Secondary cell





Secondary cells are rechargeable by passing current as electrode reactions can be reversed e. g. lead storage battery, Ni-Cd storage cell.

Lead storage battery:

It contains 6 voltaic cells in a row . It is used in automobiles, invertors etc.

Anode: Spongy lead

Cathode: Grid of lead packed with PbO_2

Electrolyte: 38% by mass aqueosus solution of H_2SO_4

At anode: Pb + SO^{2-}_4 \to PbSO_4 + 2e^-

At cathode: PbO_2

SO^{-2}_4 + 4H^+ + 2e^- \to PbSO_4 + 2H_2O

Net reaction: Pb + PbO_2 + 4H^+ + 2so^{-2}_4 \to PbSO_4 + 2H_2O

  • E_{cell} is 2.04 volt

During discharging H_2SO_ 4is consumed.

 

Nickel-Cadmium Batteries:

Anode: Cd

Cathode: Ni (III) compound supported on Ni or NiO_2 reactions:

At anode: Cd(s) + 2OH^-(aq.) \to Cd(OH)_2 (s) + e^- \\[3mm] \text{At cathode}: 2NiO(OH)(s) + 2H_2O(l) + 2e^- \to 2Ni(OH)_2(s) + 2OH^-(aq.) \\[3mm] \line(1,0){250} \\[3mm] \text{Net reaction}: \\[3mm] Cd(s) + 2NiO(OH)(s) +2H_2O(l) \to Cd(OH)_2(s) + 2Ni(OH)_2(s) \\ \line(1,0){250}



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