One of the biggest obstacles to large-scale use of hydrogen-powered fuel cells is in how to store the hydrogen, a task which currently requires high pressure,… which, itself, is energy intensive. Scientists at Lawrence Berkeley National Laboratory are aiming to solve this problem by creating new materials in which to store the hydrogen.
“We’re working on materials called metal-organic frameworks to increase the capacity of hydrogen gas in a pressure cylinder, which would be the fuel tank,” said Jeffrey Long, a Berkeley Lab scientist who co-lead the project along with Berkeley Lab computational chemist Martin Head-Gordon. “With these materials, we’re working on storing the hydrogen without the use of very high pressures, which will be safer and also more efficient without the significant compression energy losses.”
According to Berkeley Lab, “metal-organic frameworks (MOFs) are three-dimensional sponge-like framework structures that are composed primarily of carbon atoms and are extremely lightweight.”
“What’s very special about these materials is that you can use synthetic chemistry to modify the surfaces within the materials and make it attractive for hydrogen to stick on the surface,” Long explained.
Vehicles can currently store enough hydrogen to achieve a range close to 300 miles, but that requires the hydrogen to be stored at extremely high pressures, which is not only expensive and energy intensive, but also potentially catastrophically unsafe.
Long’s research has allowed him to store more than double the hydrogen currently modeled, but only at very low temperatures.
“It’s still very much basic research on how to create revolutionary new materials that would boost the capacity by a factor of four or five at room temperature,” he said. “We have an idea of what kinds of frameworks we might make to do this.”
Long’s approach is to create frameworks with lightweight metal sites on the surface, making it attractive for hydrogen molecules to bind to the sites. “Our approach has been to make some of the first metal-organic frameworks that have exposed metal cations on the surface,” he said. “Now we need to figure out ways of synthesizing the materials so that instead of one hydrogen molecule we can get two or three or even four hydrogen molecules per metal site. Nobody’s done that.”
At this point, Long’s partner, Martin Head-Gordon, enters the picture. Head-Gordon’s role is to work on the theory of understanding MOFs so that he can predict their hydrogen storage properties and then provide Long’s team with the sort of material they need to synthesize.
“He can do calculations on a lot of different target structures and say, here’s the best one for you guys to spend time trying to make, because synthetic chemistry is very cost and labor intensive,” Long said.
The U.S. Department of Energy recently awarded Berkeley Lab $2.1 million in funding for the three-year project, which will also include contributions by the National Institute of Standards and Technology (NIST) and General Motors (GM). The funding was part of more than $7 million awarded by DOE last month for hydrogen storage technologies in fuel cell electric vehicles.