Shinichi Kunikata

Effects of Cluster Size on Platinum–Oxygen Bonds Formation in Small Platinum Clusters

We present the results of density functional theory calculation in oxygen dissociative adsorption process on two types of isolated platinum (Pt) clusters: Pt4 and Pt10, by taking into account the effect of cluster reconstruction. The strength of Pt–Pt bonds in the clusters is mainly defined by d–d hybridization and interstitial bonding orbitals (IBO). Oxygen that adsorbed on the clusters is weakening the IBO and thus inducing geometry reconstruction as occurred in Pt10 cluster. However, cluster that could undergo structural deformation is found to promote oxygen dissociation with no energy barrier. The details show that maintaining well-balanced of attractive and repulsive (Hellmann–Feynman) forces between atoms is considered to be the main key to avoid any considerable rise of energy barrier. Furthermore, a modest energy barrier that gained in Pt4 cluster is presumed to be originate from inequality of intramolecular forces between atoms.

Favorable Pathway of O2 Dissociative Adsorption on a Single Platinum Adatom Coated on Gamma-Alumina (111) Surface: A Density Functional Theory Study

We have investigated the dissociative adsorption process of O2 (oxygen molecule) on a composite surface formed by coating a single platinum (Pt) adatom on a gamma-alumina (γ-Al2O3) (111) surface. This process is studied by using density functional theory (DFT) and described in terms of potential energy surfaces (PES) with respect to the molecular degrees of freedom. We compare the activation barriers and adsorption energies among typical reaction channels. Our results show that O2 dissociative adsorption is preferably occurred when this O2 molecule approaches the surface with molecular orientation inclined by 30° angle with respect to the surface normal, i.e., the condition with lowest activation barrier. The results indicate that dissociated O atoms are likely to form strong bonds with the Pt adatom by keeping distance from the alumina layer.

First-principles study on oxygen ion conduction of La2GeO5 based on the density functional theory

We performed first-principles simulations based on the density functional theory for investigations on the atomic geometry of La2GeO5, which is a fast oxygen ion conductor applicable to solid oxide fuel cells. While two experimental studies have reported contradicting results about the configuration of GeO4 tetrahedral substructures, i.e., sp2- or sp3-like, we found that only the sp3-like form is stable. We confirmed that the favorability of oxygen sites for vacancy formation is fundamentally affected by this configuration. The bonding mechanisms between atoms are discussed based on analyses of atomic distances and electronic density of states.