NOVELTY - Providing a operational transfer function of a hydrogen gas stream for removing not only water vapor, but also minute quantities of other types of gas impurities such as oxygen, carbon monoxide and carbon dioxide.    USE - For retaining and storing a concentrated volume of hydrogen gas, useful in a thermal hydrogen compressor.    ADVANTAGE - The inventive metal hydride material purifies the hydrogen during the storage or operation. It is capable of repeatedly absorbing and discharging gaseous hydrogen.    DETAILED DESCRIPTION - A metal hydride material, in a thermal hydrogen compressor (60), comprises a mixture of water vapor absorbing particles, metal hydride particles and noble material in powder form.    INDEPENDENT CLAIMS are also included for:    (a) a hydrogen compressor comprising an inlet for hydrogen gas fed at a low inlet pressure and an outlet for hydrogen gas at high pressure, having at least two sets of connected unit chambers and at least two heat exchangers for providing heat exchange between corresponding pairs of unit chambers, comprising a first unit chamber in communication with the inlet through a one-way valve adapted to admit hydrogen gas into the chamber at a low inlet pressure, the chamber containing a first hydride material having an adsorption pressure below the low inlet pressure at a first temperature; heat exchange mechanism associated with the first unit chamber adapted to operate alternately to maintain the first unit chamber at or below the first temperature and to raise the temperature of the first unit chamber to a second temperature higher than the first; a second unit chamber in communication with the first unit chamber through a one-way valve adapted to prevent flow of hydrogen gas from the second unit chamber to the first unit chamber and containing a second hydride material forming a less stable hydride than the first hydride material and having a plateau pressure, at a temperature below the second temperature, less than the plateau pressure of the first hydride material at the second temperature; heat exchange mechanism associated with the second unit chamber adapted to operate alternately to maintain the second unit chamber at a temperature lower than the second temperature and at a third temperature higher than the first; a third unit chamber in communication with the second unit chamber through a one-way valve adapted to prevent flow of hydrogen gas from the third unit chamber to the second unit chamber and in communication with the outlet, the third unit chamber containing a third hydride material forming a less stable hydride than the second hydride material and having a plateau pressure, at a temperature below the third temperature, less than the plateau pressure of the second hydride material at the third temperature; heat exchange mechanism associated with the third unit chamber adapted to operate alternately to maintain the third unit chamber at a temperature lower than the third temperature and at a fourth temperature higher than the first temperature; and control mechanism (76) for alternating the temperature of the heat exchange mechanisms above, to maintain the lower of the two temperatures associated with any single chamber unit when hydrogen gas is being absorbed by the hydride material in the unit chamber and at the higher of the two temperatures when hydrogen is present in and being desorbed from the hydride material in the unit chamber; and    (b) a device utilizing the application of heat to change the pressure of hydrogen gas within an enclosed container comprising a metal hydride material as above for retaining and storing a concentrated volume of hydrogen gas.    The first unit chamber further comprises a hydrogen vent that is controlled by the control mechanism for venting hydrogen gas from the first unit chamber at predetermined intervals and for a predetermined amount of time. The metal hydride material(s) include noble metal in the form of a metallic powder comprising platinum black, palladium black or ruthenium black.    DESCRIPTION OF DRAWING(S) - The figure shows in a schematic diagram, the configuration of a thermal hydrogen compressor utilizing the hydrogen purification device.    Thermal hydrogen compressor (60)    Control mechanism (76)    Hot and cold water circulation subsystems (72, 74)    Outlet pipe (18)    Heat exchange unit (62)    Containers with hydride beds (64A, 64B)    Hydrogen inlet pipes (82A, 82B, 84A, 84B)    Pressure relief switch (108)    Internal outlet pipe (118)    One way check valve (106)    Low pressure switch (100)    Compressor (10)