Odourless and invisible, hydrogen is the most abundant element in the universe,
and has the potential to provide a clean, near-infinite source of energy.
It’s already used in oil refining and fertiliser manufacture.
But despite efforts, and a lot of hype, it has never taken off as a fuel.
That could be about to change, as the need to tackle climate change becomes more acute.
Analysts agree that much of the global economy can be decarbonised in the near term
by electrifying things like cars and heating, and by using renewables to generate power.
But something else will be needed to clean up other carbon-intensive sectors such as
aviation, shipping, long-haul trucking and heavy industry like concrete and steel manufacture.
Enter hydrogen.
Hydrogen gas does not emit carbon when burnt and has been touted by some as
the ideal replacement for fossil fuels in these problem sectors.
Despite the abundance of hydrogen as an element, its atoms do not exist by themselves.
They need to be separated from other elements in order to be used to deliver energy.
This can be done in a number of different ways, each colour coded according to emissions produced.
At the dirtier end of scale is brown hydrogen, made from coal.
Grey hydrogen is made from natural gas, a process that still creates a lot of carbon waste.
The cleaner blue variety is also made from natural gas, but with carbon capture
technology that stores the CO2, rather than spilling it out into the atmosphere.
Green hydrogen tops the eco-friendly table.
It’s produced by the electrolysis of water using renewable energy.
An electric current produced from wind or solar splits water molecules into hydrogen and oxygen.
Green hydrogen is attracting the attention of investors and policymakers
as the world scrambles to cut emissions.
But there is a catch.
The costs of green hydrogen remain too high at around $5 per kg.
To be competitive with fossil fuels, this figure needs to fall below $1 per kg.
Analysts say that could happen within the next few decades, or even sooner,
as agencies like the US Energy Department get behind research and development.
If it does take off, it’s estimated that the hydrogen
economy could be worth as much as $2.5tn by 2050.