Search

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 BxN 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 BxN 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 A-2, significantly smaller than that of δ6-borophene. Among them, B3N and B5N exhibit not only a remarkably high storage capacity of 1805-3153 mAh/g but also a low barrier energy and open-circuit voltage. Moreover, B2N 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. BxN 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.

Powder densification for specified shaped metal-organic frameworks (MOFs) is desirable for most applications. The obtainment of such properties is challenging, one of which is the rapid crystal-to-amorphous transition (framework collapse) of MOFs under pressure. Herein, we found that the residual guests of the MOF-5 synthesis process could form binding groups based on the hydrogen-bonding networks of water. The improved processability and ease of compression, which did not promote rapid structure collapse, can be achieved in the guest-loaded MOF-5. Correspondingly, enhanced volumetric specific surface area and methane uptake of MOF-5 were obtained. This work focuses on a commonly neglected but positive function of the residual guests in MOFs, besides supporting the framework. MOFs loaded with multiple types of guests show attractive mechanical properties via guest-guest and guest-host interactions for powder densification, highlighting their commercial applications.

Polymers with excellent comprehensive performance toward enhanced stability and mechanical strength are attractive for matrix loading of tunable porous and inherently brittle metal−organic frameworks (MOFs). Polyethersulfone (PES) with high mechanical strength (elastic modulus = ~2.6 GPa) is one of the best polymeric materials widely applied in gas and liquid separations but hindered by its ability to adhere to MOFs surface. The combination of the interface width, porosity, atomic density, and hydrogen bonding number and strength strongly influences MOFs/PES compatibility. ZIF-8 is one of the most frequently investigated MOFs, and exhibits excellent interface compatibility with PES, which is confirmed by both computational and experimental analyses. The desired porosity and adsorption properties of ZIF-8 are retained in ZIF-8/PES composites. This study sheds light on the theoretical understanding and characterization of hybrid material systems with diverse differences between brittle MOFs and stiff polymers.

To date, compared with that of lithium oxygen batteries, the operation of lithium air batteries is still a great challenge due to the highly deteriorated cathode performances in air, including worse discharge capacities and OER/ORR dynamics. Herein, we propose hydroxylated carbon black as an improved deposition support, which not only functions as a conductive agent, but also improves the morphology of the discharge products. These improvements can significantly enhance the discharge properties and chargeability of the gas cathode, particularly in simulated air or ambient air. For example, the hydroxylated carbon black doubles the energy output of the air cathode in ambient air. It is believed that increased defects and hydroxyls on the hydroxylated carbon surface might play an important role. By the first principle calculation, it is revealed that a strong affinity between the hydroxyls and Li2O2 occurs, and this facilitates the nucleation of Li2O2. It is believed that the promoted nucleation can restrain the growth of the discharge products due to the competitive relationship between nucleation and growth of new phase in chemical reactions. Finally, smaller Li2O2 nanosheets formed on the hydroxylated carbon cathode instead of the dense discharge product layer, avoid the block of the porous cathode, thus benefiting the electrochemical performances. These results show that besides developing better catalysts, hydroxylation of carbon matrix is also an effective strategy to enhance the electrochemical performances of the lithium air battery.

A promising lead-free ferroelectric material, Bi0.5Na0.5TiO3 (BNT), was recently proposed as an oxide ion conductor. In a survey of BNT perovskite-structured oxides that exhibit ionic conductive grain, it was found to be highly sensitive to stoichiometry and the synthesis processes. The conduction mechanism and defect properties of these BNT therefore could be greatly influenced. Herein, we show composites made by a ferroelectric matrix of acceptor-doped BNT with a slight amount of Ag2O in which the defect and transport properties could be tailored through different sintering atmospheres. The bulk conductivity increased dramatically by ∼2800 times to 1.36 mS cm−1 at 502 °C.

Bi4Ti3O[Formula: see text]/Bi2S3 heterostructures with enhanced visible light photocatalytic activity are successfully synthesized via a two-step synthesis route based on a sol–gel hydrothermal method and a subsequent hydrothermal-ion exchange reaction technique. The structures, composition, morphologies and light absorption capability of Bi4Ti3O[Formula: see text]/Bi2S3 heterostructures are verified by XRD, XPS, SEM, TEM and UV-Vis diffuse reflectance spectra, respectively. Results indicated that Bi2S3 nanorods are grown on the surface of the spherical structure assembled by criss-cross nanosheets of Bi4Ti3O[Formula: see text] after ion exchange reaction. The photocatalytic tests reveal that the Bi4Ti3O[Formula: see text]/Bi2S3 heterostructures showed much higher photocatalytic activity than pure Bi4Ti3O[Formula: see text] or Bi2S3. The tight interconnection between the two semiconductors will facilitate the photoinduced carriers’ separation. Owing to the easy preparation and excellent property, the obtained Bi4Ti3O[Formula: see text]/Bi2S3 heterostructures may be promising photocatalysts for practical application.