Hydrogen Economy

Hydrogen economy

One proposed way to meet the need for new energy sources is to burn hydrogen as a fuel in industry and power plants and possibly also in homes and motor.This proposal is referred to hydrogen economy.

Advantages of hydrogen economy

1) Dihydrogen releases large quantities of heat on combustion. The energy released by combustion of fuels like dihydrogen, methane, LPG as compared in terms of the same amount in mole, mass and volume.On mass to mass basis, dihydrogen can release more energy than gasoline i.e. Octane number is about 3 times.

Energy released on combustion (in KJ)	Dihydrogen (in gaseous state)	Dihydrogen (in liquid state)	LPG	CH4 gas	Octane( in liquid state)
per mole	286	285	2220	880	5511
per gram	143	142	50	53	47
per litre	12	9968	25590	35	34005

2) Burning of hydrogen in air or dioxygen not only liberates large amount of energy but yields water as the only product.Burning of hydrogen produces no pollutant like SO₂ that are responsible for acid rain ,nor carbon dioxide that is responsible for the greenhouse effect ,nor carcinogenic hydrocarbons nor lead compounds.

There are two major barriers in achieving the goal of hydrogen economy

1) To find out a cheap method for large scale production of dihydrogen.

Two methods  which have been proposed are :

a)Electrolysis of water and the thermochemical reactions cycle. The first method is not economically viable since the cost of production of dihydrogen by electrolysis of water is so high that almost all dihydrogen is obtained from natural gas which itself is in short supply.

b) The other method involves series of thermochemical reactions in which the only things consumed are water and heat and only products are hydrogen and oxygen while all the other species are recycled.

2) To find out an effective means of storing dihydrogen.

 The gaseous dihydrogen because of its bulk, is difficult to store, but liquid dihydrogen can be stored relatively easily and safely in cryogenic tanks.

It is also feasible to transport liquid dihydrogen by road or rail tankers of 20000 US gallons capacity.It can also be stored in underground tanks and transported by pipelines. However it may not be convenient to store liquid dihydrogen in a home or in a car since the boiling point of dihydrogen is very low.

Dihydrogen must be kept out of contact with oxygen or air with which it forms explosive mixture. The only alternative left is to store dihydrogen or metal  in an alloy as interstitial hydride.