Understanding the oxidation chemistry of Ti_(3)C_(2)T_(x)(MXene)sheets and their catalytic performances

Transition metal carbides and nitrides(MXenes)nanosheets are attractive two-dimensional(2D)materials,but they suffer from oxidation/degradation issues during storage and/or applications due to their sensitivity to water and oxygen.Despite the great research progress,the exact oxidation kinetics of Ti_(3)C_(2)T_(x)(MXene)and their final products after oxidation are not fully understood.Herein,we systematically tracked the oxidation process of few-layer Ti_(3)C_(2)T_(x) nanosheets in an aqueous solution at room temperature over several weeks.We also studied the oxidation effects on the electrocatalytic properties of Ti_(3)C_(2)T_(x) for hydrogen evolution reaction and found that the overpotential to achieve a current density of 10 mA cm^(-2)increases from 0.435 to 0.877 V after three weeks of degradation,followed by improvement to stabilized values of around 0.40 V after eight weeks.These results suggest that severely oxidized MXene could be a promising candidate for designing efficient catalysts.According to our detailed experimental characterization and theoretical calculations,unlike previous studies,black titanium oxide is formed as the final product in addition to white Ti(IV)oxide and disordered carbons after the complete oxidation of Ti_(3)C_(2)T_(x).This work presents significant advancements in better understanding of 2D Ti_(3)C_(2)T_(x)(MXene)oxidation and enhances the prospects of this material for various applications.

CdS-modified one-dimensional g-C_3N_4 porous nanotubes for efficient visible-light photocatalytic conversion

A heterojunction photocatalyst based on porous tubular g-C3N4 decorated with CdS nanoparticles was fabricated by a facile hydrothermal co-deposition method.The one-dimensional porous structure of g-C3N4 provides a higher specific surface area,enhanced light absorption,and better separation and transport performance of charge carriers along the longitudinal direction,all of which synergistically contribute to the superior photocatalytic activity observed.The significantly enhanced catalytic efficiency is also a benefit originating from the fast transfer of photogenerated electrons and holes between g-C3N4 and CdS through a built-in electric field,which was confirmed by investigating the morphology,structure,optical properties,electrochemical properties,and photocatalytic activities.Photocatalytic degradation of rhodamine B(RhB)and photocatalytic hydrogen evolution reaction were also carried out to investigate its photocatalytic performance.RhB can be degraded completely within 60 min,and the optimum H2 evolution rate of tubular g-C3N4/CdS composite is as high as 71.6μmol h^–1,which is about 16.3 times higher than that of pure bulk g-C3N4.The as-prepared nanostructure would be suitable for treating environmental pollutants as well as for water splitting.

NiFe-based nanostructures on nickel foam as highly efficiently electrocatalysts for oxygen and hydrogen evolution reactions

Water splitting,as an advanced energy conversion technology,consists of two half reactions,including oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).However,the ideal electrocatalysts are noble metal based catalysts.Their high cost and scarcity in earth seriously restrict the large deployments.Ni Fe-based materials have attracted great attention in recent years due to their excellent catalytic properties for OER and HER.Nevertheless,their conductivity and electrochemical stability at high current density are unsatisfactory,resulting in ineffective water splitting due to high impedance and low stability.Recently,a series of catalysts coating Ni Fe-based materials on 3 D nickel foam were found to be extremely stable under the circumstance of high current density.In this review,we summarized the recent advances of NiFe-based materials on nickel foam for OER and HER,respectively,and further provided the perspectives for their future development.

Strategies on the application of stem cells based therapies for the treatment of optic neuropathies

The retinal ganglion cells(RGCs)are not able to regenerate following optic nerve injury resulting in an irreversible vision loss in patients with optic neuropathies including glaucoma.Recent findings in ocular regeneration have opened promising avenues to apply stem cell-based modalities to restore vision in progressive optic neuropathies.Stem cellbased therapies can help to improve retinal regeneration by solving two major problems:(1)by preventing secondary degeneration of RGCs and preserving the remaining vision,and(2)by replacing degenerated RGCs and promoting RGC axon regeneration in the damaged area.

A magnetic field strategy to porous Pt-Ni nanoparticles with predominant (111) facets for enhanced electrocatalytic oxygen reduction

For the first time, we developed porous Pt-Ni alloying nanoparticles with predominant(111) facets under intense magnetic fields. Electrochemical analysis revealed that the Pt-Ni alloying nanoparticles obtained at 2 Tesla exhibited a superior catalytic activity and durability for oxygen reduction reaction. This work demonstrated that the imposition of intense magnetic field could be considered as a new approach for developing efficient alloying electrocatalysts with preferential facets.

A focus review on 3D printing of wearable energy storage devices

Three-dimensional(3D)printing has gained popularity in a variety of applications,particularly in the manufacture of wearable devices.Aided by the large degree of freedom in customizable fabrication,3D printing can cater towards the practical requirements of wearable devices in terms of light weight and flexibility.In particular,this focus review aims to cover the important aspect of wearable energy storage devices(WESDs),which is an essential component of most wearable devices.Herein,the topics discussed are the fundamentals of 3D printing inks used,the optimizing strategies in improving the mechanical and electrochemical properties of wearable devices and the recent developments and challenges of wearable electrochemical systems such as batteries and supercapacitors.It can be expected that,with the development of 3D printing technology,realization of the full potential of WESDs and seamless integration into smart devices also needs further in-depth investigations.

Controllable synthesis of Fe–N4 species for acidic oxygen reduction

Controllable design and synthesis of catalysts with the target active sites are extremely important for their applications such as for the oxygen reduction reaction(ORR)in fuel cells.However,the controllably synthesizing electrocatalysts with a single type of active site still remains a grand challenge.In this study,we developed a facile and scalable method for fabricating highly efficient ORR electrocatalysts with sole atomic Fe-N4 species as the active site.Herein,the use of cost-effective highly porous carbon as the support not only could avoid the aggregation of the atomic Fe species but also a feasible approach to reduce the catalyst cost.The obtained atomic Fe-N4 in activated carbon(aFe@AC)shows excellent ORR activity.Its half-wave potential is 59 mV more negative but 47 mV more positive than that of the commercial Pt/C in acidic and alkaline electrolytes,respectively.The full cell performance test results show that the aFe@AC sample is a promising candidate for direct methanol fuel cells.This study provides a general method to prepare catalysts with a certain type of active site and definite numbers.

Recent advances in flexible alkaline zinc-based batteries:Materials,structures,and perspectives

The development of wearable electronic systems has generated increasing demand for flexible power sources.Alkaline zinc(Zn)-based batteries,as one of the most mature energy storage technologies,have been considered as a promising power source owing to their exceptional safety,low costs,and outstanding electrochemical performance.However,the conventional alkaline Zn-based battery systems face many challenges associated with electrodes and electrolytes,causing low capacity,poor cycle life,and inferior mechanical performance.Recent advances in materials and structure design have enabled the revisitation of the alkaline Zn-based battery technology for applications in flexible electronics.Herein,we summarize the up-to-date works in flexible alkaline Zn-based batteries and analyze the strategies employed to improve battery performance.Firstly,we introduce the three most reported cathode materials(including Ag-based,Ni-based,and Co-based materials)for flexible alkaline Zn-based batteries.Then,challenges and modifications in battery anodes are investigated.Thirdly,the recently advanced gel electrolytes are introduced from their properties,functions as well as advanced fabrications.Finally,recent works and the advantages of sandwich-type,fiber-type and thin film-type flexible batteries are summarized and compared.This review provides insights and guidance for the design of high-performance flexible Zn-based batteries for next-generation electronics.

A review on nanoconfinement engineering of red phosphorus for enhanced Li/Na/K-ion storage performances

Secondary batteries are widely used in energy storage equipment.To obtain high-performance batteries,the development and utilization of electrode materials with cheap price and ideal theoretical gravimetric and volumetric specific capacities have become particularly important.Naturally abundant and low-cost red phosphorus(RP)is recognized as an anode material with great promise because it has a theoretical capacity of 2596 mA h g^(-1) in lithium-ion batteries(LIBs)and sodium-ion batteries(SIBs).However,owing to the inferior discharging,the capacity of pure RP has a fast decay.Nanoconfinement of RP nanoparticles within porous carbon framework is one of the efficient methods to overcome these problems.In this review,we introduce the recent progress of RP confinement into carbon matrix as an energy storage anode material in LIBs,SIBs and potassium-ion batteries(PIBs).The synthetic strategies,lithiation/sodia tion/potassiation mechanism,and the electrochemical performances of RP/carbon composites(RP/C)with kinds of designed structures and P-C and P-O-C bond by kinds of methods are included.Finally,the challenges and perspectives of RP faced in the application development as anodes for LIBs/SIBs/PIBs are covered.This review will strengthen the understanding of composites of RP nanoparticles in porous carbon materials and aid researchers to carry out future work rationally.

More from less:improving solar steam generation by selectively removing a portion of evaporation surface

Using minimal photothermal material to achieve maximum evaporation rate is extremely important for practical applications of interfacial solar evaporation technology.In this work,we found that with the increase in the size of evaporation surfaces,the evaporation rate decreased.Both experimental and numerical simulation results confirmed that when the evaporation surface size increased,the middle portion of the evaporation surface acted as a‘‘dead evaporation zone”with little contribution to water evaporation.Based on this,the middle portion of the evaporation surface was selectively removed,and counterintuitively,both the evaporation rate and vapor output were increased due to the reconfigured and enhanced convection above the entire evaporation surface.As such,this work developed an important strategy to achieve a higher evaporation rate and increased vapour output while using less material.

Advances in haemostatic sponges: Characteristics and the underlying mechanisms for rapid haemostasis

In traumatized patients, the primary cause of mortality is uncontrollable continuous bleeding and unexpected intraoperative bleeding which is likely to increase the risk of complications and surgical failure. High expansion sponges are effective clinical practice for the treatment of wound bleeding (irregular/deep/narrow) that are caused by capillaries, veins and even arterioles as they possess a high liquid absorption ratio so can absorb blood platelets easily in comparison with traditional haemostasis treatments, which involve compression, ligation, or electrical coagulation etc. When in contact with blood, haemostatic sponges can cause platelet adhesion, aggregation, and thrombosis, preventing blood from flowing out from wounds, triggering the release of coagulation factors, causing the blood to form a stable polymerized fibre protein, forming blood clots, and achieving the goal of wound bleeding control. Haemostatic sponges are found in a variety of shapes and sizes. The aim of this review is to facilitate an overview of recent research around haemostatic sponge materials, products, and technology. This paper reviews the synthesis, properties, and characteristics of haemostatic sponges, together with the haemostasis mechanisms of haemostatic sponges (composite materials), such as chitosan, cellulose, gelatin, starch, graphene oxide, hyaluronic acid, alginate, polyethylene glycol, silk fibroin, synthetic polymers silver nanoparticles, zinc oxide nanoparticles, mesoporous silica nanoparticles, and silica nanoparticles. Also, this paper reviews commercial sponges and their properties. In addition to this, we discuss various in-vitro/in-vivo approaches for the evaluation of the effect of sponges on haemostasis .

One-step In-situ Synthesis of Vacancy-rich CoFe2O4@Defective Graphene Hybrids as Bifunctional Oxygen Electrocatalysts for Rechargeable Zn-Air Batteries

Developing efficient catalysts toward both oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)is the core task for rechargeable metal-air batteries.Although integration of two active components should be an effective method to produce the bifunctional catalysts in principle,traditional techniques still can not attain fine tunable surface structure during material-hybridization process.Herein,we present a facile short-time in-situ argon(Ar)plasma strategy to fabricate a high-performance bifunctional hybrid catalyst of vacancy-rich CoFe2O4 synergized with defective graphence(r-CoFe2O4@DG).Reflected by the low voltage gap of 0.79V in two half-reaction measurements,the striking capability to catalyze ORR/OER endows it excellent and durable performance in rechargeable Zn-air batteries,with a maximum power density of 155.2mW/cm^2 and robust stablility(up to 60h).Further experimental and theoretical studies validate its remarkable bifunctional energetics root from plasma-induced surface vacancy defects and interfacial charge polarization between DG and CoFe2O4.

Nano-confined ammonia borane for chemical hydrogen storage

There is a great demand for a sufficient and sustainable energy supply. Hence, the search for applicable hydrogen storage materials is extremely important owing to the diversified merits of hydrogen energy. In this regard, ammonia borane （NH3BH3, AB） containing 19.6wt-% hydrogen has been considered as a promising material for hydrogen storage applications to realize the ＂hydrogen economy＂, but with limits from slow kinetics of hydrogen release and by-product of trace gases such as ammonia and borazine. In this review, we introduce the recent research on AB, regarding to the nanoconfinement effect on improving the kinetics at a relatively low temperature and the prevention/reduction of undesirable gas formation.

Self-assembly fabrication of lignin-derived carbon with dual heteroatoms doping for high-performance supercapacitor

Renewable and low-cost biomass is an ideal sustainable alternative to petroleum-based resources,but producing biomass-based carbon electrode with high performances remains a challenge.Herein,we propose a facile self-assembly strategy to fabricate a biomass-derived N,S co-doping carbon electrode from lignosulfonate without any activation or template process.Taking advantage of the coordination between Fe ions and lignosulfonate,the resultant carbon exhibits a spherical structure with abundant graphitized nanosheets,leading to a high specific surface area with rational pore structure,which are beneficial to the electron/ion transport and storage.The high contents of doping N(8.47 wt%)and S(2.56 wt%)significantly boost the electrochemical performances.As a supercapacitor electrode,the carbon material displays high specific capacitance of 390 F g^(-1),excellent cycling stability and high energy density of 14.7 W h kg^(-1)at a power density of 450 W kg^(-1).This study provides a potential strategy for synthesizing cost-effective heteroatom-doped carbon materials from biomass with abundant functional groups and heteroatom sources,such as chitosan,collagen,and gelatin.

Copper nanowires decorated with TiO_(2−x) from MXene for enhanced electrocatalytic nitrogen oxidation into nitrate under vacuum assistance

The green synthesis of nitrate(NO_(3)^(−))via electrocatalytic nitrogen oxidation reaction(NOR)is a promising strategy for artificial nitrogen fixation,which shows great advantages than traditional nitrate synthesis based on Haber–Bosch and Ostwald processes.But the poor N_(2)absorption,high bond energy of N≡N(941 kJ·mol^(−1)),and competing multi-electron-transfer oxygen evolution reaction(OER)limit the activity and selectivity.Herein,we fabricated MXene-derived irregular TiO_(2)−x nanoparticles anchored Cu nanowires(Cu-NWs)electrode for efficient electrocatalytic nitrogen oxidation,which exhibits a NO_(3)−yield of 62.50μg·h^(−1)·mgcat^(−1)and a Faradaic efficiency(FE)of 22.04%,and a significantly enhanced NO_(3)−yield of 92.63μg·h^(−1)·mgcat^(−1),and a FE of 40.58%under vacuum assistance.The TiO_(2)−x/Cu-NWs electrode also shows excellent reproducibility and stability under optimal experimental conditions.Moreover,a Zn-N_(2)reaction device was assembled with TiO_(2−x)/Cu-NWs as an anode and Zn plate as a cathode,obtaining an extremely high NO_(3)−yield of 156.25μg·h^(−1)·mgcat^(−1).The Zn-nitrate battery shows an open circuit voltage(OCV)of 1.35 V.This work provides novel strategies for enhancing the performance of ambient N_(2)oxidation to obtain higher NO_(3)^(−)yield.

van der Waals type II carbon nitride homojunctions for visible light photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution reaction(PC-HER)provides a solution to energy crisis and environmental pollution.Herein,different graphitic carbon nitride(g-C_(3)N_(4))-based van der Waals(vdW)type II homojunctions have been fabricated and g-C_(3)N_(4)/Kdoped g-C_(3)N_(4)nanosheets have an outstanding PC-HER rate of 1,243μmol·h^(−1)·g^(−1)under visible light,higher than that of bulk g-C_(3)N_(4),doped g-C_(3)N_(4)nanosheets,and mixed nanosheets.The enhanced PC-HER performance can be ascribed to the cooperative effects of the shortened bandgap,enlarged specific surface area,matched type II energy band structure,“face to face”vdW charge interaction,and peculiarly partite positions of the conduction and valence bands in different layers.Besides,the type II junctions were found superior to binary type II junction.This study highlights the synergistic effect of different strategies in improving the PC-HER capacities of g-C_(3)N_(4),especially the application of particular vdW junctions,and provides new insights to the structures and mechanism.

Size effect of semiconductor quantum wells in excitonic spin generation under drift

The excitonic spin polarization in dependence of the size of semiconductor quantum well(QW)was investigated by observing the two different circular polarizations of photoluminescence(PL).From the measurements of PL in QWs,it was found that there is a difference between the two different polarization conditions,which is caused by spindependent phase-space filling.The PL spin polarization was estimated from the signals of the left and right circularly polarized PL and was found to depend on the size of the wells as well as on the strength of the bias field.The effects of the size of the well and applied electric field on the excitonic PL spin polarization were studied.

Asymmetrical Obstacles Enable Unilateral Inertial Focusing and Separation in Sinusoidal Microchannel

Inertial microfluidics uses the intrinsic fluid inertia in confined channels to manipulate the particles and cells in a simple,high-throughput,and precise manner.Inertial focusing in a straight channel results in several equilibrium positions within the cross sections.Introducing channel curvature and adjusting the cross-sectional aspect ratio and shape can modify inertial focusing positions and can reduce the number of equilibrium positions.In this work,we introduce an innovative way to adjust the inertial focusing and reduce equilibrium positions by embedding asymmetrical obstacle microstructures.We demonstrated that asymmetrical concave obstacles could break the symmetry of original inertial focusing positions,resulting in unilateral focusing.In addition,we characterized the influence of obstacle size and 3 asymmetrical obstacle patterns on unilateral inertial focusing.Finally,we applied differential unilateral focusing on the separation of 10-and 15-μm particles and isolation of brain cancer cells(U87MG)from white blood cells(WBCs),respectively.The results indicated an excellent cancer cell recovery of 96.4%and WBC rejection ratio of 98.81%.After single processing,the purity of the cancer cells was dramatically enhanced from 1.01%to 90.13%,with an 89.24-fold enrichment.We believe that embedding asymmetric concave microobstacles is a new strategy to achieve unilateral inertial focusing and separation in curved channels.