Effects of nanopores and sulfur doping on hierarchically bunched carbon fibers to protect lithium metal anode

Studies on three-dimensional structured carbon templates have focused on how to guide homogeneous lithium metal nucleation and growth for lithium metal anodes(LMAs).However,there is still insufficient evidence for a key factor to achieve their high electrochemical performance.Here,the effects of nanopores and sulfur doping on carbon-based nanoporous host(CNH)electrode materials for LMAs were investigated using natural polymer-derived CNHs.Homogeneous pore-filling behaviors of lithium metal in the nanopores of the CNH electrode materials were first observed by ex situ scanning electron microscopy analysis,where the protective lithium metal nucleation and growth process led to significantly high Coulombic efficiency(CE)of~99.4%and stable 600 cycles.In addition,a comparison study of CNH and sulfurdoped CNH(S-CNH)electrodes,which differ only in the presence or absence of sulfur,revealed that sulfur doping can cause lower electrochemical series resistance,higher CE value,and better cycling stability in a wide range of current densities and number of cycles.Moreover,S-CNH-based LMAs showed high electrochemical performance in full-cell Li-S battery tests using a sulfur copolymer cathode,where a high energy density of 1370Wh kgelectrode−1 and an excellent power density of 4120Wkgelectrode−1 were obtained.

Tuning the oxygen evolution electrocatalysis on NiFe-layered double hydroxides via sulfur doping

We report a facile way to prepare sulfur(S) doped Ni4/5 Fe1/5-layered double hydroxide(LDH) electrocatalysts for oxygen evolution reaction(OER). The influence of S doping amount on the OER activity of the resulted Ni Fe-LDHs was studied and the optimal surface S content was ca. 0.43 at%. The developed S-doped Ni Fe-LDH exhibits excellent OER catalyst activity in 1.0 M KOH with overpotential of only 257 m V at the current density of 10 m A cm^-2. Moreover, the catalyst could maintain high activity after 30 h stability test. The high activity of the S-doped Ni Fe-LDH catalysts may originate from the synergistic effect between S and the Fe sites. This work provides a simple but efficient way to improve the OER performance of transition metal oxides/(oxy)hydroxides.

Approaching Superior Potassium Storage of Carbonaceous Anode Through a Combined Strategy of Carbon Hybridization and Sulfur Doping

Carbonaceous materials are promising anode candidates for potassium-ion batteries(PIBs)given its high conductivity,stable property,and abundant resource,while its practical implementation is still hampered by its limited capacity and inferior rate behavior.Herein,we report a superior carbonaceous anode through a combined strategy of carbon hybridization and heteroatom doping.In this composite,hollow carbon spindles(HCS)were anchored on the surface of graphene(G)followed with sulfur doping treatment,aiming to integrate the high conductivity of graphene,the good structure stability of HCS,and the S doping-induced ample active sites.As a PIB anode,the S-G@HCS composite can display high capacity(301 mAh g^(-1)at 0.1 A g^(-1)after 500 cycles)and long-term cyclability up to 1800 cycles at 2 A g^(-1).Impressively,it can deliver an outstanding rate capacity of 215 mAh g^(-1)at 10 A g^(-1),which is superior to most carbon anodes as-reported so far for PIBs.Experimental and theoretical analysis manifests that the construction of graphene/amorphous carbon interface as well as S doping enables the regulation of electronic structure and ion adsorption/transportation properties of carbonaceous material,thus accounting for the high capacity and superior rate capability of S-G@HCS composite.

Regulation of the selective hydrogenation performance of sulfur-doped carbon-supported palladium on chloronitrobenzene

The overall performance of metal catalysts can be efficiently adjusted by modifying carbon carriers with different valence sulfur precursors.The wet impregnation technique successfully prepared carbon material carriers doped with varying sources of sulfur(Na_(2)SO_(4),NaHSO_(3),Na_(2)S·9H_(2)O).Palladium carbon catalysts doped with different sulfur precursors had been prepared with the aid of the liquid-phase reduction method of the selective hydrogenation of o-chloronitrobenzene(o-CNB)to o-chloroaniline(o-CAN).The catalyst prepared for Na_(2)S·9H_(2)O as a precursor has excellent performance,and the selectivity for o-CAN is more than 99.9%at 100%conversion.In addition,the characterization results show that with the decrease of S valence,the electronic effect between S and Pd increases,and the outer electron shift of Pd increases,which reduces the adsorption and dissociation ability of Pd to hydrogen,resulting in excellent selectivity.The effects provided a good idea for the hydrogenation of o-CNB and a different point of view on sulfur doping in a variety of hydrogenation reactions.

Synthesis of N-type semiconductor diamonds with sulfur,boron co-doping in FeNiMnCo-C system at high pressure and high temperature

A series of diamonds with boron and sulfur co-doping were synthesized in the Fe Ni Mn Co-C system by temperature gradient growth（TGG） under high pressure and high temperature（HPHT）. Because of differences in additives, the resulting diamond crystals were colorless, blue-black, or yellow. Their morphologies were slab, tower, or minaret-like. Analysis of the x-ray photoelectron spectra（XPS） of these diamonds shows the presence of B, S, and N in samples from which N was not eliminated. But only the B dopant was assuredly incorporated in the samples from which N was eliminated. Resistivity and Hall mobility were 8.510 Ω·cm and 760.870 cm^2/V·s, respectively, for a P-type diamond sample from which nitrogen was eliminated. Correspondingly, resistivity and Hall mobility were 4.211×10^5 Ω·cm and 76.300 cmΩ2/V·s for an N-type diamond sample from which nitrogen was not eliminated. Large N-type diamonds of type Ib with B–S doping were acquired.

Accelerating solar driven CO_(2) reduction via sulfur-doping boosted water dissociation and proton transfer

Exploring efficient photocatalysts for solar driven CO_(2) reduction with water(H_(2)O)as a proton donor is highly imperative but remains a great challenge because the synchronous enhancement of CO_(2) activation,H_(2)O dissociation and proton transfer is hardly achieved on a photocatalyst.Particularly,the sluggish H_(2)O dissociation impedes the photocatalytic CO_(2) reduction reaction involving multiple proton–electron coupling transfer processes.Herein,a sulfur-doped BiOCl(S-BiOCl)photocatalyst with abundant oxygen vacancies(OV)is developed,which exhibits broadband-light harvesting across solar spectrum and distinct photothermal effect due to photochromism.For photocatalytic CO_(2) reduction with H_(2)O in a gas–solid system,the high CO yield of 49.76μmol·g_(cat)^(-1)·h^(-1) with 100%selectivity is achieved over the S-BiOCl catalyst under a simulated sunlight.The H_(2)O-assisted CO_(2) reduction reaction on S-BiOCl catalyst is triggered by photocatalysis and the photothermal heating further enhances the reaction rate.The kinetic isotope experiments indicate that the sluggish H_(2)O dissociation affects the whole photocatalytic CO_(2) reduction process.The presence of oxygen vacancies promotes the adsorption and activation of H_(2)O and CO_(2),and the doped S sites play a crucial role in boosting H_(2)O dissociation and accelerating the dynamic migration of hydrogen species.As a result,the ingenious integration of OV defects,S sites and photothermal effect in S-BiOCl catalyst conjointly contributes to the significant improvement in photocatalytic CO_(2) reduction performance.

Tuning Structural and Electronic Configuration of FeN_(4) via External S for Enhanced Oxygen Reduction Reaction

The Fe-N-C material represents an attractive oxygen reduction reaction electrocatalyst,and the FeN_(4)moiety has been identified as a very competitive catalytic active site.Fine tuning of the coordination structure of FeN_(4)has an essential impact on the catalytic performance.Herein,we construct a sulfur-modified Fe-N-C catalyst with controllable local coordination environment,where the Fe is coordinated with four in-plane N and an axial external S.The external S atom affects not only the electron distribution but also the spin state of Fe in the FeN_(4)active site.The appearance of higher valence states and spin states for Fe demonstrates the increase in unpaired electrons.With the above characteristics,the adsorption and desorption of the reactants at FeN_(4)active sites are optimized,thus promoting the oxygen reduction reaction activity.This work explores the key point in electronic configuration and coordination environment tuning of FeN_(4)through S doping and provides new insight into the construction of M-N-C-based oxygen reduction reaction catalysts.

High sulfur-doped hard carbon anode from polystyrene with enhanced capacity and stability for potassium-ion storage

Carbonaceous materials are regarded as a promising anode material for potassium ion batteries(PIBs)due to their high electronic conductivity, abundant resources and low cost. However, relatively low storage capacity and structural instability still hinder their practical application. Herein, high sulfur-doped hard carbon(SHC-3) with a sulfur up to 27.05 at% is synthesized from polystyrene and sulfur as precursors. As an anode for PIBs, the SHC-3 delivers a superb cycling stability and rate performance(298.1 mAh g^(-1)at 100 mA g^(-1) for 1000 cycles, a capacity retention of 95.2%;220.2 mAh g^(-1)at 500 mA g^(-1) after 5200 cycles). The potassium storage of SHC-3 exhibits excellent cyclic stability at both low and high rates.Structure and kinetic studies demonstrate that the larger interlayer spacing(0.382 nm) of the SHC-3 accelerates the diffusion of potassium ions and effectively alleviates the volume expansion, and thus maintains the structure stability during the process of potassization/de-potassization. Meanwhile, the density functional theory calculation shows that the doped sulfur atoms provide abundant active sites for the adsorption of potassium ions, thereby increasing the reversible capacity of PIBs. This work provides a new scheme for the design of carbonaceous anode materials with high capacity and long cycle life.

Enhanced Pseudo‑Capacitive Contributions to High‑Performance Sodium Storage in TiO2/C Nanofibers via Double Effects of Sulfur Modification

Pseudo-capacitive mechanisms can provide higher energy densities than electrical double-layer capacitors while being faster than bulk storage mechanisms.Usually,they suffer from low intrinsic electronic and ion conductivities of the active materials.Here,taking advantage of the combination of TiS2 decoration,sulfur doping,and a nanometer-sized structure,as-spun TiO2/C nanofiber composites are developed that enable rapid transport of sodium ions and electrons,and exhibit enhanced pseudo-capacitively dominated capacities.At a scan rate of 0.5 mV s−1,a high pseudo-capacitive contribution(76%of the total storage)is obtained for the S-doped TiS2/TiO2/C electrode(termed as TiS2/S-TiO2/C).Such enhanced pseudocapacitive activity allows rapid chemical kinetics and significantly improves the high-rate sodium storage performance of TiO2.The TiS2/S-TiO2/C composite electrode delivers a high capacity of 114 mAh g−1 at a current density of 5000 mA g−1.The capacity maintains at high level(161 mAh g−1)even after 1500 cycles and is still characterized by 58 mAh g−1 at the extreme condition of 10,000 mA g−1 after 10,000 cycles.

Hierarchically porous Fe/N/S/C nanospheres with high-content of Fe-Nx for enhanced ORR and Zn-air battery performance

Heteroatom-doped carbon-based transition-metal single-atom catalysts(SACs) are promising electrocatalysts for oxygen reduction reaction(ORR). Herein, with the aid of hierarchically porous silica as hard template, a facile and general melting perfusion and mesopore-confined pyrolysis method was reported to prepare single-atomic Fe/N–S-doped carbon catalyst(FeNx/NC-S) with hierarchically porous structure and well-defined morphology. The FeNx/NC-S exhibited excellent ORR activity with a half-wave potential(E_(1/2)) of 0.92 V, and a lower overpotential of 320 mV at a current density of 10 mA cm^(-2)for OER under alkaline condition. The remarkable electrocatalysis performance can be attributed to the hierarchically porous carbon nanospheres with S doping and high content of Fe-Nx sites(up to 3.7 wt% of Fe), resulting from the nano-confinement effect of the hierarchically porous silica spheres(NKM-5) during the pyrolysis process. The rechargeable Zn-air battery with FeNx/NC-S as a cathode catalyst demonstrated a superior power density of 194.5 mW cm-2charge–discharge stability. This work highlights a new avenue to design advanced SACs for efficient sustainable energy storage and conversion.

Tuning nitrogen defects and doping sulfur in carbon nitride for enhanced visible light photocatalytic activity

Defect construction and heteroatom doping are effective strategies for improving photocatalytic activity of carbon nitride(g-C_(3)N_(4)).In this work,N defects were successfully prepared via cold plasma.High-energy electrons generated by plasma can produce N defects and embed sulfur atoms into g-C_(3)N_(4).The N defects obviously promoted photocatalytic degradation performance that was 7.5 times higher than that of pure g-C_(3)N_(4).The concentration of N defects can be tuned by different power and time of plasma.With the increase in N defects,the photocatalytic activity showed a volcanic trend.The g-C_(3)N_(4)with moderate concentration of N defects exhibited the highest photocatalytic activity.S-doped g-C_(3)N_(4)exhibited 11.25 times higher photocatalytic activity than pure g-C_(3)N_(4).It provided extra active sites for photocatalytic reaction and improved stability of N defects.The N vacancy-enriched and S-doped g-C_(3)N_(4)are beneficial for widening absorption edge and improving the separation efficiency of electron and holes.

Nanopore design of sulfur doped hollow carbon nanospheres for superior potassium-ion battery anodes

Sulfur doped carbonaceous materials are promising anodes for potassium-ion batteries because of their ability to bridge active sites and induce C/S electron coupling,resulting in increased ion storage capacitance However,the large potassium ions could cause significant volume expansion and structure collapse during operation in sulfur doped carbonaceous anodes,which lead to rapidly capacity sacrifice during long-term cycling.Nanopore design for anchoring sulfur atom in carbon skeleton is a novel way to alleviate the structure collapse and maintain the cycling stability.Therefore,this study developed a controlled nanopore and sulfur doped carbon sphere structure(S-NPHCSs).In potassium-ion batteries S-NPHCSs anode demonstrated exceptional performance with a high reversible capacity of 247 mAh·g^(–1)after 50 cycles at 0.2 A·g^(–1)and delivered a long cycle stability of 600 cycles at a high current density of 1.0 A·g^(–1).Interconnected nanopores and doped sulfur structure not only expand the accumulation space and offer ample active sites for diffusion and adsorption of potassium ions,but also build stable channels through nanopore structure to ensure the cyclic stability.This finding provides a fundamental theory for designing nanopore structures and introducing sulfur doped carbonaceous materials to enhance capacitive potassium storage and long cycle stability.

In situ sulfur-doped mesoporous tungsten oxides for gas sensing toward benzene series

Benzene series as highly toxic gases have inevitably entered human life and produce great threat to human health and ecological environment,and thus it is distinctly meaningful to monitor benzene series with quickly,real-time and efficient technique.Herein,novel sulfur-doped mesoporous WO_(3)materials were synthesized via classical in-situ solvent evaporation induced co-assembly strategy combined with doping engineering,which possessed highly crystallized frameworks,high specific surface area(40.9–63.8 m^(2)/g)and uniform pore size(~18 nm).Benefitting from abundant oxygen vacancy and defects via S-doping,the tailored mesoporous S/m WO_(3)exhibited excellent benzene sensing performance,including high sensitivity(50 ppm vs.48),low detection limit(ca.500 ppb),outstanding selectivity and favorable stability.In addition,the reduction of band gap resulted from S-doping promotes the carrier migration in the sensing materials and the reaction at the gas–solid sensing interfaces.It provides brand-new approach to design sensitive materials with multiple reaction sites.

Atomically Dispersed Fe-N_4 Modified with Precisely Located S for Highly Efficient Oxygen Reduction

Immobilizing metal atoms by multiple nitrogen atoms has triggered exceptional catalytic activity toward many critical electrochemical reactions due to their merits of highly unsaturated coordination and strong metal-substrate interaction.Herein,atomically dispersed Fe-NC material with precise sulfur modification to Fe periphery(termed as Fe-NSC) was synthesized,X-ray absorption near edge structure analysis confirmed the central Fe atom being stabilized in a specific configuration of Fe(N3)(N-C-S).By enabling precisely localized S doping,the electronic structure of Fe-N4 moiety could be mediated,leading to the beneficial adjustment of absorption/desorption properties of reactant/intermediate on Fe center.Density functional theory simulation suggested that more negative charge density would be localized over Fe-N4 moiety after S doping,allowing weakened binding capability to *OH intermediates and faster charge transfer from Fe center to O species.Electrochemical measurements revealed that the Fe-NSC sample exhibited significantly enhanced oxygen reduction reaction performance compared to the S-free Fe-NC material(termed as Fe-NC),showing an excellent onset potential of 1.09 V and half-wave potential of 0.92 V in 0.1 M KOH.Our work may enlighten relevant studies regarding to accessing improvement on the catalytic performance of atomically dispersed M-NC materials by managing precisely tuned local environments of M-Nx moiety.

Carbon coated ultrasmall anatase TiO_2 nanocrystal anchored on N,S-RGO as high-performance anode for sodium ion batteries

Anatase TiO_2 has been investigated as one of the most promising anode materials for sodium ion batteries(SIBs)with low cost and high theoretical capacity.Herein,a composite material of TiO_2 /N,S-RGO@C with carbon coated ultrasmall anatase TiO_2 anchored on nitrogen and sulfur co-doped RGO matrix was successfully prepared by a rational designed process.The composite structure exhibited ultrasmall crystal size,rich porous structure,homogeneous heteroatoms doping and thin carbon coating,which synergistically resulted in elevated electron and ion transfer.The anode exhibited high rate capacities with good reversibility under high rate cycling.The carbon coating was investigated to be effective to prevent active material falling and lead to long term cycling performance with a high capacity retention of 181 m Ah g^(à1)after 2000cycles at 2 C.Kinetic studies were carried out and the results revealed that the superior performance of the composite material were derived from the decreased charge transfer resistance and elevated ion diffusion.Results suggested that the TiO_2 /N,S-RGO@C composite is a promising anode material for sodium ion batteries.

Large single crystal diamond grown in FeNiMnCo-S-C system under high pressure and high temperature conditions

Large diamonds have successfully been synthesized from FeNiMnCo-S-C system at temperatures of 1255-1393 ℃and pressures of 5.3-5.5 GPa.Because of the presence of sulfur additive,the morphology and color of the large diamond crystals change obviously.The content and shape of inclusions change with increasing sulfur additive.It is found that the pressure and temperature conditions required for the synthesis decrease to some extent with the increase of S additive,which results in left down of the V-shape region.The Raman spectra show that the introduction of additive sulfur reduces the quality of the large diamond crystals.The x-ray photoelectron spectroscopy（XPS） spectra show the presence of S in the diamonds.Furthermore,the electrical properties of the large diamond crystals are tested by a four-point probe and the Hall effect method.When sulfur in the cell of diamond is up to 4.0 wt.%,the resistance of the diamond is 9.628×105 Ω·cm.It is shown that the large single crystal samples are n type semiconductors.This work is helpful for the further research and application of sulfur-doped semiconductor large diamond.

UV light driven high-performance room temperature surface acoustic wave NH_(3) gas sensor using sulfur-doped g-C_(3)N_(4) quantum dots

Nanomaterials integrated surface acoustic wave(SAW)gas sensing technology has emerged as a promising candidate for realtime toxic gas sensing applications for environmental and human health safety.However,the development of novel chemical interface based on two-dimensional(2D)sensing materials for SAW sensors for the rapid and sensitive detection of NH_(3)gas at room temperature(RT)still remains challenging.Herein,we report a highly selective RT NH_(3)gas sensor based on sulfur-doped graphitic carbon nitride quantum dots(S@g-C_(3)N_(4)QD)coated langasite(LGS)SAW sensor with enhanced sensitivity and recovery rate under ultraviolet(UV)illumination.Fascinatingly,the sensitivity of the S@g-C_(3)N_(4)QD/LGS SAW sensor to NH_(3)(500 ppb)at RT is dramatically enhanced by~4.5-fold with a low detection limit(~85 ppb),high selectivity,excellent reproducibility,fast response/recovery time(70 s/79 s)under UV activation(365 nm)as compared to dark condition.Additionally,the proposed sensor exhibited augmented NH_(3)detection capability across the broad range of relative humidity(20%–80%).Such remarkable gas sensing performances of the as-prepared sensor to NH_(3)are attributed to the high surface area,enhanced functional groups,sulfur defects,UV photogenerated charge carriers,facile charge transfer in the S@g-C_(3)N_(4)QD sensing layer,which further helps to improve the gas molecules adsorption that causes the increase in conductivity,resulting in larger frequency responses.The gas sensing mechanism of S@g-C_(3)N_(4)QD/LGS SAW sensor is ascribed to the enhanced electroacoustic effect,which is supported by the correlation of resistive type and COMSOL Multiphysics simulation studies.We envisage that the present work paves a promising strategy to develop the next generation 2D g-C_(3)N_(4)based high responsive RT SAW gas sensors.

Facile synthesis of S-doped reduced TiO_(2-x) with enhanced visible-light photocatalytic performance

A different approach to synthesize visible‐light‐active sulfur(S)‐doped reduced titania(S‐TiO2‐x)using thiourea dioxide as both the S source and reductant was developed.The structure,morphology,and optical and electronic properties of the as‐prepared S‐TiO2‐x samples were examined by multiple techniques,such as X‐ray diffraction,transmission electron microscopy,X‐ray photoelectron spectroscopy,ultraviolet‐visible diffuse reflectance spectroscopy,Brunauer‐Emmett‐Teller and photocurrent measurements,and electrochemical impedance spectroscopy.The photocatalytic activity of S‐TiO2‐x was evaluated by photodegradation of organic Rhodamine B under visible‐light irradiation.The degradation rate of Rhodamine B by S‐TiO2‐x obtained by calcination was about31,2.5,and3.6times higher than those of pure TiO2,pristine TiO2‐x,and S‐doped TiO2,respectively.In addition,the as‐prepared S‐TiO2‐x exhibited long‐term stable photocatalytic performance in the degradation of Rhodamine B under visible‐light illumination.This report reveals a new approach to prepare stable and highly efficient solar light‐driven photocatalysts for water purification.

Low-temperature selective synthesis of metastableα-MoC with electrochemical properties:Electrochemical co-reduction of CO_(2)and MoO_(3)in molten salts

Metastable molybdenum carbide(α-MoC),as a catalyst and an excellent support for metal catalysts,has been widely used in thermo/electro-catalytic reactions.However,the selective synthesis ofα-MoC remains a great challenge.Herein,a simple one-pot synthetic strategy for the selective preparation of metastableα-MoC is proposed by electrochemical co-reduction of CO_(2)and MoO_(3)in a low-temperature eutectic molten carbonate.The synthesizedα-MoC shows a reed flower-like morphology.By controlling the electrolysis time and monitoring the phase and morphology of the obtained products,the growth process ofα-MoC is revealed,where the carbon matrix is deposited first followed by the growth ofα-MoC from the carbon matrix.Moreover,by analyzing the composition of the electrolytic products,the formation mechanism forα-MoC is proposed.In addition,through this one-pot synthetic strategy,S-dopedα-MoC is successfully synthesized.Density functional theory(DFT)calculations reveal that S doping enhanced the HER performance ofα-MoC by facilitating water absorption and dissociation and weakening the bond energy of Mo-H to accelerate H desorption.The present work not only highlights the valuable utilization of CO_(2) but also offers a new perspective on the design and controllable synthesis of metal carbides and their derivatives.

Bimetallic Sulfide/Sulfur Doped T3C2TA:MXene Nanocomposites as High-performance Anode Materials for Sodium-ion Batteries

The application of transition metal dichalcogenides(TMDs)as anode materials in sodium-ion batteries(SIBs) has been hindered by low conductivity and poor cyclability.Herein,we report the synthesis of CoxFe1-xS2 bimetallic sulfide/sulfur-doped Ti3C2 MXene nanocomposites(CoxFe1-xS2@S-Ti3C2)by a facile co-precipitation process and thermal-sulfurization reaction.The interconnected 3D frameworks consisting of MXene nanosheets can effectively buffer the volume change and enhance the charge transfer.In particular,sulfur-doped MXene nanosheets provide rich active sites for sodium storage and restrain sulfur loss during charging/discharging processes,leading the increase of specific capacity and cycling the stability of anode materials.As a result,CoxFe1-xS2@S-Ti3C2 anodes exhibited high capacity,high rate capability and long cycle life(399mA·h/g at 5A/g with an 94% capacity retention after 600 cycles).