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Stabilization of Atomically Dispersed Metallic Catalysts for Electrochemical Energy Applications
Published in Wei Yan, Xifei Li, Shuhui Sun, Xueliang Sun, Jiujun Zhang, Atomically Dispersed Metallic Materials for Electrochemical Energy Technologies, 2023
Junjie Li, Xiaozhang Yao, Yi Guan, Kieran Doyle-Davis, Xueliang Sun
In recent years, single-atom catalysts (SAC) have attracted considerable interest due to their remarkable catalytic performance, which seems to be the best scenario to solve the issue mentioned above.6–9 When the size of metal species decreases from nanoparticle (NP) to single atom, the atom utilization efficiency reaches the maximum as all atoms act as the active center with high dispersion and uniformity. More importantly, as the atoms are atomically dispersed, the single atoms always display a highly unsaturated coordination environment. The unique local structure and electronic properties lead to their outstanding catalytic activity and selectivity in some reactions, which showed much improved catalytic performance over NPs-based catalysts. However, with a decrease in size from NPs to a single atom, it simultaneously increases the surface free energy that improves the mobility of supported single-atom thus leading to the formation of clusters/NPs through aggregation.10,11 Therefore, increasing the stability of SACs by some efficient strategies is important. In this chapter, we first briefly describe the challenges and opportunities for SACs and then highlight the recent progress to achieve stable SACs. Further, we will summarize the recent work regarding the electrochemical energy applications of SACs. Finally, the summary and perspective for single-atom catalysis are discussed.
n = 1-8) Nanoalloy Clusters
Published in Francisco Torrens, A. K. Haghi, Tanmoy Chakraborty, Chemical Nanoscience and Nanotechnology, 2019
Prabhat Ranjan, Tanmoy Chakraborty, Ajay Kumar
Density functional theory (DFT) is the most popular approach of quantum mechanics to study the electronic properties of matter.7,60 Due to its computational friendly behavior, DFT is a widely accepted method to study the many-body systems. In the domain of material science research, particularly in super conductivity of metal-based alloys,61 magnetic properties of nanoalloy clusters,62 quantum fluid dynamics, molecular dynamics,63,64 and nuclear physics,65,66 DFT has gained a huge importance. The study of DFT covers three major domains, that is, theoretical, conceptual, and computational.67-70 Conceptual density functional theory (CDFT) is established as an important approach to study the chemical reactivity of materials.71-73 The CDFT is highlighted following Parr’s dictum “Accurate calculation is not synonymous with useful interpretation. To calculate a molecule is not to understand it.”74 We have rigorously applied conceptual density functional based global and local descriptors for studying of physi-cochemical properties of nano-engineering materials and drug designing process.75-89
Semiconductor Optical Memory Devices
Published in Inamuddin, Mohd Imran Ahamed, Rajender Boddula, Tariq Altalhi, Optical Properties and Applications of Semiconductors, 2023
Umbreen Rasheed, Fayyaz Hussain, Rana Muhammad Arif Khalil, Muhammad Imran
Electronic properties play a crucial role in determining the nature of the material and hence predicting its specific use for a particular application. These properties assist to analyze the basic requirement of optical memory devices, i.e., their existence in bistable state. In theoretical physics, density of states (DOS) versus energy plots are used for the description of electronic properties. DOS plots of the four composites are shown in Figure 3.3. In all DOS plots, dashed line is indicating Fermi level for the highest occupied energy level, whereas left and right side of this Fermi level is illustrating valence band and conduction band, respectively. Bandgaps of the four composites calculated using VASP are summarized in Table 3.3. In DOS plots of the four composites, bandgap with no defect states indicates the insulating nature. DOS plots in Figure 3.3 for II–VI (BeS, BeTe) and III–V (BN, GaAs) semiconductors indicate their existence in HRS. Measured bandgap also predicts the energy of incident light radiations required to switch the optical memory devices based on these materials to LRS. Incident light radiation being an external stimulus may create photogenerated electrons switching the device into conducting state. In this way, these four composites may be used to achieve bistable states in optical memory devices. This bandgap may be treated as potential well. Higher bandgap may be used as deeper potential well having capability to store a greater number of electrons. Higher bandgap of BN is depicting its most suitable candidate for optical memory applications. This is due to the capability to create more charge trapping centers with longer lifetime. Longer lifetime is attributed to their generation deep inside the energy gap when exposed to light.
Synthesis, characterisation, biological and theoretical studies of novel pyridine derivatives
Published in Molecular Physics, 2022
P. S. Pradeep Kumar, K. Sunil, B. S. Chethan, N. K. Lokanath, N. Madan, A. M. Sajith
In this present research work series of novel pyrazole derivatives (AL1–AL12) were synthesised with good yields and these compounds were characterised by various analytical and spectroscopic techniques. Various electronic properties were studied using the DFT. The DFT analysis showed that the electron density in the HOMO of the compounds is mainly distributed over the pyrazole group. Furthermore, the synthesised compounds were screened for their antibacterial activity against two gram positive bacterial strains namely S. aureus, and M. luteus, and a gram negative bacterial strain namely E.coli. As from the MEP analysis of the compounds, due to the substitution of the methoxy group as a substituent large electronegative region was observed in the compound AL11, and hence it showed potent antibacterial activity against M. Luteus compared to all the other synthesised compounds.
Stability of X-IV-IV half Heusler semiconductor alloys: a DFT study
Published in Molecular Physics, 2021
The properties investigated in this work were achieved using the Quantum Espresso (QE) simulation package. The structural and electronic properties investigated were analyzed using the density functional theory (DFT). The hH semiconductors crystallize in the face-centred cubic structures belonging to the space group with space group number 216. Three possible Wyckoff positions were considered; ZYX, YZX, and XYZ, as reported in Table 1. The most stable and energetically favoured structure is the ZXY phase, as can be seen from Figure 1. The Ni atoms occupy Wyckoff position 4c (1/4, 1/4, 1/4), 4b (1/2,1/2, 1/2) is occupied by any of Si, Sn or Ge, while Hf occupies the 4a site (0, 0, 0). The remaining 4d (3/4, 3/4, 3/4) site is empty. In the ZXY phase, Ni is coordinated octahedrally in the position by the two other elements: HfSi, -HfSn or -HfGe, while Hf and X are tetrahedrally coordinated at and respectively. The crystal structure of the alloys was optimized by carrying out a fixed cell optimization relaxation calculation by applying the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm for the optimization of the ions with a possible shift in the x, y and z directions [54]. It is observed that there is an infinitesimal change in the atomic positions in the crystal structures studied.
First-principles computation of new series of quaternary Heusler alloys CoScCrZ (Z = Al, Ga, Ge, In): a study of structural, magnetic, elastic and thermal response for spintronic devices
Published in Molecular Physics, 2020
M. Shakil, Hafsa Arshad, M. Zafar, M. Rizwan, S. S. A. Gillani, Shabbir Ahmed
All the basic physical properties such as magnetism, chemical bonding, hardness and superconductivity are related to electronic properties of the materials. The main purpose of this work is to investigate the HM character of CoScCrZ (Z = Al, Ga, Ge, In) quaternary HAs. The electronic properties including BS and DOS are calculated based on optimised lattice constants and volumes. The BS were calculated along high-symmetry points of 1st BZ and are shown in Figures 4–7. The nature of BG can also be determined from BS. The materials in which valance-band maxima (VBM) and conduction-band minima (CBM) lie at gamma (), the nature of BG is direct and otherwise it is indirect. The positive values of VBM or CBM indicates that this energy is above the Fermi energy while the negative values correspond to the energy below the Fermi energy. The BG energy obtains by subtracting the CBM energy from VBM and HM energy gap refers to the difference between Fermi energy and VBM. From Table 6, it can be concluded that the values of VBM energies are negative and of CBM are positive for CoScCrAl, CoScCrGa, CoScCrGe and CoScCrIn which also corresponds to their HM character. The nature of BG for CoScCrAl, CoScCrGa, CoScCrGe and CoScCrIn is indirect because VBM is lie at gamma () and CBM is located at another symmetry point L and X.