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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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During the charging and discharging of a nickel-iron cell
corrosive fumes are produced
water is neither formed nor absorbed
nickel hydroxide remains unsplit
its e.m.f. remains constant
water is neither formed nor absorbed
Quick Summary: In a nickel-iron (Edison) storage cell, the chemical reactions during both charging and discharging involve the transfer of oxygen between the positive and negative plates. Because the total amount of water in the electrolyte remains unchanged, water is neither formed nor absorbed during the cycle.
In a nickel-iron (Edison) storage cell, the chemical reactions during both charging and discharging involve the transfer of oxygen between the positive and negative plates. Because the total amount of water in the electrolyte remains unchanged, water is neither formed nor absorbed during the cycle.
2Ni(OH)3+Fe⇌2Ni(OH)2+Fe(OH)2 — The net chemical reaction
The overall chemical reaction of the cell is: 2Ni(OH)3+Fe⇌2Ni(OH)2+Fe(OH)2. During discharge, the nickel hydroxide Ni(OH)3 is reduced to Ni(OH)2 at the positive plate, and the iron Fe is oxidized to Fe(OH)2 at the negative plate. Since the electrolyte (potassium hydroxide solution) merely acts as a medium for the transfer of ions and does not participate in the net stoichiometric change regarding water content, the specific gravity of the electrolyte remains effectively constant.
The electrolyte used is Potassium Hydroxide (KOH) with lithium hydrate.
The electrolyte does not undergo any chemical change, so its density remains constant.
These batteries are known for their high mechanical strength and long life.
They are generally not used for starting automotive engines due to high internal resistance.
Extremely long service life and durability
Can withstand electrical abuse such as overcharging and short-circuiting
Ability to remain idle for long periods without damage
Lower energy efficiency compared to Lead-Acid batteries
High cost of manufacturing
High internal resistance limits discharge rates
Railway carriage lighting
Mining lamps
Heavy duty industrial power systems
Because the specific gravity of the electrolyte does not change, a hydrometer cannot be used to determine the state of charge of a nickel-iron battery.
Option A is incorrect because no corrosive fumes (like those in lead-acid cells) are emitted in significant quantities; Option C is incorrect as nickel hydroxide is the active material that converts; Option D is incorrect as the terminal voltage varies with load.
B is correct — During the chemical cycle of a nickel-iron cell, the electrolyte concentration remains constant because water is neither consumed nor produced in the net reaction.
Always remember that unlike lead-acid batteries, the specific gravity of the electrolyte in a nickel-iron battery is not an indicator of the state of charge.