Oxygen Activation on Four-Atom Metal Clusters and Alloys

The dissociation of oxygen molecules and generation of two separated oxygen atoms is an important step in fuel cells. The activation of the bond linking two oxygen atoms in the oxygen molecule usually needs large activation barriers on metals utilized as catalysts. In the present study, the characterization and catalytic performance of four-atom Al nanocluster (Al4) as well as XAl3 (X = Ti and Sc) nanoalloys in activation of the oxygen molecule are investigated using density functional theory. Our results show that the tetrahedral isomer of the Al4 nanocluster lies lower in energy (Ecoh = −33.35 kcal/mol) than does the corresponding rhombus isomer (Ecoh = −31.05 kcal/mol). Also, transition metal (Ti and Sc) doping reduces the reactivity of the Al4 nanocluster. In consistent with the suggestion of reactivity descriptors used in the present study, our results reveal that the maximum catalytic performance in activation of the oxygen-oxygen bond is related to the pristine Al4 clusters. The energy barrier of O2 activation on the Al4 system (21.26 kcal/mol) exhibits that the activation of the bond linking of two oxygen atoms on Al4 is kinetically preferable. In this respect, our study shows that the Al4 nanocluster can be considered as an excellent catalyst for activation the oxygen molecule.