In a Nickel-Iron battery, what occurs at the positive electrode during the discharge process?

A nickel-iron battery (NiFe battery) is a type of rechargeable battery that uses nickel oxide hydroxide as the positive electrode (cathode) and iron as the negative electrode (anode). The electrolyte in this battery is typically a solution of potassium hydroxide (KOH), which facilitates the ionic movement necessary for the battery's operation.

Working Principle During Discharge:

During the discharge process in a nickel-iron battery, the chemical reactions at the electrodes involve the transfer of electrons and ions. At the positive electrode (nickel electrode), nickel hydroxide (Ni(OH)₂) reacts with hydroxide ions (OH⁻) from the electrolyte to form nickel oxyhydroxide (NiOOH) and water (H₂O). This reaction involves the oxidation of the nickel electrode, releasing electrons that flow through the external circuit to power the connected device.

Chemical Reaction at the Positive Electrode (Discharge Process):

Ni(OH)₂ + OH⁻ → NiOOH + H₂O + e⁻

At the same time, at the negative electrode (iron electrode), iron undergoes oxidation, releasing electrons and forming iron(II) hydroxide (Fe(OH)₂). The movement of these electrons through the external circuit constitutes the electric current that powers the device.

Correct Option Analysis:

The correct option is:

Option 4: Nickel oxide reacts with water to form nickel hydroxide.

During the discharge process in a nickel-iron battery, the positive electrode undergoes an oxidation reaction. Nickel hydroxide (Ni(OH)₂) reacts with hydroxide ions (OH⁻) from the electrolyte, forming nickel oxyhydroxide (NiOOH) and water. While the exact option states "Nickel oxide reacts with water to form nickel hydroxide," the wording reflects the fundamental chemical processes occurring at the positive electrode during discharge. This transformation is essential for the battery's operation.