Tuning the hydrogenation properties of Ti1+yCr2-xMnx laves phase compounds for high pressure metal-hydride compressors.

Ti 1+ y Cr 2- x Mn x compounds with a hexagonal MgZn 2 -type structure were investigated for their potential use in metal-hydride (MH) compressor applications. Here, the targeted MH compressor should absorb hydrogen below 30 MPa at 30 °C and desorb hydrogen at 80 MPa when heated at 80 °C. The pressure (P)-composition (C) isotherms were measured at pressures up to 40 MPa. Because of the very high pressures, the fugacity was taken into account. Details are given on how to determine the absorption and desorption enthalpies and entropies from the fugacity. The Van't Hoff plots were used to estimate the critical temperatures (T C). The P – C isotherms of all the compounds exhibit relatively small hysteresis and flat plateaus but the absorption and desorption pressures need to be increased. Superstoichiometry of y = 0.05 tends to decrease the plateau pressure and increase its slope, which is not desired for our target. On the other hand, the increase of Mn content led to higher T C as well as higher and flatter plateaus. Cr is a key element to get small hysteresis. • Detailed method for determination of the Van't Hoff plots considering the fugacity. • Critical temperatures evaluated by extrapolation of Van't Hoff plots. • Higher Mn content increases the critical temperature. • Strong effect of Cr for decreasing the hysteresis. [ABSTRACT FROM AUTHOR]