Liquid hydrogen

Liquid hydrogen
IUPAC name
Liquid hydrogen
Other names
Hydrogen (cryogenic liquid); hydrogen, refrigerated liquid; LH2, para-hydrogen
3D model (JSmol)
RTECS numberMW8900000
UN number1966
Molar mass2.02 g·mol−1
AppearanceColorless liquid
Density70.85 g/L (4.423 lb/cu ft)[1]
Melting point−259.14 °C (14.01 K; −434.45 °F)[2]
Boiling point−252.87 °C (20.28 K; −423.17 °F)[2]
Highly flammable (F+)
NFPA 704
571 °C (1,060 °F; 844 K)[2]
Explosive limitsLEL 4.0%; UEL 74.2% (in air)[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Liquid hydrogen (LH2 or LH2) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.

To exist as a liquid, H2 must be cooled below hydrogen's critical point of 33 K. However, for hydrogen to be in a fully liquid state without boiling at atmospheric pressure, it needs to be cooled to 20.28 K[3] (−423.17 °F/−252.87 °C).[4][5] One common method of obtaining liquid hydrogen involves a compressor resembling a jet engine in both appearance and principle. Liquid hydrogen is typically used as a concentrated form of hydrogen storage. As in any gas, storing it as liquid takes less space than storing it as a gas at normal temperature and pressure. However, the liquid density is very low compared to other common fuels. Once liquefied, it can be maintained as a liquid in pressurized and thermally insulated containers.

There are two spin isomers of hydrogen; liquid hydrogen consists of 99.79% parahydrogen and 0.21% orthohydrogen.[6]


In 1885 Zygmunt Florenty Wróblewski published hydrogen's critical temperature as 33 K; critical pressure, 13.3 atmospheres; and boiling point, 23 K.

Hydrogen was liquefied by James Dewar in 1898 by using regenerative cooling and his invention, the vacuum flask. The first synthesis of the stable isomer form of liquid hydrogen, parahydrogen, was achieved by Paul Harteck and Karl Friedrich Bonhoeffer in 1929.

Other Languages
беларуская: Вадкі вадарод
беларуская (тарашкевіца)‎: Вадкі вадарод
Ελληνικά: Υγρό υδρογόνο
한국어: 액체수소
Bahasa Indonesia: Hidrogen cair
Bahasa Melayu: Hidrogen cecair
日本語: 液体水素
română: Hidrogen lichid
српски / srpski: Tečni vodonik
srpskohrvatski / српскохрватски: Tečni vodonik
suomi: Nestevety
Türkçe: Sıvı hidrojen
українська: Рідкий водень
Tiếng Việt: Hydro lỏng
中文: 液氢