Fuel cell car: Put the metal hydride tablets in the tank

Drive up to the petrol station, authenticate, plug on the nozzle, fill up, continue driving: Using a fuel cell car should be as easy as using a conventional combustion vehicle. In practice, however, this is not the case. A new technology that scientists at Helmholtz Center in Geesthacht (HZG) – Develop Center for Materials and Coastal Research is supposed to change that.

In order to fill enough hydrogen into a tank, the element that is gaseous at normal temperatures must either be liquefied or compressed. To liquefy it has to be cooled down to about minus 253 degrees Celsius, which is energy-intensive and requires good insulation. It is common for the hydrogen to be compressed and to enter the vehicle at a pressure of 700 bar.

But that also requires some technical effort: compressors generate the pressure required to refuel at around 950 bar. The tanks must be designed to withstand this pressure. If a car has been refueled, the next car has to wait a few minutes until the compressors have built up enough pressure again. For example, six refuelings per hour are allowed the hydrogen filling station in the government district of Berlin.

Refueling could be much easier with the procedure developed by the team of the HZG around Thomas Klassen: "We are working on metal hydrides for hydrogen storage", explains the head of the Materials Technology division in an interview with Metals like titanium or magnesium form a connection with the hydrogen, that is the metal hydride.

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"The metal powder absorbs hydrogen like a sponge", he says. The hydrogen atoms are built into the metal grid. The reaction with the metal is exothermic, which means that heat is released. So that the hydrogen is released again in a controlled manner, heat must be added accordingly. That could come from the fuel cell, for example. The cell works at 80 degrees and an efficiency of up to 65 percent, so it emits about a third of waste heat. It normally escapes, but could be used for it.

The metals are in powder form. However, the HZG researchers do not simply pour metal powder into a tank. The powder is pressed into tablets beforehand. These are threaded onto a pipe that runs through the tank. The hydrogen enters the tank through the pipe and leaves it again. However, the tank must be double-walled so that a medium can add or remove heat.

The whole thing has some great advantages over a pressure tank, Klassen says.

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