Synergistic coupling of 0D-2D heterostructure from ZnO and Ti_(3)C_(2)T_(x)MXene-derived TiO_(2)for boosted NO_(2)detection at room temperature

2D MXenes are highly attractive for fabricating high-precision gas sensors operated at room temperature(RT)due to their high surface-to-volume ratio.However,the limited selectivity and low sensitivity are still long-standing challenges for their further applications.Herein,the self-assembly of 0D-2D heterostructure for highly sensitive NO_(2) detection was achieved by integrating ZnO nanoparticles on Ti_(3)C_(2)Tx MXene-derived TiO_(2) nanosheets(designated as ZnO@MTiO_(2)).ZnO nanoparticles can not only act as spacers to prevent the restacking of MTiO_(2) nanosheets and ensure effective transfer for gas molecules,but also enhance the sensitivity of the sensor the through trapping effect on electrons.Meanwhile,MTiO_(2) nanosheets facilitate gas diffusion for rapid sensor response.Benefiting from the synergistic effect of individual components,the ZnO@MTiO_(2)0D-2D heterostructure-based sensors revealed remarkable sensitivity and excellent selectivity to low concentration NO_(2) at RT.This work may facilitate the sensing application of MXene derivative and provide a new avenue for the development of high-performance gas sensors in safety assurance and environmental monitoring.

Engineering and understanding SnS_(0.5)Se_(0.5)@N/S/Se triple-doped carbon nanofibers for enhanced sodium-ion batteries

Tin-based chalcogenides have attracted tremendous attention as an anode material for sodium storage owing to their unique structure and high theoretical capacity. Unfortunately, the large volume change and poor conductivity lead to sluggish reaction kinetics and poor cycling performance. Herein, SnS_(0.5)Se_(0.5)nanoparticles coupled with N/S/Se triple-doped carbon nanofibers(SnS_(0.5)Se_(0.5)@NSSe-C) are designed and synthesized through electrospinning and annealing process. Benefiting from the synergistic effects of SnS_(0.5)Se_(0.5)and NSSe-C, the SnS_(0.5)Se_(0.5)@NSSe-C nanofibers exhibit a high reversible capacity and ultralong cycle life at higher current density for sodium-ion batteries. Furthermore, the sodium storage mechanism and electrochemical reaction kinetics of the SnS_(0.5)Se_(0.5)@NSSe-C composite are characterized by the in-situ measurements. The theoretical calculations further reveal the structural advantages of SnS_(0.5)Se_(0.5)@NSSeC composite, which exhibits a high adsorption energy of Na+. This work can provide a novel idea for the synthesis of ternary tin-based chalcogenides and is beneficial for the investigation of their reaction kinetics.

Recent development of three-dimension printed graphene oxide and MXene-based energy storage devices

The research for three-dimension(3D)printing carbon and carbide energy storage devices has attracted widespread exploration interests.Being designable in structure and materials,graphene oxide(GO)and MXene accompanied with a direct ink writing exhibit a promising prospect for constructing high areal and volume energy density devices.This review not only summarizes the recent advances in 3D printing energy storage devices including printing methods,ink rheological properties,and different energy storage systems,but also discusses the printing methods related to energy storage.In addition,the binder or additive free of two-dimensional carbide materials is quite important for the present electrochemical energy storage devices,which also are presented.

Advancing MXene-based integrated microsystems with microsupercapacitors and/or sensors:Rational design,key progress,and challenging perspectives

The escalating demand for micro/nano-sized devices,such as micro/nano-robots,intelligent portable/wearable microsystems,and implantable medical microdevices,necessitates the expeditious development of integrated microsystems incorporating energy conversion,storage,and consumption.Critical bottlenecks in microscale energy storage/sensors and their integrated systems are being addressed by exploring new technologies and new materials,e.g.,MXene,holding great potential for developing lightweight and deformable integrated microdevices.This review summarizes the latest progress and milestones in the realization of MXene-based micro-supercapacitors(MSCs)and sensor arrays,and thus discusses the design fundamentals and key advancements of MXene-based energy conversion-storageconsumption integrated microsystems.Finally,we outline the key challenges in fabricating MXenebased MSCs/sensors and their self-powered integrated microsystems,which is crucial for their practical applications.Particularly,we illuminate viable solutions to such unsolved issues and highlight the exciting opportunities.

In situ growth of NiSe_(2) nanocrystalline array on graphene for efficient hydrogen evolution reaction

Nickel selenide electrocatalysts for hydrogen evolution reaction(HER)with a high efficiency and a lowcost have a significant potential in the development of water splitting.However,the inferiority of the high overpotential and poor stability restricts their practical applications.Herein,a composite nanostructure consists of ultrasmall NiSe_(2) nanocrystals embedded on graphene by microwave reaction is reported.The prepared NiSe_(2)/reduced graphite oxide(rGO)electrocatalyst exhibited a high HER activity with an overpotential of 158 mV at a current density of 10 mA/cm^(2) and a corresponding moderate Tafel slope of 56 mV/dec in alkaline electrolyte.In addition,a high retention of electrochemical properties(approximately 100%)was demonstrated with an unchangeable microstructure after 100 h of continuous operation.

In Situ Transmission Electron Microscopy and Three-Dimensional Electron Tomography for Catalyst Studies

An in-depth understanding of the catalytic reaction mechanism is the key to designing efficient and stable catalysts. In situ transmission electron microscope(TEM) is the most powerful tool to visualize and analyze the microstructures of catalysts during catalysis. In situ TEM combined with three-dimensional(3D) electron tomography(ET) reconstruction technique enables interrogations of catalysts’ structural dynamics and chemical changes in high temporal and spatial dimensions. In this review, we discuss and summarize the recent advances in in situ TEM together with 3D ET for catalyst studies. Topics include the latest research progress of in situ TEM imaging as well as 3D visualization and quantitative analysis of catalysts. We also pay particular attention to artificial intelligence(AI)-enhanced smart 3D ET. These include deep learning(DL)-based data compression and storage for the analysis of large TEM data, recovery of wedge-shaped information lost in 3D ET reconstructions, and DL models for reducing residual artifacts in 3D reconstructed images. Finally, the challenges and development prospects of current in situ TEM and 3D ET research are discussed.

2.4 V ultrahigh-voltage aqueous MXene-based asymmetric micro-supercapacitors with high volumetric energy density toward a self-sufficient integrated microsystem

Two-dimensional MXenes are key high-capacitance electrode materials for micro-supercapacitors(MSCs)catering to integrated microsystems.However,the narrow electrochemical voltage windows of conventional aqueous electrolytes(≤1.23 V)and symmetric MXene MSCs(typically≤0.6 V)substantially limit their output voltage and energy density.Highly concentrated aqueous electrolytes exhibit lower water molecule activity,which inhibits water splitting and consequently widens the operating voltage window.Herein,we report ultrahigh-voltage aqueous planar asymmetric MSCs(AMSCs)based on a highly concentrated LiCl-gel quasi-solid-state electrolyte with MXene(Ti3C2Tx)as the negative electrode and MnO_(2) nanosheets as the positive electrode(MXene//MnO_(2)-AMSCs).The MXene//MnO_(2)-AMSCs exhibit a high voltage of up to 2.4 V,attaining an ultrahigh volumetric energy density of 53 mWh cm−3.Furthermore,the in-plane geometry and the quasi-solid-state electrolyte enabled excellent mechanical flexibility and performance uniformity in the serially/parallel connected packs of our AMSCs.Notably,the MXene//MnO_(2)-AMSC-based integrated microsystem,in conjunction with solar cells and consumer electronics,could efficiently realize simultaneous energy harvesting,storage,and conversion.The findings of this study provide insights for constructing high-voltage aqueous MXene-based AMSCs as safe and self-sufficient micropower sources in smart integrated microsystems.

高熵MXenes在储能和催化中的应用展望

In less than a decade,MXenes,a family of two-dimensional(2D)transition-metal carbide/nitrides,have pushed the boundaries of electrochemical performance attained by various energy storage devices[1].The all-round excellent achievements of MXene so far are reminiscent of the "graphene era" thanks to their unique features,such as hydrophilicity,conductivity,and redox pseudocapacitance.The functions of MXene could be tuned by modifying the surface functional groups using various chemical treatments like alkalization by KOH or molten-salt synthesis[1].In addition to the functional groups,various permutations and combinations of multiple transition metals are also possible which further enrich the properties of MXenes compared to mono-transition-metal MXenes(MTMs)[1]and boost the structural and oxidation stability for energy storage and catalysis.

Metal-organic frameworks derived flower-like Co_3O_4/nitrogen doped graphite carbon hybrid for high-performance sodium-ion batteries

In this work, a novel flower-like cobalt-based metal organic frameworks(MOFs) self-assembled by Co^(2+) and nicotinic acid have been designed and synthesized. After a simple annealing treatment, Co_3O_4 nanoparticles in-situ decorating on nitrogen doped graphite carbon-sheet(Co_3O_4/NC) were obtained. The resultant Co_3O_4/NC hybrid with unique flower-like structure and ration combination of Co_3O_4 nanoparticles and nitrogen doped graphite carbon, endowing the hybrid with enhanced electrical conductivity,short ion diffusion pathways and rich porosity to the materials, which can largely alleviate the problems of Co_3O_4 such as inferior intrinsic electrical conductivity, sluggish ion kinetics and large volume change upon cycling. When evaluated as anode material for sodium-ion batteries(SIBs), the Co_3O_4/NC hybrid exhibits satisfied reversible capacity(213.9 mAh g^(-1) after 100 cycles at 0.1 A g^(-1) ), excellent rate capability(145.4 m Ah g^(-1) at 2 A g^(-1) and 130.1 mAh g^(-1) at 4 A g^(-1) ) and robust long-term cycling stability(120.1 m Ah g^(-1) after 2000 cycles at 0.5 A g^(-1) ), showing great potential for high-performance SIBs.