Metal hydrides for a low-temperature three-stage hydrogen compressor

In this study, three alloys were prepared via arc melting and their hydrogen properties were determined to assess the feasibility of constructing a three-stage metal hydride compressor. With C14 as the main phase and BCC as a secondary phase, these alloys had small grain sizes and long grain boundaries. Their first activation was dependent on the thickness of the surface oxide and the amount of high angle grain boundaries. These alloys showed fast hydrogen kinetics, high storage capacity, along with relatively flat equilibrium plateau pressures - an important characteristic for effective hydrogen compression. Pressure composition isotherm measurements confirmed that the three alloys could be used to build a three-stage hydrogen compressor, raising hydrogen pressure from 70 to 875 bar by cycling the hydrides between 20 °C for absorption and 90 °C for desorption. At such low operating temperatures, low grade waste heat could be used to drive the compression process. • Three alloys with a high hydrogen capacity, flat plateau and low hysteresis were synthesised. • Their hydrogen storage properties were correlated to their physiochemical properties. • A compressor with these three alloys could compress hydrogen from 70 to 875 bar at 90 °C. • The low compression temperature allows simple heat management. • The low temperature operation allows for the use of waste heat for hydrogen compression.