Fuel cells `:` Fuel cells are galvanic cells in which the chemical energy of fuel cell is directly converted into electrical energy. A type of fuel cell is a hydrogen `-` oxygen fuel cell. It consists of two electrodes made up of two porous graphite impregnated with a catalyst `(` platinum, silver, or metal oxide `).` The electrodes are placed in aqueous solution of `NaOH` . Oxygen and hydrogen are continuously fed into the cell. Hydrogen gets oxidized to `H^(o+)` which is neutralized by `overset(c-)(O)H, i.e.,` anodic reaction. At cathode, `O_(2)` gets reduced to `overset(c-)(O)H` Hence, the net reaction is The overall reaction has `DeltaH=-285.6 kJ mol^(-1)` and `DeltaG=-237.4 kJ mol^(-1)` at `25^(@)C` A fuel cell is `I.` A voltaic cell in which continuous supply of fuels are sent at anode to perform oxidation. `II.` A voltaci cell in which fuels such as `:CH_(4),H_(2),` and `CO` are used up at anode. `III.` One which involves the reaction of `H_(2)-O_(2)` fuel cell such as `:` Anode `:2H_(2)O+4overset(c-)(O)H rarr 4H_(2)O(l)+4e^(c-)` Cathode `: O_(2)+2H_(2)O(l) =4e^(-) rarr 4overset(c-)(O)H` `IV.` The efficiency of `H_(2)-O