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a The crystal structure of 2D hydrogen boride. The solid lines show the unit cell. b Phonon dispersion and density of states of 2D hydrogen boride
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Heat energy in solids is carried by phonons and electrons. However, in most two-dimensional (2D) materials, the contribution from electrons to total thermal conduction is much lower than that for phonons. In this work, through first-principles calculations combined with non-equilibrium Green’s function theory, we studied electron and phonon thermal...
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... phonon and electron thermal conductance in the recently experimentally fabricated 2D hydrogen boride sheet, 27 via a systematic study of electron and phonon quantum transport using first-principles calculation combined with non-equilibrium Green's function theory. The computational details are shown in Methods section and supporting information, Fig. S1. Unlike the usually observed reduction in phonon thermal conductance induced by tensile strain, the orbitally driven electrical thermal conductance exhibits abnormal strain dependence. As carbon's neighbor in the periodic table, boron has been expected to form graphene-like 2D structure borophene for many years. 28-32 2D boron sheets, ...
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... strength and phonon instability The hydrogenated graphene-like borophene, in another word, 2D hydrogen boride, is illustrated in Fig. 1a. Its unit cell consists of 4 hydrogen atoms and 4 boron atoms. It shows a graphene-like honeycomb lattice with a flat plane made from boron atoms, with two layers of hydrogen atoms are decorated on both sides of the B-B bonds. The optimized lattice constants are a = 5.298 Å and b = 2.987 Å. For convenience, we define the B-B bonds ...
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... bridged by the hydrogen atoms as Bond-1, and the B-B bonds without hydrogen bridging as Bond-2. The lengths of Bond-1(r 1 ) and Bond-2 (r 2 ) are 1.82 Å and 1.72 Å, respectively. The B-H bond length was found to be 1.32 Å. The structural parameters are in excellent agreement with previous report. 51 The calculated phonon dispersion is shown in Fig. 1b. Correspondingly, we present atomic motions of vibrational modes in Fig. S2. There is no sign of imaginary frequencies in the phonon dispersion which accordingly confirms the thermodynamic stability of this attractive 2D material. Around the Γ point, there are three acoustic modes, two of them (longitudinal acoustic and transverse ...
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... phonon thermal conductance can be obtained from the phonon non-equilibrium Green's function (NEGF) method based on the calculated force constant matrix. As shown in Fig. S1, the sample is connected to left and right heat reservoirs, which are assumed to be in thermal equilibrium with temperature T H and T C , respectively. The thermal conductance can be described by the Landauer formula: 61 σðTÞ ¼ 1 ...
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... The common structures of borophene allotropes are triangular, hexagonal and triangular-hexagonal mixed structures. [22][23][24] Borophene can be made by various methods, such as chemical vapor decomposition on a metal substrate, molecular beam epitaxy, and liquid exfoliation, to produce 2D at boron. [25][26][27][28][29] In 2015, Mannix et al. 30 successfully prepared wrinkled triangular borophene (2-Pmmn) on Ag (111) surface by experiments. ...
Electric double-layer supercapacitors (EDLCs) have attracted much attention in the energy storage field due to their advantages such as high output power, long service life, safety and high efficiency. However, their low energy density limits their application. Aiming at the problem of the low energy density of EDLCs, improving quantum capacitance (CQ) of electrode materials is an effective strategy. In this paper, we systematically studied the effects of vacancy, doping, and metal atom adsorption on the CQ of borophene using first-principles calculations. The results show that S and N doping greatly enhance the charge accumulation of borophene at positive and negative potential, respectively. The maximum CQ values of S-doped and N-doped borophene are 157.3 μF cm⁻² (0.38 V) and 187.8 μF cm⁻² (−0.24 V), respectively. Both of them can serve as ideal candidates for the positive (S-doped one) and negative (N-doped one) electrodes of EDLCs. Besides, metal Al atom-adsorbed borophene can also effectively enhance the CQ, with a maximum value of 109.1 μF cm⁻².
... HB sheets have been experimentally verified to exhibit excellent solid acid catalytic activity 9,10 , specific metal ion reducibility 11,12 , semimetal electronic properties 13 , highly-sensitive gas-sensor applicability 8 , and light-responsive hydrogen release 14 . Furthermore, theoretical studies have revealed the intriguing electronic 15 , optical, and thermal properties 16,17 of HB sheets, as well as their possible applications in rechargeable Li/Na ion battery electrodes 18,19 , hydrogen release devices 20,21 , reversible hydrogen storage 22 , current limiters 23 , photodetectors 23 , individual amino acid sensors 24 , and anodes for rechargeable potassium-ion batteries with high capacities, low voltages, and high rate-performance 25 . Furthermore, the formation of HB sheets paves the way for the conceptual development of new types of HB materials [26][27][28][29][30][31][32] . ...
Hydrogen boride (HB) sheets are metal-free two-dimensional materials comprising boron and hydrogen in a 1:1 stoichiometric ratio. In spite of the several advancements, the fundamental interactions between HB sheets and discrete molecules remain unclear. Here, we report the adsorption of CO2 and its conversion to CH4 and C2H6 using hydrogen-deficient HB sheets. Although fresh HB sheets did not adsorb CO2, hydrogen-deficient HB sheets reproducibly physisorbed CO2 at 297 K. The adsorption followed the Langmuir model with a saturation coverage of 2.4 × 10−4 mol g−1 and a heat of adsorption of approximately 20 kJ mol−1, which was supported by density functional theory calculations. When heated in a CO2 atmosphere, hydrogen-deficient HB began reacting with CO2 at 423 K. The detection of CH4 and C2H6 as CO2 reaction products in a moist atmosphere indicated that hydrogen-deficient HB promotes C–C coupling and CO2 conversion reactions. Our findings highlight the application potential of HB sheets as catalysts for CO2 conversion. Boron-containing materials have experimentally and theoretically been shown to be promising materials for CO2 capture and conversion. Here, hydrogen-deficient 2D hydrogen boride sheets are shown to physisorb CO2 and promote conversion to methane and ethane.
... The electron contribution to thermal conductivity was relatively less investigated for 2D materials. He et al. [94] predicted high electronic and lattice thermal conductance of 2D hydrogen boride, i.e., hydrogenated graphene-like borophene, through the AGF approach. Specifically, its lattice part is found to be comparable to that of graphene, while the electronic part is almost 10 times of that of graphene, rendering hydrogen boride much more thermally and electrically conductive. ...
Thermal transport properties have attracted extensive research attentions over the past decades. First-principles-based approaches have proved to be very useful for predicting the thermal transport properties of materials and revealing the phonon and electron scattering or propagation mechanisms in materials and devices. In this review, we provide a concise but inclusive discussion on state-of-the-art first-principles thermal modeling methods and notable achievements by these methods over the last decade. A wide range of materials are covered in this review, including two-dimensional materials, superhard materials, metamaterials, and polymers. We also cover the very recent important findings on heat transfer mechanisms informed from first principles, including phonon–electron scattering, higher-order phonon–phonon scattering, and the effect of external electric field on thermal transport. Finally, we discuss the challenges and limitations of state-of-the-art approaches and provide an outlook toward future developments in this area.
... Heat dissipation is the most important factor affecting and limiting the performance of modern electronic devices [31][32][33][34][35][36]. Thus, how divacancies affect heat transport performance of graphene and graphene nanodevices is an important question. ...
The effects of divacancy, including isolated defects and extended line defects (ELD), on the thermal transport properties of graphene nanoribbons (GNRs) are investigated using the Nonequilibrium Green’s function method. Different divacancy defects can effectively tune the thermal transport of GNRs and the thermal conductance is significantly reduced. The phonon scattering of a single divacancy is mostly at high frequencies while the phonon scattering at low frequencies is also strong for randomly distributed multiple divacancies. The collective effect of impurity scattering and boundary scattering is discussed, which makes the defect scattering vary with the boundary condition. The effect on thermal transport properties of a divacancy is also shown to be closely related to the cross section of the defect, the internal structure and the bonding strength inside the defect. Both low frequency and high frequency phonons are scattered by 48, d5d7 and t5t7 ELD. However, the 585 ELD has almost no influence on phonon scattering at low frequency region, resulting in the thermal conductance of GNRs with 585 ELD being 50% higher than that of randomly distributed 585 defects. All these results are valuable for the design and manufacture of graphene nanodevices.
... Hydrogen boride is a 2D material with hydrogen atoms bridging the hexagonal boron network. Recently, He et al calculated the thermal conductance of 2D hydrogen boride [231]. It was found that the lattice thermal conductance in hydrogen boride was comparable as in graphene (4.07 nW K −1 nm 2 versus 4.1 nW K −1 nm 2 ), but electron thermal conductance in hydrogen boride (3.6 nW K −1 nm 2 ) was almost ten times that of graphene. ...
Almost 15 years have gone ever since the discovery of graphene as a single atom layer. Numerous papers have been published to demonstrate its high electron mobility, excellent thermal and mechanical as well as optical properties. We have recently seen more and more applications towards using graphene in commercial products. This paper is an attempt to review and summarize the current status of the research of the thermal properties of graphene and other 2D based materials including the manufacturing and characterization techniques and their applications, especially in electronics and power modules. It is obvious from the review that graphene has penetrated the market and gets more and more applications in commercial electronics thermal management context. In the paper, we also made a critical analysis of how mature the manufacturing processes are; what are the accuracies and challenges with the various characterization techniques and what are the remaining questions and issues left before we see further more applications in this exciting and fascinating field.
Monolayer boron nanosheet, commonly known as borophene, has garnered significant attention in recent years due to its unique structural, electronic, mechanical, and thermal properties. This review paper provides a comprehensive overview of the advancements in the synthetic strategies, tunable properties, and prospective applications of borophene, specifically focusing on its potential in energy storage devices. The review begins by discussing the various synthesis techniques for borophene, including molecular beam epitaxy (MBE), chemical vapor deposition (CVD), and chemical methods, such as ultrasonic exfoliation and thermal decomposition of boron‐containing precursors. The tunable properties of borophene, including its electronic, mechanical, and thermal characteristics, are extensively reviewed, with discussions on its bandgap engineering, plasmonic behavior, and thermal conductivity. Moreover, the potential applications of borophene in energy storage devices, particularly as anode materials in metal‐ion batteries and supercapacitors, along with its prospects in other energy storage systems, such as sodium‐oxygen batteries, are succinctly, discussed. Hence, this review provides valuable insights into the synthesis, properties, and applications of borophene, offering much‐desired guidance for further research and development in this promising area of nanomaterials science.
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Borophene gathered large interest owing to its polymorphism and intriguing properties such as Dirac point, inherent metallicity, etc. but oxidation limits its capabilities. Hydrogenated borophene was recently synthesized experimentally to harness its applications. Motivated by experimental work, in this paper, using first-principles calculations and Boltzmann transport theory, we study the freestanding β 12 borophene nanosheet doped and functionalized with hydrogen (H), lithium (Li), beryllium (Be), and carbon (C) atoms at different β 12 lattice sites. Amongst all possible configurations, we screen two stable candidates, pristine and hydrogenated β 12 borophene nanosheets. Both nanosheets possess dynamic and mechanical stability while the hydrogenated sheet has different anisotropic metallicity compared to pristine sheet leading to enhancement in brittle behaviour. Electronic structure calculations reveal that both nanosheets host dirac cones, while hydrogenation leads to shift and enhancement in tilt of the dirac cones. Further hydrogenation leads to the appearance of additional fermi pockets in the fermi surface. Transport calculations reveals that the lattice thermal conductivity changes from 12.51 to 0.22 Wm ⁻¹ K ⁻¹ (along armchair direction) and from 4.42 to 0.07 Wm ⁻¹ K ⁻¹ (along zigzag direction) upon hydrogenation at room temperature (300 K), demonstrating a large reduction by two orders of magnitude. Such reduction is mainly attributed to decreased phonon mean free path and relaxation time alongwith the enhanced phonon scattering rates stemming from high frequency phonon flat modes in hydrogenated nanosheet. Comparatively larger weighted phase space leads to increased anharmonic scattering in hydrogenated nanosheet contributing to ultra-low lattice thermal conductivity. Consequently, hydrogenated β 12 nanosheet exhibits a comparatively higher thermoelectric figure of merit (∼0.75) at room temperature along armchair direction. Our study demonstrates the effects of functionalization on transport properties of freestanding β 12 borophene nanosheets which can be utilized to enhance the thermoelectric performance in two-dimensional systems and expand the applications of boron-based two-dimensional materials.
A two-dimensional (2D) Dirac semimetal with concomitant superconductivity has been long sought but rarely reported. It is believed that light-element materials have the potential to realize this goal owing to their intrinsic lightweight and metallicity. Here, based on the recently synthesized β 12 hydrogenated borophene, we investigate its counterpart named β 12-B 5 H 3. Our first-principles calculations suggest it has good stability. β 12-B 5 H 3 is a scarce Dirac semimetal demonstrating a strain-tunable phase transition from three Dirac cones to a single Dirac cone. Additionally, β 12-B 5 H 3 is also a superior phonon-mediated superconductor with a superconducting critical temperature of 32.4 K and can be further boosted to 42 K under external strain. The concurrence of Dirac fermions and superconductivity, supplemented with dual tunabilities, reveals β 12-B 5 H 3 is an attractive platform to study either quantum phase transition in 2D Dirac semimetal or the superconductivity or the exotic physics brought about by their interplay.
