New insights into the electrochemical and thermodynamic properties of AB-type ZrNi hydrogen storage alloys by native defects and H-doping: Computational experiments

In this study, we perform a computational experiment to inspect the impact of native Zr/Ni defects and H-doping atoms on the electrochemical and thermodynamic properties of the AB-type ZrNi alloys. The Korringa-Kohn-Rostoker (KKR) method integrated with the coherent potential approximation (CPA) was employed to execute the calculations. The results revealed that native Zr/Ni defects and hydrogen doping have a beneficial effect on the hydrogen storage properties of the studied compounds by decreasing the stability and decomposition temperature. In particular, we find that with an optimal concentration of native Zr/Ni defects and H-doping, the obtained values of the decomposition temperature are in accordance with the required values for the practical use of nickel-metal hydride (Ni-MH) batteries as a negative electrodes (253 to 318 K) as well as powering proton exchange membrane (PEM) fuel cells (289 to 393 K). Using the density of states (DOS), this decrease can be explained by the diminution of the number of Zr and Ni atoms that establish strong bonds with H atoms and by the shift of the total DOS toward the higher energies. The electrochemical capacity of Zr1-x-yNiH3+y and ZrNi1-x-yH3+y compounds increases to reach values of 550 and 540 mAh/g, respectively. These values are almost twice higher compared to the compounds currently used in the market based on the AB5-type alloy LaNi5 (300 mAh/g). These findings of enhanced electrochemical and thermodynamic properties could provide useful clues for the development of better ZrNi-based materials for Ni-MH batteries, PEM fuel cells and other related areas.