Controlled Synthesis of Hollow Cu2‐xTe Nanocrystals Based on the Kirkendall Effect and Their Enhanced CO Gas‐Sensing Properties

This paper develops a facile solution‐based method to synthesize hollow Cu_2‐xTe nanocrystals (NCs) with tunable interior volume based on the Kirkendall effect. Transmission electron microscopy images and time‐dependent absorption spectra reveal the temporal growth process from solid copper nanoparticles to hollow Cu_2‐xTe NCs. Furthermore, the as‐prepared hollow Cu_2‐xTe NCs show enhanced sensitivity for the detection of carbon monoxide (CO), which is often referred to as the “silent killer”. The response and recovery time of the as‐prepared sensor for the detection of 100 ppm CO gas are estimated to be about 21 and 100 s, respectively, which are sufficient to render it a promising candidate for effective CO gas‐sensing applications. Such enhanced performance is achieved owing to the small grain size and large specific area of the hollow nanostructures. Therefore, the obtained hollow NCs based on the Kirkendall effect may have the potential as new functional blocks for high‐performance gas sensors.     

Collaborative Design of Hollow Nanocubes,In Situ Cross‐Linked Binder,and Amorphous Void@SiOx@C as a Three‐Pronged Strategy for Ultrastable Lithium Storage

Although silicon‐based materials are ideal candidate anodes for high energy density lithium‐ion batteries, the large volumetric expansion seriously damages the integrity of the electrodes and impedes commercial processes. Reasonable electrode design based on adjustable structures of silicon and strong binders prepared by a facile method is still a great challenge. Herein, a three‐pronged collaborative strategy via hollow nanocubes, amorphous Void@SiO_x@C, and in situ cross‐linked polyacrylic acid and d ‐sorbitol 3D network binder (c‐PAA‐DS) is adopted to maintain structural/electrode integrality and stability. The all‐integrated c‐PAA‐DS/Void@SiO_x@C electrode delivers excellent mechanical property, which is attributed to ductility of the c‐PAA‐DS binder and high adhesion energy between Void@SiO_x@C and c‐PAA‐DS calculated by density functional theory. Benefiting from the synergistic effect of accommodation of the hollow structure, protection of outer carbon shell, amorphous Void@SiO_x@C, and strong adhesive c‐PAA‐DS binder, c‐PAA‐DS/Void@SiO_x@C shows excellent electrochemical performance. Long cycling stability with a reversible capacity of 696 mAh g^?1 is obtained, as well as tiny capacity decay after 500 cycles at 0.5 A g^?1 and high‐rate performance. The prelithiated Void@SiO_x@C||LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) full cell is also assembled and shows a reversible capacity of 157 mAh g^?1 at 0.5 C, delivering an excellent capacity retention of 94% after 160 cycles.     

Orientation‐Dependent Strain Relaxation and Chemical Functionalization of Graphene on a Cu(111) Foil

Epitaxial graphene grown on single crystal Cu(111) foils by chemical vapor deposition is found to be free of wrinkles and under biaxial compressive strain. The compressive strain in the epitaxial regions (0.25–0.40%) is higher than regions where the graphene is not epitaxial with the underlying surface (0.20–0.25%). This orientation‐dependent strain relaxation is through the loss of local adhesion and the generation of graphene wrinkles. Density functional theory calculations suggest a large frictional force between the epitaxial graphene and the Cu(111) substrate, and this is therefore an energy barrier to the formation of wrinkles in the graphene. Enhanced chemical reactivity is found in epitaxial graphene on Cu(111) foils as compared to graphene on polycrystalline Cu foils for certain chemical reactions. A higher compressive strain possibly favors lowering the formation energy and/or the energy gap between the initial and transition states, either of which can lead to an increase in chemical reactivity.     

In Situ Encapsulating α‐MnS into N,S‐Codoped Nanotube‐Like Carbon as Advanced Anode Material: α → β Phase Transition Promoted Cycling Stability and Superior Li/Na‐Storage Performance in Half/Full Cells

Incorporation of N,S‐codoped nanotube‐like carbon (N,S‐NTC) can endow electrode materials with superior electrochemical properties owing to the unique nanoarchitecture and improved kinetics. Herein, α‐MnS nanoparticles (NPs) are in situ encapsulated into N,S‐NTC, preparing an advanced anode material (α‐MnS@N,S‐NTC) for lithium‐ion/sodium‐ion batteries (LIBs/SIBs). It is for the first time revealed that electrochemical α → β phase transition of MnS NPs during the 1st cycle effectively promotes Li‐storage properties, which is deduced by the studies of ex situ X‐ray diffraction/high‐resolution transmission electron microscopy and electrode kinetics. As a result, the optimized α‐MnS@N,S‐NTC electrode delivers a high Li‐storage capacity (1415 mA h g^?1 at 50 mA g^?1), excellent rate capability (430 mA h g^?1 at 10 A g^?1), and long‐term cycling stability (no obvious capacity decay over 5000 cycles at 1 A g^?1) with retained morphology. In addition, the N,S‐NTC‐based encapsulation plays the key roles on enhancing the electrochemical properties due to its high conductivity and unique 1D nanoarchitecture with excellent protective effects to active MnS NPs. Furthermore, α‐MnS@N,S‐NTC also delivers high Na‐storage capacity (536 mA h g^?1 at 50 mA g^?1) without the occurrence of such α → β phase transition and excellent full‐cell performances as coupling with commercial LiFePO₄ and LiNi_0.6Co_0.2Mn_0.2O₂ cathodes in LIBs as well as Na₃V₂(PO₄)₂O₂F cathode in SIBs.