Scientists at the US National Institute of Standards and Technology (NIST) have a new approach to storing hydrogen in future fuel-cell-powered cars.
Their idea is to create molecular-scale ‘veins’ of iron permeating grains of magnesium, much like a network of capillaries. According to NIST, the iron veins may transform magnesium from a promising candidate for hydrogen storage into a real-world solution.
Hydrogen has been touted as an alternative to petrol but the lack of a safe, fast way to store it on board a vehicle has been seen as a drawback.
According to NIST materials scientist Leo Bendersky, iron-veined magnesium could overcome this hurdle.
The combination of lightweight magnesium laced with iron could rapidly absorb and release sufficient quantities of hydrogen so that grains made from the two metals could form the fuel tank for hydrogen-powered vehicles.
‘Powder grains made of iron-doped magnesium can get saturated with hydrogen within 60 seconds and they can do so at only 150°C and fairly low pressure, which are key factors for safety in commercial vehicles,’ said Bendersky.
Grains of pure magnesium are said to be effective at absorbing hydrogen gas, but only at high temperatures and pressures — conditions that let them store enough hydrogen to power a car for a few hundred kilometres.
A practical material would need to hold at least six per cent of its own weight in hydrogen gas and be able to be charged safely with hydrogen in the same amount of time as is required to fill a car with petrol today.
The NIST team used a new measurement technique they devised that uses infrared light to explore what would happen if the magnesium were evaporated and mixed together with small quantities of other metals to form fine-scale mixtures.
The team found that iron formed capillary-like channels within the grains, creating passageways for hydrogen transport within the metal grains that allow hydrogen to be drawn inside extremely fast.
According to Bendersky, the magnesium-iron grains could hold up to seven per cent hydrogen by weight.
He added that the measurement technique could be valuable more generally, as it can reveal details of how a material absorbs hydrogen more effectively than the more commonly employed technique of X-ray diffraction — a method that is limited to analysing a material’s averaged properties.