SCIENTIFIC EDUCATIONAL CENTER science idea

Employees of the Faculty of Chemistry of Moscow State University have improved the reaction of interaction of magnesium hydride with water, promising for the generation of hydrogen, which is used in fuel cells. The authors found that the addition of alkali metal salts, ammonium and /or magnesium increases the yield of hydrogen from 22% to almost 100%, while the rate of hydrogen flow increases eight times.

Autonomous hydrogen sources are used to power compact fuel cells of low power: chargers for electronics or power supply systems for consumers located in remote and isolated places. The most affordable way to produce hydrogen for such sources is the interaction of a light metal (aluminum or magnesium) or its hydride with water. By themselves, hydrides are more efficient than metals, because they contain "their own" hydrogen released in the oxidation reaction in addition to hydrogen from water. However, under normal conditions, aluminum, magnesium and their hydrides interact with water extremely reluctantly, so scientists are actively looking for ways to increase their reactivity.

Lyudmila Sevastyanova, Semyon Klyamkin and Vladimir Stupnikov, employees of the Laboratory of High-Pressure Chemistry of the Department of Chemical Technology and New Materials of the Chemical Faculty of Moscow State University, under the guidance of the head of the laboratory Boris Bulychev, presented a new work. Its goal is to select methods for preparing materials and simple aqueous solutions so that their interaction is accompanied by the largest amount of hydrogen released and a sufficiently high speed.

"Now there are two approaches to solving this problem. The first is to modify the hydrogen-generating material itself using mechanochemistry methods. The activity of metals and hydrides in the oxidation reaction with water increases in this case not only due to the formation of crystal lattice defects, but also due to the introduction of alloying additives. For magnesium, these are metals of the iron triad that create galvanic pairs with magnesium. For aluminum – gallium and indium, which destroy the grain structure (Rebinder effect). There is another solution that is very simple from a chemical point of view – to use acid or alkali to dissolve metals or their hydrides. Such reactions take place quickly and efficiently. However, the chemical properties of acids and alkalis greatly limit their use. We had to look for something more neutral," explained Semyon Klyamkin, co-author of the study, Doctor of Chemical Sciences, Professor of the Department of Chemical Technology and New Materials at the Faculty of Chemistry of Moscow State University.

The researchers suggested using neutral salt solutions, such as ammonium or magnesium chlorides and bromides, for the oxidation of magnesium hydride. With their participation, it is possible to achieve almost 100% hydrogen yield in this reaction without changing the acidity of the solution. In addition, the process is much faster.

The mechanism of action of salts is not yet fully understood. It is most likely that in reaction with water, insoluble hydroxides are formed on the surface of the hydride, which prevents further penetration of water and actually stops the reaction. The presence of salts due to complexation contributes to the dissolution of these hydroxides or simply makes them more "loose".

In future studies, the authors plan to continue developing activation methods that allow expanding the use of magnesium, aluminum and their hydrides as relatively cheap and easy-to-obtain hydrogen generators.

The article was published in the International Journal of Hydrogen Energy
PHOTO © Julia Chernova

Source: Lomonosov Moscow State University, sci-dig.ru