Understanding the Nickel-Iron Cell

A nickel-iron cell, also known as an Edison battery, is a type of rechargeable alkaline secondary battery. It uses nickel(III) oxyhydroxide as the positive plate and iron as the negative plate, with an alkaline electrolyte of potassium hydroxide.

This question asks specifically about the material used for the positive plate in a nickel-iron cell.

Components of a Nickel-Iron Cell

A typical nickel-iron cell consists of several key components:

• Positive Plate: This is one of the electrodes where oxidation or reduction reactions occur during charging and discharging.
• Negative Plate: This is the other electrode involved in the electrochemical reactions.
• Electrolyte: This is the ionic conductor between the positive and negative plates.
• Container: Holds the components together.

Material of the Positive Plate

In a nickel-iron cell, the positive plate is constructed from nickel hydroxide. This material undergoes chemical changes during the charging and discharging cycles of the battery.

Let's look at the options provided:

• Nickel hydroxide: This is a compound of nickel and hydroxide, commonly used in alkaline batteries.
• Ferrous hydroxide: This is a compound of iron and hydroxide, related to iron which is used in the negative plate.
• Lead peroxide: This is a compound of lead and oxygen, typically used in lead-acid batteries, not nickel-iron cells.
• Potassium hydroxide: This is a compound of potassium and hydroxide, which serves as the electrolyte in nickel-iron cells, not the plate material.

Based on the composition of the nickel-iron cell, the positive plate is made of nickel hydroxide.

Therefore, the material used for the positive plate of a nickel-iron cell is nickel hydroxide.

Revision Table: Nickel-Iron Cell Components

Additional Information on Nickel-Iron Batteries

Nickel-iron batteries are known for their long lifespan and robustness, especially in harsh conditions. They are resistant to overcharging and discharging, unlike some other battery types.

The reactions occurring during discharge are approximately:

• Positive plate: \(\text{NiOOH} + \text{H}_2\text{O} + \text{e}^- \rightarrow \text{Ni(OH)}_2 + \text{OH}^-\)
• Negative plate: \(\text{Fe} + 2\text{OH}^- \rightarrow \text{Fe(OH)}_2 + 2\text{e}^-\)
• Overall reaction: \(\text{NiOOH} + \text{Fe} + \text{H}_2\text{O} \rightarrow \text{Ni(OH)}_2 + \text{Fe(OH)}_2\)

During charging, these reactions are reversed.

While they offer durability, nickel-iron cells typically have a lower energy density and higher self-discharge rate compared to modern battery technologies like lithium-ion.