When a charging current is applied to a nickel-cadmium battery, the cells emit gas toward which part of the cycle?

When a charging current is applied to a nickel-cadmium battery, the cells emit gas toward which part of the cycle?

• A. At the very start
• B. Toward the end of the charging cycle
• C. Throughout charging
• D. Only after full discharge

Answer: (B)

Gas emission in a nickel-cadmium cell happens when the charging current starts driving water in the alkaline electrolyte to split, producing hydrogen at the negative electrode and oxygen at the positive electrode. This gas formation doesn’t appear much at the very beginning of charging because the cell’s reactions are mainly storing energy. As the cell approaches full charge, the driving potential becomes high enough that electrolysis (water splitting) occurs if charging continues, so gas bubbles begin to form and are vented. That’s why gas is observed toward the end of the charging cycle rather than at the start or uniformly throughout.

Gas emission in a nickel-cadmium cell happens when the charging current starts driving water in the alkaline electrolyte to split, producing hydrogen at the negative electrode and oxygen at the positive electrode. This gas formation doesn’t appear much at the very beginning of charging because the cell’s reactions are mainly storing energy. As the cell approaches full charge, the driving potential becomes high enough that electrolysis (water splitting) occurs if charging continues, so gas bubbles begin to form and are vented. That’s why gas is observed toward the end of the charging cycle rather than at the start or uniformly throughout.