New solutions for a climate-friendly fuel
Hydrogen storage tank. Photo: HZG/Christian Schmid
Hydrogen is considered to be a promising energy carrier for the future. In principle, it can be produced in a regenerative and climate-neutral way and converted pollutantfree into electricity in a fuel cell or internal combustion engine – the exhaust contains nothing but pure water vapour. For road transport, it is additionally interesting that vehicles powered by hydrogen have a far greater range than electric and can be refueled faster. HZG researchers are working on new concepts for both hydrogen tanks and the efficient production of this energy-rich gas.
Storage in metal hydrides
Metal hydrides. Foto: HZG/Christian Schmid
Currently, fuel-cell cars initially save the hydrogen in massive tanks, which has to withstand a pressure of up to 700 bar. They can be refuelled quickly but the technological effort to make the pressurised tank safe is considerable. This is why the Helmholtz-Zentrum Geesthacht is taking another route – by saving the gas in chemical compounds, known as metal hydrides.
In practice, light metals such as magnesium and lithium are used, laced with the semimetal boron. Hydrogen can be inserted into the crystal lattice of these compounds efficiently and with minimum space requirements – a good store with theoretical safety advantages.
In Geesthacht, they have been able to combine two of these hydrides into one new, promising material. It is capable of storing more hydrogen per volume and weight than with pressurized tanks or in liquid form.
The storage tank developed in Geesthacht. Photo: HZG/Julia Knop
But there are still a few challenges: to get the hydrogen out of the tank again, it has to be heated. The temperatures required for this are currently still too high. It would be ideal if the store could be supplied with the waste heat from the fuel cell, without having to heat it additionally. A further problem is that the particles of metal powder that are used tend to clump over time. To prevent this, the researchers want to coat the nanometre-small powder particles with extremely thin polymer shells.
In principle, it takes a really long time to fill the new storage tank. The HZG scientists have already been able to solve this problem in an outstanding way. Together with European partners from research and industry they developed Europe’s largest tank based on complex metal hydrides. It can be charged to 80 percent of its capacity in just ten minutes.
The production of hydrogen using sunlight
The HZG experts are treading new paths in the climate-friendly production of hydrogen. Instead of producing the gas in the usual way using electrolysis, where water molecules are split using electrical current, they are attempting to generate it using sunlight. The principle: the light hits electrodes in a dipping bath and releases the hydrogen there in the form of little bubbles. For this to happen, the electrodes have to be coated in a catalyst for example ferric or titanium oxide. The inner structure of this catalyst is crucial. A complex, foam-like structure with pores of various sizes appears to be particularly suitable. The long-term potential sounds promising: if people clad the extent of the roofs of their homes with hydrogengenerating modules, they could obtain sufficient fuel for the family vehicle.