(i) The term "hydrogen economy" refers to the vision of using hydrogen as a low-carbon energy source – replacing, for example, gasoline as a transport fuel or natural gas as a heating fuel. Hydrogen is attractive because whether it is burned to produce heat or reacted with air in a fuel cell to produce electricity, the only byproduct is water. (ii) It is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic compounds. (iii) Syngas is the abbreviation for Synthesis gas. This is a gas mixture that comprises of carbon monoxide, carbon dioxide and hydrogen. The syngas is produced due to the gasification of a carbon containing fuel to a gaseous product that has some heating value. Some of the examples of syngas are as follows – gasification of coal, waste to energy gasification, steam reforming of natural gas to generate hydrogen. (iv) The water-gas shift reaction (WGSR) describes the reaction of carbon monoxide and water vapor to form carbon dioxide and hydrogen (the mixture of carbon monoxide and hydrogen is known as water gas): CO + H2O CO2 + H. 2. (v) A fuel cell produces electricity through a chemical reaction, but without combustion. It converts hydrogen and oxygen into water, and in the process also creates electricity. It’s an electro-chemical energy conv- ersion device that produces electricity, water, and heat.