How to make a lead-acid storage battery
name: Oxidation-reduction of lead as an electrochemical reaction
Pb + 2 H2O → PbO2 + 4H+ + 4e-
2 H+ + 2 e- → H2
Pb + 2 H2O → PbO2 + 2 H2
PbO2 + 4 H+ + SO42- + 2e- → PbSO4 + 2 H2O /anode/
Pb + SO42- → PbSO4 + 2e- /cathode/
Pb + PbO2 + 2 H2SO4 → 2 PbSO4 + 2 H2O
PbSO4 + 2 H2O → PbO2 + 4 H+ + SO42- + 2e- /anode/
PbSO4 + 2e- → Pb + SO42- /cathode/
2 PbSO4 + 2 H2O → Pb + PbO2 + 2 H2SO4
The principle of operation of lead-acid batteries is based on the electrochemical reactions of lead and lead dioxide in an aqueous solution of sulfuric acid.
When the external power source is connected to the electrodes of the battery, the electrochemical reaction of lead oxide and sulfuric acid begins, metallic lead is oxidized to lead sulfate (the classic version battery). In fact, the electrochemical processes in the battery are more complicated.
During discharge the recovery of lead dioxide occurs on the anode, and the oxidation of lead on the cathode. Reversible reactions occur during charging. Electrolysis of water starts to overcharge the battery, lead sulfate after exhaustion, while oxygen is released at the anode (positive electrode) and hydrogen is released on the cathode (negative electrode).
As a result, the spent sulfuric acid from the electrolyte during discharge of the battery (when the density of the electrolyte decreases as the concentration of the acid solution is reduced during charging and, when the sulfuric acid is released in the reactions with the electrolyte solution of lead sulfate, the density of electrolyte increases). At the end of charging, when the amount of lead sulfate on the electrodes decreases below a certain critical value the process of water electrolysis begins to dominate. Hydrogen and oxygen are extracted from the electrolyte in the form of bubbles - the so-called "boiling" overcharge. This undesirable phenomenon should be possibly avoided while charging, as water is consumed and the concentration and density of the electrolyte increases. Loss of water by electrolysis fills the battery banks refilling of distilled water.