Desarrollo de electrodos tubulares de BSCF para soporte de celdas de cerámicas protónicas, con aplicación en la síntesis electroquímica de amoniaco.
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Date
2025
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Universidad de Concepción
Abstract
El creciente interés en fuentes de energía limpias, eficientes y sostenibles han impulsado el desarrollo de distintas tecnologías, una de ellas es la producción de combustibles limpios, como el hidrógeno verde. Una de las problemáticas de este vector energético es que tiene una baja densidad energética y su transporte implica una alta complejidad. Para Chile es de gran interés encontrar compuestos que mejoren la forma de transportar este tipo de energía; el amoníaco (NH3) ha surgido como un vector energético estratégico, por su alta densidad energética y por contar con una infraestructura global establecida. Sin embargo, la producción de NH3 tradicional, el proceso de Haber-Bosch, es energéticamente muy demandante, ya que requiere presiones y temperaturas muy altas, además de generar residuos contaminantes. Para descarbonizar esta síntesis se propone una vía electroquímica, específicamente el uso de celdas electroquímicas protónicas cerámicas o PCECs por sus siglas en inglés, las cuales actúan como reactores que utilizan la energía eléctrica renovable, junto a hidrógeno verde y nitrógeno del aire, a presiones y temperaturas moderadas, logrando sintetizar amoniaco verde. El presente trabajo tiene como objetivo el desarrollo de electrodos tubulares, con funcionalidad de soporte de la celda electroquímica cerámica, con aplicación en la síntesis de amoniaco por vía electroquímica. Se eligió esta forma de celda ya que, a diferencia de una configuración planar, facilita la recolección de los gases y posee una mayor resistencia al estrés térmico. Estos electrodos, en su proceso de conformado, utilizan una pasta cerámica en base a aditivos poliméricos y un material cerámico del tipo perovskita, Ba0.5Sr0.5Co0.8Fe0.2O3-d. Este último material fue seleccionado por su alta conductividad iónica y su aplicación en síntesis de amoniaco. La técnica utilizada en el proceso corresponde a la extrusión, método extendido en la industria lo que facilita el posible escalado para obtener electrodos tubulares. La pasta cerámica estaba compuesta por ácido esteárico como surfactante, etanol como solvente, dimetilformamida (DMF) como solvente auxiliar, dioctil ftalato (DOP) como plastificante y etilcelulosa como aglomerante, todos estos aditivos se conocen como binder. Luego que estos aditivos se mezclan en una proporción especifica, se continúa con el espolvoreo progresivo de los sólidos. A partir de los resultados alcanzados, se determinó que la proporción con 20% de DOP en el binder otorga una mejor combinación de plasticidad, cohesión y estabilidad. Por otra parte, a partir del análisis reológico, se reveló que la pasta obtenida tenía un comportamiento dilatante de la mezcla, el cual ajustado al modelo de Ostwald de Waele entrega unos parámetros 𝐾=5.976 y 𝑛=2.711. 3 Así también, los tratamientos térmicos de sinterización evidenciaron un gran influencia de la tasa de calentamiento en la microestructura de electrodo sintetizado, resultando que la velocidad de calentamiento máxima de 1°C/min permite una eliminación gradual de los aditivos orgánicos y una sinterización estable a los 1100°C. Por otro lado, a partir de las imágenes mediante SEM, se observó una microestructura compacta y con poros definidos. En conjunto, los resultados obtenidos en esta investigación validan el uso de esta metodología propuesta como una alternativa en la producción de cátodos tubulares de BSCF, estableciendo una base experimental para una futura integración en pruebas electroquímicas en una PCEC.
The growing interest in clean, efficient and sustainable energy sources has driven the development of different technologies. One of them is the production of clean fuels such as green hydrogen, which faces problems related to its low energy density and the high complexity of its transport. For Chile, there is great interest in finding compounds that improve the way this type of energy is transported. Ammonia (NH3) has emerged as a strategic energy vector, due to its high energy density and established global infrastructure. However, traditional NH3 production, the Haber-Bosch process, is very energy demanding, as it requires very high pressures and temperatures, besides generating polluting residues. To decarbonize this synthesis, an electrochemical route is proposed, specifically the protonic ceramic electrochemical cells or PCECs, which act as reactors that use renewable electrical energy, along with green hydrogen and nitrogen from the air, at moderate pressures and temperatures, achieving the synthesis of green ammonia. The present work aims to develop tubular electrodes that also function as the structural support of the ceramic electrochemical cell, with application in the electrochemical synthesis of ammonia. This cell shape was selected because, in contrast to a planar configuration, it facilitates gas collection and possesses greater resistance to thermal stress. These electrodes use a ceramic paste based on polymeric additives and Ba0.5Sr0.5Co0.8Fe0.2O3-d (BSCF), a perovskite material selected for its conductivity and application potential. Using an extrusion technique, a widely used industrial method that facilitates the potential scaling up to produce tubular electrodes. The methodology proposed in this work uses stearic acid as surfactant, and a binder composed of ethanol as a principal solvent, dimethylformamide (DMF) as an auxiliary solvent, dioctyl phthalate (DOP) as a plasticizer, and ethyl cellulose as a binder, which is mixed in a specific proportion through the progressive sprinkling of the solids. It was determined that the proportion with 20% DOP in the binder provides a better combination of plasticity, cohesion and stability. A rheological analysis reveals a dilatant behavior of the mixture, which, when fitted to the Ostwald de Waele model, yields parameters 𝐾=5.976 and 𝑛=2.711. The thermal sintering tests showed a strong influence of the maximum heating rate on the structure, revealing that a maximum heating rate of 1°C/min allows the gradual elimination of organic additives and a stable sintering at 1100°C. On the other hand, SEM images revealed a compact microstructure with defined pores. Altogether, the results obtained in this research validate the use of the proposed methodology as an 5 alternative to produce tubular BSCF cathodes, establishing an experimental foundation for their future integration into electrochemical testing in PCEC.
The growing interest in clean, efficient and sustainable energy sources has driven the development of different technologies. One of them is the production of clean fuels such as green hydrogen, which faces problems related to its low energy density and the high complexity of its transport. For Chile, there is great interest in finding compounds that improve the way this type of energy is transported. Ammonia (NH3) has emerged as a strategic energy vector, due to its high energy density and established global infrastructure. However, traditional NH3 production, the Haber-Bosch process, is very energy demanding, as it requires very high pressures and temperatures, besides generating polluting residues. To decarbonize this synthesis, an electrochemical route is proposed, specifically the protonic ceramic electrochemical cells or PCECs, which act as reactors that use renewable electrical energy, along with green hydrogen and nitrogen from the air, at moderate pressures and temperatures, achieving the synthesis of green ammonia. The present work aims to develop tubular electrodes that also function as the structural support of the ceramic electrochemical cell, with application in the electrochemical synthesis of ammonia. This cell shape was selected because, in contrast to a planar configuration, it facilitates gas collection and possesses greater resistance to thermal stress. These electrodes use a ceramic paste based on polymeric additives and Ba0.5Sr0.5Co0.8Fe0.2O3-d (BSCF), a perovskite material selected for its conductivity and application potential. Using an extrusion technique, a widely used industrial method that facilitates the potential scaling up to produce tubular electrodes. The methodology proposed in this work uses stearic acid as surfactant, and a binder composed of ethanol as a principal solvent, dimethylformamide (DMF) as an auxiliary solvent, dioctyl phthalate (DOP) as a plasticizer, and ethyl cellulose as a binder, which is mixed in a specific proportion through the progressive sprinkling of the solids. It was determined that the proportion with 20% DOP in the binder provides a better combination of plasticity, cohesion and stability. A rheological analysis reveals a dilatant behavior of the mixture, which, when fitted to the Ostwald de Waele model, yields parameters 𝐾=5.976 and 𝑛=2.711. The thermal sintering tests showed a strong influence of the maximum heating rate on the structure, revealing that a maximum heating rate of 1°C/min allows the gradual elimination of organic additives and a stable sintering at 1100°C. On the other hand, SEM images revealed a compact microstructure with defined pores. Altogether, the results obtained in this research validate the use of the proposed methodology as an 5 alternative to produce tubular BSCF cathodes, establishing an experimental foundation for their future integration into electrochemical testing in PCEC.
Description
Tesis presentada para optar al título de Ingeniero/a Civil Químico/a.
Keywords
Electrodos, Electroquímica, Amoníaco