Diseño racional de catalizadores NiO–Nb para aplicaciones energéticas mediante síntesis verde asistida por extracto de Aloe vera.
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Date
2025
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Universidad de Concepción
Abstract
En esta investigación se desarrolló un enfoque de síntesis verde para la obtención de nanopartículas bimetálicas de óxido de níquel dopadas con niobio (NiO-Nb), utilizando extracto de Aloe vera como agente reductor y estabilizante natural. Esta estrategia apunta a sustituir métodos tradicionales que emplean precursores tóxicos y costosos, alineándose con los principios de la química sustentable. Las nanopartículas fueron diseñadas como electrocatalizadores para la reacción de reducción de oxígeno (ORR), un proceso clave en tecnologías electroquímicas como las celdas de combustible de cerámica protónica (PCFCs).
El estudio se basó en un diseño racional que consideró el ajuste sistemático de parámetros críticos como la concentración de extracto vegetal, el agente surfactante, la temperatura de calcinación, el pH de la solución, la velocidad de agitación y el contenido de Nb. A través de caracterizaciones estructurales como XRD, Raman, TEM, SEM-EDS y caracterizaciones fisicoquímicas como TGA, BET, TPR-H2, se determinó que la formulación con 10% de extracto de Aloe vera y un dopaje de 5% en masa de Nb permiten obtener nanopartículas con buena cristalinidad, tamaño reducido (~10-12 nm), buena superficie específica y una dispersión homogénea del dopante. La disminución en el consumo de H2, observada en TPR-H2 para las muestras dopadas con Nb, refleja un cambio en la naturaleza de los sitios reducibles, posiblemente debido a la incorporación de Nb que genera especies más estables frente a la reducción.
La evaluación electroquímica en celda de tres electrodos, mediante técnicas como voltametría cíclica (CV) y voltametría de barrido lineal (LSV) de electrodos de Au recubiertos con los electrocatalizadores de NiO-Nb sintetizados, revelaron que los electrodos de Au/NiO-5%Nb exhiben la mejor respuesta redox, con un sobrepotencial de inicio más favorable y mayor simetría anódica/catódica, superando a los electrodos de Au/NiO-3%Nb, Au/NiO-7%Nb y al electrodo de Au sin recubrimiento con electrocatalizador tanto para ORR como OER.
En conjunto los resultados validan la viabilidad de una ruta de síntesis verde para obtener electrocatalizadores activos y sostenibles para la ORR, destacando la formulación con 10% de extracto de Aloe vera y 5% de Nb como la más prometedora dentro del rango de condiciones evaluadas.
In this research, a green synthesis approach was developed for the preparation of niobium-doped nickel oxide bimetallic nanoparticles (NiO–Nb), using Aloe vera extract as a natural reducing and stabilizing agent. This strategy aims to replace traditional methods that involve toxic and costly precursors, aligning with the principles of sustainable chemistry. The nanoparticles were designed as electrocatalysts for the oxygen reduction reaction (ORR), a key process in electrochemical technologies such as protonic ceramic fuel cells (PCFCs). The study was based on a rational design that systematically adjusted critical parameters such as plant extract concentration, surfactant agent, calcination temperature, solution pH, stirring rate, and Nb content. Through structural characterizations such as XRD, Raman, TEM, SEM-EDS, and physicochemical techniques including TGA, BET, and H2-TPR, it was determined that the formulation with 10% Aloe vera extract and 5 wt.% Nb doping yields nanoparticles with good crystallinity, reduced size (~10-12 nm), high specific surface area, and homogeneous dopant dispersion. The decrease in H2 consumption observed in H2-TPR for the Nb-doped samples reflects a change in the nature of reducible sites, possibly due to the incorporation of Nb leading to more stable species against reduction. Electrochemical evaluation using techniques such as cyclic voltammetry (CV) and linear sweep voltammetry (LSV) in a three-electrode cell setup with Au electrodes coated with the synthesized NiO-Nb electrocatalysts revealed that Au/NiO-5%Nb electrodes exhibit the best redox response, with a more favorable onset overpotential and greater anodic/cathodic symmetry, outperforming the Au/NiO-3%Nb, Au/NiO-7%Nb electrodes, and the bare Au electrode without electrocatalyst coating both in ORR and in OER. Overall, the results validate the feasibility of a green synthesis route for obtaining active and sustainable electrocatalysts for the ORR, highlighting the formulation with 10% Aloe vera extract and 5% Nb as the most promising within the evaluated range of conditions.
In this research, a green synthesis approach was developed for the preparation of niobium-doped nickel oxide bimetallic nanoparticles (NiO–Nb), using Aloe vera extract as a natural reducing and stabilizing agent. This strategy aims to replace traditional methods that involve toxic and costly precursors, aligning with the principles of sustainable chemistry. The nanoparticles were designed as electrocatalysts for the oxygen reduction reaction (ORR), a key process in electrochemical technologies such as protonic ceramic fuel cells (PCFCs). The study was based on a rational design that systematically adjusted critical parameters such as plant extract concentration, surfactant agent, calcination temperature, solution pH, stirring rate, and Nb content. Through structural characterizations such as XRD, Raman, TEM, SEM-EDS, and physicochemical techniques including TGA, BET, and H2-TPR, it was determined that the formulation with 10% Aloe vera extract and 5 wt.% Nb doping yields nanoparticles with good crystallinity, reduced size (~10-12 nm), high specific surface area, and homogeneous dopant dispersion. The decrease in H2 consumption observed in H2-TPR for the Nb-doped samples reflects a change in the nature of reducible sites, possibly due to the incorporation of Nb leading to more stable species against reduction. Electrochemical evaluation using techniques such as cyclic voltammetry (CV) and linear sweep voltammetry (LSV) in a three-electrode cell setup with Au electrodes coated with the synthesized NiO-Nb electrocatalysts revealed that Au/NiO-5%Nb electrodes exhibit the best redox response, with a more favorable onset overpotential and greater anodic/cathodic symmetry, outperforming the Au/NiO-3%Nb, Au/NiO-7%Nb electrodes, and the bare Au electrode without electrocatalyst coating both in ORR and in OER. Overall, the results validate the feasibility of a green synthesis route for obtaining active and sustainable electrocatalysts for the ORR, highlighting the formulation with 10% Aloe vera extract and 5% Nb as the most promising within the evaluated range of conditions.
Description
Tesis presentada para optar al título profesional de Ingeniero/a Civil Químico/a.
Keywords
Nanopartículas, Áloe vera, Electroquímica