Which reaction occurs at the cathode of a lead-storage battery that is being recharged?

Reaction on positive electrode (cathode):

PbSO₄ ₍s₎ + 2H₂O ₍l₎ → 2e⁻ + PbO₂ ₍s₎ + 4H⁺ ₍aq₎ + SO₄²⁻ ₍aq₎.

s - solid.

l - liquid.

aq - dissolve in water.

PbSO4 is converted to Pb at one electrode (anode) and to PbO₂ at the other (cathode). Lead battery can be recharged, during recharging, an external source of energy is used.