Fe0.1O4), contact layer (LaNi0.6Fe0.4O3), cathode (La0.6Sr0.4FeO3), interlayer (Sm0.2Ce0.8O1.9), electrolyte (ZrO2)0.92(Y2O3)0.08 and anode (Ni0.3O-(ZrO2)0.92(Y2O3)0.08) material, obtaining reproducible pure samples and amounts up to 12 g for each batch, being able to increase easily this amount to lots of hundred of grams. The obtained materials have been characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray fluorescence (XRF), X-ray diffraction (XRD), dilatometry, scanning electron microscopy (SEM), particle size distribution and conductivity measurements.Ministerio de Economía, Industria y Competitividad (MAT2016-76739-R) (AEI/FEDER, UE) and (MAT2015-2015-86078-R) Dpto. Educación del Gobierno Vasco (IT-630-13) European Regional Development Fund (ERDF). Ministerio de Economía y Competitividad (BES-2014-068433

Electrochemical and degradation behaviour study of different SOFC compounds

Presentación en: The Energy and Materials Research Conference - EMR2017. Lisbon (Portugal), 5-7 April 2017The present work is focused on manufacturing processes of the solid oxide fuel cell (SOFC) components with previously self-synthesized materials by combustion method [1-2]. The configuration used consists of planar electrolyte-supported symmetric cells, with dense yttria-stabilized zirconia (YSZ) membranes about 20mm diameter and a thickness near 300μm. Ni-yttria-stabilized zirconia cermet (Ni-YSZ) [3] and La0.6Sr0.4FeO3 (LSF40) [4] layers were deposited on the surfaces of the electrolyte as anode and cathode, respectively. In order to decrease the interlayer reactivity and improve the contact between them, Ce0.8Sm0.2O1.9 (SDC), LaNi0.6Fe0.4O3 (LNF60) and MnCo1.9Fe0.1O4 (MCF10) were added in different combinations as protection barrier [5], contact layer [6] and protective layer [7] material, respectively. The deposition of the different compounds has been carried out by manual colloidal spraying, using an organic base solution, or by screen printing. Cross section SEM images have been done to study morphologically the different starting layers. In order to study the degradation of the samples after 500h of exposure time at a temperature of 800 ºC, the energy-dispersive X-ray spectroscopy analysis of the cross sectional micrographs has been evaluated. Electrochemical impedance spectroscopy was used to characterize the electrochemical properties of the different components and multilayer structures.Economía, Industria y Competitividad (MAT2016-76739-R) (AEI/FEDER, UE) and (MAT2015-2015-86078-R) Dpto. Educación of the Basque Goverment (IT-630-13). European Regional Development Fund (ERDF). A. Wain-Martin thanks Ministerio de Economía y Competitividad for funding his work (BES-2014-068433)

Negative correlation of doping and conductivity in Ln1-xMxCr0.9Ni0.1O3 (Ln = La and/or Nd; M = Sr and/or Ca; x≤0.25) perovskites prepared by combustion synthesis as anode materials for SOFCs

A series of chromite perovskites with the general formula Ln1−xMxCr0.9Ni0.1O3 (Ln = La and/or Nd; M = Sr and/or Ca; x ≤ 0.25) has been prepared by three combustion synthesis routes using a different combustible substance each time: glycine, urea and sucrose. In order to isolate the effect of divalent dopant concentration from the A cation steric effects, the whole group has a fixed mean A cation radius, ≈ 1.22 Å, and cation size disorder, σ2(rA) ≈ 0.0001 Å2, but variable doping x. Their crystal structure, microstructure, electrical properties and expansion coefficients have been investigated on the basis of their possible use as anode materials for intermediate temperature solid oxide fuel cells (SOFC). Cell parameters, grain sizes, expansion coefficients and conductivities all are found to be dependent on x and the combustible substance used. The most interesting relationship is the negative dependence of the conductivity with x under H2 atmosphere: conductivity decreases with doping which is the opposite to the expected behavior for a p-type doped perovskites and has not been reported before.Ministerio de Economía y Competitividad, MAT2016-76739-R // Dpto. Educación, Política Lingüística y Cultura of the Basque Government, IT-630-1

Materiales para su aplicación en celdas SOFCs

Poster presentado en la conferencia: XXXV Bienal de la Real Sociedad Española de Química (A Coruña, 19-23 de Julio de 2015)Se han sintetizado cinco compuestos (La0.4Sr0.6FeO3, LaNi0.6Fe0.4O3, Zr0.8Y0.2O1.9 , Sm0.2Ce0.8O1.9 y MnCo1.9Fe0.1O4) mediante la técnica de combustión glicina - nitrato (G/N = 1) [1], para su utilización como cátodo, electrolito, barrera, capas de contacto y protectoras, en celdas de combustible de óxido sólido de temperatura intermedia (IT-SOFC). Las muestras se han caracterizado mediante difracción de rayos X (DRX) y microscopía electrónica de barrido (MEB), técnicas que han permitido analizar las estructuras y la morfología de los diferentes compuestos. La difracción de rayos X sobre muestra policristalina ha permitido identificar tanto el sistema cristalino de los compuestos como su grupo espacial. Microestructuralmente todos los materiales presentan un tamaño de grano pequeño y superficies homogéneas y porosas.Ministerio de Economía y Competitividad (MAT2013-42092-R), Dpto. de Educación, Política Lingüística y Cultura del Gobierno Vasco (IT-630-13),Fondo Europeo de Desarrollo Regional (FEDER) y Ministerio de Economía y Competitividad (BES-2014-068433)

Nuevas cromitas de composición La1-xMxCr0.9Ni0.1O3(M=Sr, ND, Ca; x<0.3) con tamaño de A y desorden fijados, para su uso como ánodos de pilas SOFCs

Póster presentado en el XIV Congreso Nacional de Materiales (CNMAT) en Gijón (España), del 8 al 10 de Junio de 2016El desarrollo de nuevos materiales y la optimización de las técnicas de fabricación son claves para conseguir reducir la temperatura de operación, y con ello, el coste, de sistemas de generación de energía como las pilas de combustible de óxido sólido, SOFC [1]. Los métodos de combustión, se proponen como la vía de síntesis para la preparación de materiales a emplear en esta tecnología [2]. Los ánodos habituales de las pilas SOFC son cermets de metales como el níquel o cobre junto con el material de electrolito (ceria o circonia dopadas). Entre los principales problemas de esos ánodos está el de la deposición de carbón cuando se usan combustibles económicos como el metano. En este sentido, se ha observado que el óxido de cromo dopado con estroncio (La,Sr)CrO3, además de ser un buen conductor electrónico tipo p, no cataliza la deposición de carbono, por lo que es un ánodo potencial para la oxidación directa de metano. Las cromitas son buenas conductoras de la electricidad (dopadas o sin dopar), pero su actividad catalítica mejora considerablemente si el dopaje se da con metales de transición (Mn,Fe,Co,Ni,Cu) en la posición del cromo [3]. En esta investigación se ha realizado un estudio del efecto del dopaje en A, pero fijando el tamaño promedio de A (en 1.22 Å) y el desorden de esta posición (0.0001 Å2), que está asociado a la diferencia de tamaños de esos elementos. Se han sintetizado cuatro compuestos de la serie La1‐xMxCr0.9Ni0.1O3 (M=Sr, Nd, Ca o sus combinaciones; con x=0.10, 0.15, 0.20 y 0.25) mediante el método de combustión con glicina‐nitrato. Los resultados preliminares por difracción de rayos X en muestra policristalina indican que son fases rómbicas con simetría Pnma. En el presente trabajo se mostrarán los resultados de tamaño de grano de los mismos, estudiados por microscopía electrónica de barrido (MEB) y los datos de conductividad electrónica y dilatometría (TEC).Esta investigación ha sido financiada por el Dpto. Educación, Política Lingüística y Cultura del Gobierno Vasco (IT-630-13), Ministerio de Economía y Competitividad (MAT2013-42092-R)y el Fondo Europeo de Desarrollo Regional (FEDER)

Celdas de pilas de oxidó solido, avance en el procesado de materiales

Póster presentado en el XIV Congreso Nacional de Materiales (CNMAT) en Gijón (España), del 8 al 10 de Junio de 2016Este trabajo está enfocado a la síntesis y al procesado de los componentes de las pilas de combustible de óxido sólido (SOFC). La configuración empleada consiste en celdas (ánodo/electrolito/cátodo) soportadas por el electrolito. Se han sintetizado los compuestos, NiO-(ZrO2)0.92(Y2O3)0.08, (ZrO2)0.92(Y2O3)0.08 y La0.6Sr0.4FeO3 como ánodo, electrolito y cátodo, respectivamente. Con objeto de disminuir la reactividad electrolito-cátodo, se ha empleado una barrera Ce0.8Sm0.2O1.9 entre ambos componentes. En buen acuerdo con K. Vidal y col. 1 se ha utilizado la técnica de combustión por glicina-nitrato para la síntesis de los compuestos. La evaluación de la pureza, morfología y conductividad se ha llevado a cabo mediante difracción de rayos X (XRD) (método Rietveld), microscopía electrónica de barrido (MEB) y medidas de conductividad en bulk a través del método de cuatro puntos. Para el procesado del electrolito se ha empleado una prensa hidráulica, obteniéndose pastillas de 20 mm de diámetro y 500μm de espesor. Éstas se han sinterizado a 1450 ºC durante 4 h en aire, con objeto de alcanzar las propiedades físico-químicas adecuadas. La deposición del ánodo, cátodo y barrera se ha realizado por spray manual coloidal, empleándose una solución en base orgánica. Para analizar el comportamiento electroquímico de la estructura multicapa, se han realizado medidas de impedancia a 800 ºC durante 100 h. La degradación de los sistemas se ha estudiado a partir de análisis por energía dispersiva de rayos X (EDX) mediante el análisis de las micrografías de las secciones transversales. Agradecimientos: Esta investigación haEsta investigación ha sido financiada por el Dpto. Educación, Política Lingüística y Cultura del Gobierno Vasco (IT-630-13) y al Ministerio de Economía y Competitividad (MAT2013-42092-R). Ministerio de Economía y Competitividad por la beca (BES-2014-068433)