Enhancement of hydrogenation kinetics and thermodynamic properties of ZrCo_1-xCr_x (x= 0-0.1) alloys for hydrogen storage

The vacuum arc melting method was used to prepare ZrCo_1-xCr_x (x=0, 0.025, 0.05, 0.075, 0.1) alloys. Afterward, the crystal structure, hydrogenation kinetics, thermodynamic properties, and disproportionation performance of ZrCo_1-xCr_x (x=0-0.1) alloys were investigated. The x-ray diffraction spectra demonstrated that ZrCo_1-xCr_x (x=0-0.1) alloys contained ZrCo and ZrCo₂ phases, and their corresponding hydrides consisted of ZrCoH₃ and ZrH phases. The activation behaviors of Cr-substituted samples were significantly promoted. The activation time of ZrCo was 7715 s while that of ZrCo_0.9Cr_0.1 was 195 s. The improvement of kinetics can be attributed to the catalytic hydrogenation of ZrCr₂. The activation energy for the hydrogenation of ZrCo was 44.88-kJ·mol^-1 H₂ and decreased to 40.34-kJ·mol^-1 H₂ for ZrCo_0.95Cr_0.05. The plateau pressure and width of the pressure-composition-temperature curves decreased slightly as Cr content increased. The extent of disproportionation of ZrCo was 83.68% after being insulated at 798 K for 10 h and decreased slightly to 70.52% for ZrCo_0.9Cr_0.1. The improvement of anti-disproportionation performance can be attributed to increase in the activation energy of disproportionation from 167.46-kJ·mol^-1 H₂ for ZrCo to 168.28-kJ·mol^-1 H₂ for ZrCo_0.95Cr_0.05.