Biodegradable FeMnSi sputter-coated macroporous polypropylene membranes for the sustained release of drugs

Pure Fe and FeMnSi thin films were sputtered on macroporous polypropylene (PP) membranes with the aim to obtain biocompatible, biodegradable and, eventually, magnetically-steerable platforms. Room-temperature ferromagnetic response was observed in both Fe- and FeMnSi-coated membranes. Good cell viability was observed in both cases by means of cytotoxicity studies, though the FeMnSi-coated membranes showed higher biodegradability than the Fe-coated ones. Various strategies to functionalize the porous platforms with transferrin-Alexa Fluor 488 (Tf-AF488) molecules were tested to determine an optimal balance between the functionalization yield and the cargo release. The distribution of Tf-AF488 within the FeMnSi-coated PP membranes, as well as its release and uptake by cells, was studied by confocal laser scanning microscopy. A homogeneous distribution of the drug within the membrane skeleton and its sustained release was achieved after three consecutive impregnations followed by the addition of a layer made of gelatin and maltodextrin, which prevented exceedingly fast release. The here-prepared organic-inorganic macroporous membranes could find applications as fixed or magnetically-steerable drug delivery platforms

The impact of Mn nonstoichiometry on the oxygen mass transport properties of La0.8Sr0.2MnyO3±δ thin films

Oxygen mass transport in perovskite oxides is relevant for a variety of energy and information technologies. In oxide thin films, cation nonstoichiometry is often found but its impact on the oxygen transport properties is not well understood. Here, we used oxygen isotope exchange depth profile technique coupled with secondary ion mass spectrometry to study oxygen mass transport and the defect compensation mechanism of Mn-deficient La0.8Sr0.2Mn (y) O-3 +/-delta epitaxial thin films. Oxygen diffusivity and surface exchange coefficients were observed to be consistent with literature measurements and to be independent on the degree of Mn deficiency in the layers. Defect chemistry modeling, together with a collection of different experimental techniques, suggests that the Mn-deficiency is mainly compensated by the formation of La-x(Mn) antisite defects. The results highlight the importance of antisite defects in perovskite thin films for mitigating cationic nonstoichiometry effects on oxygen mass transport properties

Advanced Thin Film Electrode Materials for Application in Solid Oxide Cells

La indústria energètica està actualment a la vora d'una transició cap un paradigma sostenible potenciat per les energies renovables. Entre les alternatives als combustibles fòssils, l'ús de sistemes basats en cel·les d'òxid sòlid (SOC) és un candidat prometedor. Les SOC són les tecnologies més eficients de generació elèctrica i producció d'hidrogen, cosa que les fa una solució interessant per sistemes d'energia reversibles. No obstant, la seva aplicació en solucions reals es troba normalment limitada per la presència de processos activats tèrmicament, la qual cosa restringeix la seva operació al rang d'altes temperatures. Per conseqüent, aquests dispositius pateixen regularment de degradació induïda per processos tèrmics. Això fa que hi hagi un clar interès per descobrir nois materials que i) presentin activitat electroquímica millorada a baixes temperatures i ii) mantinguin el seu rendiment en el temps. S'ha demostrat que l'ús d'elèctrodes de capa fina basats en nanoestructures millora el rendiment a temperatures molt més baixes. Aquesta tesi s'ha focalitzat en el desenvolupament te materials altament funcionals basats en capa fina com a elèctrodes SOC. La investigació portada a terme s'ha dividit en tres parts principals: i) desenvolupament de nanocompòsits de La0.75Sr0.25Cr0.5Mn0.5O3 (LSCrMn) i Ce0.8Sm0.2O2 (SDC) per a la seva aplicació en elèctrodes de combustible i simètrics; ii) la caracterització de les propietats funcionals de la llibreria La0.8Sr0.2MnxCoyFe1-x-yO3 (LSMCF) per aplicació com elèctrodes d'oxigen; iii) la implementació de materials d'elèctrode de capa fina en diferents arquitectures de cel·la. La primera part de la tesi cobreix el desenvolupament d'elèctrodes nanocompòsits basats en capa fina. En primer lloc, nanocompòsits cermet de Ni-Ce0.9Gd0.1O2 (NiCGO) s'han estudiat com elèctrodes de combustible. S'ha trobat un nanocompòsit dens de LSCrMn-SDC que presenta alta activitat electroquímica baix condicions tant reductores com oxidants, sense apreciació de degradació significativa. Més estudis s'han realitzat per la optimització de la microestructura, aconseguint millorar el rendiment front l'oxidació d'hidrogen. La segona part de la tesi investiga la llibreria de LSMCF per la seva aplicació en elèctrodes d'oxigen. L'LSMCF s'ha estudiat per mitjans de metodologies d'alt rendiment per la caracterització completa de les propietats estructurals i electrocatalítiques. Els resultats mostren alta cinètica de transport d'oxigen per les regions riques en Fe/Co, així com baixa energia d'activació pels compostos co-dopats. Estudis del rendiment front la degradació han mostrat un comportament d'alta estabilitat per l'LSMCF co-dopat i l'La0.8Sr0.2MnO3 (LSM), en comparació amb l'La0.8Sr0.2CoO3 (LSC) i l'La0.8Sr0.2FeO3 (LSF). A la part final de la tesi s'ha estudiat la integració de materials en capa fina per elèctrodes en dispositius SOC complets. L'ús de capes fines de La0.9Sr0.1CrO3 (LSCr) com elèctrodes simètric s'ha analitzat per mitjà de l'operació baix condicions de ciclat redox. L'ús de capes fines d'LSC i SDC en sistemes reversibles SOC s'ha estudiat baix operació en modes de cel·les de combustible i electròlisi. Finalment, la integració de materials en capa fina en micro-SOCs s'ha estudiat, aconseguint fabricar dispositius a nivell de prova de concepte sobre substrats de silici. Aquest manuscrit ofereix un estudi exhaustiu del desenvolupament de materials funcionals basats en capa fina destinats a superar les limitacions que afecten als elèctrodes de les SOC. L'ús de processos de nanoenginyeria i metodologies combinatorials per la recerca en materials es presenten com aproximacions prometedores per al descobriment de materials d'elèctrode d'alt rendiment. La integració exitosa d'aquest tipus de materials en diferents arquitectures es proposa com a validació de la versatilitat en els àmbits d'aplicació dels materials en capa fina investigats.La industria energética está actualmente al borde de una transición hacia un paradigma sostenible potenciado por las energías renovables. Entre las alternativas a los combustibles fósiles, el uso de sistemas basados en celdas de óxido sólido (SOC) es un candidato prometedor. Las SOC son las tecnologías más eficientes de generación eléctrica y producción de hidrógeno, cosa que las hace una solución interesante para sistemas de energía reversibles. No obstante, su aplicación en soluciones reales se encuentra normalmente limitada por la presencia de procesos activados térmicamente, lo cual restringe su operación al rango de altas temperaturas. Por consiguiente estos dispositivos sufren regularmente de degradación inducida por procesos térmicos. Esto hace que haya un claro interés por descubrir nuevos materiales que i) presenten actividad electroquímica mejorada a bajas temperaturas y ii) mantengan su rendimiento en el tiempo. Se ha demostrado que el uso de electrodos de capa fina basados en nanoestructuras mejora el rendimiento a temperaturas mucho más bajas. Esta tesis se ha enfocado en el desarrollo de materiales altamente funcionales basados en capa fina como electrodos SOC. La investigación llevada a cabo se ha dividido en tres partes principales: i) desarrollo de nanocompuestos de La0.75Sr0.25Cr0.5Mn0.5O3 (LSCrMn) y Ce0.8Sm0.2O2 (SDC) para su aplicación en electrodos de combustible y simétricos; ii) la caracterización de las propiedades funcionales de la librería La0.8Sr0.2MnxCoyFe1-x-yO3 (LSMCF) para aplicación como electrodos de oxígeno; iii) la implementación de materiales de electrodo de capa fina en diferentes arquitecturas de celda. La primera parte de la tesis cubre el desarrollo de electrodos nanocompuestos basados en capa fina. En primer lugar, nanocompuestos cermet de Ni-Ce0.9Gd0.1O2 (NiCGO) se han estudiado como electrodos de combustible. Se ha encontrado un nanocompuesto denso de LSCrMn-SDC que presenta alta actividad electroquímica bajo condiciones tanto reductoras como oxidantes, sin apreciación de degradación significativa. Más estudios se han realizado para la optimización de la microestructura, consiguiendo mejorar el rendimiento frente a la oxidación de hidrógeno. La segunda parte de la tesis investiga la librería de LSMCF para su aplicación en electrodos de oxígeno. El LSMCF se ha estudiado por medio de metodologías de alto rendimiento para la caracterización completa de las propiedades estructurales y electrocatalíticas. Los resultados muestran alta cinética de transporte de oxígeno para las regiones ricas en Fe/Co, así como baja energía de activación para los compuestos co-dopados. Estudios del rendimiento frente a la degradación han mostrado un comportamiento con alta estabilidad para el LSMCF co-dopado y el La0.8Sr0.2MnO3 (LSM) en comparación con el La0.8Sr0.2CoO3 (LSC) y el La0.8Sr0.2FeO3 (LSF). En la parte final de la tesis se ha estudiado la integración de materiales de capa fina para electrodos en dispositivos SOC completos. El uso de capas finas de La0.9Sr0.1CrO3 (LSCr) como electrodos simétricos se ha analizado por medio de la operación bajo condiciones de ciclado redox. El uso de capas finas de LSC y SDC en sistemas reversibles SOC se ha estudiado bajo operación en modos de celda de combustible y de electrólisis. Finalmente, la integración de materiales de capa fina en micro-SOCs se ha estudiado, consiguiendo fabricar dispositivos a nivel de prueba de concepto sobre sustratos de silicio. Este manuscrito ofrece un estudio exhaustivo del desarrollo de materiales funcionales basados en capa fina destinados a superar las limitaciones que afectan a los electrodos de las SOC. El uso de procesos de nanoingeniería y metodologías combinatoriales para la investigación en materiales se presentan como aproximaciones prometedoras para el descubrimiento de materiales de electrodo de alto rendimiento. La integración exitosa de este tipo de materiales en distintas arquitecturas se propone como validación de la versatilidad en los ámbitos de aplicación de los materiales de capa fina investigados.The energy industry is currently on the verge of transitioning into a sustainable paradigm powered by renewable energies. Among the alternatives to fossil fuel-driven technologies, the use of solid oxide cell (SOC) systems is a promising candidate. SOCs are the most efficient technologies for electrical power generation and hydrogen production, making them an interesting solution for reversible energy systems. Nonetheless, the expansion of SOC technologies into real life applications is often hindered by the presence of thermally activated processes, restricting the operation to the high temperature regime. Consequently, thermally-driven degradation is regularly experienced in these devices. There is a clear interest then in the discovery of new materials that i) present enhanced electrochemical activity at lower temperatures and ii) keep their performance over time. The use of thin film electrodes based on engineered nanostructures has been demonstrated to improve the performance at much lower operational temperatures. This thesis is then focused on the development of thin film-based highly functional materials for SOC electrode application. The research carried out has been divided in three main parts: i) development of La0.75Sr0.25Cr0.5Mn0.5O3 (LSCrMn) and Ce0.8Sm0.2O2 (SDC) nanocomposites for application in fuel and symmetric electrodes; ii) characterization of the functional properties of the La0.8Sr0.2MnxCoyFe1-x-yO3 (LSMCF) library for application as oxygen electrodes; iii) implementation of thin film electrode materials under different cell architectures. The first part of the thesis deals with the development of thin film-based nanocomposite electrodes. First, Ni-Ce0.9Gd0.1O2 (NiCGO) cermet nanocomposites were studied as promising fuel electrodes. Additionally, all-ceramic LSCrMn-SDC heterostructures were also investigated. Specifically, a dense LSCrMn-SDC nanocomposite was found to present remarkable electrochemical activity under both reducing and oxidizing conditions, with no significant degradation observed. Further studies were carried out for the optimization of the heterostructures microstructure, leading to enhanced performance for hydrogen oxidation. The second part of this thesis investigated the LSMCF library for application as oxygen electrodes. The complete library was fabricated in a single process by means of combinatorial deposition. LSMCF was then studied by high-throughput methodologies for full characterization of the structural and electrocatalytic properties. The results showed high oxygen kinetics for the Fe- and Co-rich regions and remarkable low activation energy for the intermixed co-doped compositions studied. Studies on degradation performance showed distinctive behaviour with remarkable stability of the co-doped LSMCF and La0.8Sr0.2MnO3 (LSM) with respect to single La0.8Sr0.2CoO3 (LSC) and La0.8Sr0.2FeO3 (LSF). Analyses beyond the subsurface revealed the presence of highly off-stoichiometric regions and apparent overall increase of defect size and defect density. In the final part of the thesis, the integration of thin film electrode materials in full SOC devices have been studied. Specifically, the use of La0.9Sr0.1CrO3 (LSCr) thin films as symmetric electrodes has been analysed by operating a cell under redox cycling conditions. The use of thin film LSC and SDC in reversible SOC systems was studied under fuel cell and electrolysis operation modes. Finally, the integration of all-ceramic thin film materials in micro-SOCs was explored, with successful fabrication of proof-of-concept devices supported in silicon. This manuscript offers a thorough study for the development of thin film-based functional materials aimed to overcome the limitations affecting SOC electrodes. The use of nanoengineering processes and combinatorial methods for material research are presented as promising routes for the discovery of electrode materials with enhanced performance. The successful integration of these type of materials in different device architectures is proposed as validation of the versatility in application of the thin film materials investigated.Universitat Autònoma de Barcelona. Programa de Doctorat en Ciència de Material

Advanced Thin Film Electrode Materials for Application in Solid Oxide Cells

La indústria energètica està actualment a la vora d'una transició cap un paradigma sostenible potenciat per les energies renovables. Entre les alternatives als combustibles fòssils, l'ús de sistemes basats en cel·les d'òxid sòlid (SOC) és un candidat prometedor. Les SOC són les tecnologies més eficients de generació elèctrica i producció d'hidrogen, cosa que les fa una solució interessant per sistemes d'energia reversibles. No obstant, la seva aplicació en solucions reals es troba normalment limitada per la presència de processos activats tèrmicament, la qual cosa restringeix la seva operació al rang d'altes temperatures. Per conseqüent, aquests dispositius pateixen regularment de degradació induïda per processos tèrmics. Això fa que hi hagi un clar interès per descobrir nois materials que i) presentin activitat electroquímica millorada a baixes temperatures i ii) mantinguin el seu rendiment en el temps. S'ha demostrat que l'ús d'elèctrodes de capa fina basats en nanoestructures millora el rendiment a temperatures molt més baixes. Aquesta tesi s'ha focalitzat en el desenvolupament te materials altament funcionals basats en capa fina com a elèctrodes SOC. La investigació portada a terme s'ha dividit en tres parts principals: i) desenvolupament de nanocompòsits de La0.75Sr0.25Cr0.5Mn0.5O3 (LSCrMn) i Ce0.8Sm0.2O2 (SDC) per a la seva aplicació en elèctrodes de combustible i simètrics; ii) la caracterització de les propietats funcionals de la llibreria La0.8Sr0.2MnxCoyFe1-x-yO3 (LSMCF) per aplicació com elèctrodes d'oxigen; iii) la implementació de materials d'elèctrode de capa fina en diferents arquitectures de cel·la. La primera part de la tesi cobreix el desenvolupament d'elèctrodes nanocompòsits basats en capa fina. En primer lloc, nanocompòsits cermet de Ni-Ce0.9Gd0.1O2 (NiCGO) s'han estudiat com elèctrodes de combustible. S'ha trobat un nanocompòsit dens de LSCrMn-SDC que presenta alta activitat electroquímica baix condicions tant reductores com oxidants, sense apreciació de degradació significativa. Més estudis s'han realitzat per la optimització de la microestructura, aconseguint millorar el rendiment front l'oxidació d'hidrogen. La segona part de la tesi investiga la llibreria de LSMCF per la seva aplicació en elèctrodes d'oxigen. L'LSMCF s'ha estudiat per mitjans de metodologies d'alt rendiment per la caracterització completa de les propietats estructurals i electrocatalítiques. Els resultats mostren alta cinètica de transport d'oxigen per les regions riques en Fe/Co, així com baixa energia d'activació pels compostos co-dopats. Estudis del rendiment front la degradació han mostrat un comportament d'alta estabilitat per l'LSMCF co-dopat i l'La0.8Sr0.2MnO3 (LSM), en comparació amb l'La0.8Sr0.2CoO3 (LSC) i l'La0.8Sr0.2FeO3 (LSF). A la part final de la tesi s'ha estudiat la integració de materials en capa fina per elèctrodes en dispositius SOC complets. L'ús de capes fines de La0.9Sr0.1CrO3 (LSCr) com elèctrodes simètric s'ha analitzat per mitjà de l'operació baix condicions de ciclat redox. L'ús de capes fines d'LSC i SDC en sistemes reversibles SOC s'ha estudiat baix operació en modes de cel·les de combustible i electròlisi. Finalment, la integració de materials en capa fina en micro-SOCs s'ha estudiat, aconseguint fabricar dispositius a nivell de prova de concepte sobre substrats de silici. Aquest manuscrit ofereix un estudi exhaustiu del desenvolupament de materials funcionals basats en capa fina destinats a superar les limitacions que afecten als elèctrodes de les SOC. L'ús de processos de nanoenginyeria i metodologies combinatorials per la recerca en materials es presenten com aproximacions prometedores per al descobriment de materials d'elèctrode d'alt rendiment. La integració exitosa d'aquest tipus de materials en diferents arquitectures es proposa com a validació de la versatilitat en els àmbits d'aplicació dels materials en capa fina investigats.La industria energética está actualmente al borde de una transición hacia un paradigma sostenible potenciado por las energías renovables. Entre las alternativas a los combustibles fósiles, el uso de sistemas basados en celdas de óxido sólido (SOC) es un candidato prometedor. Las SOC son las tecnologías más eficientes de generación eléctrica y producción de hidrógeno, cosa que las hace una solución interesante para sistemas de energía reversibles. No obstante, su aplicación en soluciones reales se encuentra normalmente limitada por la presencia de procesos activados térmicamente, lo cual restringe su operación al rango de altas temperaturas. Por consiguiente estos dispositivos sufren regularmente de degradación inducida por procesos térmicos. Esto hace que haya un claro interés por descubrir nuevos materiales que i) presenten actividad electroquímica mejorada a bajas temperaturas y ii) mantengan su rendimiento en el tiempo. Se ha demostrado que el uso de electrodos de capa fina basados en nanoestructuras mejora el rendimiento a temperaturas mucho más bajas. Esta tesis se ha enfocado en el desarrollo de materiales altamente funcionales basados en capa fina como electrodos SOC. La investigación llevada a cabo se ha dividido en tres partes principales: i) desarrollo de nanocompuestos de La0.75Sr0.25Cr0.5Mn0.5O3 (LSCrMn) y Ce0.8Sm0.2O2 (SDC) para su aplicación en electrodos de combustible y simétricos; ii) la caracterización de las propiedades funcionales de la librería La0.8Sr0.2MnxCoyFe1-x-yO3 (LSMCF) para aplicación como electrodos de oxígeno; iii) la implementación de materiales de electrodo de capa fina en diferentes arquitecturas de celda. La primera parte de la tesis cubre el desarrollo de electrodos nanocompuestos basados en capa fina. En primer lugar, nanocompuestos cermet de Ni-Ce0.9Gd0.1O2 (NiCGO) se han estudiado como electrodos de combustible. Se ha encontrado un nanocompuesto denso de LSCrMn-SDC que presenta alta actividad electroquímica bajo condiciones tanto reductoras como oxidantes, sin apreciación de degradación significativa. Más estudios se han realizado para la optimización de la microestructura, consiguiendo mejorar el rendimiento frente a la oxidación de hidrógeno. La segunda parte de la tesis investiga la librería de LSMCF para su aplicación en electrodos de oxígeno. El LSMCF se ha estudiado por medio de metodologías de alto rendimiento para la caracterización completa de las propiedades estructurales y electrocatalíticas. Los resultados muestran alta cinética de transporte de oxígeno para las regiones ricas en Fe/Co, así como baja energía de activación para los compuestos co-dopados. Estudios del rendimiento frente a la degradación han mostrado un comportamiento con alta estabilidad para el LSMCF co-dopado y el La0.8Sr0.2MnO3 (LSM) en comparación con el La0.8Sr0.2CoO3 (LSC) y el La0.8Sr0.2FeO3 (LSF). En la parte final de la tesis se ha estudiado la integración de materiales de capa fina para electrodos en dispositivos SOC completos. El uso de capas finas de La0.9Sr0.1CrO3 (LSCr) como electrodos simétricos se ha analizado por medio de la operación bajo condiciones de ciclado redox. El uso de capas finas de LSC y SDC en sistemas reversibles SOC se ha estudiado bajo operación en modos de celda de combustible y de electrólisis. Finalmente, la integración de materiales de capa fina en micro-SOCs se ha estudiado, consiguiendo fabricar dispositivos a nivel de prueba de concepto sobre sustratos de silicio. Este manuscrito ofrece un estudio exhaustivo del desarrollo de materiales funcionales basados en capa fina destinados a superar las limitaciones que afectan a los electrodos de las SOC. El uso de procesos de nanoingeniería y metodologías combinatoriales para la investigación en materiales se presentan como aproximaciones prometedoras para el descubrimiento de materiales de electrodo de alto rendimiento. La integración exitosa de este tipo de materiales en distintas arquitecturas se propone como validación de la versatilidad en los ámbitos de aplicación de los materiales de capa fina investigados.The energy industry is currently on the verge of transitioning into a sustainable paradigm powered by renewable energies. Among the alternatives to fossil fuel-driven technologies, the use of solid oxide cell (SOC) systems is a promising candidate. SOCs are the most efficient technologies for electrical power generation and hydrogen production, making them an interesting solution for reversible energy systems. Nonetheless, the expansion of SOC technologies into real life applications is often hindered by the presence of thermally activated processes, restricting the operation to the high temperature regime. Consequently, thermally-driven degradation is regularly experienced in these devices. There is a clear interest then in the discovery of new materials that i) present enhanced electrochemical activity at lower temperatures and ii) keep their performance over time. The use of thin film electrodes based on engineered nanostructures has been demonstrated to improve the performance at much lower operational temperatures. This thesis is then focused on the development of thin film-based highly functional materials for SOC electrode application. The research carried out has been divided in three main parts: i) development of La0.75Sr0.25Cr0.5Mn0.5O3 (LSCrMn) and Ce0.8Sm0.2O2 (SDC) nanocomposites for application in fuel and symmetric electrodes; ii) characterization of the functional properties of the La0.8Sr0.2MnxCoyFe1-x-yO3 (LSMCF) library for application as oxygen electrodes; iii) implementation of thin film electrode materials under different cell architectures. The first part of the thesis deals with the development of thin film-based nanocomposite electrodes. First, Ni-Ce0.9Gd0.1O2 (NiCGO) cermet nanocomposites were studied as promising fuel electrodes. Additionally, all-ceramic LSCrMn-SDC heterostructures were also investigated. Specifically, a dense LSCrMn-SDC nanocomposite was found to present remarkable electrochemical activity under both reducing and oxidizing conditions, with no significant degradation observed. Further studies were carried out for the optimization of the heterostructures microstructure, leading to enhanced performance for hydrogen oxidation. The second part of this thesis investigated the LSMCF library for application as oxygen electrodes. The complete library was fabricated in a single process by means of combinatorial deposition. LSMCF was then studied by high-throughput methodologies for full characterization of the structural and electrocatalytic properties. The results showed high oxygen kinetics for the Fe- and Co-rich regions and remarkable low activation energy for the intermixed co-doped compositions studied. Studies on degradation performance showed distinctive behaviour with remarkable stability of the co-doped LSMCF and La0.8Sr0.2MnO3 (LSM) with respect to single La0.8Sr0.2CoO3 (LSC) and La0.8Sr0.2FeO3 (LSF). Analyses beyond the subsurface revealed the presence of highly off-stoichiometric regions and apparent overall increase of defect size and defect density. In the final part of the thesis, the integration of thin film electrode materials in full SOC devices have been studied. Specifically, the use of La0.9Sr0.1CrO3 (LSCr) thin films as symmetric electrodes has been analysed by operating a cell under redox cycling conditions. The use of thin film LSC and SDC in reversible SOC systems was studied under fuel cell and electrolysis operation modes. Finally, the integration of all-ceramic thin film materials in micro-SOCs was explored, with successful fabrication of proof-of-concept devices supported in silicon. This manuscript offers a thorough study for the development of thin film-based functional materials aimed to overcome the limitations affecting SOC electrodes. The use of nanoengineering processes and combinatorial methods for material research are presented as promising routes for the discovery of electrode materials with enhanced performance. The successful integration of these type of materials in different device architectures is proposed as validation of the versatility in application of the thin film materials investigated

Nanostructured La0.75Sr0.25Cr0.5Mn0.5O3–Ce0.8Sm 0.2O2 Heterointerfaces as All-Ceramic Functional Layers for Solid Oxide Fuel Cell Applications

International audienceThe use of nanostructured interfaces and advanced functional materials opens up a new playground in the field of solid oxide fuel cells. In this work, we present two all-ceramic thin-film heterostructures based on samarium-doped ceria and lanthanum strontium chromite manganite as promising functional layers for electrode application. The films were fabricated by pulsed laser deposition as bilayers or self-assembled intermixed nanocomposites. The microstructural characterization confirmed the formation of dense, well-differentiated, phases and highlighted the presence of strong cation intermixing in the case of the nanocomposite. The electrochemical properties─solid/gas reactivity and in-plane conductivity─are strongly improved for both heterostructures with respect to the single-phase constituents under anodic conditions (up to fivefold decrease of area-specific resistance and 3 orders of magnitude increase of in-plane conductivity with respect to reference single-phase materials). A remarkable electrochemical activity was also observed for the nanocomposite under an oxidizing atmosphere, with no significant decrease in performance after 400 h of thermal aging. This work shows how the implementation of nanostructuring strategies not only can be used to tune the properties of functional films but also results in a synergistic enhancement of the electrochemical performance, surpassing the parent materials and opening the field for the fabrication of high-performance nanostructured functional layers for application in solid oxide fuel cells and symmetric system

Tailored nano-columnar La2NiO4 cathodes for improved electrode performance

International audienceLa2NiO4 is a very promising cathode material for intermediate and low temperature solid oxide cell applications, due to its good electronic and ionic conductivity, together with its high oxygen exchange activity with a low activation energy. Oxygen incorporation and transport in La2NiO4 (L2NO4) thin films are limited by surface reactions. Hence, tailoring the morphology is expected to lead to an overall improvement of the electrode performance. We report the growth of nano-architectured La2NiO4 thin film electrodes by Pulsed Injection Metal Organic Chemical Vapour Deposition (PI-MOCVD), achieving vertically gapped columns with a multi-fold active surface area, leading to much faster oxygen exchange. This nano-columnar structure is rooted in a dense bottom layer serving as a good electronic and ionic conduction pathway. The microstructure is tuned by modification of the growth temperature and characterised by SEM, TEM and XRD. We studied the effect of surface activity by electrical conductivity relaxation measurements in fully dense and nano-columnar La2NiO4 thin films of various thicknesses grown on several different single crystal substrates. Our results demonstrate that the increased surface area, in combination with the opening of different surface terminations, leads to a significant enhancement of the total exchange activity in our films with an optimized nano-architectured microstructur

Biodegradable FeMnSi sputter-coated macroporous polypropylene membranes for the sustained release of drugs

Pure Fe and FeMnSi thin films were sputtered on macroporous polypropylene (PP) membranes with the aim to obtain biocompatible, biodegradable and, eventually, magnetically-steerable platforms. Room-temperature ferromagnetic response was observed in both Fe- and FeMnSi-coated membranes. Good cell viability was observed in both cases by means of cytotoxicity studies, though the FeMnSi-coated membranes showed higher biodegradability than the Fe-coated ones. Various strategies to functionalize the porous platforms with transferrin-Alexa Fluor 488 (Tf-AF488) molecules were tested to determine an optimal balance between the functionalization yield and the cargo release. The distribution of Tf-AF488 within the FeMnSi-coated PP membranes, as well as its release and uptake by cells, was studied by confocal laser scanning microscopy. A homogeneous distribution of the drug within the membrane skeleton and its sustained release was achieved after three consecutive impregnations followed by the addition of a layer made of gelatin and maltodextrin, which prevented exceedingly fast release. The here-prepared organic-inorganic macroporous membranes could find applications as fixed or magnetically-steerable drug delivery platforms

Unravelling the Origin of Ultra‐Low Conductivity in SrTiO3_3 Thin Films: Sr Vacancies and Ti on A‐Sites Cause Fermi Level Pinning

Different SrTiO$_3$ thin films are investigated to unravel the nature of ultra-low conductivities recently found in SrTiO$_3$ films prepared by pulsed laser deposition. Impedance spectroscopy reveals electronically pseudo-intrinsic conductivities for a broad range of different dopants (Fe, Al, Ni) and partly high dopant concentrations up to several percent. Using inductively-coupled plasma optical emission spectroscopy and reciprocal space mapping, a severe Sr deficiency is found and positron annihilation lifetime spectroscopy revealed Sr vacancies as predominant point defects. From synchrotron-based X-ray standing wave and X-ray absorption spectroscopy measurements, a change in site occupation is deduced for Fe-doped SrTiO$_3$ films, accompanied by a change in the dopant type. Based on these experiments, a model is deduced, which explains the almost ubiquitous pseudo-intrinsic conductivity of these films. Sr deficiency is suggested as key driver by introducing Sr vacancies and causing site changes (Fe$_{Sr}$ and Ti$_{Sr}$) to accommodate nonstoichiometry. Sr vacancies act as mid-gap acceptor states, pinning the Fermi level, provided that additional donor states (most probably Ti$_{Sr}^{\bullet\bullet}$) are present. Defect chemical modeling revealed that such a Fermi level pinning also causes a self-limitation of the Ti site change and leads to a very robust pseudo-intrinsic situation, irrespective of Sr/Ti ratios and doping

Unravelling the Origin of Ultra-Low Conductivity in SrTiO3 Thin Films: Sr Vacancies and Ti on A-Sites Cause Fermi Level Pinning

Different SrTiO3 thin films are investigated to unravel the nature of ultra-low conductivities recently found in SrTiO3 films prepared by pulsed laser deposition. Impedance spectroscopy reveals electronically pseudo-intrinsic conductivities for a broad range of different dopants (Fe, Al, Ni) and partly high dopant concentrations up to several percent. Using inductively-coupled plasma optical emission spectroscopy and reciprocal space mapping, a severe Sr deficiency is found and positron annihilation lifetime spectroscopy revealed Sr vacancies as predominant point defects. From synchrotron-based X-ray standing wave and X-ray absorption spectroscopy measurements, a change in site occupation is deduced for Fe-doped SrTiO3 films, accompanied by a change in the dopant type. Based on these experiments, a model is deduced, which explains the almost ubiquitous pseudo-intrinsic conductivity of these films. Sr deficiency is suggested as key driver by introducing Sr vacancies and causing site changes (Fe-Sr and Ti-Sr) to accommodate nonstoichiometry. Sr vacancies act as mid-gap acceptor states, pinning the Fermi level, provided that additional donor states (most probably TiSr center dot center dot$${\rm{Ti}}_{{\rm{Sr}}}{ \bullet \bullet }$$) are present. Defect chemical modeling revealed that such a Fermi level pinning also causes a self-limitation of the Ti site change and leads to a very robust pseudo-intrinsic situation, irrespective of Sr/Ti ratios and doping.ISSN:1616-3028ISSN:1616-301