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Hydrogen

Hydrogen is an element with the chemical symbol H. It is the lightest and simplest element. It has a nucleus that consists of just a single proton, and a single negatively-charged electron moves around that nucleus.
Hydrogen occurs in enormous quantities on Earth, mostly in combination with other chemical elements. It is part of water (H₂O) for example, but it is often also combined with carbon in the form of petroleum,, natural gas and biomass. Only 1% of the hydrogen on Earth exists in a pure form, which means that it is not a natural source of energy. In order to use it – for example in a fuel cell – it first has to be produced by the electrolysis of water (splitting the H₂ off from the H₂O) or by reforming natural gas (CH₄), whereby the natural gas is converted into hydrogen and CO₂.

Hydrogen gas (H₂) that is used in vehicles is a colourless, odourless gas that is totally harmless to humans. It is not corrosive, radioactive, toxic or carcinogenic. Hydrogen gas is extremely light: one-fourteenth as heavy as normal air. If it is released it rises immediately, which makes it safer in use than natural gas or LPG, which settle. Compared with other gases, hydrogen is highly flammable, which is why strict requirements are laid down for the electrical and mechanical components of installations in which it is used. These requirements are set out in the ATEX directives for explosion protection material.

Because the boiling point of hydrogen is extremely low (-252°C), making it liquid takes a lot of energy. Special technical facilities are required for this.
Despite hydrogen’s being so light, it does have a high energy content. A kilo of hydrogen provides 120 MJ of energy, compared with 50 MJ for natural gas and 46 MJ for petrol.