We have performed density functional theory (DFT) calculations to study the gas (CO, CO2, NO, and NO2) sensing mechanism of pure and doped (B@, N@, and B–N@) graphene surfaces. The calculated ...adsorption energies of the various toxic gases (CO, CO2, NO, and NO2) on the pure and doped graphene surfaces show, doping improves adsorption energy and selectivity. The electronic properties of the B–N@graphene surfaces change significantly compared to pure and B@ and N@graphene surfaces, while selective gas molecules are adsorbed. So, we report B–N codoping on graphene can be highly sensitive and selective for semiconductor-based gas sensor.
Developing highly efficient and durable electrocatalysts for the oxygen reduction reaction (ORR) is the key to improving the performance of proton exchange membrane fuel cells (PEMFCs) for future ...energy applications. Pt-Based electrocatalysts show the greatest promise for this reaction, among which nanostructure-based catalysts have been identified as potential candidates owing to their morphology, geometry, and size-dependent activities which were revealed from experimental and theoretical studies. The fundamental aspects of the origin of activity enhancement of nanostructure-based catalysts are manifested in the finest form in recent advancements in ORR catalyst design processes. Also, it is one of the areas of research where theoretical studies have contributed to a significant extent to developing tools and techniques which are currently applied in a wide range in the electrocatalysis scenario beyond fuel cell catalysis. This review covers the recent progress in Pt-based nanostructure catalysts for the ORR. This review delves into a comprehensive analysis of effective utilization of theoretically obtained insights into the experimental design of efficient Pt-nanostructure ORR catalysts as well as identifying the origin of their activities. A detailed discussion of the ORR mechanism on low and high-index facets, nanostructure morphologies, and composition, shape and size dependent activities of Pt-based catalysts is included as emphasized from theoretical perspectives. The underlying factors behind the experimentally reported excellent ORR activities of nanostructure-based catalysts are analysed by a detailed investigation of theoretically important factors such as binding energy, reaction barrier, overpotential and strain effects. Finally, challenges and future research directions towards experimental design of efficient ORR catalysts by using the knowledge gained from theory are also addressed.
A comprehensive evaluation of Pt-nanostructure-based electrocatalysts for the oxygen reduction reaction.
Stanene is a quantum spin Hall insulator and a promising material for electronic and optoelectronic devices. Density functional theory (DFT) calculations are performed to study the band gap opening ...in stanene by elemental mono-doping (B, N) and co-doping (B-N). Different patterned B-N co-doping is studied to change the electronic properties of stanene. A patterned B-N co-doping opens the band gap in stanene and its semiconducting nature persists under strain. Molecular dynamics (MD) simulations are performed to confirm the thermal stability of such a doped system. The stress-strain study indicates that such a doped system is as stable as pure stanene. Our work function calculations show that stanene and doped stanene have a lower work function than graphene and thus are promising materials for photocatalysts and electronic devices.
Graphite dual-ion batteries represent a potential battery concept for large-scale stationary storage of electricity, especially when constructed free of lithium and other chemical elements with ...limited natural reserves. Owing to their non-rocking-chair operation mechanism, however, the practical deployment of graphite dual-ion batteries is inherently limited by the need for large quantities of electrolyte solutions as reservoirs of all ions that are needed for complete charge and discharge of the electrodes. Thus far, lithium-free graphite dual-ion batteries have employed moderately concentrated electrolyte solutions (0.3-1 M), resulting in rather low cell-level energy densities of 20-70 Wh kg
. In this work, we present a lithium-free graphite dual-ion battery utilizing a highly concentrated electrolyte solution of 5 M potassium bis(fluorosulfonyl)imide in alkyl carbonates. The resultant battery offers an energy density of 207 Wh kg
, along with a high energy efficiency of 89% and an average discharge voltage of 4.7 V.
Recently synthesized two-dimensional hydrogen boride (HB) with a hexagonal boron network offers excellent opportunities for nanoscale electronic device applications. Herein, we have proposed a type ...of field-effect transistor (FET) nanodevice based on a two-dimensional HB sheet for individual identification of amino acids. Using first-principles consistent-exchange van der Waals density-functional (vdW-DF-cx) calculations, we have studied the effects produced by the adsorption of each amino acid on the electronic properties of the HB-based nanodevice for its detection. The adsorption energies, adsorption heights, and the charge transfer of each amino acid can be deliberated as demonstrative of all 10 amino acids: alanine (Ala), arginine (Arg), aspartic (Asp), glutamic acid (Glu), glycine (Gly), histidine (His), lysine (Lys), phenylalanine (Phe), proline (Pro), and tyrosine (Tyr). Furthermore, the electronic transport properties of the HB nanodevice and HB + amino acid setup are studied by the nonequilibrium Green’s function (NEGF) formalism combined with the density functional theory (DFT) approach. Our results show that the adsorption of each amino acid on the HB nanodevice gives Fano resonance in the electronic transmission function. The sensitivity analysis and current–voltage (I–V) characteristic results indicate that selective detection of amino acids is possible. Thus, we believe that the HB-based device may be promising for the prospect of protein sequencing.
The design of an efficient and selective catalyst for hydrogen peroxide (H
O
) formation is highly sought due to its industrial importance. As alternatives to a conventional Pd-Au alloy-based ...catalyst, three cuboctahedral core-shell nanoclusters (Au
@Pt
, Co
@Pt
and Au
Co
@Pt
NCs) have been investigated. Their catalytic activities toward H
O
formation have been compared with that of pure Pt cuboctahedral NC (Pt
). Much attention has been devoted to thermodynamic and kinetic parameters to find out the feasibility of the two-electron (2e
) over the four-electron (4e
) oxygen reduction reaction (ORR) to improve the product selectivity (H
O vs. H
O
). Elementary steps corresponding to H
O
formation are significantly improved over the Au
Co
@Pt
NC catalyst compared with the pure core-shell NCs and periodic surface based catalysts. Furthermore, the Au
Co
@Pt
NC favours H
O
formation via the much desired Langmuir-Hinshelwood mechanism. The potential-dependent study shows that the H
O
formation is thermodynamically favourable up to 0.43 V on the Au
Co
@Pt
NC and thus the overpotential for the 2e
ORR process is significantly lowered. Besides, the Au
Co
@Pt
NC is highly selective for H
O
formation over H
O formation.
Density functional theory (DFT) calculations are performed to understand and address the previous experimental results that showed the reduction of nitrobenzene to aniline prefers direct over ...indirect reaction pathways irrespective of the catalyst surface. Nitrobenzene to aniline conversion occurs
via
the hydroxyl amine intermediate (direct pathway) or
via
the azoxybenzene intermediate (indirect pathway). Through our computational study we calculated the spin polarized and dispersion corrected reaction energies and activation barriers corresponding to various reaction pathways for the reduction of nitrobenzene to aniline over a Ni catalyst surface. The adsorption behaviour of the substrate, nitrobenzene, on the catalyst surface was also considered and the energetically most preferable structural orientation was elucidated. Our study indicates that the parallel adsorption behaviour of the molecules over a catalyst surface is preferable over vertical adsorption behaviour. Based on the reaction energies and activation barrier of the various elementary steps involved in direct or indirect reaction pathways, we find that the direct reduction pathway of nitrobenzene over the Ni(111) catalyst surface is more favourable than the indirect reaction pathway.
Density functional theory (DFT) calculations are performed to understand and address the previous experimental results that showed the reduction of nitrobenzene to aniline prefers direct over indirect reaction pathways irrespective of the catalyst surface.
Interpretation of size evolution is an essential part of nanocluster transformation processes for unraveling the mechanism at an atom-precision level. Here we report the transformation of a ...non-superatomic Au23 to a superatomic Au36 nanocluster via Au28 cluster formation, activated by the bulky 4-tert-butylbenzenethiol ligand. Time-dependent matrix-assisted laser desorption ionization mass spectrometry data revealed that the conversion proceeds through ligand exchange followed by the size focusing method, ultimately leading to size growth. We also validated this transformation through time-dependent ultraviolet–visible data. Density functional theory calculations predicted that the kernel of the Au28 cluster evolved through a linear combination of molecular orbitals of the fragment of 2e– units (Au4 2+ and Au3 +) from the kernel of the Au23 cluster. Periodic growth of gold cores through continuous growth of Au4 tetrahedral unit leads to the formation of the Au36 cluster from the Au28 cluster. These results reinforce the plausibility of size evolution through the growth mechanism during the transformation process. Differential pulse voltammetry studies showed that the highest occupied molecular orbital–lowest unoccupied molecular orbital gap inversely varies with the kernel size of these clusters. Photophysical experiments support the molecular-like intersystem crossing rather than core–shell relaxation to these clusters. The trends of photoluminescence lifetime were found to be the reverse of those of the energy gap law. The increment of lifetimes for the larger cluster can be mainly due to the contribution of both hot carriers and band-edge carriers.
Due to the drawbacks in commercially known lithium-ion batteries (LIB) such as safety, availability, and cost issues, aluminum batteries are being hotly pursued in the research field of energy ...storage. Al being abundant, stable, and possessing high volumetric capacity has been found to be attractive among the next generation secondary batteries. Various unwanted side reactions in the case of aqueous electrolytes have shifted the attention toward nonaqueous electrolytes for Al batteries. Unlike LIBs, Al batteries are based on intercalation/deintercalation of ions on the cathode side and deposition/stripping of Al on the anodic side during the charge/discharge cycle of the battery. Hence, to provide a clear understanding of the recent developments in Al batteries, we have presented an overview concentrating on the choice of suitable cathodes and electrolytes involving aluminum chloride derived ions (AlCl4 –, AlCl2 +, AlCl2+, etc.). We elaborate the importance of innovation in terms of structure and morphology to improve the cathode materials as well as the necessary properties to look for in a suitable nonaqueous electrolyte. The significance of computational modeling is also discussed. The future perspectives are discussed which can improve the performance and reduce the manufacturing cost simultaneously to conceive Al batteries for a wide range of applications.
Abstract
In this article, we predict the emergence of non-trivial band topology in the family of XX′Bi compounds having
$$P\overline{6}2m$$
P
6
¯
2
m
(# 189) space group. Using first principles ...calculations within hybrid functional framework, we demonstrate that NaSrBi and NaCaBi are strong topological insulator under controlled band engineering. Here, we propose three different ways to engineer the band topology to get a non-trivial order: (i) hydrostatic pressure, (ii) biaxial strain (due to epitaxial mismatch), and (iii) doping. Non-triviality is confirmed by investigating bulk band inversion, topological Z
2
invariant, surface dispersion and spin texture. Interestingly, some of these compounds also show a three dimensional topological nodal line semi-metal (NLS) state in the absence of spin orbit coupling (SOC). In these NLS phases, the closed loop of band degeneracy in the Brillouin zone lie close to the Fermi level. Moreover, a drumhead like flat surface state is observed on projecting the bulk state on the 001 surface. The inclusion of SOC opens up a small band gap making them behave like a topological insulator.
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