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The fuel cell, an increasingly popular device in the automotive sector, creates a power source when coupled with hydrogen. The hydrogen can be made from natural gas or electrolysis of water and then compressed for storage. The challenge: How do you store hydrogen at low pressure?

Dr. Karen Swider Lyons, Head of Alternative Energy in the U.S. Naval Research Laboratory, applied the fuel cell to unmanned air vehicles. During this week’s Tech Briefs webcast presentation, Advances in Unmanned System Propulsion, a reader asked Lyons:

Dr. Karen Swider Lyons

What are the latest advancements of hydrogen storage in carbon nanotubes?

Dr. Karen Swider Lyons: If you can imagine a compressed hydrogen tank, you have hydrogen, and then your other material is that hydrogen tank; you’ve got aluminum and carbon overwrapped fibers. If you had the hydrogen stored on carbon nanotubes at low temperatures, you have a very, very lightweight metal tank, but you often need to carry a heater to heat up the carbon. Then, it gets very complicated, modulating the hydrogen that is coming out of the alternative solid storage into the fuel cell.

We always have to keep 20-30 psi outside of the fuel cell; you often need ballast storage to do that. What we've seen with these alternative hydrogen systems is that their weight keeps growing and growing. They're so complex that we just end up going back to compressed hydrogen.

Even cryogenic hydrogen looked great on paper. Then, when we actually did it, all the benefits started to disappear before us as we worked with the system, because it got very complex to implement. That's the reason why the automotive industry is going 100 percent with compressed hydrogen.

What do you think? Share your comments and questions below.

Also: Read more Propulsion tech briefs.

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