Density functional study of adsorption and desorption dynamics of hydrogen in zirconium doped aluminium clusters

To reduce the greenhouse effect and as a fuel alternatives hydrogen is used as a secure and clean energy. But there are some challenges in the storage of hydrogen energy, the present accurate dynamics of adsorption and release of hydrogen. We report the adsorption and desorption of hydrogen atoms (up to eight) on the ZrAl_m (m = 3 to 7) clusters using density functional theory within B3PW91/LANL2DZ basis sets in the GAUSSIAN 09 package. Adsorption energy for per hydrogen atom in all clusters is found in the range of ?2.5 eV to ?3.3 eV, which shows the chemisorption of hydrogen on the ZrAl_m clusters. Change in the DOS with number of hydrogen is attributed to the charge transfer between the ZrAl_m clusters and hydrogen atoms. Highest HOMO-LUMO gap of 3.055 eV is found for the ZrAl₃H₇ cluster which indicates that the ZrAl₃H₇ cluster is chemically more stable. Work function values for hydrogen doped clusters are in the range of 3.5 eV–4.4 eV which suggests the low optical absorption in considered clusters. The calculated enthalpy difference further confirms the chemisorption of hydrogen on ZrAl_m clusters ZrAl₃H_n and ZrAl₇H_n(for n = 1 to 5 and 7) are more exothermic than other considered clusters. Desorption energies per hydrogen for these clusters are found lower than the some of the best catalytic clusters Pd₁₃ and Pt₁₃ indicating more catalytic active nature.