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

Mikrobølgesyntese og karakterisering af nikkelhydroxid-nanoplader

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.

Forfatter Spotlight: En hurtig, mikrobølgeassisteret hydrotermisk syntese af nikkelhydroxid-nanoark 

Effekt af mikrobølgesyntesebetingelser på strukturen af nikkelhydroxidnanoark

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  

Karakterisering og analyse af α-Ni (OH) 2 nanoark

For at karakterisere morfologien og sammensætningen af mikrobølgesyntetiserede nikkelhydroxidnanoark af SEM og EDS skal prøven fremstilles ved at suspendere en lille mængde nikkelhydroxidpulver i en milliliter ethanol ved anvendelse af en vandbadsonikator. Derefter dropstøbes nikkelhydroxid- og ethanolblandingen på en SEM-stub og fordampes ethanolen ved at opvarme stubben i en prøveovn ved 70 grader Celsius, før SEM-mikrografierne og EDS-spektrene opsamles. For at bestemme nanoarkenes overfladeareal og porøsitet tilsættes 25 mg nikkelhydroxidnanoark i prøveglasset.Udfør en foranalyse afgasnings- og tørringsprocedure under vakuum ved 120 grader Celsius i 16 timer. Til sidst overføres prøveglasset fra afgasningsporten til analyseporten for at opsamle nitrogenisotermer. Til strukturel analyse ved hjælp af røntgendiffraktion eller XRD fyldes prøvebrønden i en XRD-holder med nulbaggrundspulver med nikkelhydroxid.Saml pulver røntgendiffraktogrammer ved hjælp af en kobber K-alfa strålingskilde mellem en 2-theta på 2 til 80 grader med en 0,01 trin trin. Udstyr den svækkede samlede reflektans eller ATR-fastgørelse til Fourier Transform infrarødt spektrometer eller FTIR-spektrometer. Tryk en lille mængde nikkelhydroxidpulver mellem to glasglas for at skabe en pellet.Placer derefter nikkelhydroxidpelleten på silicium ATR-krystallen og opnå et FTIR-spektrum mellem 404.000 gensidige centimeter som et gennemsnit på 16 individuelle scanninger med en opløsning på fire gensidige centimeter. SEM afslørede, at mikrobølgesyntetiseret nikkelhydroxid var sammensat af tilfældigt sammenvævede ultratynde nanoarkaggregater. Ved at øge reaktionstemperaturen fra 120 til 180 grader Celsius øgede imidlertid laterale arkdimensioner af individuelle nanoark i aggregaterne.Ved at øge reaktionstiden fra 13 til 30 minutter ved 120 grader Celsius øgede de nukleerede aggregatstørrelser fra ca. tre til fem mikron. EDS viste en ensartet fordeling af nikkel, ilt, kulstof og nitrogen inden for alle de syntetiserede nanoark. Nanoarkene havde BET-overfladearealer fra 61 til 85 kvadratmeter pr. gram, gennemsnitlig porediameter på 21 til 35 angstromer og kumulative dårlige volumener på 0,4 til 0,6 kubikcentimeter pr. gram.XRD-mønstrene i alle tre mikrobølgesyntetiserede prøver viste karakteristiske toppe af alfa-nikkelhydroxid. Imidlertid påvirkede reaktionstid og temperatur toppene, som det fremgår af forskydningen af 001-planet. ATR-FTIR-spektrene af de mikrobølgesyntetiserede nanoark viste karakteristisk nikkeloxidgittertilstand.Tilstande fra liganderne og strukturelle molekyler, cyanatbånd og alfahydroxidgittertilstande. Forøgelse af reaktionstemperaturen fra 120 til 180 grader Celsius ændrede frekvenserne og de relative intensiteter af cyanat-, nitrat-, hydroxyl- og vandvibrationstilstandene.

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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 ...