Catalizadores bifuncionales basados en estructuras tipo perovskita para baterías zinc-aire
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Valencia Osorio, Laura Margarita
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Con esta tesis se pretende contribuir al desarrollo tecnológico del almacenamiento de energía en baterías recargables zinc-aire, tecnología que actualmente se encuentra en la etapa de desarrollo [1]–[4]. Esta tecnología es de las más promisorias para almacenamiento de baja, mediana y gran escala; igualmente se cree que puede ser de las tecnologías más económicas ya que utiliza el oxígeno del aire, considerado un reactivo gratuito, y zinc que es un metal abundante, en lugar de otros metales u óxidos escasos y de alto costo, como es el caso del litio [5]. Específicamente se hace la evaluación de la actividad y estabilidad electrocatalíticas de diferentes óxidos tipo perovskita (Sm_0.5 Sr_0.5 CoO_(3-δ) (SSC)., Sm_0.5 Sr_0.5 Co_0.8 Fe_0.2 O_(3-δ) (SSCF), Ce_0.05 Sr_0.95 CoO_(3-δ) (CSC), La_0.6 Sr_0.4 Co_0.8 Fe_0.2 O_(3-δ) (LSCF)), en el proceso de catálisis de las reacciones de reducción y evolución de oxígeno, correspondientes a los procesos de descarga y carga respectivamente en el cátodo de la batería. Lo anterior con el fin de determinar el o los compuesto(s) más promisorio(s) como catalizador(es) bifuncional(es), uno de los desafíos más importantes por resolver en esta tecnología [6]. Se pudo encontrar que el método de calcinación directa en el proceso de síntesis de los óxidos tipo perovskita, permite obtener la estructura cristalina adecuada para que el catalizador tenga actividades y estabilidades electrolíticas significativas tanto en la reducción, como en la evolución de oxígeno. En general se tomó LSCF como una referencia ya que según la literatura es de los compuestos más promisorios, sin embargo, se hizo una caracterización electroquímica completa, pues en ninguna fuente se reporta de esta manera, en general se logró obtener resultados positivos, lo que confirma lo afirmado por los diferentes autores respecto a este compuesto. Por otro lado, se encontró que SSCF es prometedor en términos de reducción de sobrepotenciales y la estabilidad catalítica, siendo más promisorio que SSC. Para CSC se encontró que la actividad es altamente significativa en medios alcalinos, sin embargo, no es estable con el número de ciclos, por lo que se recomienda doparlo con hierro, ya que se encontró también que en general los compuestos dopados con hierro son los más estables independientemente de su calcinación.
Abstract: This thesis aims to contribute to rechargeable zinc-air batteries, which is under development in technological terms [1]–[4]. This technology is highly promising for low, medium and large scale storage; Moreover, it may be the lowest cost technology since it requires two reagents: oxygen from the air, which is considered a free reagent, and metallic zinc which is abundant, instead of another scarce and expensive metals and oxides, as lithium [5]. Specifically, the evaluation of the electrocatalytic activity and stability of different perovskite type oxides (Sm_0.5 Sr_0.5 CoO_(3-δ) (SSC), Sm_0.5 Sr_0.5 Co_0.8 Fe_0.2 O_(3-δ) (SSCF), Ce_0.05 Sr_0.95 CoO_(3-δ) (CSC), La_0.6 Sr_0.4 Co_0.8 Fe_0.2 O_(3-δ) (LSCF)) was carried out in both, oxygen reduction and evolution cathodic reactions, corresponding to the discharge and charge processes respectively. The foregoing in order to determine the most promising compound(s) as bifunctional catalyst(s), which is the most important challenge to be solved in this technology [6]. Direct calcination method in perovskite type oxides provides suitable crystalline structure to enhance the electrocatalytic activity and stability in both, oxygen reduction and evolution reactions. LSCF was taken as reference since according to the literature reports, it is one of the most promising compounds. However, a complete electrochemical characterization was made, since it is not reported in this way in any source. Positive results were obtained, which confirms the authors affirmations regarding this compound. On the other hand, it was found that SSCF is a promising compound in terms of overpotentials reduction and catalytic stability, being more promising than SSC. CSC provides a suitable catalytic activity in alkaline media, however, it is not stable with the number of cycles, so a structural doping with iron is recommended, since the iron doped compounds are the most stable regardless of its calcination process.
Abstract: This thesis aims to contribute to rechargeable zinc-air batteries, which is under development in technological terms [1]–[4]. This technology is highly promising for low, medium and large scale storage; Moreover, it may be the lowest cost technology since it requires two reagents: oxygen from the air, which is considered a free reagent, and metallic zinc which is abundant, instead of another scarce and expensive metals and oxides, as lithium [5]. Specifically, the evaluation of the electrocatalytic activity and stability of different perovskite type oxides (Sm_0.5 Sr_0.5 CoO_(3-δ) (SSC), Sm_0.5 Sr_0.5 Co_0.8 Fe_0.2 O_(3-δ) (SSCF), Ce_0.05 Sr_0.95 CoO_(3-δ) (CSC), La_0.6 Sr_0.4 Co_0.8 Fe_0.2 O_(3-δ) (LSCF)) was carried out in both, oxygen reduction and evolution cathodic reactions, corresponding to the discharge and charge processes respectively. The foregoing in order to determine the most promising compound(s) as bifunctional catalyst(s), which is the most important challenge to be solved in this technology [6]. Direct calcination method in perovskite type oxides provides suitable crystalline structure to enhance the electrocatalytic activity and stability in both, oxygen reduction and evolution reactions. LSCF was taken as reference since according to the literature reports, it is one of the most promising compounds. However, a complete electrochemical characterization was made, since it is not reported in this way in any source. Positive results were obtained, which confirms the authors affirmations regarding this compound. On the other hand, it was found that SSCF is a promising compound in terms of overpotentials reduction and catalytic stability, being more promising than SSC. CSC provides a suitable catalytic activity in alkaline media, however, it is not stable with the number of cycles, so a structural doping with iron is recommended, since the iron doped compounds are the most stable regardless of its calcination process.