Textured Asymmetric Membrane Electrode Assemblies of Piezoelectric Phosphorene and Ti_(3)C_(2)T_(x)MXene Heterostructures for Enhanced Electrochemical Stability and Kinetics in LIBs

Black phosphorus with a superior theoretical capacity(2596 mAh g^(-1))and high conductivity is regarded as one of the powerful candidates for lithium-ion battery(LIB)anode materials,whereas the severe volume expansion and sluggish kinetics still impede its applications in LIBs.By contrast,the exfoliated two-dimensional phosphorene owns negligible volume variation,and its intrinsic piezoelectricity is considered to be beneficial to the Li-ion transfer kinetics,while its positive influence has not been discussed yet.Herein,a phosphorene/MXene heterostructure-textured nanopiezocomposite is proposed with even phosphorene distribution and enhanced piezo-electrochemical coupling as an applicable free-standing asymmetric membrane electrode beyond the skin effect for enhanced Li-ion storage.The experimental and simulation analysis reveals that the embedded phosphorene nanosheets not only provide abundant active sites for Li-ions,but also endow the nanocomposite with favorable piezoelectricity,thus promoting the Li-ion transfer kinetics by generating the piezoelectric field serving as an extra accelerator.By waltzing with the MXene framework,the optimized electrode exhibits enhanced kinetics and stability,achieving stable cycling performances for 1,000 cycles at 2 A g^(-1),and delivering a high reversible capacity of 524 m Ah g^(-1)at-20℃,indicating the positive influence of the structural merits of self-assembled nanopiezocomposites on promoting stability and kinetics.

3D Printing of NiCoP/Ti3C2 MXene Architectures for Energy Storage Devices with High Areal and Volumetric Energy Density

Designing high-performance electrodes via 3D printing for advanced energy storage is appealing but remains challenging.In normal cases,light-weight carbonaceous materials harnessing excellent electrical conductivity have served as electrode candidates.However,they struggle with undermined areal and volumetric energy density of supercapacitor devices,thereby greatly impeding the practical applications.Herein,we demonstrate the in situ coupling of NiCoP bimetallic phosphide and Ti3C2 MXene to build up heavy NCPM electrodes affording tunable mass loading throughout 3D printing technology.The resolution of prints reaches 50μm and the thickness of device electrodes is ca.4 mm.Thus-printed electrode possessing robust open framework synergizes favorable capacitance of NiCoP and excellent conductivity of MXene,readily achieving a high areal and volumetric capacitance of 20 F cm^-2 and 137 F cm^-3 even at a high mass loading of^46.3 mg cm^-2.Accordingly,an asymmetric supercapacitor full cell assembled with 3D-printed NCPM as a positive electrode and 3D-printed activated carbon as a negative electrode harvests remarkable areal and volumetric energy density of 0.89 mWh cm^-2 and 2.2 mWh cm^-3,outperforming the most of state-of-the-art carbon-based supercapacitors.The present work is anticipated to offer a viable solution toward the customized construction of multifunctional architectures via 3D printing for high-energy-density energy storage systems.

Bio-templated formation of defect-abundant VS2 as a bifunctional material toward high-performance hydrogen evolution reactions and lithium-sulfur batteries

Transition metal chalcogenides have nowadays garnered burgeoning interest owing to their fascinating electronic and catalytic properties,thus possessing great implications for energy conversion and storage applications.In this regard,their controllable synthesis in a large scale at low cost has readily become a focus of research.Herein we report diatomite-template generic and scalable production of VS2 and other transition metal sulfides targeting emerging energy conversion and storage applications.The conformal growth of VS2over diatomite template would endow them with defect-abundant features.Throughout detailed experimental investigation in combination with theoretical simulation,we reveal that the enriched active sites/sulfur vacancies of thus-derived VS2 architectures would pose positive impacts on the catalytic performance such in electrocatalytic hydrogen evolution reactions.We further show that the favorable electrical conductivity and highly exposed sites of VS2 hold promise for serving as sulfur host in the realm of Li-S batteries.Our work offers new insights into the templated and customized synthesis of defect-rich sulfides in a scalable fashion to benefit multifunctional energy applications.

Applications of 2D-Layered Palladium Diselenide and Its van der Waals Heterostructures in Electronics and Optoelectronics

The rapid development of two-dimensional(2D)transition-metal dichalcogenides has been possible owing to their special structures and remarkable properties.In particular,palladium diselenide(PdSe_(2))with a novel pentagonal structure and unique physical characteristics have recently attracted extensive research inter-est.Consequently,tremendous research progress has been achieved regarding the physics,chemistry,and electronics of PdSe_(2).Accordingly,in this review,we recapitulate and summarize the most recent research on PdSe_(2),including its structure,properties,synthesis,and appli-cations.First,a mechanical exfoliation method to obtain PdSe_(2) nanosheets is introduced,and large-area synthesis strate-gies are explained with respect to chemical vapor deposition and metal selenization.Next,the electronic and optoelectronic properties of PdSe_(2) and related hetero-structures,such as field-effect transistors,photodetectors,sensors,and thermoelec-tric devices,are discussed.Subsequently,the integration of systems into infrared image sensors on the basis of PdSe_(2) van der Waals heterostructures is explored.Finally,future opportunities are highlighted to serve as a general guide for physicists,chemists,materials scientists,and engineers.Therefore,this com-prehensive review may shed light on the research conducted by the 2D material community.

Applications of Carbon Nanotubes in the Internet of Things Era

The post-Moore's era has boosted the progress in carbon nanotube-based transistors.Indeed,the 5 G communication and cloud computing stimulate the research in applications of carbon nanotubes in electronic devices.In this perspective,we deliver the readers with the latest trends in carbon nanotube research,including high-frequency transistors,biomedical sensors and actuators,brain–machine interfaces,and flexible logic devices and energy storages.Future opportunities are given for calling on scientists and engineers into the emerging topics.

High-throughput computational screening of oxide double perovskites for optoelectronic and photocatalysis applications

Oxide double perovskites A2 B’B"O6 are a class of emerging materials in the fields of optoelectronics and catalysis.Due to the chemical flexibilities of perovskite structures,there are multiple elemental combinations of cations A,B’,and B",which leading to tremendous candidates.In this study,we comprehensively screened stable oxide double perovskite A2 B’B"O6 from a pool of 2,018 perovskite candidates using a high-throughput computational approach.By considering a tolerance factor(t)-octahedral factor(μ) phase diagram,138 candidates with Fm 3 m, P21/c,and R3 c phases were selected and systematically studied via first-principles calculations based on density functional theory.The screening procedure finally predicted the existence of 21 stable perovskites,and 14 among them have never been reported.Verification with existing experimental results demonstrates that the prediction accuracy for perovskite formability is approximately 90%.The predicted oxide double perovskites exhibit quasi-direct bandgaps ranging from 0 to 4.4 eV with a significantly small direct-indirect bandgap difference,balanced electron and hole effective masses,and strong optical absorptions.The newly predicted oxide double perovskites may enlarge the pool of material candidates for applications in optoelectronics and photocatalysis.This study provides a route for computational screening of novel perovskites for functional applications.

Biomass Template Derived Boron/Oxygen Co-Doped Carbon Particles as Advanced Anodes for Potassium-Ion Batteries

Among various anode candidates for potassium-ion batteries,carbonaceous materials have attracted significant attention due to their overwhelming advantages including cost-effectiveness and environmental benignity.However,the inferior specific capacity and the sluggish reaction kinetics hinder the further development in this realm.Herein,we report biomass templated synthesis of boron/oxygen heteroatom co-doped carbon particles(BO-CPs)via direct plasma-enhanced chemical vapor deposition.With the combined advantages of abundant active sites,large accessible surface area,and functional groups,BO-CP anode exhibits high reversible specific capacity(426.5 mAh g^(-1)at 0.1 A g^(-1))and excellent rate performance(166.5 mAh g^(-1)at 5 A g^(-1)).The K-ion storage mechanism is probed by operando Raman spectroscopy,ex situ X-ray photoelectron spectroscopy/electrochemical impedance spectroscopy,galvanostatic intermittent titration technique measurements,and theoretical simulations.The synergistic effect of boron and oxygen co-doping greatly facilitates the performance of carbon-based anode,wherein boron dopant improves the conductivity of carbon framework and the oxygen dopant affords ample active sites and thus harvests additional specific capacity.This work is anticipated to propel the development of high-performance anode materials for emerging energy storage devices.

High performance columnar-like Fe2O3@carbon composite anode via yolk@shell structural design

Conversion-type reaction anode materials with high specific capacity are attractive candidates to improve lithium ion batteries(LIBs), yet the rapid capacity fading and poor rate capability caused by drastic volume change and low electronic conductivity greatly hinder their practical applications. To circumvent these issues, the successful design of yolk@shell Fe2 O3@C hybrid composed of a columnar-like Fe2O3 core within a hollow cavity completely surrounded by a thin, self-supported carbon(C) shell is presented as an anode for high-performance LIBs. This yolk@shell structure allows each Fe2O3 core to swell upon lithiation without deforming the carbon shell. This preserves the structural and electrical integrity against pulverization, as revealed by in situ transmission electron microscopy(TEM) measurement. Benefiting from these structural advantages, the resulting electrode exhibits a high reversible capacity(1013 m Ah g-1 after80 cycles at 0.2 A g-1), outstanding rate capability(710 m Ah g-1 at 8 A g-1) and superior cycling stability(800 m Ah g-1 after 300 cycles at 4 A g-1). A Li-ion full cell using prelithiated yolk@shell Fe2 O3@C hybrid as the anode and commercial Li CoO2(LCO) as the cathode demonstrates impressive cycling stability with a capacity retention of 84.5% after 100 cycles at 1 C rate, holding great promise for future practical applications.

Spatially Bandgap-Graded Mo S2（1-x）Se2x Homojunctions for Self-Powered Visible–Near-Infrared Phototransistors

Ternary transition metal dichalcogenide alloys with spatially graded bandgaps are an emerging class of two-dimensional materials with unique features,which opens up new potential for device applications.Here,visible–near-infrared and self-powered phototransistors based on spatially bandgap-graded MoS2(1−x)Se2x alloys,synthesized by a simple and controllable chemical solution deposition method,are reported.The graded bandgaps,arising from the spatial grading of Se composition and thickness within a single domain,are tuned from 1.83 to 1.73 eV,leading to the formation of a homojunction with a builtin electric field.Consequently,a strong and sensitive gate-modulated photovoltaic effect is demonstrated,enabling the homojunction phototransistors at zero bias to deliver a photoresponsivity of 311 mA W−1,a specific detectivity up to^10^11 Jones,and an on/off ratio up to^10^4.Remarkably,when illuminated by the lights ranging from 405 to 808 nm,the biased devices yield a champion photoresponsivity of 191.5 A W−1,a specific detectivity up to^1012 Jones,a photoconductive gain of 10^6–10^7,and a photoresponsive time in the order of^50 ms.These results provide a simple and competitive solution to the bandgap engineering of two-dimensional materials for device applications without the need for p–n junctions.

A novel one-step reaction sodium-sulfur battery with high areal sulfur loading on hierarchical porous carbon fiber

Room temperature sodium-sulfur(RT Na-S)batteries are gaining extensive attention as attractive alternatives for large-scale energy storage,due to low cost and high abundancy of sodium and sulfur in nature.However,the dilemmas regarding soluble polysulfides(Na_(2)Sn,4<n<8)and the inferior reaction kinetics limit their practical application.To address these issues,we report the activated porous carbon fibers(APCF)with small sulfur molecules(S2-4)confined in ultramicropores,to achieve a reversible single-step reaction in RT Na-S batteries.The mechanism is investigated by the in situ UV/vis spectroscopy,which demonstrates Na2S is the only product during the whole discharge process.Moreover,the hierarchical carbon structure can enhance areal sulfur loading without sacrificing the capacity due to thorough contact between electrolyte and sulfur electrode.As a consequence,the APCF electrode with 38 wt%sulfur(APCF-38S)delivers a high initial reversible specific capacity of 1412 mAh g^(-1) and 10.6mAh cm^(-2)(avg.areal sulfur loading:7.5 mg cm^(-2))at 0.1 C(1C=1675 mA g^(-1)),revealing high degree of sulfur utilization.This study provides a new strategy for the development of high areal capacity RT Na-S batteries.

Insight into the reaction mechanism of sulfur chains adjustable polymer cathode for high-loading lithium-organosulfur batteries

Small molecules with adjustable sulfur atoms in the confined structure were acted as precursor for the synthesis of polymer cathodes for lithium-organosulfur batteries.Among them,poly(diallyl tetrasulfide)(PDATtS)delivered a high capacity of 700 mAh g^(-1),stable capacity retention of 85%after 300 cycles,high areal capacity~4 m Ah cm^(-2) for electrode with up to 10.3 mg cm^(-2) loading.New insight into the reaction mechanism of PDATtS electrode that radicals arisen from the homolytic cleavage of S-S bond in PDATtS reacted with Li+to generate thiolates(RSLi)and insoluble lithium sulfides(Li_(2)S)or lithium disulfide(Li_(2)S_(2))was clearly verified by in-situ UV/Vis spectroscopy,nuclear magnetic resonance(NMR)studies and density-functional theory(DFT)calculations.Therefore,based on the unique reaction mechanism,problems of rapid capacity fading due to the formation of soluble polysulfide intermediates and their serious shuttle effect in conventional lithium-sulfur(Li-S)batteries was totally avoided,realizing the dendrite-free lithium sulfur batteries.This study sets new trends for avenues of further research to advance Li-S battery technologies.

Confining TiO_2 Nanotubes in PECVD-Enabled Graphene Capsules Toward Ultrafast K-Ion Storage: In Situ TEM/XRD Study and DFT Analysis

Titanium dioxide(TiO2) has gained burgeoning attention for potassium-ion storage because of its large theoretical capacity,wide availability,and environmental benignity.Nevertheless,the inherently poor conductivity gives rise to its sluggish reaction kinetics and inferior rate capability.Here,we report the direct graphene growth over TiO2 nanotubes by virtue of chemical vapor deposition.Such conformal graphene coatings effectively enhance the conductive environment and well accommodate the volume change of TiO2 upon potassiation/depotassiation.When paired with an activated carbon cathode,the graphene-armored TiO2 nanotubes allow the potassium-ion hybrid capacitor full cells to harvest an energy/power density of 81.2 Wh kg-1/3746.6 W kg-1.We further employ in situ transmis sion electron microscopy and ope rando X-ray diffraction to probe the potassium-ion storage behavior.This work offers a viable and versatile solution to the anode design and in situ probing of potassium storage technologies that is readily promising for practical applications.

Non-precious metal electrocatalysts for two-electron oxygen electrochemistry: Mechanisms, progress, and outlooks

Hydrogen peroxide (H_(2)O_(2)) is a valuable chemical for a wide variety of applications. The environmentally friendly production route of the electrochemical reduction of O_(2)to H_(2)O_(2) has become an attractive alternative to the traditional anthraquinone process. The efficiency of electrosynthesis process depends considerably on the availability of cost-effective catalysts with high selectivity, activity, and stability.Currently, there are many outstanding issues in the preparation of highly selective catalysts, the exploration of the interface electrolysis environment, and the construction of electrolysis devices, which have led to extensive research efforts. Distinct from the existing few comprehensive review articles on H_(2)O_(2) production by two-electron oxygen reduction, the present review first explains the principle of the oxygen reduction reaction and then highlights recent advances in the regulation and control strategies of different types of catalysts. Key factors of electrode structure and device design are discussed. In addition,we highlight the promising co-production combination of this system with renewable energy or energy storage systems. This review can help introduce the potential of oxygen reduction electrochemical production of high-flux H_(2)O_(2) to the commercial market.

Direct insight into sulfiphilicity-lithiophilicity design of bifunctional heteroatom-doped graphene mediator toward durable Li-S batteries

The practical applications of lithium-sulfur(Li-S)battery have been greatly hindered by the severe polysulfide shuttle at the cathode and rampant lithium dendrite growth at the anode.One of the effective solutions deals with concurrent management of both electrodes.Nevertheless,this direction remains in a nascent stage due to a lack of material selection and mechanism exploration.Herein,we devise a temperature-mediated direct chemical vapor deposition strategy to realize the controllable synthesis of three-dimensional boron/nitrogen dual-doped graphene(BNG)particulated architectures,which is employed as a light-weighted and multi-functional mediator for both electrodes in Li-S batteries.Benefiting from the“sulfiphilic”and“lithiophilic”features,the BNG modified separator not only enables boosted kinetics of polysulfide transformation to mitigate the shuttle effect but also endows uniform lithium deposition to suppress the dendritic growth.Theoretical calculations in combination with electro-kinetic tests and operando Raman analysis further elucidate the favorable sulfur and lithium electrochemistry of BNG at a molecular level.This work offers direct insight into the mediator design via controllable synthesis of graphene materials to tackle the fundamental challenges of Li-S batteries.

Polypyrrole reinforced ZIF-67 with modulated facet exposure and billion-fold electrical conductivity enhancement towards robust photocatalytic CO_(2) reduction

The implementation of metal organic frameworks(MOFs) as the co-catalysts in hybrid photocatalytic systems puts requirements on both their charge-carrying capability and solvent stability. In the current study, in order to simultaneously promote the electrical conductivity and water stability of ZIF-67, an insitu monomer trapping strategy is deployed to synthesize polypyrrole(PPy)-reinforced ZIF-67 ensembles.Through coordination modulation, the incremental addition of pyrrole monomers enables to alter the crystal morphology of ZIF-67 from rhombic dodecahedra to truncated rhombic dodecahedra, and further to cubes. Upon polymerization, the resulted composite, in comparison to ZIF-67, demonstrates a billionfold conductivity enhancement, much improved chemical stability in pronated solvents, as well as largely retained specific surface area and porosity, enabling it functioning as an outstanding co-catalyst for catalyzing robust photocatalytic CO_(2) reduction. Furthermore, a PPy-mediated electron harvest and relay mechanism is proposed for rationalizing the enhanced photocatalytic performance.

Designing solar-cell absorber materials through computational high-throughput screening

Although the efficiency of CH3 NH3 PI3 has been refreshed to 25.2%,stability and toxicity remain the main challenges for its applications.The search for novel solar-cell absorbers that are highly stable,non-toxic,inexpensive,and highly efficient is now a viable research focus.In this review,we summarize our recent research into the high-throughput screening and materials design of solar-cell absorbers,including single perovskites,double perovskites,and materials beyond Perovskites.BazrS3(single perovskite),Ba2 BiNbS6(double perovskite),HgAl2 Se4(spinel),and IrSb3(skutterudite)were discovered to be potential candidates in terms of their high stabilities,appropriate bandgaps,small carrier effective masses,and strong optical absorption.

Design of experiments unravels insights into selective ethylene or methane production on evaporated Cu catalysts

As a highly tempting technology to close the carbon cycle,electrochemical CO_(2)reduction calls for the development of highly efficient and durable electrocatalysts.In the current study,Design of Experiments utilizing the response surface method is exploited to predict the optimal process variables for preparing high-performance Cu catalysts,unraveling that the selectivity towards methane or ethylene can be simply modulated by varying the evaporation parameters,among which the Cu film thickness is the most pivotal factor to determine the product selectivity.The predicted optimal catalyst with a low Cu thickness affords a high methane Faradaic efficiency of 70.6%at the partial current density of 211.8 m A cm^(-2),whereas that of a high Cu thickness achieves a high ethylene selectivity of 66.8%at267.2 m A cm^(-2)in the flow cell.Further structure-performance correlation and in-situ electrospectroscopic measurements attribute the high methane selectivity to isolated Cu clusters with low packing density and monotonous lattice structure,and the high ethylene efficiency to coalesced Cu nanoparticles with rich grain boundaries and lattice defects.The high Cu packing density and crystallographic diversity is of essence to promoting C–C coupling by stabilizing*CO and suppressing*H coverage on the catalyst surface.This work highlights the implementation of scientific and mathematic methods to uncover optimal catalysts and mechanistic understandings toward selective electrochemical CO_(2)reduction.

Synergistic effect from coaxially integrated CNTs@MoS_(2)/MoO_(2) composite enables fast and stable lithium storage

Molybdenum oxide/sulfide materials are extensively evaluated as high-capacity anode candidates for lithium ion batteries.However,they suffer from rapid capacity decay and poor kinetics.Herein,we report on synergistic effect from structurally integrated coaxial CNTs@MoS_(2)/MoO_(2) composite material on lithium storage,in which MoS_(2)/MoO_(2) nanosheets are conformally decorated on carbon nanotubes(CNTs).In-situ synchrotron X-ray diffraction measurement is performed to elucidate synergistic effect among three MoS_(2),MoO_(2) and CNTs components for lithium storage.Reaction mechanism exploration reveals that the MoO_(2) component undergoes reversible Li^(+)intercalation via forming a stable Li_(0.98) MoO_(2) phase over a voltage range of 3.0 to 0.01 V vs.Li^(+)/Li,without experiencing the conversion reaction into metallic Mo,which contributes to long-term stability during charge/discharge cycles.Meanwhile,lithium storage of MoS_(2) is through lithium and sulfur reversible reaction after the initial conversion reaction of lithiated MoS_(2) forming Li_(2)S and Mo.The CNTs component enhances electronic conductivity and structural stability by minimizing volume change and reaction strains in the CNTs@MoS_(2)/MoO_(2) composite anode.A desired 68.2%capacity retention upon 2000 cycles at 10 A/g has been demonstrated for the CNTs@MoS_(2)/MoO_(2) anode,revealing prominent reaction kinetics and structural stability for fast and stable lithium storage,superior to various Mo-based anode materials previously reported.The findings from this study,with the unique insight into the role of structural integrity in combining MoS_(2)/MoO_(2) materials with the CNTs substrate,offers a strategy for designing composite anode materials for superior lithium storage performance.

Cobalt coordination with pyridines in sulfurized polyacrylonitrile cathodes to form conductive pathways and catalytic M-N4S sites for accelerated Li-S kinetics

Sulfurized polyacrylonitrile(SPAN)represents a unique class of cathode material for lithium sulfur(Li-S)batteries as it eradicates the polysulfides shuttling issue in carbonate-based electrolyte.However,due to the essential chemical S-linking and organic nature of SPAN,the active mass percentage and rate capability are two bottleneck issues preventing its ultimate deployment outside of laboratories.In the current work,aiming to endow both the charge conductivity and catalytic activity to SPAN for maximizing the redox kinetics of S conversion,a freestanding nanofibrous SPAN cathode embedding conductive CNTs and atomically dispersed Co centers is fabricated via multivariate electrospinning.While the CNTs enable dramatically enhancing the fiber conductivity and generating mesoscopic porosity for facilitating charge and mass transportation,the cross-linking of SPAN by Co-N_(4) S motifs creates extra charge conduction pathways and further serves as the catalytic active sites for expediting redox S conversion.As a result,an extraordinary Li-SPAN performance is achieved with a high specific capacity up to 1856 mAh g^(-1)@0.2 C,a superb rate capability up to 10 C,and an ultra-long battery life up to 1500 cycles@1 C.Consequently,our study here provides insights into the adoption of coordination chemistry to maximize the sulfur utilization by ensuring a more complete redox conversion from SPAN to Li2 S,and vice versa.

Applications of MXenes in human-like sensors and actuators

Human beings perceive the world through the senses of sight,hearing,smell,taste,touch,space,and balance.The first five senses are prerequisites for people to live.The sensing organs upload information to the nervous systems,including the brain,for interpreting the surrounding environment.Then,the brain sends commands to muscles reflexively to react to stimuli,including light,gas,chemicals,sound,and pressure.MXene,as an emerging two-dimensional material,has been intensively adopted in the applications of various sensors and actuators.In this review,we update the sensors to mimic five primary senses and actuators for stimulating muscles,which employ MXene-based film,membrane,and composite with other functional materials.First,a brief introduction is delivered for the structure,properties,and synthesis methods of MXenes.Then,we feed the readers the recent reports on the MXene-derived image sensors as artificial retinas,gas sensors,chemical biosensors,acoustic devices,and tactile sensors for electronic skin.Besides,the actuators of MXene-based composite are introduced.Eventually,future opportunities are given to MXene research based on the requirements of artificial intelligence and humanoid robot,which may induce prospects in accompanying healthcare and biomedical engineering applications.