Rotary Engine hydrogen

Next year, several car manufacturers will start selling their first fleets of hydrogen-cell electric cars to the general public.

Powered by hydrogen fuel cells that produce electricity by combining oxygen from the air and hydrogen into water, this new generation of vehicles might finally free personal transport from polluting emissions.

However, harnessing the power of hydrogen fuel cells means that cars will have to be equipped with fuel tanks capable of safely containing the explosive hydrogen under high pressure.

Not only that, we’ll need a new network of filling stations with pumps and conduits tailored to the distribution of hydrogen gas – and high safety standards to make sure they don’t go boom.

That’s all very well, but in itself it doesn’t make hydrogen a sustainable fuel. For that, we’ll need to be able to produce the gas in a clean, environmentally friendly way.

Currently, hydrogen is produced using predominantly fossil fuel resources such as gas, coal, and oil. As long as this is the case, vehicles running on hydrogen will continue to contribute to atmospheric CO2.

But imagine if hydrogen was produced using renewable energy sources like solar or wind power; if the only carbon dioxide that was used in the process was pumped out of the atmosphere; and if hydrogen could be stored as a non-flammable, non-explosive liquid that was easy to distribute using existing pipes and pumps.

As it turns out, such a liquid actually exists – and ants came across it long before we did. Formic acid, which is a main compound of ant venom, is increasingly considered to be one of the most efficient and safe ways to store hydrogen. We have a long history of using formic acid in industry and agriculture.

It even finds its way into food, where it is used as a spice flavouring for beverages and ice creams. In Europe it’s referred to as “E236” in the ingredient list.

But ants developed it first, and it is what gives them their sometimes-painful sting.

Written out as HCO2H, it is easy to see that each molecule of formic acid carries one molecule of carbon dioxide (CO2), and one molecule of hydrogen (H2).

In fact, at 53g of hydrogen per litre, formic acid is twice as rich in hydrogen as pure hydrogen gas, compressed into the same volume under a pressure of 350 bars.

So why aren’t we using it to power our cars already? Because until now, it has been a challenge to find efficient, clean and reliable ways to produce formic acid, and then break it apart again to feed its hydrogen into hydrogen fuel cells.

What’s more, formic acid can be stored almost indefinitely as a liquid at ambient temperatures. It is non-flammable when diluted with water, and it is also transparent and safe to handle.

But over the past years, my lab at EPFL has developed and patented the necessary chemical processes to efficiently produce formic acid.

Our first success came back in 2006, when we developed a catalytic process that breaks up formic acid into carbon dioxide and hydrogen. This opened the door for using formic acid as an energy carrier, for example in motor vehicles.

Producing it sustainably was a tougher nut to crack. But in June this year we published a report outlining a single-step catalysis process to do exactly that.

Just like plants, all we need is atmospheric carbon dioxide and sunlight. While carbon dioxide can be extracted from the atmosphere or recycled from the fumes from industrial chimneys, we can also use any form of renewable energy to produce the hydrogen we need by splitting water through electrolysis into its basic components: hydrogen and oxygen.

Now we’ve solved the chemistry, we have to turn to engineering to develop emission-free transport systems. Our hope is that by drawing inspiration from ants and plants, we could eventually recapture the carbon dioxide lost when the formic acid is split up, and reuse it to produce even more formic acid.

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