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Hydrogen is a potential renewable fuel because it can easily be generated from water using electrolysis. It also burns cleanly to produce water vapour. The hope is that it could also be distributed using the same global network of liquid fuel transport that moves petrol around the planet.

But there numerous problems with this dream of a hydrogen-based economy. One of them is that hydrogen is difficult to store efficiently. Hydrogen gas has a poor energy density by volume compared to petrol. In fact, there is at least 60 percent more hydrogen in a litre of gasoline then there is in a litre of pure liquid hydrogen. In other words, hydrogen will always require bigger tanks.

So finding ways to store more of it is a huge challenge. One option is to store it as a liquid but hydrogen boils temperatures above -250 degrees centigrade and so requires bulky insulation to keep it in this state.

Another idea is to compress it. But this raises issues of safety should a hydrogen-fuelled car be involved in a collision.

That is why much of the material science research in this area has focused on chemical storage: finding materials that adsorb hydrogen efficiently and then release it again when it is required.

Now Viney Dixit and buddies at the Hydrogen Energy Center of Banaras Hindu University in India say they have discovered that carbonised coconut flesh is particularly good at this task. Today, they show that it outperforms a number of other hydrogen storage materials, particularly in its ability to work over many charging cycles.

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