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To design a catalyst for the dissociation of H 2 with better CO-tolerance performance is very important for proton exchange membrane fuel cells (PEMFCs) towards high efficiency. With slab model, the catalytic properties of overlayer Pt on Cu substrate (Pt/Cu) are analyzed by first-principle calculations. The CO saturation coverage (40%) on Pt 2 /Cu is found to be lower than that of pure Pt (about 75%). The dissociation barrier from H 2 to H is less than 0.4 eV under the saturation coverage of CO. On the basis of kinetics of proton formation, the CO-tolerance ability on double-layer Pt with Cu is found to be greatly improved compared with that on pure Pt. It is expected that Pt overlayer on Cu(1 1 1) is a potential anode material with lower cost for PEMFCs. [ABSTRACT FROM AUTHOR]

By studying the tantalum (Ta)(111) surface with X-ray photoemission spectroscopy and density functional theory, we determined binding energy values for the clean Ta(111) (+3.068 eV) and hydrogenated Ta(111) (+3.421 eV) surfaces with an isolated atom level of 18.977 eV. Using the bond–band barrier and zone-selective electron spectroscopy correlation, we investigated the mechanism of hydrogenation adsorption on the Ta(111) surface. We found the local densities of states of the first layer of Ta atoms in the reconstructed structure, which formed on the adsorbent hydrogen of the surface chemical bond contracts and dipole polarization. Moreover, we showed that on the Ta(111) surface, the hydrogen-induced surface core level shifts are dominated by quantum entrapment and are proportional to the calculated hybridized orbitals of the valence band. The latter is therefore correlated to the local surface chemical reactivity and is useful for other adsorbate systems on transition metals. [ABSTRACT FROM AUTHOR]

We have examined the atomic coordination effect on the local bond strain and the 3p core-level shift of K(1 1 0) skin and nanoclusters using a combination of the bond order–length–strength correlation notion, tight-binding approach, density functional theory calculations, and photoelectron spectroscopy measurements. It turns out that: (i) the 3p core-level shifts from 15.595 ± 0.003 eV for an isolated K atom by 2.758 eV to the bulk value of 18.353 eV; (ii) the effective atomic coordination number reduces from the bulk value of 12 to 3.93 for the first layer and to 5.81 for the second layer of K(1 1 0) skin associated with the local lattice strain of 12.76%, a binding energy density 72.67%, and atomic cohesive energy −62.46% for the skin; and (iii) K cluster size reduction lowers the effective atomic coordination number and enhances further the skin electronic attribution. Results have revealed that the 3p core-level shifts of K(1 1 0) and nanoclusters originate from perturbation of the Hamiltonian by under-coordination induced charge densification and quantum entrapment. [ABSTRACT FROM AUTHOR]

Consistency between density functional theory calculations and photoelectron spectroscopy measurements confirmed our predications on the undercoordination-induced local bond relaxation and core level shift of Na and K clusters. It is clarified that the shorter and stronger bonds between under-coordinated atoms cause local densification and local potential well depression and shift the electron binding-energy accordingly. Numerical consistency turns out the energy levels for an isolated Na ( E 2p = 31.167 eV) and K ( E 3p = 18.034 eV) atoms and their respective bulk shifts of 2.401 eV and 2.754 eV, which is beyond the scope of conventional approaches. This strategy has also resulted in quantification of the local bond length, bond energy, binding energy density, and atomic cohesive energy associated with the undercoordinated atoms. [ABSTRACT FROM AUTHOR]

• The polar nitrobenzene molecule can effectively adjust the electronic structures of g-C 3 N 4. • The most stable composite specimen has OER/ORR overpotentials of 0.27/0.39 V. • The number of active electrons can accurately estimate the OER/ORR activity of metal-free electrocatalysts. Metal-free catalyst with favorable advantages of nonpolluting, cost-effective and stable catalytic performances may be used in various redox reactions. In this paper, we design a series of C 6 H 4 NO 2 /g-C 3 N 4 composites by combining a polar nitrobenzene molecule with g-C 3 N 4 monolayer using density functional theory calculations. The electrocatalytic performances during oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are substantially improved thanks to the electron redistributions of g-C 3 N 4 substrate. One composite specimen exhibits the lowest bi-directional OER/ORR overpotentials of 0.14/0.14 V, and the most stable composite specimen has OER/ORR overpotentials of 0.27/0.39 V. The number of active electrons in active atom, as descriptor of catalytic activity, can accurately estimate the OER and ORR activity of metal-free electrocatalysts. The modification strategy would be extended to design high-efficiency metal-free electrocatalysts. [ABSTRACT FROM AUTHOR]