14. Hydrogen: from dream to reality

Like electricity, hydrogen is an energy carrier. Like electricity, it requires energy to produce. While hydrogen atoms are abundant on Earth (found in water, hydrocarbons and biomass, for example, but associated with other atoms in these compounds), hydrogen molecules (dihydrogen) are rare, and it's these that are needed for energy applications.

The majority (96%) of hydrogen produced today comes from fossil fuels: natural gas (48%), oil (30%) and coal (18%). This production emits CO ₂ and therefore contributes to global warming. Only 4% of hydrogen is produced by electrolysis, as this is a much more expensive process.

In the future, hydrogen will have to be produced by electrolysis or biochemical processes if we wish to avoid emitting CO ₂ . The problem...