Positive correlation of Nb/Cr doping with dehydrogenation performance of ZrCo-based hydrides

Abstract

It is well known that element substitution is vital to an improvement of hydrogen storage capacity degraded by hydrogen-induced disproportionation of zirconium-cobalt (ZrCo) alloy. Contrary to other studies, this work is devoted to investigating the hydrogen desorption behavior of Zr1-xNbxCo1-yCryH3 (x = 0–0.25 and y = 0–0.125) systems formed by Nb substitution and Nb/Cr co-substitution in the ZrCoH3 crystal using the first-principles calculations based on the density functional theory. Firstly, the preferred positions of Nb and Nb/Cr substitutions are determined through the minimum total energy. Lattice constants and the density of states are employed to characterize the bonding behavior between atoms. The thermodynamic properties of Zr1-xNbxCo1-yCryH3 are also assessed by the enthalpy of formation and equilibrium hydrogen pressure. It is shown that both the thermodynamic stability and dehydrogenation temperature of ZrCoH3 decrease by increasing the Nb content, which is attributed to the fact that the Zr–H and Co–H binding capabilities are weakened by the presence of Nb. In addition, there are weaker thermal stability, lower dehydrogenation temperature, smaller volume of 8e site, and comparable volume of the hydride after ZrCoH3 is co-substituted by Nb and Cr, thereby promoting the hydrogen release and enhancing the anti-disproportionation performance. Clearly, both Nb doping and Nb/Cr co-doping possess a positive effect on the hydrogen desorption ability of ZrCoH3. More importantly, it is discoverable that compared to other substitution systems, the dehydrogenation temperature is the least for the Zr0.75Nb0.25Co0.875Cr0.125 hydride, highlighting that Nb and Cr co-substitution is more beneficial to improving the dehydrogenation performance of ZrCo-based alloy.