A group of chemists at the University of Geneva (UNIGE) have just discovered a little-known bond between hydrogen atoms. Classically, these atoms break on contact with water, and the molecule they form decomposes, producing hydrogen gas. Difficult to preserve, this substance has long been used in industry, where its manufacture consumes a great deal of polluting energy. Researchers have now developed crystals that enable hydrogen to be stored. This process could be used to develop the fuel cell, an energy technology with ecological virtues. With the potential to replace the internal combustion engine, the fuel cell is the subject of intense research.
Unfortunately, some industrial techniques using hydrogen gas require fossil fuels to extract this element, which remains rare in its natural state. Paradoxically, hydrogen is also the basis for clean fuel cell technology. This invention is currently the focus of extensive research. Producing electricity from hydrogen and oxygen, and emitting only water, the fuel cell is currently generating great expectations, not only as a means of powering light appliances, but also, in the long term, as an ecological substitute for today’s car engine. But its realization still depends on two conditions: the manufacture and storage of concentrated hydrogen.
concentrated.
Dissociated hydrogen, hidden hydrogen
The work of Hans Hagemann, a chemist at the University of Geneva (UNIGE), could rapidly lead to the development of a solution. There are several methods for obtaining hydrogen: for example, the atomic dissociation of water (electrolysis). There are also certain chemical compounds that contain "hidden" hydrogen, which needs to be released. In collaboration with the ESRF (European Synchrotron Radiation Facility) in Grenoble, scientists at the UNIGE studied one such compound, sodium borohydride dihydrate. They succeeded in showing that, at the atomic level, this compound presents a very interesting bond, known as "dihydrogen".
Atomic reaction
What’s involved? On contact with water, the sodium borohydride molecule suddenly decomposes, producing hydrogen gas. There’s nothing unusual about this process, which has long been used in industrial settings. However, it remains difficult to master for domestic use. With a view to changing this situation, Hans Hagemann has prepared a hydrated crystalline form of the compound. These crystals are surprisingly stable and... rather enigmatic, from a theoretical point of view.
A question of temperature
Negatively charged borohydride atoms should instantly react with positively charged water protons to form hydrogen gas. In crystals, however, this reaction does not take place. Prospecting at the heart of the molecule using X-rays from the ESRF synchrotron, the chemists were able to understand that below 40°C, H- hydrides bind to the H+ protons of water. It’s only when heated that the two opposite charges start to react, producing the famous H2.
Hans Hagemann’s team has just won the double challenge of finding a way of conserving a rare and volatile element, and then understanding the internal chemical forces behind it. The European Journal of Inorganic Chemistry is publishing its latest cover story on these ground-breaking observations, which will undoubtedly contribute to the realization of the fuel cell.
