Two-dimensional multimetallic sulfide nanosheets with multi-active sites to enhance polysulfide redox reactions in liquid Li2S6-based lithium-polysulfide batteries

The lithium-sulfur battery has attracted enormous attention as being one of the most significant energy storage technologies due to its high energy density and cost-effectiveness.However,the "shuttle effect" of polysulfide intermediates represents a formidable challenge towards its wide applications.Herein,we have designed and synthesized two-dimensional Cu,Zn and Sn-based multimetallic sulfide nanosheets to construct multi-active sites for the immobilization and entrapment of polysulfides with offering better performance in liquid Li2S6-based lithium-polysulfide batteries.Both experimental measurements and theoretical computations demonstrate that the interfacial multi-active sites of multimetallic sulfides not only accelerate the multi-chained redox reactions of highly diffusible polysulfides,but also strengthen affinities toward polysulfides.By adopting multimetallic sulfide nanosheets as the sulfur host,the liquid Li2 S6-based cell exhibits an impressive rate capability with 1200 mAh/g and retains 580 mAh/g at 0.5 mA/cm^(2) after 1000 cycles.With high sulfur mass loading conditions,the cell with 2.0 mg/cm^(2) sulfur loading delivers a cell capacity of 1068 mAh/g and maintains 480 mAh/g with 0.8 mA/cm^(2) and 500 cycles.This study provides new insights into the multifunctional material design with multi-active sites for elevated lithium-polysulfide batteries.

Melting mechanisms of Pt-based multimetallic spherical nanoparticles by molecular dynamics simulation

The melting mechanisms of Pt-based multimetallic nanoparticles(NPs)are important to help determine their optimal melting processes.To understand the melting and coalescence behaviors of heterogeneous NPs(Pd-Pt NPs)with various sizes and compositions,molecular dynamics(MD)simulation was employed.The MD results for larger Pd-Pt NPs with an effective diameter of4.6-7.8 nm show that PtPd alloy can form at Pd/Pt interface before Pd NP melted completely,while for Pt-core/Pdshell NP and Pd-core/Pt-shell NP,PtPd alloy formed only after Pd portion melted completely.For smaller Pd-Pt NPs with an effective diameter of 2.5-4.0 nm,PdPt alloy is not formed until both Pd and Pt NPs melted completely.Besides,the coalescence process of Pd-Pt NPs depends on the melting temperature of Pt NP when Pt composition is higher than 20 at%.Furthermore,the melting mechanisms of Pd/Pt/Ir trimetallic NPs are investigated.A two-step melting process occurs in Pd-Pt-Ir NPs and Ir-core/Ptshell/Pd-shell NP,and the melting sequence of Pd-core/Ptshell/Ir-shell NP and Pt-core/Pd-shell/Ir-shell NP is different from Pd/Pt bimetallic NPs.

Fine-tuning electronic structure of N-doped graphitic carbon-supported Co-and Fe-incorporated Mo_(2)C to achieve ultrahigh electrochemical water oxidation activity

Mo_(2)C is an excellent electrocatalyst for hydrogen evolution reaction(HER).However,Mo_(2)C is a poor electrocatalyst for oxygen evolution reaction(OER).Herein,two different elements,namely Co and Fe,are incorporated in Mo_(2)C that,therefore,has a finely tuned electronic structure,which is not achievable by incorporation of any one of the metals.Consequently,the resulting electrocatalyst Co_(0.8)Fe_(0.2)-Mo_(2)C-80 displayed excellent OER catalytic performance,which is evidenced by a low overpotential of 214.0(and 246.5)mV to attain a current density of 10(and 50)mA cm^(-2),an ultralow Tafel slope of 38.4 mV dec^(-1),and longterm stability in alkaline medium.Theoretical data demonstrates that Co_(0.8)Fe_(0.2)-Mo_(2)C-80 requires the lowest overpotential(1.00 V)for OER and Co centers to be the active sites.The ultrahigh catalytic performance of the electrocatalyst is attributed to the excellent intrinsic catalytic activity due to high Brunauer-Emmett-Teller specific surface area,large electrochemically active surface area,small Tafel slope,and low chargetransfer resistance.

PtCo-based nanocatalyst for oxygen reduction reaction:Recent highlights on synthesis strategy and catalytic mechanism

Oxygen reduction reaction over Pt-based catalyst is one of the most significant cathode reactions in fuel cells.However,low reserves and high price of Pt have motivated researchers worldwide seeking enhanced utilization efficiency and durability by doping non-noble metals to form Pt-based alloy catalysts.Alloying Pt with Co has been recognized as one of the most effective approaches to achieve this goal.PtCo bimetal combination is one of the most promising candidates to synthesize highly efficient catalysts for oxygen reduction reaction(ORR)applications,owing to its relatively more suitable oxygen binding energy for four-electron transfer reactions.Recently,impressive strategies have been developed to fabricate more active and stable PtCo-based multimetallic alloys with tailorable size and morphology.This paper aims to summarize the most recent highlights on the study of the relationship between preparation strategies,morphologies,electroactivities of the PtCo-based catalyst at atomic level and further the relevant reaction mechanism.The challenges and opportunities on the further development of electrocatalysts for fuel cells are included to provide reference for the practical application.

Geochemical characteristics of sediments from the COMRA registered pioneer area (CRPA),equatorial northeastern Pacific Ocean

COMRA(China Ocean Mineral Resources Association) registered pioneer area (CRPA) is located in the western part of the area between the Clarion and Clipperton Fraction Zones (CCFZs). Based on distinctive color and bio-disturbing properties, two layers are recognized in the sediment columns from the CRPA: a pale brown layer (Unit A) on the top and a dark for layer (Unit B) in the lower part. Color division between them can be explained as a hiatus. As a resu1t, the two units are different to each other in chemical composition and sediment properties. It is found that contents of P2O5, MnO2, CaO, Na2O in sediments of older Unit B are higher, but SiO2 content is slightly lower. Based on correlation analysis, Mn and Fe in the sediments have different origins. The former is mainly precipitated in authigenic process, whilst the latter is closely related to terrigenous detritus. Therefore, the differences in chemical composition of the sediments are caused by different sedimentation settings.

Synergistic coupling of Ni_(3)ZnC_(0.7)decorated with homogeneous multimetal CoNiCuFe nitrogen-codoped carbon matrix as high-entropy catalysts for efficient overall water splitting

Due to unique electrical properties and high catalytic efficiency,transition metal nitrogen-codoped car-bide(TM-N-C)has attracted tremendous interest as a multifunctional electrocatalyst for water splitting.Unlike traditional single-source modification,herein a novel pomegranate-like high-entropy(HE)elec-trocatalyst of Ni_(3)ZnC_(0.7)decorated with homogeneous multimetal(Fe,Co,Cu,and Ni)nitrogen-codoped carbon matrix(Ni_(3)ZnC_(0.7)@CoNiCuFe-NC)is reported.It can be implemented by the simple thermal an-nealing method of multimetal codoped zeolitic imidazolate framework(ZIF).Benefiting from the syn-ergistic effects of plentiful TM-N-C species,template effect of ZIF and distinct nanoporous structure,HE electrocatalyst Ni_(3)ZnC_(0.7)@CoNiCuFe-NC exhibits outstanding electrocatalytic performance.When ap-plied in strong alkaline electrolyte(1.0 M KOH),the overpotentials of Ni_(3)ZnC_(0.7)@CoNiCuFe-NC present as low as 202 and 97 mV for oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)at 10 mA cm^(−2)current density.Surprisingly as a bifunctional electrode,it can achieve the low cell voltage of 1.53 V at 10 mA cm^(−2)current density for overall water splitting,which is comparable to conventional IrO_(2)||Pt/C electrode and superior to the recently reported analogous bifunctional catalysts.Thus,the work proposes the direction for the rational design of homogeneous distribution of TM-N-C material for water splitting in the green hydrogen energy industry.

Rh-doped PdAg nanoparticles as efficient methanol tolerance electrocatalytic materials for oxygen reduction

Direct methanol fuel cells(DMFCs)have received extensive attention on their high efficiency,high reliability,and no carbon emission.Unfortunately,the poor methanol tolerance and sluggish oxygen reduction reaction(ORR)at cathode have seriously hindered their further development.Herein we report the synthesis of a new class of Rh-doped PdAg alloy nanoparticles(NPs)for boosting ORR activity with high methanol tolerance capacity concurrently.The ORR mass activity of typical Rh_4Pd_(40)Ag_(56)NPs is 4.2 times higher than that of commercial Pt catalyst.Moreover,it shows a great methanol tolerance capability by maintaining 92.4%in ORR mass activity in alkaline solution with 0.1 mol L^(à1)methanol,against a big decrease of almost 100%for commercial Pt.Even after 30,000 potential cycles with 1.0 mol L^(à1)methanol,Rh_4Pd_(40)Ag_(56)NPs still retain ORR mass activity of up to 68.3%.DFT calculations reveal that excellent ORR performance with excellent methanol tolerance originates the active d-band-pinning engineering for an efficient site-independent electron-transfer.A generalized d-band mediated fine electron-transfer tuning path has blueprinted for effectively minimizing intrinsic ORR barriers with high current density.The present work highlights the key role of Rh doping in enhancing the ORR activity and methanol tolerance ability of PdAg NPs for future high-performance DMFCs.

Defect-Rich,Candied Haws-Shaped AuPtNi Alloy Nanostructures for Highly Efficient Electrocatalysis

The rational design and synthesis of multimetallic nanostructures(NSs)with rich defects are of significant importance for their diverse applications,including their promising usage as high-efficiency catalysts for alcohol oxidation reaction as a fuel source.Here,we report the synthesis of defect-rich,candied haws-shaped AuPtNi NSs using presynthesized gold(Au)nanowires as templates.The ternary AuPtNi NSs possess rich defects such as twins,stacking faults,and atomic steps.Impressively,the AuPtNi NSs exhibited excellent mass and specific activities toward methanol and ethanol oxidation reactions under acidic conditions.Our current work paves the way for the rational design and controlled synthesis of defect-rich multimetallic NSs to boost their performances in catalytic reactions.

Facile synthesis of metal and alloy nanoparticles by ultrasound-assisted dealloying of metallic glasses

Metal and alloy nanoparticles synthesized by chemical reduction have attracted increasing attention due to their superior physical,chemical,and biological properties.However,most chemical synthesis processes rely on the use of harsh reducing agents and complicated chemical ingredients.Herein,we report a novel reduction-agent-free and surfactant(stabilizer)-free strategy to synthesize Cu,Ag,Au,Cu-Pt,Cu-Au,Cu-Au-Pt-Pd,and Au-Pt-Pd-Cu nanoparticles by ultrasound-assisted dealloying of Mgbased metallic glasses.The formation mechanism of the metal and alloy nanoparticles is revealed by a detailed investigation of sequential intermediate products.We demonstrate that the glass-liquid phase transition of the initially dealloying metallic glasses,together with the synergistic effect of dealloying and ultrasound-driven ligament-breakage of small enough nanoporous intermediates,play key roles in preparing the uniformly dispersed metal and alloy nanoparticles.This approach greatly simplifies the up-scaling synthesis of monometallic and bimetallic nanoparticles,and also provides a general strategy for synthesizing unprecedented multimetallic nanoparticles.

Selectivity regulation of CO_(2)electroreduction on asymmetric AuAgCu tandem heterostructures

Rational design and synthesis of multimetallic nanostructures(NSs)are fundamentally important for electrochemical CO_(2)reduction reaction(CO_(2)RR).Herein,a multi-step seed-mediated growth method is applied to synthesize asymmetric AuAgCu heterostructures using Au nanobipyramids as nucleation seeds,in which their composition and structures are well controlled.We find that the selectivity of C_(2)products for CO_(2)RR could be effectively regulated by tandem catalysis and electronic effect over trimetallic AuAgCu heterostructures.Particularly,the Faraday efficiency toward ethanol could reach up to 37.5%at a potential of−0.8 V versus reversible hydrogen electrode over asymmetric Au1Ag1Cu5 heterostructures with segregated domains of three constituent metals.This work provides an efficient strategy for the synthesis of multicomponent architectures to boost their promising application in CO_(2)RR.