As the world tackles global warming, hydrogen has gained attention as a clean-energy alternative to earth-polluting fossil fuels.

Some hydrogen-powered cars and buses, which do not emit carbon dioxide, are already on public roads, and the government is hoping to display its technology by using hydrogen as a fuel for the Olympic torch and a power source for the athletes village for the 2020 Olympic and Paralympic Games in Tokyo.

Hydrogen, which does not exist on Earth as a gas, has the advantage of being produced from various energy sources such as sunlight, biomass and petroleum. A large volume of hydrogen, when compressed, can be easily stored for long periods and transported over long distances. Hydrogen fuel cells generate electricity through chemical reaction with oxygen in the air, with water and heat as the only byproducts.