NICKEL (III) HYDROXIDE: STRUCTURE, PROPERTIES, USES, RISKS - CHEMISTRY - 2024

The nickel hydroxide (III) is an inorganic compound wherein the 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 both are 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.

Crystal 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 layers are missing 3 electrons, that is, two electrons are missing from layer 4 s and one electron from layer 3 d. The electronic configuration of Ni ³⁺ in NiO (OH) is: 3 d ⁷, where is the electronic configuration of the noble gas argon.

Nomenclature

- NiO (OH): Nickel (III) oxohydroxide

- Nickel black

Properties

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 a nickel (II) and (III) oxohydroxide, Ni ₃ O ₂ (OH) ₄.

It decomposes at 140 ° C 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 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.

Electrolysis is carried out in a cell with nickel anode and 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 obtaining organic compounds with low costs and in an environmentally friendly way.

In supercapacitors

NiO (OH) together with Ni (OH) ₂ are excellent materials for supercapacitor electrodes.

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 with a doctor to rule out that it is caused by nickel.

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

All nickel compounds are classified by the International Agency for Research on Cancer, or IARC, in the category of carcinogens to 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.