As “the fuel of the future”, the expectations for hydrogen (H2) run high, with applications ranging from transportation to steel production. Nonetheless, storing the highly volatile gas is currently expensive, complicated and energy-inefficient: H2 either has to be stored in pressure tanks at 700 bar or in a liquid form cooled to -253°C.

That’s why a team at the German Electron Synchrotron (DESY), a Helmholtz research association in Hamburg, have developed an innovative method for storing hydrogen in tiny palladium spheres. It’s long been known that the precious metal absorbs H2 like a sponge but there have been obstacles to developing the concept further. Team leader Andreas Stierle explains in a press release: "Until now it has been a problem to get the hydrogen out of the material again," he says. "That's why we are trying with palladium particles that only measure around one nanometre."

The researchers’ ingenious solution has been to create an array of particles, each measuring 1.2 nanometres (around a millionth of a millimetre), that are layered like a praline chocolate, with a “nut” of iridium at the core to stabilise the palladium. The H2 sticks to the surface of the particles but never penetrates to the centre; therefore, only little heat is needed to free the gas.

It’s still early days for the technology: the next step is to find out what storage densities can be achieved. The team will also look at alternative carbon structures to carry the “palladium pralines”. For the experiments to date, a thin layer of graphene was used to arrange the particles at intervals of two and a half nanometres, but the researchers believe porous carbon sponges may be able to hold greater quantities.

The DESY team worked in collaboration with researchers from the Universitiy of Cologne and the University Hamburg.