Which of the following converts energy from the combustion of fuel directly to the electrical energy?

 

Sketch and describe the operation of ${\mathrm{H}}_2-{\mathrm{O}}_2$ fuel cell.

A fuel cell converts the chemical energy of a fuel into electrical energy. In Chapter $7$, you have learnt that hydrogen has a very high calorific value, but cannot be used the way we use other fuels because it forms an explosive mixture with air. A fuel cell is a safe way of utilising the chemical energy of hydrogen. What is great about this idea is that hydrogen can be produced by the electrolysis of water, and water is not in short supply the way fossil fuels are.
In a hydrogen fuel cell, hydrogen splits into ${\mathrm{H}}^{+}$ ions and electrons at the anode. The hydrogen ions pass through a selective membrane to the cathode. The electrons, on the other hand, travel along the external circuit (outside the cell) from the cathode to the anode, giving rise to a current that we can draw. At the anode, the hydrogen ions combine with electrons (that have travelled through the external circuit) and oxygen to form water. This is the other great thing about a hydrogen fuel cell—the only waste produced is water, which is not a pollutant. So, why have we not started using fuel cells on a large scale? That is because they are not yet efficient and inexpensive enough for common use.
What does a fuel cell do?