The name hydrogen is derived from the Greek words for water; hydro and former; genes. Hydrogen (H) has atomic number 1 and is the lightest element in the periodic table. The most common isotope of hydrogen consists of one proton and one electron. Estimates show that hydrogen is the most common element in the universe and, despite its lightness, makes up three quarters of the mass in the universe.
On earth, the hydrogen atom mostly appears as part of the water molecule, H2O. Hydrogen is also a part of many other substances, for instance in hydrocarbons, carbohydrates, and ammonia (NH3).
Hydrogen is an energy carrier and must therefore be produced from energy resources. The most used production methods are electrolysis and reforming of fossil energy e.g., natural gas. When hydrogen is produced from renewable energy, it is categorized as green hydrogen, while when generated from gas reforming with Carbon Capture and Storage (CCS) or Carbon Capture Usage and Storage (CCUS) it is known as blue hydrogen. Both green and blue hydrogen are categorized as clean energy carriers and when utilized in a Fuel Cell the only emissions are clean water and heat.