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| 3. |
- Wei, Minrui, et al.
(författare)
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Vibronic fine structure in the nitrogen 1s photoelectron spectra of molecules from Franck-Condon simulations: Azines
- 2022
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 106:2
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Tidskriftsartikel (refereegranskat)abstract
- Vibronic coupling plays a pivotal role in molecular spectroscopy. We present a theoretical study on vibrationally resolved x-ray photoelectron spectra (XPS) of seven azines (CxHyNz; pyridine, three diazines, two triazines, and one tetrazine) at the nitrogen 1s edge, to explore the vibronic coupling effects as influenced by consecutive replacement of the CH group with a N atom. Franck-Condon simulations were performed with the Duschinsky rotation effect included, where the electronic structure was calculated by the density functional theory. Validations on pyrimidine show good agreement with the experiment, weak functional dependence, and weak mode mixing effect. We observed an evident blue shift in binding energies with the increasing number of N atoms in this series, together with molecule-dependent vibronic fine structures. These molecules have either C2v or Cs molecular symmetry at the optimized core-ionized geometries. Franck-Condon-active vibrational modes were identified to be low frequency (500–1650 cm−1), totally symmetric (A1 or A′), in-plane ring deformation modes. Core ionization on N∗ always leads to elongation of the N∗−N bond length, accompanied by an increase of the ∠C−N∗−X bond angle (X=C, N). Our study predicts accurate theoretical reference spectra for the azine family and provides useful information on the properties of the core-ionized states as influenced by the structural change of CH↔N replacement.
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| 4. |
- Yang, Yi, et al.
(författare)
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Facile Hydrothermal Synthesis of Highly Efficient and Durable Ternary Ptpdcu Electrocatalysts For Methanol Oxidation Reaction : Iodide Matters
- 2022
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Ingår i: Social Science Research Network SSRN. - : Elsevier BV. - 1556-5068.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Precious metal Pt-based electrocatalysts have been widely used in methanol catalytic oxidation of anodes in direct methanol fuel cells (DMFCs). However, it has been still the challenge to decrease their cost and improve their efficiency and stability. In this study, ternary PtPdCu nanocatalysts were synthesized through a facile one-step hydrothermal synthesis method. When KI was present with a suitable amount in the synthesis, PtPdCu nanospheres with surface embedded CuI clusters (CuI/PtPdCu) were obtained. While without using KI, the prepared PtPdCu catalysts show a distinct hollow structure (h-PtPtCu). CuI/PtPdCu displays the highest specific activity with a 4 times enhancement than commercial Pt/C for methanol oxidation reaction (MOR) in an alkaline medium. The superior activity can attribute to the two aspects: i) Electronic effect originated from the highly alloyed PtPdCu. ii) synergetic effect due to the surface inlayed CuI clusters which can promote the CO intermediate removal. Furthermore, owing to the stable Pt-Pd-rich surface and its special linked hollow structure, h-PtPtCu catalyst exhibits the best durability with only a 3.6 % decay in specific activity.
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| 5. |
- Yang, Yi, et al.
(författare)
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In-situ loading synthesis of graphene supported PtCu nanocube and its high activity and stability for methanol oxidation reaction
- 2021
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 595, s. 107-117
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Tidskriftsartikel (refereegranskat)abstract
- A perfect PtCu nanocube with partial hollow structure was prepared by hydrothermal reaction and its electrocatalytic methanol oxidation reaction (MOR) was studied. The appropriate concentration of shape-control additives KI and triblock pluronic copolymers, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO19-PPO69-PEO19) (P123) play crucial roles in the final product morphology. The PtCu nanocubes can be perfectly in situ immobilizedonto graphene under the action of P123 while the structure and cubic morphologyremain unchanged. The electrochemical tests suggest that the obtained PtCu nanocube (PtCu-NCb) exhibits better MOR activity and stability than PtCu hexagon nanosheet (PtCu-NSt), PtCu nanoellipsoid (PtCu-NEs) and commercial Pt/C in alkaline medium. When in situ immobilized onto graphene, the MOR catalytic activity and stability of PtCu cubes are further improved. The markedly enhanced electrocatalytic activity and durability maybe attributed to the special cubic morphology with partial hollow structure enclosed by highly efficient facet and the probably the synergistic effect of PtCu and intermediate state CuI decorated on the surface and graphene.
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| 7. |
- Tian, Gui-Xian, et al.
(författare)
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Facile Hydrothermal Synthesis of Highly Efficient and Durable Ternary PtPdCu Electrocatalysts for the Methanol Oxidation Reaction
- 2023
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Ingår i: Advanced Energy and Sustainability Research. - : Wiley. - 2699-9412.
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Tidskriftsartikel (refereegranskat)abstract
- Precious metal Pt-based electrocatalysts have been widely used in the methanol catalytic oxidation anodes in direct methanol fuel cells. However, decreasing their cost and improving their efficiency and durability have still been challenging. Herein, ternary PtPdCu nanocatalysts are synthesized through a facile one-step hydrothermal synthesis method. When KI is present with a suitable amount in the synthesis, PtPdCu nanospheres with surface-embedded CuI clusters (CuI/PtPdCu) are fabricated. However, without KI, the prepared PtPdCu catalysts show a distinct hollow structure (h-PtPtCu). CuI/PtPdCu displays the highest specific activity with enhancement 4 times higher than commercial Pt/C for the methanol oxidation reaction in an alkaline medium. The superior activity can be attributed to two aspects: 1) the electronic effect originating from the highly alloyed PtPdCu; 2) the synergetic effect resulting from surface inlaid CuI clusters, which can promote the CO intermediate removal. Furthermore, because of the stable Pt-Pd-rich surface and its special linked hollow structure, the h-PtPtCu catalyst exhibits good durability with only a 3.6% decay in the specific activity.
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| 8. |
- Wang, Sheng-Yu, et al.
(författare)
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Interpreting the Cu-O2 Antibonding Nature in Two Cu-O2 Complexes from Cu L-Edge X-ray Absorption Spectra
- 2023
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 62:42, s. 17115-17125
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Tidskriftsartikel (refereegranskat)abstract
- Cu–O2 structures play important roles in bioinorganic chemistry and enzyme catalysis, where the bonding between the Cu and O2 parts serves as a fundamental research concern. Here, we performed a multiconfigurational study on the copper L2,3-edge X-ray absorption spectra (XAS) of two copper enzyme model complexes to gain a better understanding of the antibonding nature from the clearly interpreted structure–spectroscopy relation. We obtained spectra in good agreement with the experiments by using the restricted active space second-order perturbation theory (RASPT2) method, which facilitated reliable chemical analysis. Spectral feature interpretations were supported by computing the spin–orbit natural transition orbitals. All major features were assigned to be mainly from Cu 2p to antibonding orbitals between Cu 3d and O2 π*, Cu 3d−πO–O* (type A), and a few also to mixed antibonding/bonding orbitals between Cu 3d and O2 π, Cu 3d ± πO–O (type M). Our calculations provided a clear illustration of the interactions between Cu 3d and O2 π*/π orbitals that are carried in the metal L-edge XAS.
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| 9. |
- Xiang, Maosheng, et al.
(författare)
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Abundance Estimates for 16 Elements in 6 Million Stars from LAMOST DR5 Low-Resolution Spectra
- 2019
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Ingår i: Astrophysical Journal Supplement Series. - : IOP PUBLISHING LTD. - 0067-0049 .- 1538-4365. ; 245:2
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Tidskriftsartikel (refereegranskat)abstract
- We present the determination of stellar parameters and individual elemental abundances for 6 million stars from similar to 8 million low-resolution (R similar to 1800) spectra from LAMOST DR5. This is based on a modeling approach that we dub the data-driven Payne (DD-Payne), which inherits essential ingredients from both the Payne and the Cannon. It is a data-driven model that incorporates constraints from theoretical spectral models to ensure the derived abundance estimates are physically sensible. Stars in LAMOST DR5 that are in common with either GALAH DR2 or APOGEE DR14 are used to train a model that delivers stellar parameters (T-eff, log g, V-mic) and abundances for 16 elements (C, N, O, Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, and Ba) over a metallicity range of -4.dex < [Fe/H] < 0.6 dex when applied to the LAMOST spectra. Cross-validation and repeat observations suggest that, for S/N-pixel >= 50, the typical internal abundance precision is 0.03-0.1 dex for the majority of these elements, with 0.2-0.3 dex for Cu and Ba, and the internal precision of T-eff and log g is better than 30 K and 0.07 dex, respectively. Abundance systematics at the similar to 0.1 dex level are present in these estimates but are inherited from the high-resolution surveys' training labels. For some elements, GALAH provides more robust training labels, for others, APOGEE. We provide flags to guide the quality of the label determination and identify binary/multiple stars in LAMOST DR5. An electronic version of the abundance catalog is made publicly available.
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| 10. |
- Zhang, Jun-Rong, et al.
(författare)
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Accurate K-edge X-ray photoelectron and absorption spectra of g-C3N4 nanosheets by first-principles simulations and reinterpretations
- 2019
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 21:41, s. 22819-22830
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Tidskriftsartikel (refereegranskat)abstract
- We performed a density functional theory (DFT) study on X-ray photoelectron (XPS) and absorption (XAS) spectra of graphitic carbon nitride (g-C3N4) nanosheets at the N and C K-edges. A combined cluster-periodic approach was employed to calculate XPS spectra, in which the core ionic potential (IP) of the solid 2D material was computed by subtracting the work function (obtained with periodic conditions) from the gas phase IP (obtained with large cluster models). With amino-terminated supermolecules of different sizes, we obtained convergent spectra and provide new assignments for 5 nitrogen [1 sp(2); 4 sp(3) (bridging, tertiary, and primary/secondary amino nitrogens)] and 4 carbon (all bonded with three nitrogens) local structures. A good agreement with experiments was obtained, with the N1s (C1s) main peak position differing by 0.1-0.2 eV (0.5-0.8 eV). Our simulations show that N1s XPS of pure g-C3N4 contains only two major features at 398.6 and 401.2 eV, contributed from sp(2)-N and sp(3)-N, respectively. The chemical shifts of all sp(3)-N are so close (deviating by 0.3-0.6 eV) that terminal amino groups -NHx (x = 1, 2) will only be distinguished in high-resolution measurements. In C1s XPS, all carbons show similar (deviation < 0.2 eV) IPs, as determined by the same nearest neighbors. We further excluded the effect of shake-up satellites that may change our XPS interpretations by equivalent core hole time-dependent DFT (ECH-TDDFT) simulations. The effect of vibronic coupling is small (redistribution is only 0.1-0.3 eV to the higher-energy region) in the N1s edge as estimated from the asymmetric main peak shape, and negligible in the C1s edge. Quicker size convergence was found in XAS than XPS. In N1s XAS, we identified a weak pi* spectral feature at 400-401 eV for both -NHx and tertiary nitrogens. Our study provides a clear theoretical reference for X-ray spectral fingerprints of different local structures, which is useful for analysis of g-C3N4 based materials with various designed or unavoidable structural modifications. We also highlight our combined cluster-periodic approach in calculating the K-edge XPS spectra of general 2D materials which predicts accurate absolute values.
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