液氢
Liquid hydrogen fuel has some disadvantages. The technology is very new and the infrastructure for liquid hydrogen filling stations is currently very limited. Many of the processes commonly used in creating the fuel give off greenhouse gases, and the hydrogen produced is usually derived from finite resources. The storage of the liquid hydrogen is a major problem. Since the boiling point of liquid hydrogen is very low (-252.88 °C), it is difficult to keep the fuel cold enough to maintain its liquid form. When it warms, it evaporates. The pressure in the fuel tank then increases, and some gas must be released. Release valves are installed in these vehicles so that the pressure in the tank does not get too high, but a small amount of fuel is lost.