Study on hydrogen desorption of ZrCoH3 promoted by doping Hf and Ti with DFT

Abstract

This work aims to provide new insights into the hydrogen evolution of ZrCoH3. The transition metal elements Hf and Ti are designed to be added to ZrCoH3 by occupying Co atoms, Zr atoms, and interstitial sites. The effects of Hf and Ti atoms on the hydrogen evolution of ZrCoH3 are investigated through a first-principles study. The results show that the doping of Hf and Ti atoms can effectively improve the hydrogen desorption ability of ZrCoH3, which is related to the weak Co–H covalent interaction in the doping system, metallic properties, and the formation of Hf/Ti–H bonds. Hf atom doping has the best catalytic effect on the dehydrogenation of ZrCoH3, and the Hf atom can easily enter the ZrCoH3 body to form the Zr16Co16HfH48 compound. Although the Zr15Co16HfH48 compound has a low hydrogen dissociation energy and exhibits good hydrogen desorption performance, it requires a high energy cost when Hf occupies the Zr site in practical applications. When doped with the same element, the occupancy energy and hydrogen dissociation energy are inversely related. The hydrogen dissociation energy of ZrCoH3 is negatively correlated with the electronegativity of the dopant atom, namely, the lower the electronegativity of the dopant atom, the smaller the hydrogen dissociation energy of the system. This study confirms by simulation calculations that the use of low electronegativity metals to recombine with ZrCoH3 is an effective way to achieve ZrCoH3 destabilization.