Pt/PdAl, which comprises a PdAl core protected by a Pt monolayer, may experience Al dealloying because of the strong affinity of Al toward O. To circumvent this issue, the Pt/Os/PdAl catalyst has been designed to suppress the migration of Al by inserting an Os monolayer at the interface between the PdAl core and two Pt monolayers. On the basis of segregation energies, Al leaching from the core to the 1st layer is determined to be endothermic even under O coverage, indicating an energetic preference for Al to reside in the core structure. The Pt/Os/PdAl catalyst benefits from the energetic disadvantage of the inward movement of Os and the presence of the 2 ML Pt layer. As an ORR electrocatalyst, the relatively weak adsorption ability of Pt/Os/PdAl suggests improved ORR activity. Finally, a representative OOH association mechanism with low reaction barriers of 0.46, 0.31, 0.38 and 0.41 eV for the OOH formation, OOH dissociation, OH formation and HO formation steps suggests that the catalyst can effectively activate the O-O bond and eliminate OH, which can act as a catalytic poison. These findings suggest the design of stable sandwich catalysts as potential candidates for ORR electrocatalysis.
The structural, electronic, and magnetic properties of transition metal doped platinum clusters MPt6 (M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) are systematically studied by using the relativistic all-electron density functional theory with the generalized gradient approximation. Most of the doped clusters show larger binding energies than the pure Pt7 cluster, which indicates that the doping of the transition metal atom can stabilize the pure platinum cluster. The results of the highest occupied molecular orbital (HOMO)—lowest unoccupied molecular orbital (LUMO) gaps suggest that the doped clusters can have higher chemical activities than the pure Pt7 cluster. The magnetism calculations demonstrate that the variation range of the magnetic moments of the MPt6 clusters is from 0 μB to 7 μB, revealing that the MPt6 clusters have potential utility in designing new spintronic nanomaterials with tunable magnetic properties.
As a nonrelativistic particle constrained to remain on an (N − 1)-dimensional ((N ≥ 2)) hypersurface embedded in an N-dimensional Euclidean space, two different components pi and p j (i, j = 1, 2, 3,… N) of the Cartesian momentum of the particle are not mutually commutative, and explicitly commutation relations [ p ˆ i , p ˆ j ] ≠ 0 depend on products of positions and momenta in uncontrollable ways. The generalized Dupin indicatrix of the hypersurface, a local analysis technique, is utilized to explore the dependence of the noncommutativity on the curvatures around a local point of the hypersurface. The first finding is that the noncommutativity can be grouped into two categories; one is the product of a sectional curvature and the angular momentum, and another is the product of a principal curvature and the momentum. The second finding is that, for a small circle lying a tangential plane covering the local point, the noncommutativity leads to a rotation operator and the amount of the rotation is an angle anholonomy; and along each of the normal sectional curves centering the given point the noncommutativity leads to a translation plus an additional rotation and the amount of the rotation is one half of the tangential angle change of the arc.
We report theoretical studies on the newly discovered novel Josephson effect and scanning tunneling spectroscopy (STS) at the interface of strontium titanate/lanthanum aluminate (STO/LAO). With a phenomenological boson–fermion model, the density of states is calculated and the results are consistent with the STS experiments. A typical calculation of Josephson effect is performed, and it is in qualitative agreement with the experiments. The calculations indicate that the gap states come from the pairing of quasi-particles with a finite total momentum and the Josephson current comes from the tunneling of quasi-particle pairs with zero momentum. The quasi-particles are Bogoliubov quasi-particles. Moreover, the fits using Kulikʼs formula imply that the Josephson junction at the STO/LAO interface has a point contact with the clean superconductor limit.
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