Originally Posted by
flypaddy
Over a decade ago I was lectured on the exciting possibility of storing hydrogen in a “carbon sponge” which went some way to alleviating the fears of explosion of hydrogen tanks in a car accident. I haven’t since heard much on this technology!
The problem with the 'sponge' technology that absorbs H2, then releases it slowly is that it's heavy - even for an automotive application. The one I looked at (many years ago) - a 'sponge' that could hold enough H2 to equate to a ~20 gallon fuel tank weighed nearly two tons. Troublesome for an auto - non-starter for an aircraft.
Something I didn't mention previously - liquid H2 has another problem: The cryogenic temperatures involved are
very hard on the materials used. This means a massive maintenance burden to keep the system working properly and safely. Rocket engines and the associated hardware (pumps, etc.) only operate for minutes, then are either discarded or rebuilt before they are used again - not a practical solution for an aircraft that is expected to operate eight or more hours a day, every day, for years...