Effects of V doping on microstructure, kinetic, and thermodynamic characteristics of Zr50-xVxCo50 (x=0, 2.5, 3.5, and 5.0) hydrogen storage alloys

To improve the kinetic properties of the ZrCo alloy, Zr50-xVxCo50 (x = 0, 2.5, 3.5, and 5.0) samples were fabricated by vacuum arc-melting. The effects of the V substitution on the microstructure, hydrogen absorption/desorption kinetics, cycling stability, and antidisproportionation properties of ZrCo were systematically investigated. X-ray diffraction results show that the Zr50-xVxCo50 (x = 2.5, 3.5, and 5.0) alloys consisted of ZrCo phase and ZrV0.24Co1.76 second phase. The lattice parameter and cell volume gradually decreased with the increase in the V content. The initial activation behavior was improved for the Zr50-xVxCo50 (x = 2.5, 3.5, and 5.0) samples because of the catalytic effect of the ZrV0.24Co1.76 second phase. Additionally, the equilibrium pressure of hydrogen absorption increased and the plateau width decreased with the increase in the V content. To obtain thermodynamic and kinetic data, Delta H and E-a were calculated using the Van't Hoff equation and Kissinger equation. Delta H of the Zr50-xVxCo50 (x = 0, 2.5, 3.5, and 5.0)-H system was reduced from 90.12 to 72.52 kJ.mol(-1), while E-a of ZrCoH3 decreased from 113.38 +/- 4.2 to 94.13 +/- 2.9 kJ.mol(-1) for hydrogen desorption, which is beneficial for the hydrogenation/dehydrogenation reaction. Furthermore, the cycling stability and antidisproportionation properties were enhanced after the V addition, particularly for the Zr47.5V2.5Co50 alloy exhibiting an excellent initial activation behavior.