ZnS has great potentials as an anode for lithium storage because of its high theoretical capacity and resource abundance; however, the large volume expansion accompanied with structural collapse and low conductivity of ZnS cause severe capacity fading and inferior rate capability during lithium storage. Herein, 0D-2D ZnS nanodots/Ti3C2Tx MXene hybrids are prepared by anchoring ZnS nanodots on Ti3C2Tx MXene nanosheets through coordination modulation between MXene and MOF precursor (ZIF-8) followed with sulfidation. The MXene substrate coupled with the ZnS nanodots can synergistically accommodate volume variation of ZnS over charge–discharge to realize stable cyclability. As revealed by XPS characterizations and DFT calculations, the strong interfacial interaction between ZnS nanodots and MXene nanosheets can boost fast electron/lithium-ion transfer to achieve excellent electrochemical activity and kinetics for lithium storage. Thereby, the as-prepared ZnS nanodots/MXene hybrid exhibits a high capacity of 726.8 mAh g−1 at 30 mA g−1, superior cyclic stability (462.8 mAh g−1 after 1000 cycles at 0.5 A g−1), and excellent rate performance. The present results provide new insights into the understanding of the lithium storage mechanism of ZnS and the revealing of the effects of interfacial interaction on lithium storage performance enhancement.
Owing to lightweight, abundant reserves, low cost, and nontoxicity, B-based two-dimensional (2D) materials, e.g., borophene, exhibit great potential as new anode materials with higher energy density for Li-ion batteries (LIBs). However, exfoliation of borophene from the Ag substrate remains the most daunting challenge due to their strong interfacial interactions, significantly restricting its practical applications. In this study, through first-principles swarm-intelligence structure calculations, we have found several Boron-rich boron nitride B x N materials (x = 2, 3, 4, and 5) with increased stability and weakened interactions with the Ag(111) substrate compared with δ6-borophene. A high cohesive energy and superior dynamical, thermodynamic, and mechanical stability provide strong feasibility for their experimental synthesis. The obtained B x N materials exhibit a high mechanical strength (94−226 N/m) and low interfacial bonding with the Ag substrate, from −0.043 to −0.054 eV Å −2 , significantly smaller than that of δ6-borophene. Among them, B 3 N and B 5 N exhibit not only a remarkably high storage capacity of 1805−3153 mAh/g but also a low barrier energy and open-circuit voltage. Moreover, B 2 N showed a cross-sheet motion with a low barrier of 0.24 eV, which is unique compared with the in-plane diffusion in most other 2D electrode materials restricted by their quasi-flat geometry. B x N also exhibits excellent cyclability with improved metallic conductivity upon Li-ion intercalation, showing great potential in LIB applications. This study opens up a new avenue to explore B-rich 2D electrode materials in energy applications and provide instructive insights into borophene functionalization and exfoliation.
Developing covalent organic frameworks (COFs) with good
electrical
conductivity is essential to widen their range of practical applications.
Thermal annealing is known to be a facile approach for enhancing conductivity.
However, at higher temperatures, most COFs undergo amorphization and/or
thermal degradation because of the lack of linker rigidity and physicochemical
stability. Here, we report the synthesis of a conductive benzoxazole-linked
COF/carbon hybrid material (BCOF-600C) by simple thermal annealing.
The fused-aromatic benzoxazole and biphenyl building units endow the
resulting COF with excellent physicochemical stability against high
temperatures and strong acids/bases. This allows heat treatment to
further enhance electrical conductivity with minimal structural alteration.
The robust crystalline structure with periodically incorporated nitrogen
atoms allowed platinum (Pt) atoms to be atomically integrated into
the channel walls of BCOF-600C. The resulting electrocatalyst with
well-defined active sites exhibited superior catalytic performance
toward hydrogen evolution in acidic media.
The linker swing motion in the zeolitic imidazolate framework ZIF-90 is investigated by density functional theory (DFT) calculation, molecular dynamics (MD) and grandcanonical Monte Carlo (GCMC) simulations. The relation between the terminal aldehyde group rotation and the linker swing motion is revealed. The extremely high activation energy of the linker swing motion in ZIF-90 can be attributed to the asymmetric geometry and electron distribution of aldehyde groups. The change in the gate structure resulting from the linker rotation is used to understand the guest adsorption in ZIF-90. This study shows that it is possible to tune the linker swing motion and then the properties of ZIF-90 by manipulating the terminal group rotation. The results highlight
Understanding guest diffusion in nanoporous host–guest systems is crucial in the efficient design of metal–organic frameworks (MOFs) for chemical separation and drug delivery applications.
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