Nickel (III) Hydroxide: Structure, Properties, Uses, Risks

Nickel (III) hydroxide is an inorganic compound where nickel metal has an oxidation number of 3+. Its chemical formula is Ni (OH) 3 . According to the sources consulted, until now it has not been possible to verify the existence of nickel (III) hydroxide Ni (OH) 3 , but it has been possible to obtain nickel (III) oxo-hydroxide, NiO (OH).

Nickel (III) oxohydroxide NiO (OH) is a black crystalline solid that crystallizes in two forms: the beta and the gamma forms. The most common crystalline form of NiO (OH) is beta.

Structure of nickel (III) oxohydroxide, NiO (OH). Blue = nickel, red = oxygen, white = hydrogen. Author: Smokefoot. Source: Own work. Source: Wikipedia Commons

NiO (OH) can be obtained by oxidation of nickel (II) nitrate solutions (Ni (NO 3 ) 2 ) with chlorine (Cl 2 ) or bromine (Br 2 ) in the presence of potassium hydroxide (KOH). Nickel (III) oxohydroxide is very soluble in acids. It has application in nickel batteries, in supercapacitors and as a regenerable catalyst.

Nickel (III) oxo-hydroxide NiO (OH) and nickel (II) hydroxide Ni (OH) 2 are found together in the operation of most of their applications, since they are both part of the same oxide equation. reduction.

Being a nickel compound, NiO (OH) presents the same risks as other nickel salts, that is, skin irritation or dermatitis and cancer.

Article index

  • one

    Crystalline structure

  • two

    Electronic configuration

  • 3

    Nomenclature

  • 4

    Properties (edit)

    • 4.1

      Physical state

    • 4.2

      Solubility

    • 4.3

      Other properties

  • 5

    Applications

    • 5.1

      In nickel batteries

    • 5.2

      In electrocatalysis as a regenerable catalyst

    • 5.3

      In supercapacitors

    • 5.4

      In oxidation of metal ions

  • 6

    Risks

  • 7

    References

Crystalline structure

Nickel (III) oxohydroxide crystallizes in two forms: beta and gamma. The beta form β-NiO (OH) has a very similar structure to β-Ni (OH) 2 , which seems logical since the former comes from the oxidation of the latter.

The gamma γ-NiO (OH) form is the oxidation product of nickel (II) hydroxide in its alpha form, α-Ni (OH) 2 . Like the latter, gamma has a layered structure with alkali metal ions, anions and water interspersed between the layers.

Electronic configuration

In NiO (OH), nickel is in the 3+ oxidation state, which means that its outermost shells are missing 3 electrons, that is, two electrons are missing from shell 4 s and one electron from shell 3 d . The electron configuration of Ni 3+  in NiO (OH) is: [Ar] 3 d 7 , where [Ar] is the electron configuration of the noble gas argon.

Nomenclature

– NiO (OH): Nickel (III) oxohydroxide

– Nickel black

Properties (edit)

Physical state

Black crystalline solid.

Solubility

NiO (OH) oxohydroxide is very soluble in acids. The gamma phase dissolves in sulfuric acid with evolution of oxygen.

Other properties

In hot water it becomes nickel (II) and (III) oxohydroxide, Ni 3 O 2 (OH) 4 .

It decomposes at 140 ºC into nickel (II) oxide (NiO), water and oxygen.

The gamma phase (γ-NiO (OH)) can be obtained in various ways, for example, treating nickel with a molten mixture of sodium peroxide (Na 2 O 2 ) and sodium hydroxide (NaOH) at 600 ° C and cooling in frozen water.

The gamma phase decomposes on heating to 138 ° C.

Applications

In nickel batteries

Edison’s nickel-iron battery, in which KOH is used as the electrolyte, is based on the reaction of nickel (III) oxohydroxide with iron:

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Fe + 2NiO (OH) + H 2 O ⇔ Fe (OH) 2  + 2Ni (OH) 2

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It is a reversible oxidation-reduction reaction.

A series of chemical and electrochemical processes take place at the anode of these batteries. Here is a general outline:

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β-Ni (OH) 2        ⇔ β-NiO (OH) + H + + e

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Aging ↑ ↓ Overload

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α-Ni (OH) 2        ⇔ γ-NiO (OH) + H + + e

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In nickel battery technology, nickel (III) oxohydroxide NiO (OH) is called “nickel active mass”.

Nickel rechargeable batteries. Author: Superusergeneric. Source: Own work. Source: Wikipedia Commons.

In electrocatalysis as a regenerable catalyst

NiO (OH) has been used successfully in the electrosynthesis of azopyrazoles, through the electrocatalytic oxidation of aminopyrazoles. Its usefulness in the synthesis of carboxylic acids starting from alcohols or carbonyl compounds has also been proven.

Obtaining a carboxylic acid by means of the oxidation of an alcohol catalyzed by NiO (OH). Source: Originally from en.wikipedia. Author Original uploader was V8rik at en.wikipedia. Source: Wikipedia Commons

Another example is the quantitative conversion of hydroxymethylpyridine to a pyridinecarboxylic acid. In this case, the steel or nickel electrode corresponding to the anode is covered with a layer of NiO (OH). The medium in which the electrolysis takes place is alkaline.

In these reactions, NiO (OH) acts as a reduction-oxidation mediator, or “redox” mediator.

The electrolysis is carried out in a cell with a nickel anode and a titanium cathode, in an alkaline medium. During the process, Ni (OH) 2 is formed on the surface of the nickel anode, which is quickly oxidized to NiO (OH):

Ni (OH) 2 + OH e  ⇔ NiO (OH) + H 2 O

NiO (OH) reacts with the organic substrate and the desired organic product is obtained, regenerating Ni (OH) 2 :

NiO (OH) + organic compound → Ni (OH) 2  + product

As Ni (OH) 2 regenerates, the catalysis reaction is continued.

The use of NiO (OH) as an electrocatalyst allows to obtain organic compounds with low costs and in an environmentally friendly way.

In supercapacitors

The NiO (OH) together with Ni (OH) 2 excellent form materials for supercapacitor electrodes (of the English supercapacitors ).

Ni (OH) 2 + OH   ⇔ NiO (OH) + H 2 O + e

They have a high capacitance, low cost and, according to some references, low environmental impact.

Capacitors in an electronic circuit. Author: PDPhotos. Source: Pixabay.

However, they have low conductivity. This is solved by using nanoparticles of said compounds, since this increases the surface area and decreases the distance required for diffusion, which ensures a high speed of transfer of electrons and / or ions.

In oxidation of metal ions

One of the commercial applications of nickel (III) oxohydroxide is based on its ability to oxidize cobalt (II) ions in solution to cobalt (III) ions.

Risks

In solution, nickel is more stable as a Ni 2+ ion , therefore it is not usual to come into contact with Ni 3+ solutions . However, the precautions are the same, as nickel, whether metallic, in solution or in the form of its solid salts, can cause skin sensitization.

It is advisable to use protective equipment and clothing, such as a face shield, gloves, and safety shoes. All of this must be used whenever there is a possibility of coming into contact with nickel solutions.

If dermatitis occurs, it should be treated by a doctor to rule out nickel-related causes.

Regarding the possibility of inhalation, it is good practice to keep airborne concentrations of nickel salts dust very low, by means of local ventilation, and to use respiratory protection when necessary.

All nickel compounds are classified by the International Agency for Research on Cancer, or IARC (English acronym for the International Agency for Research on Cancer ), in the category of carcinogens for humans.

This is based on epidemiological and experimental data.

References

  1. Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. Fourth Edition. John Wiley & Sons.
  2. Lyalin, BV et al. Electrosynthesis of azopyrazoles via the oxidation of N-alkylaminopyrazoles on a NiO (OH) anode in aqueous alkali – A green method for NN homocoupling. Tetrahedron Letters. 59 (2018) 2741-2744. Recovered from sciencedirect.com.
  3. Liuyang, Zhang, et al. (2018). Nickel-based materials for supercapacitors. Materials Today. Recovered from sciencedirect.com
  4. Ettel, VA and Mosolu, MA (1977). Preparation of Nickel Black. US Patent No. 4,006,216. February 1, 1977.
  5. Scharbert, B. (1993). Process for oxidizing hydroxymethylpyridine derivatives to pyridinecarboxylic acid derivatives at nickel oxide hydroxide anodes. US Patent No. 5,259,933. November 9, 1993.
  6. Kirk-Othmer (1994). Encyclopedia of Chemical Technology. Volume 17. Fourth Edition. John Wiley & Sons.
  7. Ullmann’s Encyclopedia of Industrial Chemistry. (1990). Fifth Edition. Volume A 17. VCH Verlagsgesellschaft mbH.
  8. McBreen, James. (1997). Nickel Hydroxides. In Handbook of Battery Materials. VCH Publisher. Recovered from osti.gov.

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