Question

Why don,t we use hydrogen as a fuel?

Answer 1

The question is partly wrong. We do use hydrogen as fuel, but its use is limited.
Hydrogen is used as fuel in rocket engines and spacecrafts. Hydrogen-oxygen fuel cells are extensively used in many space expeditions.

The actual question is why we don't use hydrogen as fuel for our daily needs, like cooking, in cars or bikes , etc.

There are mainly 2 reasons why hydrogen cannot be used as fuel for daily needs.

First is the high reactivity of Hydrogen. Hydrogen reacts with oxygen in a explosive manner. We require serious and expensive units to control the reaction. If uncontrolled , reaction can be explosive.

The second reason is difficulty to store hydrogen. Hydrogen being a gas cannot be stored in normal vessels, like coal or petrol or diesel. We require high pressure safety vessels for this. Also, hydrogen is lighter than most other gases, so it easily escapes into atmoshere . Also, hydrohen atoms are very small. If you take a glass vessel, fill hydrogen and close it with a lid, still hydrogen atoms can escape. The atoms being so small, can actually diffuse through glass and steel, and escape container.

Other reasons are...
Hydrogen has no smell, so its impossible to detect leaks. So, if hydrogen leaks, you will never know, and it may cause explosions.
Impure Hydrogen burns with blue flame and pop sound, but , pure H burns with no flame. Yes...if you burn pure H, you will not see any fire, just heat. So, even if Hydrogen is burning, you cannot detect it with normal eyes, you will need infrared cameras.

So, even though H is good fuel, we cannot economically burn it in small environments like cars or hosehold, So, we donot depend primarly on H as fuel.