If hydrogen-powered cars are going to be commonplace in the relatively near future, scientists will have to discover and utilize a means of mobile storage for the colorless, odorless gas.
That’s the main thrust of research at Wake Forest University by assistant professor of physics Timo Thonhauser and his team. Thonhauser’s effort got a major boost with the August announcement that he won a National Science Foundation career award for his excellence as a teacher-scholar – which came with a $426,572 grant.
With the help of two graduate assistants who started in September, Thonhauser is focused on storing hydrogen as a lightweight, compact energy carrier for mobile applications. Methods for storing hydrogen – currently used in industrial processes, rocket fuel and spacecraft propulsion – include high pressures, cryogenics and chemical compounds that release hydrogen upon heating.
Although underground storage in gas tanks is useful for providing grid energy storage for intermittent energy sources including wind power, “We’re thinking about what we could do in a car,” Thonhauser said.
“The idea is to change the cars of the future where we don’t have to worry about safety concerns. A gas tank can be very heavy if I just bury it in the ground. It doesn’t matter how heavy it is. But if you want to take the same gas tank and put it in the trunk of a car, it very much matters how heavy it is.”
Currently, hydrogen-powered cars exist largely as prototypes. Thonhauser said their mainstream use is a growing necessity: “Petroleum-based fuels are going to be gone eventually. It’s not a question of if they’re going to run out; it’s a question of when. Hydrogen itself could be a replacement for the energy carrier.”
The research “is almost exclusively about how we can revolutionize transport. That could be cars, trucks, maybe even airplanes. For these things, you’ve got to be very careful about the weight.”
That revolution could also involve light rail. A 2009 international conference in Charlotte included a discussion of opportunities for hydrail manufacture and deployment in the area.
Thonhauser and his team aren’t the typical research scientists in a lab.
“I’m a theoretical condensed matter physicist” working with a computer and pencil and paper, he said. “We ask computers to solve the laws of quantum mechanics for us, and apply them to the materials of interest.” He said the team works on a computer at Wake Forest “that connects roughly 1,300 computers at the same time that we ask to do our calculations. ... They might take months to finish a simple calculation.”
They’re trying to determine whether any of three materials – magnesium borohydride, ammonia borane and special alkanes – could be used to create a safe and efficient storage solution for hydrogen.
“There’s a very funny thing going on that’s difficult to wrap your head around,” Thonhauser said. “If you look into a gas bottle, it’s basically empty inside, right? Then you put your gas in and you have gas inside. But if I was to fill the gas bottle with some kind of material and then added the hydrogen, I could get even more in than would have been possible without the material inside.
“The gas bottle becomes sort of a sponge. You fill it inside with this material that sort of sucks up hydrogen. ... You want the material that sucks up the hydrogen. These three materials have hydrogen incorporated in their molecular structure.
“In other words, you can actually think of water as a hydrogen storage material, because it has oxygen and hydrogen. In some senses, there’s a lot of hydrogen in there. The only problem is, it’s terribly difficult to get out.”
The chemical properties of hydrogen are such that it would be dangerous to pump it into a pressurized gas tank. But there are other challenges.
“Conventionally, what people would think is, ‘Let’s just take (hydrogen) and put it in a gas bottle,’ ” Thonhauser said. “I’m sure you’ve seen gas bottles on trucks on the highway. And people do that.
“The only problem is, you cannot get enough hydrogen into the gas bottle. ... You could drive your car with a gas bottle for 50 miles, but then you’re out of hydrogen. We want to be able to drive 300 to 400 miles before we need to refuel.”
Problems and cost
Hydrogen occurs in nature but must be extracted chemically for use. “It’s the most abundant element in the universe,” Thonhauser said. “But it’s not necessarily in the form that we can use it. Look at water. The whole ocean is full of hydrogen, but it’s not usable the way it’s found in water. So where do we get it from?”
He cited that as one of three scientific reasons that hydrogen-powered cars are absent in any significant quantity. The second and main problem, he said, is that “even if we had a mechanism that gets us to hydrogen in the exact form that we need it, it’s terribly difficult to store.”
The other problem is that even if that mechanism and a way to store hydrogen were identified, it would require a process that gets the energy back out of it. Thonhauser said that last issue is mostly solved: “There are these objects called fuel cells that do exactly that. They’re not actually converting the hydrogen, but they have a reaction going on with hydrogen such that in the end you get electricity out of it.”
The cost of such a process is also a concern. Without getting into specific numbers, Thonhauser said there are many potential expenses.
“How much does it cost to convert hydrogen?” he said. “How expensive is it to build a tank that I could put it in my car? A regular gas tank is fairly cheap, made out of thin metal. The third thing is, what does it cost to get the energy back out of the hydrogen? We need a fuel cell that does that – and how expensive are those?
“Of course the gasoline processing that’s used currently in cars is very cheap, because we had 100 years to perfect it. So although (the hydrogen-powered car) might be more expensive at the moment, I’m convinced that it will become cheaper if we really have it in place and it grows and it becomes more of a business.”
The result could yield major environmental benefits. “Clean energy is one of the driving forces about hydrogen,” Thonhauser said. “It’s in some senses renewable, and it burns in a completely clean reaction with oxygen.
“If you get hydrogen together with oxygen and you burn it in your fuel cells in your car, the only byproduct is water. ... There are tiny traces of things that are unfavorable, but nothing like in a gasoline car.”
Asked for a timetable to find an answer for mobile hydrogen storage, Thonhauser said “within 20 years.” David Harrison, a graduate student on the team, agreed with that estimate and added there will be other complications.
“Even if we were to find the perfect storage material, there are still the problems of production and usage, as well as all the engineering work that would have to be done,” he said.
Fellow grad student Evan Welchman said hydrogen-powered cars would have worldwide benefits: “With rapid population and economic growth in developing countries, more and more people are gaining the means to drive from place to place. With all of these new vehicles, curbing the amount of greenhouse gases emitted into the atmosphere is a hugely important component of our campaign to limit climate change.”
Welchman’s excitement about the project reflects the team’s energy. “I get to do research in an area that has the potential to affect the socio-political face of the planet and ensure that our children will be able to frolic under a clear sky,” he said. “How cool is that?”