Hydrogen - Rau's IAS

Why Hydrogen?

A general trend towards development of better fuels is hydrogen-rich fuels.
This means more of hydrogen in the fuel and less of carbon or more hydrogen to every carbon atom. Eg: Natural gas 4 hydrogen to every carbon as opposed to very little hydrogen in coal.
This is because just like carbon, hydrogen is also combustible, i.e. it mixes with oxygen in the air and gives heat.
In addition, moving from a solid to a liquid and then finally to a gaseous state energy carrier.

It is important to understand that all fuels we have seen so far are energy carriers.
Hydrogen is the best energy carrier as there are no harmful impact (read carbon emissions)
This is because hydrogen is not freely available on earth, but it is in abundance in the form of in water and hydrocarbons.
However, to extract hydrogen from water or hydrocarbons you need to expend energy and the energy spent in extracting hydrogen is much more than the amount of energy the so-extracted hydrogen gives out. This is why hydrogen is energy carrier and not an energy source. (in fact all fuels we have seen are energy carriers)

Hydrogen is highly combustible i.e. it mixes readily with oxygen to produce heat.

Further the amount of energy out of this process is about 3 times higher than that you get when you burn petrol. (26 Kcal/gm for hydrogen compared to 10 Kcal/gm for gasoline).

However, the problem with hydrogen is that it has low density, meaning the amount of hydrogen mass you can hold in 1 liter is about 71 grams.
That means the tank size at normal temperature and pressure to hold hydrogen is very big.
In other words, though the fuel itself is lightweight the tank size and therefore the weight of the tank goes higher.
This puts a limitation on hydrogen being used as a fuel in private transport.
Thus, hydrogen is suitable for large vehicles like buses which requires a limited range but can hold a large tank.
This requires hydrogen to compressed at high pressure. Alternately you can liquify hydrogen by compressing and taking away heat.

You can’t mine hydrogen. There is virtually no hydrogen gas (or liquid) in the environment.
But there’s lots of hydrogen in water and in fossil fuels (hydrocarbons)-but not “free” hydrogen, the molecule H2.
That’s what we want for the hydrogen economy.
Two major sources of hydrogen on earth are water and hydrocarbons
From hydrocarbons
Take any hydrocarbon and treat it with steam we get syn gas which is a source of hydrogen.
Any hydrocarbon+H2Oà CO+H2
Hydrocarbon could be either fossil or biofuel or even organic waste.
However, hydrocarbon source of hydrogen is again a problem because the left over carbon has to go to atmosphere.
This makes it dirty. That’s why hydrogen from these sources is colour coded with ‘dirty’ colours like grey, blue, black etc.

Budget 2021-22 proposed the National Hydrogen Mission to make India the hub of green hydrogen production.
In Feb 2022 the National Green Hydrogen Policy was formulated.
In 2023, the cabinet approved Rs.19,744 crore towards other Mission components.

Pass electricity through water, it will split it into its constituent Hydrogen and oxygen.
Process where electricity is used to make a chemical change that wouldn’t happen otherwise.
In a normal situation oxygen pulls electrons and hydrogen pushes its electron.
In case of electrolysis, water is split into hydrogen and oxygen and for this to happen hydrogen has to gain electron and oxygen has to lose electron which is the opposite to what happen normally.
This requires energy which is what electricity gives.
So, take a battery use the energy to pull the electrons out of oxygen and push it towards hydrogen.
If the electricity you use to split water comes from renewable source, it gives you green hydrogen, the cleanest source of hydrogen.

Burn it in directly IC engine, blend it with another gaseous fuel or use it in fuel cell.
Hydrogen being combustible can be used directly in IC engine. However, the efficiency is very low, hardly 25-30%.
Alternately we blend hydrogen with natural gas. This is what is called H-CNG.