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•The effect of interlayer spacing on the catalytic performance of MoS2 is confirmed.•The dependence of interlayer spacing and MoS2 catalytic performance was established for the first ...time.•The catalytic performance of MoS2 can be regulated in an orderly manner by adjusting the interlayer spacing.•The variation of interlayer spacing will improve the electron transfer ability of MoS2 catalytic sites.•More than 20% interlayer spacing expansion greatly improves the catalytic performance of MoS.
The effect of interlayer spacing on the catalytic properties of MoS2 is systematically investigated by the ab-initio calculation. The results show that the expansion of interlayer spacing is beneficial to the catalytic hydrogen evolution when the hydrogen coverage on MoS2 is 25% and 50%. In particular, at 25% hydrogen coverage, the controllable tuning of the catalytic properties of MoS2 can be achieved by orderly tuning the interlayer spacing. When hydrogen coverage is up to 75% and 100%, the negative effect of interlayer spacing on the catalytic hydrogen evolution of MoS2 is negligible. Importantly, the 20% interlayer expansion is a critical state. If the interlayer expansion exceeds 20%, the catalytic properties of MoS2 will be greatly improved, which provides an idea to control the catalytic properties of MoS2 through tuning the interlayer spacing. Finally, the enhanced effect of interlayer expansion on the catalytic properties of MoS2 stems from the fact that the expansion of the interlayer spacing causes the occupancy density of the partially occupied antibonding orbitals near the Fermi level of Mo atoms to increase and move toward the high-energy region, which enhances the electron transfer of Mo.
Ever since the isolation of single-layer graphene in 2004, two-dimensional layered structures have been among the most extensively studied classes of materials. To date, the pool of two-dimensional ...materials (2DMs) continues to grow at an accelerated pace and already covers an extensive range of fascinating and technologically relevant properties. An array of experimental techniques have been developed and used to characterize and understand these properties. In particular, Raman spectroscopy has proven to be a key experimental technique, thanks to its capability to identify minute structural and electronic effects in nondestructive measurements. While high-frequency (HF) intralayer Raman modes have been extensively employed for 2DMs, recent experimental and theoretical progress has demonstrated that low-frequency (LF) interlayer Raman modes are more effective at determining layer numbers and stacking configurations and provide a unique opportunity to study interlayer coupling. These advantages are due to 2DMs’ unique interlayer vibration patterns where each layer behaves as an almost rigidly moving object with restoring forces corresponding to weak interlayer interactions. Compared to HF Raman modes, the relatively small attention originally devoted to LF Raman modes is largely due to their weaker signal and their proximity to the strong Rayleigh line background, which previously made their detection challenging. Recent progress in Raman spectroscopy with technical and hardware upgrades now makes it possible to probe LF modes with a standard single-stage Raman system and has proven crucial to characterize and understand properties of 2DMs. Here, we present a comprehensive and forward-looking review on the current status of exploiting LF Raman modes of 2DMs from both experimental and theoretical perspectives, revealing the fundamental physics and technological significance of LF Raman modes in advancing the field of 2DMs. We review a broad array of materials, with varying thickness and stacking configurations, discuss the effect of in-plane anisotropy, and present a generalized linear chain model and interlayer bond polarizability model to rationalize the experimental findings. We also discuss the instrumental improvements of Raman spectroscopy to enhance and separate LF Raman signals from the Rayleigh line. Finally, we highlight the opportunities and challenges ahead in this fast-developing field.
•Gradational, polymerized C60-coated CNT interlayer for lithium–sulfur batteries.•Perm-selectively ultra-microporous physical barrier with mean pore size of 0.7 nm.•Catalytic immobiliser for ...polysulfides with chemical functionalised degree of 59.3%•Low decay rate of 0.066% per cycle at 5C after 400 cycles.
The electrochemical application of plasma-induced polymerized fullerene (PC60), wherein C60-derived radicals play physical and chemical functions, representing an important frontier in fullerene derivatives. We prepared a dual-functional interlayer of a gradationally PC60-coated carbon nanotube (CNT) matrix, where the population of C60-originating carbon moieties decreased linearly across the CNT@PC60 from the separator to the sulfur electrode in a lithium–sulfur battery (LSB). The three-dimensional CNT@PC60 interlayer acted as both a physical ionic shield, impeding the shuttle effect, and a catalytic immobilizer, enhancing the kinetics of sulfur conversion. The synergistic effectiveness of the dual perm-selective CNT@PC60 interlayers in confining polysulfide species enabled delivery by the LSB with a high specific capacity of 829 mAh g−1 and an ultra-low decay rate of 0.066% per cycle over 400 cycles at 5C. The role of PC60 in this superior electrochemical performance is the different physical and chemical characteristics of the ends of the interlayer. The PC60-rich side acts as a physical barrier with a mean pore size of 0.7 nm, which enables the penetration of lithium ions only without polysulfide intrusion. Meanwhile, the PC60-poor side formed a catalytic immobilizer because of its higher chemical functionalized degree.
MXenes, an emerging class of conductive two-dimensional materials, have been regarded as promising candidates in the field of electrochemical energy storage. The electrochemical performance of their ...representative Ti3C2 T x , where T represents the surface termination group of F, O, or OH, strongly relies on termination-mediated surface functionalization, but an in-depth understanding of the relationship between them remains unresolved. Here, we studied comprehensively the structural feature and electrochemical performance of two kinds of Ti3C2 T x MXenes obtained by etching the Ti3AlC2 precursor in aqueous HF solution at low concentration (6 mol/L) and high concentration of (15 mol/L). A significantly higher capacitance was recognized in a low-concentration HF-etched MXene (Ti3C2 T x –6M) electrode. In situ Raman spectroscopy and X-ray photoelectron spectroscopy demonstrate that Ti3C2 T x –6M has more components of the −O functional group. In combination with X-ray diffraction analysis, low-field 1H nuclear magnetic resonance spectroscopy in terms of relaxation time unambiguously underlines that Ti3C2 T x –6M is capable of accommodating more high-mobility H2O molecules between the Ti3C2 T x interlayers, enabling more hydrogen ions to be more readily accessible to the active sites of Ti3C2 T x –6M. The two main key factors (i.e., high content of −O functional groups that are involved bonding/debonding-induced pseudocapacitance and more high-mobility water intercalated between the MXene interlayers) simultaneously account for the superior capacitance of the Ti3C2 T x –6M electrode. This study provides a guideline for the rational design and construction of high-capacitance MXene and MXene-based hybrid electrodes in aqueous electrolytes.
Sensitive dependence of the electronic structure on the number of layers in few-layer phosphorene raises a question about the true nature of the interlayer interaction in so-called “van der Waals ...(vdW) solids”. We performed quantum Monte Carlo calculations and found that the interlayer interaction in bulk black phosphorus and related few-layer phosphorene is associated with a significant charge redistribution that is incompatible with purely dispersive forces and not captured by density functional theory calculations with different vdW corrected functionals. These findings confirm the necessity of more sophisticated treatment of nonlocal electron correlation in total energy calculations.
Various interlayers developed recently for inserting between the cathode and the anode of Li-S batteries to improve the energy storage performance have been discussed and analyzed.
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...Lithium-sulfur (Li-S) batteries have great potential in next-generation energy storage due to its high theoretical specific capacity and energy density. However, there are several challenges to the practical application of Li-S batteries including the growth of lithium dendrites and the shuttle effect of polysulfide. Introducing interlayeres (freestanding or coated on the separator) is an effective approach to reduce these obstacles and improve the electrochemical performance of Li-S batteries. In this review, we briefly summarize the interlayer materials and structures modified on both cathodic and anodic sides including (i) carbon-based materials, (ii) polymers, (iii) inorganic metal compounds, (iv) metal–organic frameworks, as well as (v) the novel separators in recent years. We also systematically address the fabrication processes, assembling methods, and functions of interlayers for enhancing the performance of Li-S batteries. Furthermore, the prospects and outlooks of the future development of advanced interlayers and separators are also presented.
Although Ti3C2 MXene has shown great potential in energy storage field, poor conductivity and restacking between MXene flakes seriously hinders the maximization of its capacitance. Herein, a new ...strategy to solve the problems is developed. Gallery Al atoms in Ti3AlC2 are partially removed by simple hydrothermal etching to get Ti3C2Tx reserving appropriate Al interlayers (Ti3C2Tx@Al). Ti3C2Tx@Al keeps stable layered structure rather than isolated Ti3C2Tx flakes, which avoids flake restacking. The removal of partial Al frees up space for easy electrolyte infiltration while the reserved Al as “electron bridges” ensures high interlayer conductivity. As a result, the areal capacitance reaches up to 1087 mF cm−2 at 1 mA cm−2 and over 95% capacitance is maintained after 6000 cycles. The all‐solid‐state supercapacitor (ASSS) based on Ti3C2Tx@Al delivers a high capacitance of 242.3 mF cm−2 at 1 mV s−1 and exhibits stable performance at different bending states. Two ASSSs in tandem can light up a light‐emitting diode under the planar or wrapping around an arm. The established strategy provides a new avenue to improve capacitance performances of MXenes.
Gallery Al atoms in Ti3AlC2 are partially removed by simple hydrothermal etching. The removal of Al frees up space for easy electrolyte infiltration while the reserved Al as “electron bridges” ensures high interlayer conductivity. The areal capacitance reaches to 1087 mF cm−2 at 1 mA cm−2. The strategy provides a new avenue to improve capacitance performances of MXenes.
Aqueous Zn-ion batteries present low-cost, safe, and high-energy battery technology but suffer from the lack of suitable cathode materials because of the sluggish intercalation kinetics associated ...with the large size of hydrated zinc ions. Herein we report an effective and general strategy to transform inactive intercalation hosts into efficient Zn
storage materials through intercalation energy tuning. Using MoS
as a model system, we show both experimentally and theoretically that even hosts with an originally poor Zn
diffusivity can allow fast Zn
diffusion. Through simple interlayer spacing and hydrophilicity engineering that can be experimentally achieved by oxygen incorporation, the Zn
diffusivity is boosted by 3 orders of magnitude, effectively enabling the otherwise barely active MoS
to achieve a high capacity of 232 mAh g
, which is 10 times that of its pristine form. The strategy developed in our work can be generally applied for enhancing the ion storage capacity of metal chalcogenides and other layered materials, making them promising cathodes for challenging multivalent ion batteries.
Stacking order has a strong influence on the coupling between the two layers of twisted bilayer graphene (BLG), which in turn determines its physical properties. Here, we report the investigation of ...the interlayer coupling of the epitaxially grown single-crystal 30°-twisted BLG on Cu(111) at the atomic scale. The stacking order and morphology of BLG is controlled by a rationally designed two-step growth process, that is, the thermodynamically controlled nucleation and kinetically controlled growth. The crystal structure of the 30°-twisted bilayer graphene (30°-tBLG) is determined to have quasicrystal-like symmetry. The electronic properties and interlayer coupling of the 30°-tBLG are investigated using scanning tunneling microscopy and spectroscopy. The energy-dependent local density of states with in situ electrostatic doping shows that the electronic states in two graphene layers are decoupled near the Dirac point. A linear dispersion originated from the constituent graphene monolayers is discovered with doubled degeneracy. This study contributes to controlled growth of twist-angle-defined BLG and provides insights on the electronic properties and interlayer coupling in this intriguing system.
This study focuses on one of the bottlenecks facing the concrete 3D printing technology, the lack of proper bonding between the two adjacent layers of 3D printed concrete. Herein, a new polymer ...consisting of black carbon and sulfur was used to glue the two layers together. The experimental results, verified via molecular dynamics and density functional theory calculations, showed a considerable increase in the interlayer bonding strength. Two-fold rise in interlayer tensile strength as well as chemical cohesion depicted by scanning electron microscopy proves this approach to be successful in providing enhanced bonding between two adjacent printed mortar layers without hindering the printing process. The improvement arises from different types of forces in the interlayer region of modified samples, compared to that of the interlayer region of original sample. The uniform surface provided by the hardened polymer is a good substrate for the top layer in addition to extending the time gap between printing layers. This novel method can accelerate the automation of the construction industry, while reducing the costs in terms of both human labor and capital.
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