According to About.com, at standard pressure, hydrogen has a boiling point of minus 252.762 degrees Celsius, so converting it from a gas to liquid requires compressing and cooling it. Hydrogen is normally an odorless, colorless gas. It is so light in weight, it is able to diffuse from Earth's atmosphere.
Technifab Products, Inc. says it takes a large amount of energy to compress and chill hydrogen to a liquid. These energy requirements result in a loss of 30 percent of the energy the liquid stores. Storage requires highly insulated and reinforced tanks to maintain temperature and pressure.
NASA uses liquid hydrogen and liquid oxygen as a fuel and oxidizer for its rockets. Its launch pads include vacuum bottles, where the fuel is stored under pressure. Allowing a small amount of the liquid hydrogen to convert back into a gas provides the pressure needed to transfer the liquid from the storage tank into the rocket fuel tank.
The Office of Energy Efficiency & Renewable Energy reports, "On-board hydrogen storage for transportation applications continues to be one of the most technically challenging barriers to the widespread commercialization of hydrogen-fueled vehicles." For hydrogen-fueled vehicles to become competitive with those already on the road, the challenge is finding a safe and affordable method of storage that allows enough fuel to drive the vehicle 300 miles on a single fill.