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`
Suppose the concentration of hydroxide ion in the cell is doubled, then the cell voltage will be

Options

A. reduced by half
B. increased by a factor of 2
C. increased by a factor of 4
D. uncharged

Answer

D

Explanation

IF `EMF` of `2OH^(-) +H_(2) hArr 2H_(2)O +2e^(-) =E_(1)^(@)`
Hence `DeltaG_(1)^(@) =- 2FE_(1)^(@)`
IF` OH^(-)` conc. Is doubled then equation becomes
`4OH^(-) +2H_(2) hArr 4H_(2)O +4e^(-) -E_(2)^(@)`
Also `DeltaG_(2)^(@) = 2DeltaG_(2)^(@)`
`rArr -4FE_(2)^(@) = 2 xx (-2FE_(1)^(@))`
`rArr -4FE_(1)^(@) =- 4FE_(1)^(@)`
`rArr E_(2)^(@) - E_(1)^(@)`
Hence `E^(@)` is uncharged.