NN°°2308 II qquuaarrtteerrllyy II jJuanlyu 2a0r1y3 2013 Focus | 27 Today, the process is perfectly functional. “To ensure rapid absorption of the hydrogen onto the magnesium, the metal is transformed into a nanostructured powder,” explains Patricia de Rango, a chemist at CNRS’s Institut Néel in Grenoble. “To speed up the absorption process even further, we mix the powder with a small percentage of transition metals that activate the reaction. The powder is then compressed into wafers that are eventually stacked up in a tank.” Between 2006 and 2008, de Rango and her fellow researchers built a first tank with a storage capacity of 110 g—and increased it ten-fold by 2010.3 This research led to the creation of McPhy Energy, a company that manufactures and markets hydrogen tanks, mostly dedicated to storing renewable energy. In solar power, for example, part of the electricity generated by the photovoltaic panels serves to produce and store hydrogen. It can then be used in a fuel cell to generate electricity in the absence of sunlight. This year, McPhy Energy will deliver a 24 kg hydrogen storage facility (representing 800 kilowatt hours of energy) for MYRTE,4 a Corsicabased research platform that is developing renewable hydrogen sources for integration into the power grid. The project (involving researchers from the SPE5 laboratory) aims to deploy a solar power station linked to the electrical grid, thus demonstrating that hydrogen can indeed compensate for the intermittent nature of renewable energy sources. Inside the hydrogen tank, the magnesium hydride must be heated to 300°C to release its precious gas, a complex process that requires relatively large amounts of energy. This is why the current system is limited to fixed-location applications and cannot be used in embedded systems. To overcome this problem, the researchers have started investigating new metal hydrides that can function at more moderate temperatures. Aluminum-based hydrides, for example, release hydrogen at about 100°C. Yet the chemical reaction involved is very delicate and the resulting storage capacity relatively low. Other potential candidates include alloys of rare earth and nickel, or of titanium and vanadium, which offer the tremendous advantage of working at room temperature—and the major disadvantage of a very unfavorable ratio of mass to quantity of hydrogen stored. “For a vehicle, a hydrogen tank built using these metals would weigh at least 500 kg. On the other hand, their ideal operating temperature would make them suitable for small portable systems like cell phones and laptop computers,” adds Latroche. SMALLER SOLUTIONS To take the principle further, researchers are trying to develop hydrides that can function at negative temperatures. “We are trying to develop a beverage can-sized tank that can be carried in a backpack and could be used at temperatures as low as –20°C—which is impossible with today’s portable batteries,” reports Salvatore Miraglia of the Institut Néel. “We have already identified a few promising compounds, including one made up of titanium, chromium, and manganese.” Does this mean that cars with metal hydride tanks will be ubiquitous on our roads? “The specifications are very restrictive,” Pourcelly says. “The material must be able to store large quantities of hydrogen without taking up much space and keep working for several thousand charge-discharge cycles. In addition, it would have to be fast-reacting to deliver quick bursts of power for acceleration, for example.” In the marathon to develop a viable hydrogen fuel cell, many candidates are in the running, but few will finish the race. J. B. 01. Institut européen des membranes (CNRS / Université Montpellier-II / É cole nationale supérieure de chimie de M ontpellier). 02. Institut de chimie et des matériaux de Paris-Est (CNRS / Université Paris-Est Créteil V al-de-Marne). 03. In collaboration with CRETA (Consortium de recherches pour l’émergence des technologies avancées) and LEGI (Laboratoire des écoulements géophysiques et industriels). 04. M ission hydrogène renouvelable pour l’intégration au réseau électrique. 05. Sciences pour l’environnement (CNRS / Université de Corse). Contact information: Gérald Pourcelly > email@example.com Michel Latroche > firstname.lastname@example.org Patricia de Rango > email@example.com Salvatore Miraglia > firstname.lastname@example.org 23 Researchers at the IEM are studying the use of boron hydrides for hydrogen storage. 24 Synthesis of a new boron hydride. © p hotos 23-24 : e . perrin /CNRS Photothèque 23 24 Further information available on the online version of the magazine i A photo gallery on ongoing energy research at CNRS . Hydrogen at the wheel (2010, 20 min.) Film by Luc Ronat, produced by CNRS Images.
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