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.

Diamond/β-SiC film as adhesion-enhanced interlayer for top diamond coatings on cemented tungsten carbide substrate

In present work, diamond/β-SiC composite interlayers were deposited on cemented tungsten carbide（WC-6%Co） substrates by microwave plasma enhanced chemical vapor deposition（MPCVD） using H2,CH4 and tetramethylsilane（TMS） gas mixtures. The microstructure, chemical bonding, element distribution and crystalline quality of the composite interlayers were systematically characterized by means of field-emission scanning electron microscopy（FE-SEM）, X-ray diffraction（XRD）, X-ray photoelectron spectrometer（XPS）, electron probe microanalysis（EPMA）, Raman spectroscopy and transmission electron microscropy（TEM）. The influences of varying TMS flow rates on the diamond/β-SiC composite interlayers were investigated. Through changing the TMS flow rates in the reaction gas, the volume fraction of β-SiC in the composite interlayers were tunable in the range of 12.0%–68.1%. XPS and EPMA analysis reveal that the composite interlayers are composed of C, Si element with little cobalt distribution. The better crystallinity of the diamond in the composite is characterized based on the Raman spectroscopy, which are helpful to deposit top diamond coatings with high quality. Then, the adhesion of top diamond coatings were estimated using Rockwell C indentation analysis, revealing that the adhesion of top diamond coatings on the WC-6%Co substrates can be improved by the interlayers with the diamond/β-SiC composite structures. Comprehensive TEM interfacial analysis exhibits that the cobalt diffusion is weak from WC-6%Co substrate to the composite interlayer. The homogeneous microcrystalline diamond coatings with the most excellent adhesion can be fabricated on the substrates with the composite interlayer with the β-SiC/diamond ratio of about 45%. The composite structures are appropriate for the application in high-efficiency mechanical tool as a buffer layer for the deposition of the diamond coating.

Growth behavior of CVD diamond films with enhanced electron field emission properties over a wide range of experimental parameters

In this study, diamond films were synthesized on silicon substrates by microwave plasma enhanced chemical vapor deposition（CVD） over a wide range of experimental parameters. The effects of the microwave power,CH;/H;ratio and gas pressure on the morphology, growth rate, composition, and quality of diamond films were investigated by means of scanning electron microscope（SEM）, X-ray diffraction（XRD）, Raman spectroscopy and X-ray photoelectron spectroscopy（XPS）. A rise of microwave power can lead to an increasing pyrolysis of hydrogen and methane, so that the microcrystalline diamond film could be synthesized at low CH;/H;levels. Gas pressure has similar effect in changing the morphology of diamond films, and high gas pressure also results in dramatically increased grain size. However,diamond film is deteriorated at high CH;/H;ratio due to the abundant graphite content including in the films. Under an extreme condition of high microwave power of 10 kW and high CH;concentration, a hybrid film composed of diamond/graphite was successfully formed in the absence of N;or Ar,which is different from other reports. This composite structure has an excellent measured sheet resistance of 10-100 Ω/Sqr. which allows it to be utilized as field electron emitter. The diamond/graphite hybrid nanostructure displays excellent electron field emission（EFE） properties with a low turn-on field of 2.17 V/μm and β= 3160, therefore it could be a promising alternative in field emission applications.

Effect of oxygen terminated surface of boron-doped diamond thin-film electrode on seawater salinity sensing

Tremendous demands for highly sensitive and stable seawater salinometers have motivated intensive research on advanced electrode materials.Boron-doped diamond(BDD)is attractive in terms of its high mechanical stability and chemical inertness,but is usually hindered by its low double-layer capacitance(C_(dl))for seawater salinity detection.Here,inspired by the principle of oxygen-terminated BDD electrode endowing higher C_(dl)than hydrogen-terminated surface,we introduce the oxygen terminated surface by oxygen plasma or reactive ion etch(RIE),and the fabricated oxygen terminated BDD electrodes demonstrate high sensitivity and long-term stability in seawater salinity detection comparing with the hydrogen terminated BDD electrodes.Significantly,the as-fabricated O-BDD-RIE electrodes not only show remarkable enhanced response even better than the commercial platinum black electrodes but also display long-time stability which is weekly verified by continuous monitor for 90 days.The outstanding performance of the oxygen terminated BDD electrodes can be ascribed to the enhancement of C-O surface functional group on C_(dl).In addition,a comprehensive analysis of effective electroactive surface area(EASA)and C_(dl)proves that the surface oxygen is the major factor for the improved C_(dl).In summary,the excellent oxygen terminated BDD electrodes promise potential application in seawater salinity detection.

Integration of 3D interconnected porous microstructure and high electrochemical property for boron-doped diamond by facile strategy

Three-dimensional(3D)porous boron-doped diamond(BDD)flm is an attractive electrode material but tough to synthesize.Herein,the 3D porous BDD flms were constructed in a facile and template-free way.The BDD/non-diamond carbon(NDC)composite flms were frstly fabricated by hot flament chemical vapor deposition(HFCVD)technique,and then the porous BDD flms with 3D interconnected porous microstructure,different pore size and NDC-free diamond were achieved by selective removal of NDC.It is manifested that higher electrochemical response,large double layer capacitance(17.54 m F/cm^(2))in diamond electrodes,wide electrochemical window of 2.6 V and superior long-term stability were achieved for 3D porous BDD flm.This derives from the synergistic effect of microstructure and phase composition of the porous flms.3D interconnected structure possesses prominent improvement of effective surface area and accessible porous channel,signifcantly enhancing the species adsorption and mass transfer.The3D porous BDD flms,composed of NDC-free diamond,exhibit excellent structural stability and corrosion resistance,which favor the enhancement of long-term stability and water splitting overpotential.The facile fabricating approach and excellent structure/electrochemical character demonstrate the appealing application in many electrochemical felds for 3D porous BDD flms,such as energy storage and conversion,wastewater treatment and purifcation.