Formation of hierarchically 3D cactus-like architecture as efficient Mott-Schottky electrocatalyst for long-life Li-S batteries

Searching for new promising electrocatalysts with favorable architectures allowing abundant active sites and remarkable structure stability is an urgent task for the practical application of lithium-sulfur(Li-S)batteries.Herein,inspired by the structure of natural cactus,a new efficient and robust electrocatalyst with three-dimensional(3D)hierarchical cactus-like architecture constructed by functional zero-dimensional(0D),one-dimensional(1D),and two-dimensional(2D)components is developed.The cactus-inspired catalyst(denoted as Co@NCNT/NCNS)consists of N-doped carbon nanosheets(NCNS)and standing Ndoped carbon nanotubes(NCNT)forest with embedded Co nanoparticles on the top of NCNT,which was achieved by an in situ catalytic growth technique.The unique structure design integrates the advantages of 0D Co accelerating catalytic redox reactions,1D NCNT providing a fast electron pathway,and 2D NCNS assuring strong structure stability.Especially,the rich Mott-Schottky heterointerfaces between metallic Co and semiconductive NCNT can further facilitate the electron transfer,thus improving the electrocatalyst activity.Consequently,a Li-S battery with the Co@NCNT/NCNS modified separator achieves ultralong cycle life over 4000 cycles at 2 C with ultralow capacity decay of 0.016%per cycle,much superior over that of recently reported batteries.This work provides a new strategy for developing ultra-stable catalysts towards long-life Li-S batteries.

Controllable synthesis of metal particles by a direct current electrochemical approach

Shapes of copper and silver particles were successfully controlled by using a very simple,effective direct-current electrochemical approach without introducing any additives or templates. A diverse range of shapes and also different inner structures were thus accessible. The products prepared at relatively high potentials have flowerlike morphologies and exhibit flakes as building blocks. The uniformly thick flakes intersect mutually,have smooth surfaces and outwardly wavy edges. The particle diameter and the flake density can be easily controlled by changing potential and/or deposition time. With a decrease of potential,the particles' shapes changed from flower to bud,to sphere and to octahedron. Surface plasmon resonance (SPR) properties of the supported metal particles were investigated by UV-Vis diffuse reflectance spectra (UV-Vis DRS) and surface enhanced Raman scattering (SERS). It was found that the copper octahedra exhibited three characteristic bands,and SERS effect increases with the number of flakes within individual particles. Based on the experimental results,the mechanism for direct-current electrochemical growth of metal nanostructures was discussed.

High-performance asymmetric supercapacitors based on reduced graphene oxide/polyaniline composite electrodes with sandwich-like structure

The sandwich-like structure of reduced graphene oxide/polyaniline （RGO/PANI） hybrid electrode was prepared by electrochemical deposition. Both the voltage windows and electrolytes for electrochemical deposition of PANI and RGO were optimized. In the composites, PANI nanofibers were anchored on the surface of the RGO sheets, which avoids the re-stacking of neighboring sheets. The R（;O/PANI composite electrode shows a high specific capacitance of 466 F/g at 2 mA/cm2 than that of previously reported RGO/PANI composites. Asymmetric flexible supercapacitors applying RGO/PANI as positive electrode and carbon fiber cloth as negative electrode can be cycled reversibly in the high-voltage region of 0-1.6 V and displays intriguing performance with a maximum specific capacitance of 35.5 mF cm^-2. Also, it delivers a high energy density of 45.5 mW h cm^-2 at power density of 1250 mW cm^-2. Furthermore, the asymmetric device exhibits an excellent long cycle life with 97.6Z initial capacitance retention after 5000 cycles. Such composite electrode has a great potential for applications in flexible electronics, roll-up display, and wearable devices.2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.

Concentration-dependent Morphology Control of Pt-coated-Ag Nanowires and Effects of Bimetallic Interfaces on Catalytic Activity

Silver nanowires （NWs） coated with platinum （Pt） nanoparticles were synthesized via a galvanic partial replacement of Ag NWs in an aqueous K2PtC16 solution at room temperature. The products were char- acterized using a combination of electron microscopies, selected area electron diffraction, energy- dispersive X-ray mapping and X-ray diffraction. The surface morphology and Pt/Ag composition ratios are controlled by adjusting the K2PtC16 concentration. Different concentrations result in various surface morphologies including rough nanoparticle coating, porous and relatively smooth surfaces. The forma- tion mechanism was discussed based on the lattice constants＇ difference, concentration driven nucleation, consumption of Ag NWs, and stoichiometry of the replacement reaction. The effects of the bimetallic interface on the catalytic activity toward the reduction of 4-nitrophenol by sodium borohydride were studied. The activity of Ag-Pt NWs is highly enhanced over monometallic nanostructures, and opti- mized by a low Pt loading of 1.34 at.%, which indicates a catalytic role of the inter-metallic interface for the elecrrnn transfer.

Reduced Graphene Oxide Supported Bimetallic CobaltPalladium Nanoparticles with High Catalytic Activity towards Formic Acid Electro-oxidation

In this work,we report the growth of uniformly dispersed bimetallic cobalt-palladium nanoparticles(NPs) on reduced graphene oxide(RGO) nanosheets to prepare CoPd-RGO composites via a two-step procedure,where firstly formed Co NPs are used as seeds for the subsequent growth of Pd.The generation of Co NPs on RGO is performed by an in-situ reduction reaction with the reducer ethylene glycol under oil bath at180 ℃.According to composition,size and microstructure analyses,NPs in the resulting CoPd-RGO have an average particle size of 5 nm,and Pd is added to one side of Co NPs,thus forming Co-Pd bimetallic interfaces.The involved formation mechanism is suggested.The composite is used as an electro-catalyst for the formic acid oxidation in alkaline electrolyte,and the catalytic performance is investigated by cyclic voltammetry and chronopotentiometry etc.The results show that the composite has the highest electrocatalytic activity,the best electrochemical stability and the highest resistance to CO poisoning than those of the monometallic composite and commercial Pd black at the same loading.This is due not only to the small size of NPs with Co-Pd bimetallic interfaces providing more active atoms accessible for reactants,but also to the electric synergistic effect between metals and graphene.

Facile Synthesis of Bimetallic Au@Pd Nanoparticles with Core-shell Structures on Graphene Nanosheets

In this paper, we report a simple one-step thermal reducing method for synthesis of bimetallic Au@Pd nanoparticles with core-shell structures on the graphene surface. This new type of Au@Pd-G composites is characterized by transmission electron microscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. It is found that Au@Pd nanoparticles with an average diameter of 11 nm are well dispersed on the graphene surface, and the Au core quantity as well as the Pd shell thickness can be quantitatively controlled by loading different amounts of metallic precursors, and the involved core-shell structure formation mechanism is also discussed. The ternary Pt/Au@Pd-G composites can also be synthetized by the subsequent Pt doping. The catalytic performance of Au@Pd-G composites toward methanol electro-oxidation in acidic media is investigated. The results show that Au@Pd-G composites exhibit higher catalytic activity, better stability and stronger tolerance to CO poisoning than Pd-G and Au-G counterparts.

MOFs derived ZnSe/N-doped carbon nanosheets as multifunctional interlayers for ultralong-Life lithium-sulfur batteries

The shuttle effect and slow conversion rate of lithium polysulfides(LiPSs)have become the main obstructs to the development of lithium-sulfur(Li-S)batteries.Herein,the low cost metal-organic frameworks derived nitrogen-doped carbon nanosheets embedded with zinc selenide nanoparticles(ZnSe/NC nanosheets)were designed and synthesized for Li-S batteries.As the LiPSs trapping-layer,these nanocomposites provide some key benefits:(1)The nitrogen doping changes local electron distribution in the carbon nanosheets,thus the electrical conductivity is greatly improved for facilitating the transport of electrons/ions.(2)Nitrogen atoms and ZnSe nanoparticles play an important role in anchoring the LiPSs via chemical interactions.(3)The remarkable catalytic activity of ZnSe nanoparticles can accelerate the redox kinetics of LiPSs.As a result,the Li-S battery with the ZnSe/NC nanosheets modified separator exhibits ultralong lifespan over 1500 cycles with a small capacity loss of only 0.046%per cycle at 1 C,which is superior over those reported values.Furthermore,the Li-S battery with a high sulfur loading of 4.71 mg cm^(-2) can still maintain a high areal capacity of 4.28 mAh cm^(-2) after 50 cycles.This work provides a new route to the design of multifunctional low cost and high-performance separators for remarkably stable Li-S batteries.

Adapting Nanotech Research as Nano-Micro Hybrids Approach Biological Complexity,A Review

Today＇s emergence of nano-micro hybrid structures with almost biological complexity is of fundamental interest. Our ability to adapt intelligently to the challenges has ramifications all the way from fundamentally changing research itself, over applications critical to future survival, to posing globally existential dangers. Touching on specific issues such as how complexity relates to the catalytic prowess of multi-metal compounds, we discuss the increasingly urgent issues in nanotechnology also very generally and guided by the motto ＇Bio Is Nature＇s Nanotech＇. Technology belongs to macro-evolution; for example integration with artificial intelligence （AI） is inevitable. Darwinian adaptation manifests as integration of complexity, and awareness of this helps in developing adaptable research methods that can find use across a wide range of research. The second half of this work reviews a diverse range of projects which all benefited from ＇playful＇ programming aimed at dealing with complexity. The main purpose of reviewing them is to show how such projects benefit from and fit in with the general, philosophical approach, proving the relevance of the ＇big picture＇ where it is usually disregarded.