Hydrogen fuel can be used to store, transport, and sell renewable energy, but like any new technology, it may have surprising consequences: a study published in Nature Climate Change has found that if enough hydrogen leaks into the atmosphere, it may prolong the presence of another greenhouse gas: methane.
Methane is about 25 times more potent than carbon dioxide, but it doesn’t stay in the atmosphere as long.
The main reason methane leaves the atmosphere is that it reacts with hydroxyl, or OH, radicals in the atmosphere, which themselves have formed from reactions with water vapour and oxygen.
Hydroxyl radicals also react with and square away other trace pollutants, which has given them the nickname “detergent of the atmosphere”.
But hydrogen molecules can also react with hydroxyl radicals, turning them back into water (H2O). A lot of hydrogen in the atmosphere might use up all the detergent.
“If you emit some hydrogen into the atmosphere now, it will lead to a progressive build-up of methane in the following years,” says lead author Dr Matteo Bertagni, a researcher from the High Meadows Environmental Institute at Princeton University, US.
“Even though hydrogen only has a lifespan of around two years in the atmosphere, you’ll still have the methane feedback from that hydrogen in 30 years from now.”
The researchers found that, if the world switched to a green hydrogen-based economy but more than 9% of that hydrogen leaked into the atmosphere, it would increase the amounts of atmospheric methane.
If we transitioned to a blue hydrogen-based economy (where hydrogen is made from methane, and the emissions are captured and stored), methane emissions would need to stay under 1% to avoid a negative effect.
Even if methane leakages were kept under 0.5%, hydrogen leakages would still need to be under 4.5% to stop atmospheric methane from increasing.
“It’s imperative that we are proactive in establishing thresholds for hydrogen emissions, so that they can be used to inform the design and implementation of future hydrogen infrastructure,” says senior author Professor Amilcare Porporato, also at Princeton.
In their paper, the researchers point out that hydrogen is a very small and difficult to trap molecule, making it hard to estimate how much hydrogen will actually be leaked as more gets made.
“Managing leakage rates of hydrogen and methane will be critical,” says Bertagni.
“If you have just a small amount of methane leakage and a bit of hydrogen leakage, then the blue hydrogen that you produce really might not be much better than using fossil fuels, at least for the next 20 to 30 years.”
The researchers found that in a worst-case scenario, 65% of the benefits of a hydrogen economy could be offset by leaks in the next 20 years.
Longer term, the benefits of hydrogen start to outweigh the leakage problems. But in a 100-year scenario, the researchers still found that gas leaks could offset 22% of the benefits of hydrogen.
“If companies and governments are serious about investing money to develop hydrogen as a resource, they have to make sure they are doing it correctly and efficiently,” says Bertagni.
“Ultimately, the hydrogen economy has to be built in a way that won’t counteract the efforts in other sectors to mitigate carbon emissions.”
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