Name: Characterization and Analysis of &#945;-Ni(OH)2 Nanosheets
Uploaded: 2023-08-18T14:20:00
Description: Watch this Scientific Journal Video about Characterization and Analysis of α-NiOH2 Nanosheets at JoVE.com

characterization and analysis of &#945;-ni(oh)2 nanosheets

Síntesis y caracterización por microondas de nanohojas de hidróxido de níquel

Nickel hydroxide, Ni(OH)2, is used for numerous applications including nickel-zinc and nickel-metal hydride batteries1,2,3,4, fuel cells4, water electrolyzers4,5,6,7,8,9, supercapacitors4, photocatalysts4, anion exchangers10, and many other analytical, electrochemical, and sensor applications4,5. Ni(OH)2 has two predominant crystal structures: &#946;-Ni(OH)2 and &#945;-Ni(OH)211. &#946;-Ni(OH)2 adopts a brucite-type Mg(OH)2 crystal structure, while &#945;-Ni(OH)2 is a turbostratically layered form of &#946;-Ni(OH)2 intercalated with residual anions and water molecules from the chemical synthesis4. Within &#945;-Ni(OH)2, the intercalated molecules are not within fixed crystallographic positions but have a degree of orientational freedom, and also function as an interlayer glue stabilizing the Ni(OH)2 layers4,12. The interlayer anions of &#945;-Ni(OH)2 affect the average Ni oxidation state13 and influence the electrochemical performance of &#945;-Ni(OH)2 (relative to &#946;-Ni(OH)2) toward battery2,13,14,15, capacitor16, and water-electrolysis applications17,18.
Ni(OH)2 can be synthesized by chemical precipitation, electrochemical precipitation, sol-gel synthesis, or hydrothermal/solvothermal synthesis4. Chemical precipitation and hydrothermal synthesis routes are widely utilized in the production of Ni(OH)2, and different synthetic conditions alter the morphology, crystal structure, and electrochemical performance. The chemical precipitation of Ni(OH)2 involves adding a highly basic solution to an aqueous nickel (II) salt solution. The phase and crystallinity of the precipitate are determined by the temperature and&#160;identities&#160;and concentrations of the nickel (II) salt and&#160;basic solution used4.
Hydrothermal synthesis of Ni(OH)2 involves heating an aqueous solution of precursor nickel (II) salt in a pressurized reaction vial, allowing the reaction to proceed at higher temperatures than ordinarily allowed under ambient pressure4. Hydrothermal reaction conditions typically favor &#946;-Ni(OH)2, but &#945;-Ni(OH)2 can be synthesized by (i) using an intercalation agent, (ii) using a non-aqueous solution (solvothermal synthesis), (iii) lowering the reaction temperature, or (iv) including urea in the reaction, resulting in ammonia-intercalated &#945;-Ni(OH)24. The hydrothermal synthesis of Ni(OH)2 from nickel salts occurs via a two-step process that involves a hydrolysis reaction (equation 1) followed by an olation condensation reaction (equation 2).19
[Ni(H2O)N]2+ + hH2O &#8596; [Ni(OH)h(H2O) N-h](2-h)++ hH3O+ (1)
Ni-OH + Ni-OH2 Ni-OH-Ni + H2O (2)
Microwave chemistry has been used for the one-pot synthesis of a wide variety of nanostructured materials and is based on the ability of a specific molecule or material to convert microwave energy into heat20. In conventional hydrothermal reactions, the reaction is initiated by the direct absorption of heat through the reactor. In contrast, within microwave-assisted hydrothermal reactions, the heating mechanisms are dipolar polarization of the solvent oscillating in a microwave field and ionic conduction generating localized molecular friction20. Microwave chemistry can increase the reaction kinetics, selectivity, and yield of chemical reactions20, making it of significant interest for a scalable, industrially viable method to synthesize Ni(OH)2.
For alkaline battery cathodes, the &#945;-Ni(OH)2 phase provides improved electrochemical capacity compared with the &#946;-Ni(OH)2 phase13, and synthetic methods to synthesize &#945;-Ni(OH)2 are of particular interest. &#945;-Ni(OH)2 has been synthesized by a variety of microwave-assisted methods, which include microwave-assisted reflux21,22, microwave-assisted hydrothermal techniques23,24, and microwave-assisted base-catalyzed precipitation25. The inclusion of urea within the reaction solution significantly influences the reaction yield26, mechanism26,27, morphology, and crystal structure27. The microwave-assisted decomposition of urea was determined to be a critical component for obtaining &#945;-Ni(OH)227. Water content in an ethylene glycol-water solution has been shown to impact the morphology of microwave-assisted synthesis of &#945;-Ni(OH)2 nanosheets24. The reaction yield of &#945;-Ni(OH)2, when synthesized by a microwave-assisted hydrothermal route using an aqueous nickel nitrate and urea solution, was found to depend on the solution pH26. A prior study of microwave synthesized &#945;-Ni(OH)2 nanoflowers using a precursor solution of EtOH/H2O, nickel nitrate, and urea found that temperature (in the range of 80-120 &#176;C) was not a critical factor, provided the reaction is conducted above the urea hydrolysis temperature (60 &#176;C)27. A recent paper that studied the microwave synthesis of Ni(OH)2 using a precursor solution of nickel acetate tetrahydrate, urea, and water found that at a temperature of 150 &#176;C, the material contained both &#945;-Ni(OH)2 and &#946;-Ni(OH)2 phases, which indicates that temperature can be a critical parameter in the synthesis of Ni(OH)228.
Microwave-assisted hydrothermal synthesis can be used to produce high-surface area &#945;-Ni(OH)2 and &#945;-Co(OH)2 by using a precursor solution composed of metal nitrates and urea dissolved in an ethylene glycol/H2O solution12,29,30,31. Metal-substituted &#945;-Ni(OH)2 cathode materials for alkaline Ni-Zn batteries were synthesized using a scaled-up synthesis designed for a large-format microwave reactor12. Microwave-synthesized &#945;-Ni(OH)2 was also used as a precursor for obtaining &#946;-Ni(OH)2 nanosheets12, nickel-iridium nanoframes for oxygen evolution reaction (OER) electrocatalysts29, and bifunctional oxygen electrocatalysts for fuel cells and water electrolyzers30. This microwave reaction route has also been modified to synthesize Co(OH)2 as a precursor for cobalt-iridium nanoframes for acidic OER electrocatalysts31 and bifunctional electrocatalysts30. Microwave-assisted synthesis was also used to produce Fe-substituted &#945;-Ni(OH)2 nanosheets, and the Fe substitution ratio alters the structure and magnetization32. However, a step-by-step procedure for microwave synthesis of &#945;-Ni(OH)2 and the evaluation of how varying reaction time and temperature within a water-ethylene glycol solution affects the crystalline structure, surface area, and porosity, and local environment of interlayer anions within the material&#160;has not been previously reported.
This protocol establishes procedures for high-throughput microwave synthesis of &#945;-Ni(OH)2 nanosheets using a rapid and scalable technique. The effect of reaction temperature and time were varied and evaluated using in situ reaction monitoring, scanning electron microscopy, energy dispersive X-ray spectroscopy, nitrogen porosimetry, powder X-ray diffraction (XRD), and Fourier transform infrared spectroscopy to understand the effects of synthetic variables on reaction yield, morphology, crystal structure, pore size, and local coordination environment of &#945;-Ni(OH)2 nanosheets.

Autor destacado: Una síntesis hidrotermal rápida asistida por microondas de nanohojas de hidróxido de níquel 

Efecto de las condiciones de síntesis de microondas en la estructura de nanoláminas de hidróxido de níquel

Watch this Scientific Journal Video about Characterization and Analysis of α-NiOH2 Nanosheets at JoVE.com

Characterization and Analysis of &#945;-Ni(OH)2 Nanosheets  

Caracterización y análisis de nanohojas de α-Ni(OH)2

Para caracterizar la morfología y composición de las nanoláminas de hidróxido de níquel sintetizadas por microondas mediante SEM y EDS, se prepara la muestra suspendiendo una pequeña cantidad de polvo de hidróxido de níquel en un mililitro de etanol utilizando un sonicador en baño de agua. A continuación, se vierte la mezcla de hidróxido de níquel y etanol en un trozo de SEM y se evapora el etanol calentando el trozo en un horno de muestra a 70 grados centígrados antes de recoger las micrografías de SEM y los espectros EDS. Para determinar el área superficial y la porosidad de las nanoláminas, agregue 25 miligramos de nanoláminas de hidróxido de níquel en el tubo de muestra.Realizar un procedimiento de desgasificación y secado previo al análisis al vacío a 120 grados centígrados durante 16 horas. Por último, transfiera el tubo de muestra desde el puerto de desgasificación al puerto de análisis para recolectar isotermas de nitrógeno. Para el análisis estructural mediante difracción de rayos X o DRX, llene el pocillo de muestra de un soporte de DRX de polvo sin fondo con hidróxido de níquel.Recoja difractogramas de rayos X en polvo utilizando una fuente de radiación K-alfa de cobre entre 2-theta de 2 a 80 grados con un incremento de 0,01 pasos. Equipe el accesorio de reflectancia total atenuada o ATR en el espectrómetro infrarrojo por transformada de Fourier o FTIR. Presione una pequeña cantidad de polvo de hidróxido de níquel entre dos portaobjetos de vidrio para crear un gránulo.A continuación, coloque el gránulo de hidróxido de níquel sobre el cristal ATR de silicio y obtenga un espectro FTIR entre 404.000 centímetros recíprocos como una media de 16 escaneos individuales con una resolución de cuatro centímetros recíprocos. SEM reveló que el hidróxido de níquel sintetizado por microondas estaba compuesto por agregados de nanoláminas ultrafinas entrelazados al azar. Sin embargo, el aumento de la temperatura de reacción de 120 a 180 grados Celsius aumentó las dimensiones laterales de las nanohojas individuales en los agregados.Además, el aumento del tiempo de reacción de 13 a 30 minutos a 120 grados Celsius aumentó el tamaño de los agregados nucleados de aproximadamente tres a cinco micras. EDS mostró una distribución uniforme de níquel, oxígeno, carbono y nitrógeno dentro de todas las nanohojas sintetizadas. Las nanohojas tenían áreas de superficie BET que oscilaban entre 61 y 85 metros cuadrados por gramo, un diámetro de poro promedio de 21 a 35 angstroms y volúmenes pobres acumulados de 0,4 a 0,6 centímetros cúbicos por gramo.Los patrones XRD de las tres muestras sintetizadas por microondas mostraron picos característicos de hidróxido de níquel alfa. Sin embargo, el tiempo de reacción y la temperatura afectaron a los picos, como lo demuestra el desplazamiento del avión 001. Los espectros ATR-FTIR de las nanoláminas sintetizadas por microondas mostraron un modo de red de óxido de níquel característico.Modos de los ligandos y moléculas estructurales, bandas de cianato y modos de red de hidróxido alfa. El aumento de la temperatura de reacción de 120 a 180 grados Celsius alteró las frecuencias e intensidades relativas de los modos vibratorios de cianato, nitrato, hidroxilo y agua.

Research

JoVE Journal

Chemistry

Characterization and Analysis of &#945;-Ni(OH)2 Nanosheets

Effect of Microwave Synthesis Conditions on the Structure of Nickel Hydroxide Nanosheets

A protocol for rapid, microwave-assisted hydrothermal synthesis of nickel hydroxide nanosheets under mildly acidic conditions is presented, and the effect ...