Magnesium hydride paste as fuel

Hydrogen propulsion possible for small vehicles?

03. Februar 2021, 13:49 Uhr   |  Irina Hübner

Hydrogen propulsion possible for small vehicles?
© Fraunhofer IFAM

The power paste developed by researchers at Fraunhofer IFAM.

Can hydrogen also be used to power small vehicles? With a magnesium hydride-based paste, yes, according to Fraunhofer IFAM. Hydrogen can be chemically stored in this paste at ambient pressure, easily transported, and refilled without an expensive filling station infrastructure.

Gasoline and diesel engines that run on fossil fuels are becoming obsolete models because of climate change - instead, new propulsion options are taking off. One of the fuel hopefuls is hydrogen. It is usually injected into the pressurized tanks of vehicles at 700 times atmospheric pressure. From there, it flows into a fuel cell, where it is converted into electricity. The electricity in turn feeds an electric motor that powers the vehicle.

For cars, this approach is already quite mature: Several hundred hydrogen cars are already on Germany's roads. And the German hydrogen filling station network is to be expanded from the current 100 to 400 filling stations over the next three years. However, this is of little use for small vehicles such as e-scooters, scooters and the like: The pressure surge during refueling would be too great.

Hydrogen for e-scooters & co.

Researchers at the Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM in Dresden have now developed a hydrogen solution suitable for small vehicles: Powerpaste, which is based on the solid magnesium hydride. The starting material is powdered magnesium - one of the most common elements and therefore a readily available raw material. At 350 °C and five to six times atmospheric pressure, this is reacted with hydrogen to form magnesium hydride. Adding ester and metal salt then produces the power paste.

The power paste allows hydrogen to be chemically stored at room temperature and ambient pressure and released as required. According to Fraunhofer IFAM, this is not critical even if the scooter is left in the sun for hours in summer heat. This is because the power paste only decomposes above about 250 °C.

Instead of going to a filling station, the vehicle user changes a cartridge and also fills tap water into a water tank. This can be done both at home and on the road.

To power the vehicle, a plunger conveys the power paste out of the cartridge. Water is added from the water tank, producing gaseous hydrogen. The quantity is adjusted highly dynamically to the hydrogen demand of the fuel cell. The trick is that only half of the hydrogen comes from the power paste, while the other half is supplied by the water.

»The energy storage density of the power paste is enormous: It is much higher than that of a 700-bar pressure tank. Compared to batteries, it even has ten times the energy storage density,« emphasizes Dr. Marcus Vogt, a scientist at Fraunhofer IFAM. For the driver, this means that he achieves a similar or even higher range with the power paste than with the same amount of gasoline. According to Fraunhofer IFAM, Powerpaste also performs better in a range comparison with hydrogen compressed to 700 bar.

This makes the powerpaste interesting for cars, delivery vehicles, or range extenders that increase the range of electric cars. Large drones could significantly increase their range with the hydrogen paste and thus stay in the air for several hours instead of twenty minutes. An application of a somewhat different kind could be in camping: Here, the power paste can provide electricity for a coffee maker and toaster via a fuel cell.

Cost-intensive infrastructure becomes obsolete

While gaseous hydrogen requires a cost-intensive infrastructure, the powerpaste can also be used where such an infrastructure is lacking - i.e., where there are no hydrogen filling stations. Instead, any gas station could offer the power paste in cartridges or canisters. This is because the paste is flowable and pumpable - it can therefore also be refueled using a normal refueling process and comparatively inexpensive filling equipment.

Service stations could initially offer the power paste in smaller quantities, for example from a metal drum, and then expand the range in line with demand - with investment costs of several tens of thousands of euros. By comparison, filling stations for gaseous hydrogen at high pressure currently cost around 1 to 2 million euros per pump. Transporting the paste is also cost-effective: After all, there is no need for expensive pressurized tanks or very cold, liquid hydrogen.

Pilot center in planning

At the Fraunhofer Project Center for Energy Storage and Systems ZESS, Fraunhofer IFAM is currently setting up a production facility for power paste. This is scheduled to go into operation at the end of 2021 and will then produce up to four tons of power paste per year.

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Fraunhofer IFAM (Institut für Fertigungstechnik und Angewandte Materialforschung)