Batteries, Fuel Cells and Corrosion

Batteries: Electrochemical cells can be used as batteries. Batteries are of two kinds.
(i) Primary battery: where the reaction occurs only once and can not be reused once it becomes dead over the course of time.
For example, dry cell (Leclanche cell), Mercury cell.
(ii) Secondary battery: which can be recharged by passing current through it in the opposite direction so that it can be used again. For example lead-acid battery, Nickel-cadmium cell.

Fuel Cells:
(i) Fuel cells are the galvanic cells that convert the energy of combustion of fuels (Eg: H2, CH4, Me-OH etc.) directly into electrical energy.
(ii) Fuel cells are more efficient thermodynamically, and more of the energy of the reaction can be made available for useful work provided that the supply of reactants is maintained.
(iii) Efficiency of fuel cell \eta = \frac{Electrical\ work\ done\ during\ redox\ reaction}{\Delta H\ formed\ during\ redox\ change}=\frac{\Delta G}{\Delta H}=\frac{-nFE}{\Delta H}

Corrosion: When the metal exposed to some environment it gets converted to its oxides. The oxidative deterioration of metal is known as corrosion.
Example: Rusting of iron, tarnishing of silver, development of green coating on copper and bronze.

Oxidation: Fe_{(s)} \rightarrow Fe_{(aq)}^{2+} +2e^{-}

Reduction: O_{2(g)}+4H_{(aq)}^{+} +4e^{-}\rightarrow 2H_{2}O_{(l)}

Atmospheric oxygen oxidised Fe2+
2Fe_{(aq)}^{2+}+2H_{2}O_{(l)}+\frac{1}{2}O_{2(g)}\rightarrow Fe_{2}O_{3(s)}+ 4H_{(aq)}^{+}

Part1: View the Topic in this Video from 29:41 to 49:29

Part2: View the Topic in this Video from 15:18 to 53:50

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1. Thermodynamic efficiency of a fuel cell,
\tt \eta=\frac{\Delta G}{\Delta H}=\frac{-nFE}{\Delta H}