Hydrogen Fuel

Our present day life highly banks upon the use of fossil fuels such as coal, natural gas, LPG, gasoline, etc. for the production of energy. Our reserves of fossil fuels are getting depleted at an alarming rate and they may get exhausted by the middle of 21^st century. The reason for this shortage is that the rate of consumption of fossil fuels is much larger than the rate of their renewal.

Fig: 11.3 - Fossil fuel cycle

Alternative energy sources

Other alternative source of energy for future is the nuclear energy derived from nuclear fission or nuclear fusion processes. The use of nuclear energy mainly requires its conversion into electrical energy. Out of the world's total energy requirement only 20% constitutes electrical energy. The rest of the 80% requirement is energy in the form of heat. Conversion of nuclear energy into chemical energy for storage and transportation and disposal of nuclear waste are the problems of this technique.

Hydrogen as fuel

Hydrogen is an important alternative energy source. Some advantages of hydrogen are:

• Hydrogen is abundantly available in the combined form as water.

• Use of hydrogen as fuel provides pollution free atmosphere because its combustion product is water.

• Time required for regeneration of hydrogen is short.

• Automobiles engine burning hydrogen is about 25 to 50% more efficient than an automobile engine burning gasoline (petrol).

• Heat of combustion per gram of hydrogen is more than twice that of jet fuel.

• Hydrogen-oxygen fuel cells provide other possibilities of powering motor vehicles.

Hydrogen is excellent reducing agent and produces less atmospheric pollution than carbon. So it can replace coal in many industrial processes.

The changes in our way of life by adopting widespread uses of hydrogen is referred to as 'hydrogen economy'.

Hydrogen economy

Although hydrogen looks as very good future fuel, the problems associated with its economy are:

Availability

Hydrogen is not available as such. It does not occur in a free state in nature. The cheap production of hydrogen is a basic requirement of hydrogen economy. The source of hydrogen is water and using nuclear energy or solar energy might generate it.

Transportation

Hydrogen gas has explosive flammability and so is difficult to handle. This causes problem to its storage and transportation. A solution for this is the use of Fe-Ti alloy, which absorbs hydrogen and results in the formation of fine silvery powder. Heating the powder safely releases hydrogen gas. Such storage system is safer than storage of hydrogen as gas or liquid.

Platinum scarcity

Platinum is required as catalyst in oxygen-hydrogen fuel cells. The demand of platinum exceeds the supply. This will cause problems for fuel cells, which are highly promising energy source for automobiles.

Cost

Hydrogen is an expensive fuel because its cost of production is high.

Use of liquid hydrogen as fuel

Liquid hydrogen is used as an important rocket fuel because of its low mass and high enthalpy of combustion. The chemical reaction involved is:

Both reactants H₂ and O₂ are stored as liquids in separate tanks. The advantage of using hydrogen as a rocket fuel is:

• The product of combustion is water.

• There is no emission of environmental pollutants such as CO, SO₂, oxides of nitrogen, hydrocarbons, etc.

Although during the 'lift off' operations, these propellants power shuttle's main engine for about 8.5 min, liquid hydrogen cannot be used much because the extraction of it from water is an expensive procedure.