Question

What are fuel cells? How are they different from Galvanic cells? Give the construction of hydrogen-oxygen fuel cells.

Answer 1

Fuel Cell $\to$ In other words, a device to convert the chemical energy of fuel into electrical energy is called fuel cell.

Difference between Fuel cells and Galvanic cells-

Fuel cell	Galvanic cell
Converts the energy from the combustion of fuels such as $H_2,CO,C{H}_4,$ etc. directly into the electrical energy.	Chemical energy of the spontaneous redox reaction is converted into the electrical energy.
It is a continuous source of energy.	It is not a continuous source of energy.
It is not pollution free.	It is not pollution free
There is a continuous supply of the reactants.	The supply of the reactants is not continuous.

Construction of hydrogen-oxygen fuel cell $\to$

A fuel cell consists of two electrodes sandwiched around an electrolyte. Oxygen passes over one electrode and hydrogen over the other, generating electricity, water, and heat. Hydrogen fuel is fed into the "anode" of the fuel cell. Oxygen (or air) enters the fuel cell through the cathode. Encouraged by a catalyst, the hydrogen atom splits into a proton and an electron, which take different paths to the cathode. The proton passes through the electrolyte. The electrons create a separate current that can be utilized before they return to the cathode, to be reunited with the hydrogen and oxygen in a molecule of water.

The electrode reactions are-

At cathode:-

${O_2}_{\left(g\right)}+{H_{2}O}_{\left(l\right)}+4e^{-}⟶4{{OH}^{-}}_{(aq.)}$

At anode:-

$2{H_2}_{\left(g\right)}+4{{OH}^{-}}_{(aq.)}⟶4{H_{2}O}_{\left(l\right)}+4e^{-}$

Overall reaction:-

$2{H_2}_{\left(g\right)}+{O_2}_{\left(g\right)}⟶2{H_{2}O}_{\left(l\right)}$