Hydrogen is often heralded as a climate hero because when it is used as a fuel in things like buses or steel production, there are no direct carbon emissions (or associated warming) to worry about. As the world tries to reduce its use of fossil fuels, there could be a big demand for this carbon-free energy source.
But the way hydrogen is produced can determine how beneficial it is to the climate. That’s where the rainbow comes in. (I’ve added a quick overview table below so you can untangle all these colors.)
Last week, the European Commission published rules defining what constitutes “renewable” hydrogen: in other words, what it means for hydrogen green. Last week Science also had a fascinating story about what happens in nature, or goldhydrogen
So let’s dive into the hydrogen rainbow and find out where this fuel of the future might come from.
Why do you need hydrogen?
We already use a lot of hydrogen today, with global demand estimated at 94 million metric tons (Mt) in 2021. Most of it was used for oil refining, as well as for the production of ammonia (for fertilizer) and methanol (for chemical production).
This is likely to change in the future because it is also a good substitute for fossil fuels in transport, heavy industry and other sectors. If countries keep their climate pledges, hydrogen demand could reach 130 million tons by 2030, with about a quarter of that coming from new uses.
The problem is that hydrogen production today overwhelmingly requires fossil fuels, usually natural gas. In the production of so-called “grey” hydrogen, natural gas reacts with water to form hydrogen gas and release carbon.
However, it doesn’t have to be this way. On the one hand, we could try to capture carbon emissions from fossil-based hydrogen production (this method produces so-called blue hydrogen). This is a rather controversial approach because carbon capture is expensive and does not always work effectively.