Synthesis, properties, and applications of graphene oxide/reduced graphene oxide and their nanocomposites

Thanks to their remarkable mechanical, electrical, thermal, and barrier properties, graphene-based nanocomposites have been a hot area of research in the past decade. Because of their simple top-down synthesis, graphene oxide (GO) and reduced graphene oxide (rGO) have opened new possibilities for gas barrier, membrane separation, and stimuli-response characteristics in nanocomposites. Herein, we review the synthesis techniques most commonly used to produce these graphene derivatives, discuss how synthesis affects their key material properties, and highlight some examples of nanocomposites with unique and impressive properties. We specifically highlight their performances in separation applications, stimuli-responsive materials, anti-corrosion coatings, and energy storage. Finally, we discuss the outlook and remaining challenges in the field of practical industrial-scale production and use of graphene-derivative-based polymer nanocomposites.

Scaled-up synthesis of defect-rich layered double hydroxide monolayers without organic species for efficient oxygen evolution reaction

The scaled-up synthesis of organic-free monolayer nanomaterials is highly desirable,especially in obtaining green energy by electrocatalysis.In this study,a method for the scaled-up synthesis of the series of monolayer layered double hydroxides(LDHs)without the addition of organic solvents is reported via the separate nucleation and aging steps process.The resulting monolayer LDHs with the thicknesses of less than 1 nm showed a narrow thickness distribution.X-ray absorption fine-structure revealed that monolayer NiFe-LDH nanosheets have a number of oxygen and metal vacancies defects.As a practical application,monolayer NiFe-LDH nanosheets containing defects showed an enhanced electrocatalytic water oxidation activity compared with that of bulk NiFe-LDH.Density functional theory calculations uncovered that excellent catalytic activity is attributed to vacancies defects.The proposed method is an economical and universally applicable strategy for the scaled-up production of monolayer LDHs.

Coassembled ionic liquid/laponite hybrids as effective CO2 adsorbents

Hybrid adsorbents for COcapture were prepared by coassembling laponite（LP） nanosheets and 1-nbutyl-3-methylimidazolium chloride（BMIMCl）. The prepared BMIMCl/LP layered hybrids were systematically characterized. The interlayer distance of the BMIMCl/LP layered hybrids expanded with an increasing concentration of BMIMCl, indicating that cumulative BMIMCl was intercalated into the LP layers. The efficiency of BMIMCl toward COcapture was significantly enhanced after it was immobilized within LP layers.

Ultra-transparent nanostructured coatings via flow-induced one-step coassembly

Polyvinyl alcohol(PVA)/laponite(LP)nanocomposite coatings were fabricated via a facile one-step coassembly process.The formed nanocoatings contain a high concentration of LP nanosheets,which can be well aligned along the substrate surface during the coassembly process.Due to the highly orientated structure,the flexible nanocoatings exhibit ultra-high transparency and superior mechanical properties,and can also act as excellent gas barriers.Such nanocoatings can be exceptional candidates for a variety of applications,such as food packaging.

Novel Membranes Regenerated from Blends of Cellulose/Gluten Using Ethylenediamine/Potassium Thiocyanate Solvent System

Current industrial methods for dissolution of cellulose in making regenerated cellulose products are relatively expensive,toxic and dangerous and have environmental problems coming with the hazard chemical wastes.To solve these problems,a novel ethylenediamine and potassium thiocyanate(ED/KSCN)solvent system was developed,that is economical,ecofriendly,and highly efficient.The ED/KSCN solvent system was proven to be a suitable solvent for fabricating cellulose(blended with other polymers)membranes.In this study,gluten was used to develop nonporous membranes with cellulose.The method of casting these membranes provided better ones than the former researchers’techniques.These composite membranes’physical and mechanical properties were studied by analysis of morphology,viscosity,crystallinity,thermal behaviors,tensile properties and water absorption of membranes.Results showed that membranes are nonporous,uniform,strong,flexible,ecofriendly and renewable.Mechanical and physical properties were influenced by the ratio of cellulose/gluten.By blending 40% gluten,the tensile strength of cellulose membrane dropped to 15.89 MPa from 35.11 MPa.However,its elongation at break increased from 35.3% to 57.02% accordingly.

A Study on Nanoparticle Aerosol Filtration via Different Fibrous Filters by Using CFD Approach

Fibrous filters such as nonwoven media are generally characterized by their collection efficiency and pressure drop. The traditional computational studies in this area typically based on unrealistic over-simplified geometries with the fibers placed in a lattice perpendicular to the flow. This paper describes the filter properties made of different Nonwoven materials by using Computational Fluid Dynamics （CFD） approach. In this study, for the first time, a virtual 3- D web is generated based on the fiber orientation information obtaining from analyzing microscopic images of both long-fiber and short-fiber nonwoven structures. Pressure drop and collection efflcicucy of our virtual filter are simulated and compared with the previous analytical and numerical models as well as experiment.

Edge atomic Fe sites decorated porous graphitic carbon as an efficient bifunctional oxygen catalyst for Zinc-air batteries

The development of advanced bifunctional oxygen electrocatalysts for oxygen reduction and evolution reactions(ORR and OER) is critical to the practical application of zinc-air batteries(ZABs). Herein, a silica-assisted method is reported to integrate numerous accessible edge Fe-Nx sites into porous graphitic carbon(named Fe-N-G) for achieving highly active and robust oxygen electrocatalysis. Silica facilitates the formation of edge Fe-Nx sites and dense graphitic domains in carbon by inhibiting iron aggregation.The purification process creates a well-developed mass transfer channel for Fe-N-G. Consequently,Fe-N-G delivers a half-wave potential of 0.859 V in ORR and an overpotential of 344 m V at10 m A cm^(-2)in OER. During long-term operation, the graphitic layers protect edge Fe-Nx sites from demetallation in ORR and synergize with Fe OOH species endowing Fe-N-G with enhanced OER activity.Density functional theory calculations reveal that the edge Fe-Nx site is superior to the in-plane Fe-Nx site in terms of OH* dissociation in ORR and OOH* formation in OER. The constructed ZAB based on Fe-N-G cathode shows a higher peak power density of 133 m W cm^(-2)and more stable cycling performance than Pt/C + RuO2counterparts. This work provides a novel strategy to obtain high-efficiency bifunctional oxygen electrocatalysts through space mediation.

Li₂MnSiO₄/Carbon Composite Nanofibers as a High-Capacity Cathode Material for Li-Ion Batteries

Li2MnSiO4 has an extremely high theoretical capacity of 332 mAh?g?1. However, only around half of this capacity has been realized in practice and the capacity retention during cycling is also low. In this study, Li2MnSiO4/carbon composite nanofibers were prepared by a combination of electrospinning and heat treatment. The one-dimensional continuous carbon nanofiber matrix serves as long-distance conductive pathways for both electrons and ions. The composite nanofiber structure avoids the aggregation of Li2MnSiO4 particles, which in turn enhances the electrode conductivity and promotes the reaction kinetics. The resultant Li2MnSiO4/carbon composite nanofibers were used as the cathode material for Li-ion batteries, and they delivered high charge and discharge capacities of 218 and 185 mAh?g?1, respectively, at the second cycle. In addition, the capacity retention of Li2MnSiO4 at the first 20th cycles increased from 37% to 54% in composite nanofibers.

Frequency-dependent dielectric constant prediction of polymers using machine learning

The dielectric constant(ϵ)is a critical parameter utilized in the design of polymeric dielectrics for energy storage capacitors,microelectronic devices,and high-voltage insulations.However,agile discovery of polymer dielectrics with desirableϵremains a challenge,especially for high-energy,high-temperature applications.To aid accelerated polymer dielectrics discovery,we have developed a machine-learning(ML)-based model to instantly and accurately predict the frequency-dependentϵof polymers with the frequency range spanning 15 orders of magnitude.Our model is trained using a dataset of 1210 experimentally measuredϵvalues at different frequencies,an advanced polymer fingerprinting scheme and the Gaussian process regression algorithm.

High-Performance 3-D Fiber Network Composite Electrolyte Enabled with Li-Ion Conducting Nanofibers and Amorphous PEO-Based Cross-Linked Polymer for Ambient All-Solid-State Lithium-Metal Batteries

Solid electrolytes have gained attention recently for the development of next-generation Li-ion batteries since they can fun-damentally improve the battery stability and safety.Among various types of solid electrolytes,composite solid electrolytes(CSEs)exhibit both high ionic conductivity and excellent interfacial contact with the electrodes.Incorporating active nanofib-ers into the polymer matrix demonstrates an effective method to fabricate CSEs.However,current CSEs based on traditional poly(ethylene oxide)(PEO)polymer suffer from the poor ionic conductivity of PEO and agglomeration effect of inorganic fillers at high concentrations,which limit further improvements in Li+conductivity and electrochemical stability.Herein,we synthesize a novel PEO based cross-linked polymer(CLP)as the polymer matrix with naturally amorphous structure and high room-temperature ionic conductivity of 2.40×10^(−4)S cm^(−1).Li_(0.3)La_(0.557)TiO_(3)(LLTO)nanofibers are incorporated into the CLP matrix to form composite solid electrolytes,achieving enhanced ionic conductivity without showing filler agglomeration.The high content of Li-conductive nanofibers improves the mechanical strength,ensures the conductive network,and increases the total Li+conductivity to 3.31×10^(−4)S cm^(−1).The all-solid-state Li|LiFePO_(4)batteries with LLTO nanofiber-incorporated CSEs are able to deliver attractive specific capacity of 147 mAh g^(−1)at room temperature,and no evident dendrite is found at the anode/electrolyte interface after 100 cycles.

Polyacrylonitrile Nanofber‑Reinforced Flexible Single‑Ion Conducting Polymer Electrolyte for High‑Performance,Room‑Temperature All‑Solid‑State Li‑Metal Batteries

Single-ion conducting polymer electrolytes(SIPEs)can be formed by anchoring charge delocalized anions on the side chains of a crosslinked polymer matrix,thereby eliminating the severe concentration polarization efect in conventional dual-ion polymer electrolytes.Addition of a plasticizer into the polymer matrix confers advantages of both liquid and solid electrolytes.However,plasticized SIPEs usually face a trade-of between conductivity and mechanical strength.With insufcient strength,potentially there is short-circuiting failure during cycling.To address this challenge,a simple and mechanicallyrobust SIPE was developed by crosslinking monomer lithium(4-styrenesulfonyl)(trifuoromethylsulfonyl)imide(LiSTFSI)and crosslinker poly(ethylene glycol)diacrylate(PEGDA),with plasticizer propylene carbonate(PC),on electrospun polyacrylonitrile nanofbers(PAN-NFs).The well-fabricated polymer matrix provided fast and efective Li^(+) conductive pathways with a remarkable ionic conductivity of 8.09×10^(-4) S cm^(−1) and a superior lithium-ion transference number close to unity(t_(Li+)=0.92).The introduction of PAN-NFs not only improved the mechanical strength and fexibility but also endowed the plasticized SIPE with a wide electrochemical stability window(4.9 V vs.Li^(+)/Li)and better cycling stability.Superior longterm lithium cycling stability and dynamic interfacial compatibility were demonstrated by lithium symmetric cell testing.Most importantly,the assembled all-solid-state Li metal batteries showed stable cycling performance and remarkable rate capability both in low and high current densities.Therefore,this straightforward and mechanically reinforced SIPE exhibits great potential in the development of advanced all-solid-state Li-metal batteries.

Molecular simulation-guided and physics-informed mechanistic modeling of multifunctional polymers

Polymeric materials have a broad range of mechanical and physical properties.They have been widely used in material science,biomedical engineering,chemical engineering,and mechanical engineering.The introduction of active elements into the soft matrix of polymers has enabled much more diversified functionalities of polymeric materials,such as self-healing,electroactive,magnetosensitive,pH-responsive,and many others.To further enable applications of these multifunctional polymers,a mechanistic modeling method is required and of great significance,as it can provide links between materials’micro/nano-structures and their macroscopic mechanical behaviors.Towards this goal,molecular simulation plays an important role in understanding the deformation and evolution of polymer networks under external loads and stimuli.These molecular insights provide physical guidance in the formulation of mechanistic-based continuum models for multifunctional polymers.In this perspective,we present a molecular simulation-guided and physics-informed modeling framework for polymeric materials.Firstly,the physical theory for polymer chains and their networks is briefly introduced.It serves as the foundation for mechanistic-models of polymers,linking their chemistry,physics,and mechanics together.Secondly,the deformation of the polymer network is used to derive the strain energy density functions.Thus,the corresponding continuum models can capture the intrinsic deformation mechanisms of polymer networks.We then highlight several representative examples across multiphysics coupling problems to describe in detail for this proposed framework.Last but not least,we discuss potential challenges and opportunities in the modeling of multifunctional polymers for future research directions.

TIME AND POLING HISTORY DEPENDENT ENERGY STORAGE AND DISCHARGE BEHAVIORS IN POLY(VINYLIDENE FLUORIDE-CO-HEXAFLUOROPROPYLENE) RANDOM COPOLYMERS

We studied cycle time （0.01-10 s with triangular input waves） and poling history （continuous versus fresh poling） dependent electric energy storage and discharge behaviors in poly（vinylidene fluoride-co-hexafluoropropylene） [P（VDF- HFP）] films using the electric displacement -- the electric field （D-E） hysteresis loop measurements. Since the permanent dipoles in PVDF are orientational in nature, it is generally considered that both charging and discharging processes should be time and poling history dependent. Intriguingly, our experimental results showed that the charging process depended heavily on the cycle time and the prior poling history, and thus the D-E hysteresis loops had different shapes accordingly. However, the discharged energy density did not change no matter how the D-E loop shape varied due to different measurements. This experimental result could be explained in terms of reversible and irreversible polarizations. The reversible polarization could be charged and discharged fairly quickly （〈 5 ms for each process）, while the irreversible polarization depended heavily on the poling time and the prior poling history. This study suggests that it is only meaningful to compare the discharged energy density for PVDF and its copolymer films when different cycle times and poling histories are used.

Templated synthesis of crystalline mesoporous CeO_(2) with organosilane-containing polymers: balancing porosity, crystallinity and catalytic activity

We report the synthesis of ordered mesoporous ceria(mCeO_(2))with highly crystallinity and thermal stability using hybrid polymer templates consisting of organosilanes.Those organosilane-containing polymers can convert into silica-like nanostructures that further serve as thermally stable and mechanically strong templates to prevent the collapse of mesoporous frameworks during thermal-induced crystallization.Using a simple evaporation-induced self-assembly process,control of the interaction between templates and metal precursors allows the co-self-assembly of polymer micelles and Ce^(3+)ions to form uniform porous structures.The porosity is well-retained after calcination up to 900℃.After the thermal engineering at 700℃ for 12 h(mCeO_(2)-700-12 h),mCeO_(2) still has a specific surface area of 96 m^(2) g^(−1) with a pore size of 14 nm.mCeO_(2) is demonstrated to be active for electrochemical oxidation of sulfite.mCeO_(2)-700-12 h with a perfect balance of crystallinity and porosity shows the fastest intrinsic activity that is about 84 times more active than bulk CeO_(2) and 5 times more active than mCeO_(2) that has a lower crystallinity.

Two-dimensional MXenes:New frontier of wearable and flexible electronics

Wearable electronics offer incredible benefits in mobile healthcare monitoring,sensing,portable energy harvesting and storage,human-machine interactions,etc.,due to the evolution of rigid electronics structure to flexible and stretchable devices.Lately,transition metal carbides and nitrides(MXenes)are highly regarded as a group of thriving two-dimensional nanomaterials and extraordinary building blocks for emerging flexible electronics platforms because of their excellent electrical conductivity,enriched surface functionalities,and large surface area.This article reviews the most recent developments in MXene-enabled flexible electronics for wearable electronics.Several MXeneenabled electronic devices designed on a nanometric scale are highlighted by drawing attention to widely developed nonstructural attributes,including 3D configured devices,textile and planer substrates,bioinspired structures,and printed materials.Furthermore,the unique progress of these nanodevices is highlighted by representative applications in healthcare,energy,electromagnetic interference(EMI)shielding,and humanoid control of machines.The emerging prospects of MXene nanomaterials as a key frontier in nextgeneration wearable electronics are envisioned and the design challenges of these electronic systems are also discussed,followed by proposed solutions.

Nanofiber Materials for Lithium‑Ion Batteries

The lithium-ion(Li-ion)battery has received considerable attention in the field of energy conversion and storage due to its high energy density and eco-friendliness.Significant academic and commercial progress has been made in Li-ion battery technologies.One area of advancement has been the addition of nanofiber materials to Li-ion batteries due to their unique and desirable structural features including large aspect ratios,high surface areas,controllable chemical compositions,and abundant composite forms.In the past few decades,considerable research efforts have been devoted to constructing advanced nanofiber materials possessing conductive networks to facilitate efficient electron transport and large specific surface areas to support catalytically active sites,both for the purpose of boosting electrochemical performance.Herein,we focus on recent advancements of nanofiber materials with carefully designed structures and enhanced electrochemical properties for use in Li-ion batteries.The synthesis,structure,and properties of nanofiber cathodes,anodes,separators,and electrolytes,and their applications in Li-ion batteries are discussed.The research challenges and prospects of nanofiber materials in Li-ion battery applications are delineated.

Gamma(ɣ)‑MnO_(2)/rGO Fibered Cathode Fabrication from Wet Spinning and Dip Coating Techniques for Cable‑Shaped Zn‑Ion Batteries

Cable/fber-shaped Zn-ion batteries are designed to power wearable electronics that require high fexibility to operate on human body.However,one of technical challenges of these devices is the complexity and high cost for manufacturing fbered cathode.In this work,we demonstrated gamma manganese oxide(ɣ-MnO_(2))/reduced graphene oxide(rGO)fbered cathode fabrication using facile and cost-efective fber production and active material coating techniques.Specifcally,rGO fbers were fabricated via wet spinning,followed by chemical reduction with hydroiodic acid(HI).The synthesized rGO fber bundle was then dip-coated with a mixture ofɣ-MnO_(2),carbon black or multi-walled carbon nanotubes,and xanthan gum or polyvinylidene fuoride binder to obtainɣ-MnO_(2)/rGO fbered cathode.We studied the efect of binders and conductive materials on physical properties and electrochemical performance of the fbered cathode.It was found that hydrophobic binder had more benefts than hydrophilic binder by providing higher active material loading,better coating layer homogeneity,and more stable electrochemical performance.Cable-shaped Zn-ion batteries(CSZIBs)were then assembled by using theɣ-MnO_(2)/rGO fbered cathode,Zn wire anode,and xanthan gum polymeric gel electrolyte with 2 M ZnSO_(4) and 0.2 M MnSO_(4) salts without a separator.We investigated the battery assembling procedure on a glass slide(prototype ZIB)and in a plastic tube(cable-shaped ZIB),and evaluated their electrochemical performance.The CSZIB showed promising maximum capacity of~230 mAh/g with moderate cycling stability(80%capacity retention after 200 cycles)and high fexibility by maintaining the potential after consecutive pressing for 200 times under controlled pressing distance,duration,and testing speed.Finally,we explored ion intercalation behaviours and proposed a H^(+)/Zn^(2+)co-intercalation mechanism in ZIB withɣ-MnO_(2) active material.

Advanced Flexible Carbon‑Based Current Collector for Zinc Storage

Carbon cloth(CC)-based electrodes have attracted extensive attention for next-generation wearable energy-storage devices due to their excellent electrical conductivity and mechanical flexibility.However,the application of conventional CC-based electrodes for zinc(Zn)storage severely hinders Zn ion transport and induces deleterious Zn dendrite growth,resulting in poor electrochemical reliability.Herein,a novel oxygen plasma-treated carbon cloth(OPCC)is rationally designed as a current collector for flexible hybrid Zn ion supercapacitors(ZISs).The modified interface of OPCC with abundant oxygenated groups enables enhanced electrolyte wettability and uniform superficial electric field distribution.A prolonged working lifespan for Zn electrodeposition is achieved by the OPCC due to the improved interfacial kinetics and homogenized ion gradient.The as-prepared hybrid ZIS also delivers excellent cycling endurance(98.5%capacity retention for 1500 cycles)with outstanding operation stability under various extreme conditions.This facile surface modification strategy provides a new way for developing future flexible electrodes for wearable electronic products.

Electrospun Nanofibers Enabled Advanced Lithium−Sulfur Batteries

CONSPECTUS:Lithium−sulfur(Li−S)batteries have been extensively studied because both S and Li have high theoretical capacities,and S is abundant and environmentally friendly.However,their practical applications have been hindered by several challenges,including poor conductivity of S and its intermediates,shuttle effects of polysulfides,Li dendrite growth,etc.Tremendous efforts have been taken to tackle these issues by developing functional S host materials,separators and interlayers,solid-state electrolytes,etc.,during the past decade.Compared to structurally complicated materials and intricate preparation approaches,electrospun nanofibers have obtained tremendous interests since they have played an extremely crucial role in improving the overall performance of Li−S cells due to their unique features such as easy-setup,substantial surface area,outstanding flexibility,high porosity,excellent mechanical properties,etc.