What are the anode and cathode reactions during the...

What are the anode and cathode reactions during the discharge of a lead storage battery? How can a battery produce a potential of $12 \mathrm{~V}$ if the cell reaction has a standard potential of only $2 \mathrm{~V}$ ?

Key Concepts

Electrode Half-Reactions

In any electrochemical cell, the overall reaction is divided into two half-reactions: one oxidation and one reduction. The oxidation occurs at the anode where species lose electrons, while the reduction occurs at the cathode where species gain electrons. This separation of the reaction into two complementary processes is key to converting chemical energy into electrical work.

Electrochemical Reaction in Lead Storage Batteries

In a lead storage (lead-acid) battery during discharge, the anode (typically lead) undergoes oxidation, converting lead to lead sulfate, while the cathode (typically lead dioxide) undergoes reduction, also producing lead sulfate, with sulfuric acid acting as the electrolyte. The combined reaction results in the buildup of lead sulfate at both electrodes and the generation of electrical energy, and it is inherently reversible to allow for battery charging.

Standard Electrode Potentials

Standard electrode potentials indicate the intrinsic tendency of a half-reaction to occur under standard conditions. In the context of a lead storage battery, the cell reaction has a standard potential of about 2 V for a single cell, reflecting the energy difference between the reactants and products in that cell’s half-reactions. This value is used as the basis for constructing the overall battery’s voltage when multiple cells are connected.

Series Connection of Cells

To achieve a higher total voltage output, individual cells can be connected in series so that their voltages add together. In lead storage batteries, six cells each providing around 2 V are connected in series, resulting in a total battery voltage of approximately 12 V. This method of stacking cells is a fundamental technique in battery design to meet specific voltage requirements.

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