The alkaline battery

Electrochemical cells are batteries. One of the most common forms of battery is the alkaline battery (alkaline because potassium hydroxide is the electrolyte).

At the anode:

Unlike electrochemical cells mentioned in an earlier article, the anode is not a piece of zinc but zinc particles suspended in a KOH electrolyte (ZnKOH paste). Zinc is oxidised to Zn2+ as follows:

Zn (s) + 2OH(aq) → ZnO (s) + 2H2O (l) + 2e

The free electrons are collected at the anode collector and flow out of the battery via the anode cap when connected to an external circuit to power an electronic device (see diagram below).

At the cathode:

Returning electrons enter the battery via the cathode cap and flow along the sides to the cathode collector and then to the cathode where they participate in the following reduction reaction:

2MnO2 (s) + H2O (l) + 2eMn2O3 (s) + 2OH– (aq)

Like the anode, the cathode is not a piece of manganese (IV) oxide but a paste of manganese (IV) oxide and carbon (carbon is added to improve conductivity). The porous cellulose separator prevents the electrode materials from mixing but allows hydroxide ions produced in the cathode to migrate across it to the anode to maintain electrical neutrality.


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