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Zn-Air Battery Application of Atomically Dispersed Metallic Materials
Published in Wei Yan, Xifei Li, Shuhui Sun, Xueliang Sun, Jiujun Zhang, Atomically Dispersed Metallic Materials for Electrochemical Energy Technologies, 2023
Mingjie Wu, Gaixia Zhang, Hariprasad Ranganathan, Shuhui Sun
In addition to the direct modulation of the MOF-based materials, metal phthalocyanine and some phthalocyanine-based layered two-dimensional conjugated MOF assembled with the carbon supports via intermolecular interactions are also reported to synthesize SACs.118 For instance, Peng et al. developed a fully π-conjugated iron phthalocyanine (FePc)-rich covalent organic framework (COF) (Figure 6.7a).119 Different from the pyrolysis procedure of randomly creating single-atom sites, the obtained COF with pre-assembled Fe–N–C centers is directly riveted onto the graphene support. The electron localization function (ELF) analysis shows only van der Waals interactions. By comparing the charge density differences, the Fe–C electron pathway was confirmed by the fact that the graphene electrons were attracted to the N-coordinated Fe sites (Figure 6.7b). The as-synthesized SAC shows increased ORR catalytic performance (Figure 6.7c) and the ZAB based on the mixture of SAC and IrO2 exhibited a long-life cycle of over 300 h. Feng et al. developed a copper phthalocyanine-based 2D conjugated MOF supported on the CNTs as an air electrode of ZABs.120 The obtained 2D conjugated MOF with square-planar cobalt bis (dihydroxy) complexes (Co–O4) as linkages (PcCu–O8–Co) shows a high crystalline structure (Figure 6.7d). In-situ Raman spectro-electrochemistry and DFT verified the Co centers as the catalytic sites (Figure 6.7e).
Nanotwinning and Directed Alloying to Enhance the Strength and Ductility of Superhard Materials
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Yidi Shen, Qi An, Xiaokun Yang, William A. Goddard III
To investigate how the TBs improve the intrinsic strength of B4C, we also examined the failure process for symmetric twins, as shown in Figure 22.6b–d. Here, we also examined the bonding conditions during shear deformation by applying the electron localization function (ELF), a method to show the electronic isosurface to analyze the covalent bonding.46 Note that the lower half region of the twinned model is sheared along [100]r direction with the lower shear strength of 38.9 GPa, while the upper half region is sheared along the opposite direction [1¯00]r with a higher shear strength of 57.1 GPa.24 The failure process can be partitioned into two steps: (i) the B–C bonds between icosahedra in the lower half region are stretched and broken as the shear strain increases to 0.209, as shown in Figure 22.6b; (ii) At 0.322 shear strain, breaking the B–C bond between icosahedra in TB plane leads to a lone pair electrons on the C atoms (carbene) of icosahedra, as shown in Figure 22.6c. Then, the C-B-C chain reacts with this carbene, deconstructing the icosahedron and the C-B-C chain, as shown in Figure 22.6d.
Two-dimensional silicon nanosheets
Published in Klaus D. Sattler, Silicon Nanomaterials Sourcebook, 2017
Hideyuki Nakano, Ritsuko Yaokawa, Masataka Ohashi
The total EDOSs is presented in Figure 3.16c through f along with the partial orbital-decomposed EDOS for Si, C, and H atoms. The major contribution to the bands at and just below the highest occupied level is from the Si 2px and 2py states (Figure 3.16d), which would involve bonding between Si atoms of the nanosheet. In contrast, the main contribution to the conduction band is from the C 2px and 2py orbitals (Figure 3.16e). The deeper valence states, between ca. 4 and 10 eV below the highest occupied level, are primarily comprised of Si s states, with minor contributions from the C orbitals. The H s bands (Figure 3.16f) are generally coincident with the C px, py, and pz bands, as expected from their bonding in the phenyl groups. In addition, the overlap of the H s and Si pz states, primarily between 2 and 4 eV, indicates the formation of strong Si–H bonds, as indicated by the electron localization function (ELF) plot. Overall, the spiky profile of the CDOS indicates a weak electronic interaction between these atoms, which is also suggested by the band structure and the ELF profile.
Adsorption of graphene oxide with cellulose acetate: insights from DFT
Published in Molecular Physics, 2022
Haowen Zhang, Liyun Ding, Yumei Zhang, Tian Wu, Qin Li
The electron localisation function (ELF) [28] is an effective tool for characterising bonding by providing a vivid description of the electron distribution. The nature of the interaction between two atoms is described by the ELF value, which is defined as a value between 0 and 1. The closer the ELF value is to 1, the more probable it is that a covalent bond will be formed between two atoms. ELF value is 0 means there are no electrons. When this value is about 0.5, it indicates the presence of metal free-electron [39]. To determine whether the overlapping electron density appearing in the M1, M2, and M5 models are chemically bonded, ELF was performed on these sections, and calculation information is shown in Figure 6. In Figure 6(b), for example, the region between the O(4) and H(14) atoms appears blue with ELF values of about 0.25-0.3, which are much smaller than the ELF values for the covalent bond between the O(4) and H(2) atoms. This shows that the electrons between the O(4) and H(14) atoms are not localised, and the electron density overlap is not produced by covalent bonding. Similarly, the H(1) and O(13) atoms in the M1 model, the H(14) and O(1) atoms in the M2 model, and the H(2) and O(18) atoms in the M5 model are not covalently bonded for the electron density overlap and electron density deformation they produce during adsorption. Therefore, the nature of the electron density overlap site needs further analysis.
Comparative study of cyclic polyaniline oligomers with linear and bent structures
Published in Molecular Physics, 2022
The electron localisation function (ELF) is a function that measures the degree of electron localisation in different molecular regions and helps to understand the pair electron localisation in the spirit of Lewis structure [55]. The calculated ELF isosurfaces and corresponding Lewis structures for the repeating units of linear, bent and cyclic polyanilines at the B3LYP-D3/6-311++G(d,p) level of theory are compared in Figure 3. For simplification, the next repeating units which are similar are not shown. The large and medium disynaptic protonated basins are associated with the C–H and N–H bonds, respectively. The small disynaptic, spherical and banana shaped basins are related to the C–N and C=C bonds, respectively. The monosynaptic basin corresponds to the lone pair. A conformational change from the linear structure is shown to be required for the formation of cyclic polyaniline.
Theoretical prediction of Xe-containing polymer
Published in Molecular Physics, 2021
The electron localisation function (ELF) is another powerful method to investigate the properties of chemical bond, whose value is in the range of 0∼1. Figure 3 shows the ELF at the BCPs of Xe-N and H-Xe bonds of C5N4H10XeH2. As we can see, the colour of H-Xe bond area is yellow, whose value is around 0.75, and the colour of Xe-N bond area is green, whose value is around 0.60 in the ELF of C5N4H10XeH2 molecule. Usually, a high ELF value (the red colour area) means a covalent bond or a pair of lone electron pairs. By colour distinction, the charge distribution intuitively illustrates the nature of the covalent bond between Xe-N and H-Xe.