Boron-based Nanostructures Research Articles

Enhanced hydrogen storage of alkaline earth metal-decorated Bn (n = 3-14) nanoclusters: a DFT study.

Boron-based nanostructures hold significant promise for revolutionizing hydrogen storage technologies due to their exceptional properties and potential in efficiently accommodating and interacting with hydrogen molecules. In this paper, boron-based Bn (n = 3-14) nanoclusters decorated with alkaline earth metals (AEM = Ca and Be) were investigated for hydrogen storage applications based on density function theory (DFT) calculations. To evaluate H2 adsorption capability, the adsorption energies, frontier molecular orbitals (FMOs), natural bond orbital (NBO), and quantum theory of atoms in molecule (QTAIM) analysis are performed. The primary aim of this research work is to achieve targeted value of 5.5 wt% set by the US Department of Energy (DOE) for the year 2025. The results revealed that B5Ca2, B6Ca2, and B10Ca2 structures have the ability to hold up to 12H2 molecules with gravimetric capacities of 15.20, 14.21, and 8.60 wt%, respectively, when compared to other boron structures decorated with calcium. Similarly, for Be-decorated structure, B3Be2 structure can accommodate 3H2 molecules with gravimetric capacity of 10.59 wt%. The result of this study indicates that AEM-decorated Bn nanoclusters hold great promise as potential materials for hydrogen storage. Density functional theory (DFT) approach at ωB97XD/6-311++G(d,p) level of theory is employed to investigate the possibility of storing H2 molecules on alkaline earth metal (AEM = Ca and Be)-decorated Bn (n = 3-14) nanoclusters. All DFT computations were performed using Gaussian 09 software. To calculate frontier molecular orbitals (FMOs) and quantum theory of atoms in molecule (QTAIM) analysis, we have used GaussView and Multiwfn software, respectively.

Boron-oxy-carbide sheets: A wide voltage symmetric supercapacitor electrode with high temperature tolerance

In view of exploring the boron-based nanostructures for the application of energy storage, we have synthesized boron-oxy-carbide material with hydrothermal assisted annealing process and analyzed its performance in aqueous and organic electrolyte. The ability of BOC material to operate both in positive and negative region in Li2SO4 electrolyte encourage us to construct a symmetric device. Splendidly, the BOC material breaks the restriction of low thermodynamic potential window of water (1.23 V) equipped with high cell voltage of 2 V and shown excellent energy density of 16.15 Wh kg−1 at 500 W kg−1 of power density. To extend its operating voltage, a symmetric coin cell was fabricated and tested in TEABF4 electrolyte. As expected, the cell operates upto 3 V and shows maximum energy density of 38.75 Wh kg−1 at 1125 W kg−1 with tremendous rate capability. Moreover, the temperature dependent electrochemical behavior was tested at different temperature from −15 °C to 80 °C. The device shows considerable increment in the specific capacitance with 15.8 F g−1 at −15 °C and 26.24 F g−1 at 80 °C.

Titanium Atoms-Decorated B40 Fullerene: First-Principle Study to Predict the Structural Evolution during Hydrogen Storage

Boron-based nanostructures are considered as alternative hydrogen storage material due to its large surface area, lightweight and chemical stability. In this work, the hydrogen storage capacity and structural evolution of titanium (Ti) atoms-decorated B40 fullerene are investigated using first-principles calculations. Our result shows that Ti prefers to absorb on the outside surface of the hexagonal and heptagonal cavities of B40 ring. The average binding energy (Ebinding) for 6 Ti atoms-decorated B40 structure is calculated as 5.71 eV. The interatomic distance between two neighbor Ti atoms (5.13–5.54 A) is larger than that of Ti2 dimer (~ 2.0 A) to prevent the aggregation of Ti atoms as well as Tin cluster formation. The average adsorption energies (Eadsorption) for (Ti–nH2)6B40 (n = 2–6) structures, within a range of 0.29–0.33 eV, prove that the structures are between chemisorbed and physisorbed states (0.2–0.6 eV). We have achieved a maximum gravimetric density (H2 wt%) of 9.3 wt% exceeding the 5.5 wt% goal set by the Department of Energy, USA, by the year 2020. In addition, ab initio molecular dynamics calculations have confirmed that the (Ti–6H2)6B40 structure is stable for the hydrogen adsorption under near-ambient temperature.

Inorganic Boron-Based Nanostructures: Synthesis, Optoelectronic Properties, and Prospective Applications.

Inorganic boron-based nanostructures have great potential for field emission (FE), flexible displays, superconductors, and energy storage because of their high melting point, low density, extreme hardness, and good chemical stability. Until now, most researchers have been focused on one-dimensional (1D) boron-based nanostructures (rare-earth boride (REB6) nanowires, boron nanowires, and nanotubes). Currently, two-dimensional (2D) borophene attracts most of the attention, due to its unique physical and chemical properties, which make it quite different from its corresponding bulk counterpart. Here, we offer a comprehensive review on the synthesis methods and optoelectronics properties of inorganic boron-based nanostructures, which are mainly concentrated on 1D rare-earth boride nanowires, boron monoelement nanowires, and nanotubes, as well as 2D borophene and borophane. This review paper is organized as follows. In Section I, the synthesis methods of inorganic boron-based nanostructures are systematically introduced. In Section II, we classify their optical and electrical transport properties (field emission, optical absorption, and photoconductive properties). In the last section, we evaluate the optoelectronic behaviors of the known inorganic boron-based nanostructures and propose their future applications.

The Growth Methods and Field Emission Studies of Low-Dimensional Boron-Based Nanostructures

Based on the morphology characteristics, low-dimensional (LD) nanostructures with high aspect ratio can be usually divided into nanowire, nanocone, nanotube, nanorod, nanoribbon, nanobelt and so on. Among numerous LD nanostructures, boron-based nanostructures attracted much interest in recent years because they have high melting-point, large electric and thermal conductivity, and low work function. Compared to traditional thermal emission, field emission (FE) has notable advantages, such as lower power dissipation, longer working life, room-temperature operation, higher brightness and faster switching speed. Most studies reveal they have lower turn-on and threshold fields as well as high current density, which are believed as ideal cold cathode nanomaterials. In this review, we will firstly introduce the growth methods of LD boron-based nanostructures (boron monoelement and rare-earth metal hexaboride). Then, we will discuss their FE properties and applications. At last, the conclusions and outlook will be summarized based on the above studies.

Simple, Green, and High-Yield Production of Boron-Based Nanostructures with Diverse Morphologies by Dissolution and Recrystallization of Layered Magnesium Diboride Crystals in Water.

Layered metal diborides that contain metal atoms sandwiched between boron honeycomb planes offer a rich opportunity to access graphenic forms of boron. We recently demonstrated that magnesium diboride (MgB2 ) could be exfoliated by ultrasonication in water to yield boron-based nanosheets. However, knowledge of the fate of metal boride crystals in aqueous phases is still in its incipient stages. This work presents our preliminary findings on the discovery that MgB2 crystals can undergo dissolution in water under ambient conditions to result in precursors (prenucleation clusters) that, upon aging, undergo nonclassical crystallization preferentially growing in lateral directions by two-dimensional (2D) oriented attachment. We show that this recrystallization can be utilized as an avenue to obtain a high yield (≈92 %) of boron-based nanostructures, including nanodots, nanograins, nanoflakes, and nanosheets. These nanostructures comprise boron honeycomb planes chemically modified with hydride and oxy functional groups, which results in an overall negative charge on their surfaces. This ability of MgB2 crystals to yield prenucleation clusters that can self-seed to form nanostructures comprising chemically modified boron honeycomb planes presents a new facet to the physicochemical interaction of MgB2 with water. These findings also open newer avenues to obtain boron-based nanostructures with tunable morphologies by varying the chemical milieu during recrystallization.

From planar boron clusters to borophenes and metalloborophenes

Elemental boron and its compounds exhibit unusual structures and chemical bonding owing to the electron deficiency of boron. Joint photoelectron spectroscopy and theoretical studies over the past decade have revealed that boron clusters possess planar or quasi-planar (2D) structures up to relatively large sizes, laying the foundations for the discovery of boron-based nanostructures. The observation of the 2D B36 cluster provided the first experimental evidence that extended boron monolayers with hexagonal vacancies were potentially viable and led to the proposition of ‘borophenes’ — boron analogues of 2D carbon structures such as graphene. Metal-doping can expand the range of potential nanostructures based on boron. Recent studies have shown that the CoB18− and RhB18− clusters possess unprecedented 2D structures, in which the dopant metal atom is part of the 2D boron network. These doped 2D clusters suggest the possibilities of creating metal-doped borophenes with potentially tunable electronic, optical and magnetic properties. Here, we discuss the recent experimental and theoretical advances in 2D boron and doped boron clusters, as well as their implications for metalloborophenes. The unusual electronic characteristics of boron atoms lead boron clusters to adopt a wide variety of structural arrangements, most of which are 2D. This Perspective discusses the possibility of expanding the range of boron-based 2D structures by metal doping, as well as the use of the resulting clusters for conceptualizing metalloborophenes.

Lithium-Decorated Borospherene B40: A Promising Hydrogen Storage Medium.

The recent discovery of borospherene B40 marks the onset of a new kind of boron-based nanostructures akin to the C60 buckyball, offering opportunities to explore materials applications of nanoboron. Here we report on the feasibility of Li-decorated B40 for hydrogen storage using the DFT calculations. The B40 cluster has an overall shape of cube-like cage with six hexagonal and heptagonal holes and eight close-packing B6 triangles. Our computational data show that Lim&B40(1–3) complexes bound up to three H2 molecules per Li site with an adsorption energy (AE) of 0.11–0.25 eV/H2, ideal for reversible hydrogen storage and release. The bonding features charge transfer from Li to B40. The first 18 H2 in Li6&B40(3) possess an AE of 0.11–0.18 eV, corresponding to a gravimetric density of 7.1 wt%. The eight triangular B6 corners are shown as well to be good sites for Li-decoration and H2 adsorption. In a desirable case of Li14&B40-42 H2(8), a total of 42 H2 molecules are adsorbed with an AE of 0.32 eV/H2 for the first 14 H2 and 0.12 eV/H2 for the third 14 H2. A maximum gravimetric density of 13.8 wt% is achieved in 8. The Li-B40-nH2 system differs markedly from the previous Li-C60-nH2 and Ti-B40-nH2 complexes.

Experimental and theoretical evidence of an axially chiral borospherene.

Chirality plays an important role in chemistry, biology, and materials science. The recent discovery of the B40(-/0) borospherenes marks the onset of a class of boron-based nanostructures. Here we report the observation of axially chiral borospherene in the B(39)(-) nanocluster on the bases of photoelectron spectroscopy, global minimum searches, and electronic structure calculations. Extensive structural searches in combination with density functional and CCSD(T) calculations show that B(39)(-) has a C3 cage global minimum with a close-lying C2 cage isomer. Both the C3 and C2 B(39)(-) cages are chiral with degenerate enantiomers. The C3 global minimum consists of three hexagons and three heptagons around the vertical C3 axis. The C2 isomer is built on two hexagons on the top and at the bottom of the cage with four heptagons around the waist. Both the C3 and C2 axially chiral isomers of B(39)(-) are present in the experiment and contribute to the observed photoelectron spectrum. The chiral borospherenes also exhibit three-dimensional aromaticity, featuring σ and π double delocalization for all valence electrons. Molecular dynamics simulations reveal that these chiral B(39)(-) cages are structurally fluxional above room temperature, compared to the highly robust D(2d)B40 borospherene. The current findings add chiral members to the borospherene family and indicate the structural diversity of boron-based nanomaterials.

B22– and B23–: All-Boron Analogues of Anthracene and Phenanthrene

Clusters of boron atoms exhibit intriguing size-dependent structures and chemical bonding that are different from bulk boron and may lead to new boron-based nanostructures. We report a combined photoelectron spectroscopic and ab initio study of the 22- and 23-atom boron clusters. The joint experimental and theoretical investigation shows that B(22)(-) and B(23)(-) possess quasi-planar and planar structures, respectively. The quasi-planar B(22)(-) consists of fourteen peripheral atoms and eight interior atoms in a slightly buckled triangular lattice. Chemical bonding analyses of the closed-shell B(22)(2-) species reveal seven delocalized π orbitals, which are similar to those in anthracene. B(23)(-) is a perfectly planar and heart-shaped cluster with a pentagonal cavity and a π-bonding pattern similar to that in phenanthrene. Thus, B(22)(-) and B(23)(-), the largest negatively charged boron clusters that have been characterized experimentally to date, can be viewed as all-boron analogues of anthracene and phenanthrene, respectively. The current work shows not only that boron clusters are planar at very large sizes but also that they continue to yield surprises and novel chemical bonding analogous to specific polycyclic aromatic hydrocarbons.

B12H n and B12F n : planar vs icosahedral structures

Using density functional theory and quantum Monte Carlo calculations, we show that B12Hn and B12Fn (n = 0 to 4) quasi-planar structures are energetically more favorable than the corresponding icosahedral clusters. Moreover, we show that the fully planar B12F6 cluster is more stable than the three-dimensional counterpart. These results open up the possibility of designing larger boron-based nanostructures starting from quasi-planar or fully planar building blocks.

Synthesis of Uniform Diameter Boron-Based Nanostructures Using a Mesoporous Mg−Al2O3 Template and Tests for Superconductivity

Mg incorporated mesoporous alumina with high surface area and narrow pore size distribution was prepared by the sol−gel method to use as a template for the synthesis of boron-based nanostructures by the CVD method. The mesoporous nature of the Mg−Al2O3 was confirmed by low-angle XRD and N2 adsorption analyses. The randomly ordered pores were observed by TEM. The growth of boron-based nanostructures, such as nanowires and nanotubes, over Mg−Al2O3 is evidenced by TEM analysis. Use of BCl3 as the boron source resulted in nanowires of around 20 nm in diameter and several micrometers in length. When using B2H6 as the boron source, the diameter of the obtained nanostructures was in the range 3−4 nm, reflective of the pore diameter of Mg−Al2O3. Further loading of Mg in the form of Rieke Mg by sonication over 1% Mg−Al2O3 resulted in the growth of straight nanotubes with a uniform diameter of 3−4 nm. The NEXAFS of the boron K-edge of purified boron-based nanostructures shows characteristic peaks for the existence ...