One liter of inconspicuous powder can provide twice as much hydrogen as one liter of liquid hydrogen. Hydrogen, which could replace traditional fuels in the future, could be stored in borohydride of light metals, hope scientists from Polish - Swiss team.
Prof. Zbigniew Łodziana from the Institute of Nuclear Physics PAS in Kraków explained that instead of traditional energy sources, such as fossil fuels or nuclear fuel, resources of which continue to decrease, perhaps in the future we will increasingly use the so-called energy streams, available only temporarily. For example, solar energy can only be obtained in the day, and wind power on windy days. The acquired energy will have to be stored, to be used at the appropriate time. Scientists are looking for more effective methods of energy storage.
The team of Prof. Łodziana from the Institute of Nuclear Physics PAS, together with scientists from the Swiss Empa institute, are working on effective methods of storing hydrogen, and a new generation of rechargeable batteries. In both of these tasks, borohydrides of light metals, e.g. lithium , magnesium, aluminum or yttrium, may prove useful.
Hydrogen is a very attractive material for energy sources. It is a very light gas that emits only heat and water while burning. In addition, hydrogen has the highest energy density per mass unit (only nuclear materials are better): 1 kg of hydrogen can be used to produce approximately 33 kWh. Besides, obtaining hydrogen is not complicated (although it is still too expensive and energy inefficient), two atoms of the element are, after all, in every molecule of ordinary water. It can be released by electrolysis, applying voltage from solar cell, for example.
The problem is how to store hydrogen so that it takes up minimal space. Under normal conditions, 1L container can house only 0.1 g of this gas. In order to effectively pack hydrogen, it can be compressed or even liquefied (below -250 °C) . However, this way is not optimal either: it turns out that hydrogen can be stored more efficiently as part of chemical compounds. Then, its atoms can fill the space much more efficiently.
Such compounds include light metal borohydrides. They take the form of crystals, white powder. However, when they are heated to a temperature of 300-400 degrees, hydrogen is released. It turns out that 1 litre of powder can released two times more hydrogen than 1 litre of liquefied hydrogen. This powder is also much safer pressurized gas. The chemical reaction, which occurs in the material, is reversible - the result is a substance (also in the form of a powder), which under suitable conditions (high temperature and very high pressure of hydrogen) may be soaked with hydrogen again. According to the researcher, the material would be reusable. If borohydride were used in vehicles instead of liquefied hydrogen cylinders, waste material could be returned to facilities where it would be refilled.
Light metal borohydrides may also find other uses. They could be used to build new generation batteries, in which no liquid electrolyte would be necessary. "Each car or phone battery consists of two electrodes and the material between them, which is electrically conductive in the form of ions but does not conduct electricity in the form of electrons" - said Prof. Łodziana and added that for now there batteries use liquid electrolytes. In automotive batteries, electrolyte is sulphuric acid, in lithium-ion batteries - lithium ion conductive solutions. Scientists want to develop safer batteries that would not contain liquid. The team of Prof. Łodziana investigates whether the properties of light metal borohydrides can be so improved that they can be used in batteries.
