Effect of doping Hf on the hydrogen dissociation and diffusion mechanism on the ZrCo (110) surface

Both theoretical and experimental studies indicate that the kinetic properties of H2 storage in ZrCo can be significantly improved by element substitution. Here, both molecular and atomic hydrogen adsorption on the Hf-decorated ZrCo (110) surface have been systematically studied by employing density functional theory calculations. Through our investigation, we find that both the number of stable adsorption sites and the adsorption energy of the H atom increase when a Zr atom is substituted by a Hf atom. Conversely, the H atom diffusion barrier decreases. The increases in both the stable adsorption sites and the energy change that is caused by the decoration of Hf shows that more hydrogen might be adsorbed on the Hf-decorated ZrCo (110) surface, thereby improving the hydrogen storage capacity of the ZrCo-based alloy. In addition, the H2 dissociation barrier is lowered on the Hf-decorated surface. The adsorption mechanism of hydrogen on the decorated surface has been analyzed on the basis of several chemical bonding analysis methods. PDOS analysis shows that H s and Co s-, and d orbital hybridization energy decreases, which indicates that the adsorption strength of H atoms on the doped surface is weakened, thereby decreasing the hydrogen diffusion energy barrier. The present results are in line with prior experimental results and provide fundamental information regarding the adsorption process, which may be beneficial for understanding and estimating the hydrogen storage capacity of Hf-decorated ZrCo materials.