In a Nickel-Iron cell, which of the following best describes the working principle during the discharging process?

Explanation:

Nickel-Iron Cell Discharging Process

Definition: A Nickel-Iron (Ni-Fe) cell, also known as an Edison cell, is a type of rechargeable battery that utilizes nickel oxide hydroxide as the positive electrode and iron as the negative electrode. During the discharging process, chemical reactions occur at both electrodes to produce electrical energy.

Working Principle During Discharging: In a Nickel-Iron cell, the discharging process involves the following electrochemical reactions:

At the positive electrode (cathode), nickel oxide hydroxide (NiOOH) is reduced to nickel hydroxide (Ni(OH)₂):
NiOOH + H₂O + e^- → Ni(OH)₂ + OH^-

At the negative electrode (anode), iron (Fe) is oxidized to iron hydroxide (Fe(OH)₂):
Fe + 2OH^- → Fe(OH)₂ + 2e^-

These reactions result in the flow of electrons through an external circuit, generating electrical energy that can be utilized by connected devices. The overall cell reaction during discharge can be summarized as:
NiOOH + Fe + H₂O → Ni(OH)₂ + Fe(OH)₂

Applications: Nickel-Iron cells are commonly used in off-grid and renewable energy storage systems, emergency lighting, railway signaling, and other applications where long life and robustness are critical.

Correct Option Analysis:

The correct option is:

Option 2: Iron at the negative electrode is oxidized to iron oxide, and nickel at the positive electrode is reduced to nickel hydroxide.

This option correctly describes the electrochemical reactions occurring during the discharging process of a Nickel-Iron cell. Iron at the negative electrode undergoes oxidation, while nickel oxide hydroxide at the positive electrode undergoes reduction, leading to the generation of electrical energy.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Nickel at the positive electrode is reduced to metallic nickel, and iron hydroxide at the negative electrode is oxidized.

This option is incorrect because, during the discharging process, nickel oxide hydroxide is reduced to nickel hydroxide, not metallic nickel. Additionally, iron is oxidized to iron hydroxide, not iron hydroxide being oxidized.

Option 3: Nickel hydroxide at the positive electrode is reduced to metallic nickel, and iron is oxidized at the negative electrode.

This option is incorrect because nickel hydroxide is not reduced to metallic nickel during discharging. Instead, nickel oxide hydroxide is reduced to nickel hydroxide.

Option 4: Iron at the negative electrode is reduced to metallic iron, and nickel hydroxide at the positive electrode is oxidized.

This option is incorrect because, during discharging, iron is oxidized to iron hydroxide, not reduced to metallic iron. Additionally, nickel hydroxide is not oxidized during discharging; instead, nickel oxide hydroxide is reduced to nickel hydroxide.