Cooperative catalytic platinum species accelerating polysulfide redox reactions for Li-S batteries

The shuttle effect derived from diffusion of lithium polysulfides(LiPSs) and sluggish redox kinetic bring about poor cycling stability and low utilization of sulfur,which have always been the key challenging issues for the commercial application of lithium-sulfur(Li-S) batteries.Rational design of cathode materials to catalyze Li_(2)S dissociation/nucleation processes is an appealing and valid strategy to develop high-energy practical Li-S batteries.Herein,considering the synergistic effect of bidirectional catalysis on LiPSs conversion and enhanced chemical immobilization for LiPSs by heteroatom doping,Pt nanoparticles loaded on nitrogen-doped carbon spheres(Pt/NCS composites) were constructed as cathode materials.According to the dynamic evolution of Pt catalysts and sulfur species,Pt~0 and Pt^(2+) species were identified as active species for the accelerated dissociation and nucleation of Li_(2)S,respectively.Meanwhile,in-situ Raman results demonstrated the expedited conversion of sulfur species resulted from bidirectional catalysis of active Pt species,corresponding to boosted redox kinetics.Consequently,Pt/NCS cathode exhibited improved long-term cyclability with high initial capacity,along with enhanced rate capability.This work provides a facile approach to construct cathode materials with bidirectional catalysis on Li_(2)S dissociation/nucleation,and sheds light on a more global understanding of the catalytic mechanism of metal catalysts during LiPSs conversion.

2D titanium carbide(MXene) electrodes with lower-F surface for high performance lithium-ion batteries

MXene has shown distinctive advantages as anode materials of lithium-ion batteries. However, local surface chemistry, which was confirmed that can block ion transfer and limit redox reaction, has a significant effect on electrochemical performance. Herein, annealing MXene under hydrogen was employed for removing-F and turning-OH to-O terminations. We demonstrate that it improves the kinetics of Li-ion transport between the electrolyte and electrode. As a result, a lower interfacial charge transfer impedance was obtained. The electrochemical measurement exhibited that a nearly 2-fold increase of specific capacity was achieved for the annealed MXene.

K+alkalization promoted Ca2+intercalation in V2CTx MXene for enhanced Li storage

Although MXenes is highly attractive as anode materials of lithium ion batteries,it sets a bottleneck for higher capacity of the V2CTxMXene due to the limited interlayer space and the derived surface terminations.Herein,the cation intercalation and ion-exchange were well employed to achieve a K+and Ca2+intercalated V2CTxMXene.A larger interlayer distance and low F surface terminations were thereof obtained,which accelerates the ion transport and promotes the delicate surface of V2CTx MXene.As a result,a package of enhanced capacity,rate performance and cyclability can be achieved.Furthermore,the ion exchange approach can be extended to other 2 D layered materials,and both the interlayer control and the surface modification will be achieved.

Engineering Pt heterogeneous catalysts for accelerated liquid–solid redox conversion in Li-S batteries

The shuttle effect caused by soluble lithium polysulfides (LiPSs) deteriorates multiphase transformation reaction kinetics of sulfur species,and gives rise to an unserviceable lithium-sulfur (Li-S) battery.Catalysis,as a process optimization approach,offers an option to eliminate the intrinsic issues.However,exploring and understanding the role of catalysts on electrode reaction remains critical bottlenecks,particularly as they are prone to continuous evolution under complex dynamic environment.Herein,platinum nanoparticles loaded on MXene nanosheets,as sulfur host,and the action of catalysts on the reaction process are investigated via ex-situ monitors upon solid–liquid–solid chemical transformation of sulfur species.These traces confirm that the high performance originates from electron transfer between catalysts and LiPSs,which lowers the nucleation barrier from liquid LiPSs to solid Li_(2)S/Li_(2)S_(2).Further,the accelerated liquid–solid conversion can alleviate the accumulation of LiPSs,and boost the reaction kinetics in Li-S batteries.The findings corroborate the electronic modulation between catalysts and LiPSs,which is a generalizable strategy to optimize energy conversion efficiency of Li-S batteries.

Optimizing the electronic structure of Fe-doped Co_(3)O_(4)supported Ru catalyst via metal-support interaction boosting oxygen evolution reaction and hydrogen evolution reaction

Metal-support interaction(MSI)is an efficient way in heterogeneous catalysis and electrocatalysis to modulate the electronic structure of metal for enhanced catalytic activity.However,there are still great challenges in promoting the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)simultaneously by this way.Herein,Fe-doped Co_(3)O_(4)supported Ru(Ru/FeCo)catalysts are synthesized by MSI strategies to further improve the electrocatalytic activity and stability of the catalysts.The results show that the optimized Ru/FeCo catalyst exhibits the best catalytic performance.The HER and OER tests at10 m A/cm^(2)in 1 mol/L KOH solution show excellent overpotentials of 155 m V and 283 m V,respectively.The activity and stability enhancement can be attributed to the MSI that effectively modify the electronic structure and improve interfacial electron transfer between Ru and Fe-doped Co_(3)O_(4)(FeCo).This work provides an innovative direction for the design of high-efficiency bifunctional electrocatalysts by virtue of the MSI.

Three-dimensional architectures based on carbon nanotube bridged Ti_(2)C MXene nanosheets for Li-S batteries

Lithium-sulfur(Li-S)batteries are promising candidates for high density electrochemical energy storage systems.However,the poor conductivity of S and the shuttle effect of polysulfides are a bottleneck to practical applications.Herein,a three-dimensional architecture,based on carbon nanotube(CNT)bridged Ti_(2)C MXene nanosheets,was constructed as a sulfur host.This architecture was based on Ti atoms,which can chemically absorb polysulfides.The CNTs are highly conductive and intercalate into the MXene nanosheets to prevent their stacking and construct an interspace for polysulfides.This hybrid,as a host of S,can effectively alleviate the shuttle effect through a combination of physical confinement and chemical adsorption.This resulted in an open internal space,which served as a cathode for the loaded S to promote electron transport and enhance electrochemical kinetics of the polysulfide conversion in Li-S batteries.

Identify fine microstructure of multifarious iron oxides via O K-edge EELS spectra

Relying on the electron energy loss spectrum(EELS)of metallic elements to obtain microstructure analysis is an investigation method of the reaction mechanisms of transition metal oxides(TMOs)in catalysis,energy storage and conversion.However,the low signal from K shell owing to insufficient electron beam energy,and the complicated electronic structure in L shell of the metal element restrict the analysis of the coordination environment of the TMOs.Herein,density functional theory(DFT)calculation,Fourier transform(FT)and wavelet transform(WT)were employed to probe the relationship between the four individual peaks in O K-edge spectra of iron oxides and the microstructure information(chemical bonds and atomic coordination).The findings show that the peak amplitude ration is in a linear correlation with the valence state of Fe element,and that the coordination number obtained by radial distribution function(RDF)is favorably linearly correlative with that from the standard coordination structure model.As a result,the quantitative analysis on the change of valence state and atomic coordination in microstructure can be realized by EELS O K-edge spectra.This study establishes EELS O K-edge spectrum as a promising pathway to quantitatively analyze the valence state and atomic coordination information of TMOs,and offers an effective method to conduct microstructure analysis via the EELS spectra of the non-metal element.

Tailoring the surface structure of iron compounds to optimize the selectivity of 3-nitrostyrene hydrogenation reaction over Pt catalyst

Selective hydrogenation of substituted nitroarenes is an important reaction to obtain amines.Supported metal catalysts are wildly used in this reaction because the surface structure of supports can tune the properties of the supported metal nanoparticles(NPs)and promote the selectivity to amines.Herein,Pt NPs were immobilized on Fe OOH,Fe_(3)O_(4)andα-Fe_2O_(3)nanorods to synthesize a series of iron compounds supported Pt catalysts by liquid phase reduction method.Chemoselective hydrogenation of 3-nitrostyrene to 3-aminostyrene was used as probe reaction to evaluate the performance of the catalysts.The results show that Pt/Fe OOH exhibits the highest selectivity and activity.Fe OOH support with pores and-OH groups can tune the electronic structure of Pt NPs.The positive charge of Pt NPs supported on Fe OOH is key factor for improving the catalytic performance.

Engineering multifunctional bioadhesive powders through dynamic metal-ligand coordination

Bioadhesive gels with robust adhesion on wet and irregular tissue surfaces are desirable for clinical applications.Assembly of bioadhesive powders is an effective strategy for obtaining gels that adhere to wet and irregular tissue surfaces by absorbing interfacial water.However,current bioadhesive powders lack positive biological functions and are prone to postoperative adhesion.Here,we present a powder strategy based on metal-ligand coordination to create a series of bioadhesive polyacrylic acid(PAA)gels.In the gel network,metal ions(M^(n+))are used to coordinate with the carboxy ligands of PAA to form dynamic noncovalent crosslinks.The powders can absorb interfacial water and assemble into gels on wet and irregular tissue surfaces within a few seconds,forming an initial adhesion layer by electrostatic interactions.Furthermore,the polymers can diffuse into the tissue matrix,and metal-ligand coordination is reconstructed to enhance the adhesion.Moreover,with a cationic shield layer,the bioadhesive powders can effectively avoid postoperative adhesion.Importantly,M^(n+) ions endow the gel with customized biological functions.We demonstrate that the hemostatic,antibacterial,peroxidase-like catalytic,and photodetachment abilities of the gels by incorporating different M^(n+) ions.These advantages make the bioadhesive powder a promising platform for diverse tissue repair applications.

Insight into the role of iron in platinum-based bimetallic catalysts for selective hydrogenation of cinnamaldehyde

Selective hydrogenation of cinnamaldehyde(CAL)toward cinnamyl alcohol(COL)is an extremely important and challenging reaction.Herein,a series of Pt_(x)Fe_(y)-Al_(2)O_(3) bimetallic catalysts with varied Pt to Fe ratios were prepared by incipient wetness impregnation method.The introduction of Fe significantly modifies the electronic and surface properties of Pt,which clearly enhances the C=O hydrogenation selectivity.Among all the catalysts,Pt_(3)Fe-Al_(2)O_(3) displays the best catalytic performance and the conversion of CAL is 96.6%with 77.2%selectivity of COL within 1 h.In addition,Pt_(3)Fe-Al_(2)O_(3) had excellent reusability with 76%COL selectivity after five runs of the recycle process.Further characterization of the fresh,used and cycled catalysts revealed that the structure and electronic state of the synthesized Pt_(x)Fe_(y)-Al_(2)O_(3) are unchanged after hydrogenation reaction.The identical-location transmission electron microscopy(ILTEM)results revealed that the interaction between the nanoparticles and the supports was strong and the catalyst was relatively stable.

Reinforcing epoxy resin with nitrogen doped carbon nanotube:A potential lightweight structure material

The outstanding mechanical properties of nanocarbon materials, especially carbon nanotube（CNT）, make them one of the most promising reinforcing nanofillers for the high-performance lightweight structural material. However, the complicated but not eco-friendly surface functionalization processes（e.g. HNO3 oxidation） are generally necessary to help disperse nanocarbon materials into epoxy or build chemical bonds between them. Herein, nitrogen doped carbon nanotube（NCNT） was used to replace CNT to reinforce the epoxy resin, and the mechanical properties of the NCNT/epoxy nanocomposite showed significant superiorities over the CNT/epoxy nanocomposites. The fabrication process was simple and environmentally friendly, and avoided complicated, polluting and energy intensive surface functionalization processes. Moreover, the NCNT/epoxy suspension exhibited a relative low viscosity, which was favorable for the subsequent application. The reinforcing mechanism of NCNT was also proposed. The present work gives out an easy solution to the preparation of a high-performance nanocomposite as a potential lightweight structure material.