Effects Of S-doping Research Articles

High Sulfur-doped hollow carbon sphere with multicavity for high-performance Potassium-ion hybrid capacitors.

S doping is an effective strategy to improve the potassium-ion storage performance of carbon-based materials. However, due to the large atomic radius of S and poor thermal stability, it is challenging to synthesize carbon materials with high sulfur content by solid-phase transformation. In this work, we designed a multi-cavity structure that can confine the molten S during heat treatment and make it fully react, then achieving high S doping (7.6 at. %). As we known, S doping can also effectively increase the active sites of carbon materials to obtain higher capacity. In addition, through different ex/in-situ characterizations and DFT calculations, we confirmed that the S atoms can effectively expand the interlayer spacing of carbon, which facilitates the intercalation/deintercalation reaction of K+, thereby significantly improving the rate performance. Therefore, benefiting from the effect of S-doping, the sample exhibits high reversible specific capacity (401.0 mAh g-1 at 0.1 A/g) and rate performance (167.2 mAh g-1 at 5 A/g). The as-assembled K+ hybrid capacitor delivers both high energy density and power density (138.5Whkg-1 and 7692.5Wkg-1, respectively). This work provides a new approach to design S content carbon-based materials for high performance K+ storage.

Effect of S-doping on the magnetic and electrical properties of FeSe superconductor

Here we report on the magnetic and magneto-transport behavior of Fe-based superconductor with nominal compositions FeSe1−xSx (x=0.1 and 0.2). The impact of external hydrostatic pressure (P) and chemical pressure on the superconducting state of the FeSe system has been investigated in this work. Superconducting transition temperature (Tc) is found to be shifted towards higher temperatures with 10% S doping at the Se site of the FeSe alloy. On further increase in the doping concentration (for x=0.2), the superconducting Tc decreases. We have also observed a significant effect of external P on the superconducting properties of these S-doped alloys. Different superconducting parameters calculated from our experimental data confirm the type-II superconducting nature of the studied compounds. The signature of flux flow resistance is observed in the isothermal resistivity data as a function of the external magnetic field.

The Role of Sulfur Doping in Determining the Performance of Fe/N-C Based Electrocatalysts for Oxygen Reduction Reactions

The effect of S-doping on the performance of Fe/N-C catalysts for ORR was studied. It was found that the abundant C–S–C bonds in the sulfur-doped catalysts enhanced the ORR activity greatly, while the existence of excessive C-SOX-C bonds was adverse to the kinetics of ORR. Also, the existence of Fe was able to increase the contents of both C–S–C bond and graphite N during the pyrolysis stage of preparation, thus generating more ORR active sites. The resulted effective configurations of S (C–S–C) and active N (both graphitic N and pyridinic N), and the combination of rich hierarchical porous structure with the encased Fe3C nanoparticles were responsible for the excellent performance of catalysts. Specifically, the E1/2 of the prepared FeNSC-10S catalyst reached 0.91 V in a 0.1 M KOH electrolyte solution, which was 20 mV positive shift to the E1/2 of the 20 wt.% Pt/C commercial catalyst. The electron transfer number was determined to be 3.85−3.91 over the potential range of 0.4−0.8 V, indicating that the ORR catalytic process proceeded in a reaction pathway with nearly 4e− transfer. The developed catalyst also demonstrated a long-term stability as well as a superior methanol tolerance in alkaline conditions.

Topology conversion of 1T MoS2 to S-doped 2H-MoTe2 nanosheets with Te vacancies for enhanced electrocatalytic hydrogen evolution

Metastable 1T′ MoTe2 has attracted much attention as a cost-effective electrocatalyst for hydrogen evolution reaction (HER) in recent years. However, few studies were done over common stable 2H phase because it often exhibits inferior performance. Herein, stable 2H MoTe2 with S-doped Te vacancies has been synthesized by one-step telluride conversion of 1T MoS2 at 700°C under Ar/H2 atmosphere. It is demonstrated that the synergistic effect of S-doping and Te vacancies changes the electronic structures of the catalyst. Density functional theory (DFT) studies show that plentiful electrons accumulate on the surface S atoms in S-doped Te vacancies of 2H MoTe2 catalyst, which may be as active sites to promote HER. Moreover, the as-synthesized catalyst can be directly used as working electrode, and realizes current density of 100 mA cm−2 at overpotential of 217 mV with Tafel slope of 94 mV dec−1. This work stimulates intensive studies on the activation of inert phase of other nanocatalysts towards various reactions.

First-principles study of S-doped point defects with different charge states in monolayer g-C3N4

Non-metal-doped graphitic carbonitride (g-C3N4) can improve the redox capacity and photocatalytic activity, as a photocatalyst for the degradation of organic pollutants. In the present study, the theoretical defect models of S-doping with different doping sites and valence states were built in g-C3N4. The stability of charged defects was systematically investigated by the first-principles calculations based on the density functional theory. The effects of S-doping on the electronic structures and optical properties of g-C3N4 were revealed. According to the results, the g-C3N4 doped with positive divalent S is the most favorable defect form in energy. A new electron transfer pathway between adjacent heptazine rings on S-doped g-C3N4 was proposed. It is found that the special electronic states and the enhanced local charge density of S-doped g-C3N4 could effectively optimize the electron transport dynamic, leading to the increased reduction ability of photo-generated holes. As a result, the S-doped g-C3N4 shows better ability to separate photo-generated electron/hole pairs and improve photocatalytic efficiency with respect to the pristine g-C3N4.

Metal–Organic Framework-Derived CuS Nanocages for Selective CO 2 Electroreduction to Formate

Electroreduction of CO2 to target products with high activity and selectivity has techno-economic importance for renewable energy storage and CO2 utilization. Herein, we report a hierarchical CuS h...

Sulfur-doped carbon nanotubes as a conducting agent in supercapacitor electrodes

The electrochemical performance of sulfur-doped carbon nanotubes (S-CNTs) was investigated to confirm the S-doping effects and the possibility of their application as conducting agents in supercapacitor electrodes. S-CNTs were successfully synthesized via chemical vapor deposition using dimethyl disulfide as the carbon source. They were purified to obtain purified S-CNTs (P–S-CNTs) with diameters 30–50 nm and S content of 0.65 at%. The doped S atoms were removed partially from the P–S-CNTs by heat treatment in H2 atmosphere (De-P-S-CNTs). To compare the electrochemical performances of various conducting materials for supercapacitor electrodes, commercial activated carbon (MSP20) was used as the active material and commercial conducting agent (Super-P), commercial multi-walled CNTs (MWCNTs), De-P-S-CNTs, and P–S-CNTs were used as the conducting agents. The electrode with P–S-CNTs exhibited the highest specific capacitance at a high discharge current density of 100 mA cm−2 (120.2 F g−1) and the lowest charge-transfer resistance (6.19 Ω) that are significantly superior to those of Super-P (83.9 F g−1 and 15.16 Ω), MWCNTs (87.8 F g−1 and 17.02 Ω), and De-P-S-CNTs (90.1 F g−1 and 22.33 Ω). The superior electrochemical performance of P–S-CNTs can be attributed to the excellent electrical conductivity and pseudocapacitive contribution of the S-doping effect.

The promoting effect of S-doping on the NH3-SCR performance of MnOx/TiO2 catalyst

A series of S-doped MnOx/TiO2 catalysts were prepared by sol-gel method for the purpose of enhancing SCR performance. The obtained catalyst with mole ratio of S:Ti = 0.05:1 exhibited the best low temperature SCR performance and the widest active temperature window. According to the results of various analyses, the proper S was doped into TiO2 lattice via the replacement of Ti4+ by S4+ to generate TiOS bond, along with increasing surface area, more surface Mn4+ species and more active oxygen species (O2−). These enhanced properties improved the Brønsted acid sites and redox property of the properly S-doped MnOx/TiO2 catalyst. These advantages of S doping can essentially benefit the de-NOx ability of MnOx/TiO2 catalysts. Meanwhile, the in situ DRIFT experiments revealed that the adsorbed NH4+ and gas-phase NO2 species were greatly increased after proper S-doping, along with the enhanced reactivity of the adsorbed NH3 and NOx species. Both E-R and L-H mechanisms occurred on the S-doped catalysts, while the promoting effect of S-doping was performed by facilitating the L-H route during SCR reaction.

Ultrathin CdS shell-sensitized hollow S-doped CeO2 spheres for efficient visible-light photocatalysis

By virtue of the systematic effects of S-doping on CeO2 and the ultrathin shell structure of CdS, the CeO2−xSx@CdS nanocomposite exhibits excellent photocatalytic activity under visible-light illumination for both H2 evolution (rate up to 1147.2 μmol g−1 h−1) and RhB degradation (efficiency reached 99.8%) as compared to CeO2, CeO2−xSx, and CdS.

Effect of S-doping toward the optical properties of WO3 nanoparticles

Abstract This study discusses the S-doping effects on WO3 structure and optical constants. The SxWO3 system (x = 0, 0.05, 0.1 and 0.2) was prepared by easy sol-gel method and heat-treated at 500 °C for 8 h. The X-ray diffraction pattern revealed the formation of a single orthorhombic cell for x = 0, 0.1 and 0.2 compositions, while for x = 0.05 a monoclinic unit cell was identified. The variation of the cell parameter and the FTIR analysis (441 cm−1, W=S terminal) confirmed the doping process. The refractive index (n), the extinction coefficient (k), electrical (σe) and optical conductivity (σopt), dissipation factor (tan δ) and dielectric relaxation time (τ) were investigated. The study demonstrated that the S-doping improved some optical constants, particularly light transport properties. Moreover, high S-doping generated defects, which led to decreased electrical conductivity and charge carriers lifetime.

Improving the intrinsic properties of rGO sheets by S-doping and the effects of rGO improvements on the photocatalytic performance of Cu3Se2/rGO nanocomposites

The effects of S-doping on intrinsic properties of graphene oxide (GO) sheets such as interlayer spacing, reduction level, and electrical resistance and the influence of these properties on the photocatalytic performance of rGO/Cu3Se2 nanocomposites were investigated. A simple chemical method was used to synthesize S-doped GO sheets and a cost-effective co-precipitation method was used to decorate of the NPs on S-doped GO (as S-doped GO/NPs nanocomposites) and undoped GO (as undoped GO/NPs nanocomposites) sheets. X-ray diffraction (XRD) patterns of the products indicated that GO sheets were changed into reduced GO (rGO) sheets during the synthesis process. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed more exfoliation for the S-doped rGO sheets in comparison to the undoped rGO. X-ray photoelectron spectroscopy(XPS) indicated that S-doping caused an improve reduction level of rGO. UV–vis results revealed that S-doped rGO/NPs nanocomposites had a band-gap value around 2.2 eV that was bigger than the band-gap value of the undoped rGO/NPs that was around 1.9 eV. Room temperature photoluminescence (PL) results indicated that, the electron-hole recombination rate of S-doped rGO/NPs nanocomposites was lower than the undoped rGO/NPs nanocomposites. The photocatalytic activity under visible light irradiation for degradation of methylene blue (MB) dye showed a significant enhancement photocatalytic performance for S-doped rGO/NPs nanocomposites in comparison to the photocatalytic activity of the undoped rGO/NPs nanocomposites. Brunauer–Emmett–Teller (BET) calculation indicated a specific surface area of 251.6 and 220.7 m2 g−1 for the S-doped and undoped rGO/NPs nanocomposites, respectively. In addition, photoresponse measurements under visible light source irradiation indicated that, the electrical conductivity of rGO as an intrinsic property of the rGO sheets was increased by S-doping. Finally, according to valence band (VB) edge spectroscopy results of the samples, it was understood that a type-II heterostructure was formed by S-doped rGO/NPs with pristine NPs that was another important factor for the enhancement photocatalytic performance of this sample.

Synthesis, characterization and electrochemical properties of S-doped carbon aerogels

Heteroatom doping in carbon aerogels is critical for improving the surface areas and electronic properties of these aerogels. This paper demonstrates doping sulfur (S) atom into carbon aerogels. S-doped carbon aerogels (S-CAs) were prepared via a sol-gel process using phloroglucinol (P), resorcinol (R) and formaldehyde as the polymerization precursors with sodium carbonate (Na2CO3) as the basic catalyst and sodium 4-hydroxybenzenesulfonate (HBS) as the surfactant. The as-synthesized products were dried in normal temperature and carbonized with temperature-programmed. The effects of S-doping on the surface area and electronic properties of the S-CAs were studied by a surface area analyzer and electrochemical workstation. When the S loading was up to 1.38%, the corresponding S-CA exhibited the most optimal surface area and specific capacitance. The textural properties were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), a surface area analyzer, an X-ray diffraction spectrometer, a Raman spectrometer, the X-ray photoelectron spectroscopy (XPS) spectra, an elemental analyzer and an EDX detector, and the electrochemical properties were measured using cyclic voltammetry, galvanostatic charge–discharge measurements and electrochemical impedance spectroscopy (EIS). When the molar ratio of HBS/(P + R) was 0.05, the S loading was 1.38%, the specific surface area of the as-synthesized CA was 831 m2/g, and its specific capacitance was 105 F/g.

High rate capability by sulfur-doping into LiFePO4 matrix.

Enhanced electrochemical performance of LiFePO4 for Li-ion batteries has been anticipated by anion doping at the O-site rather than cation doping at the Fe-site. We report on the electrochemical performance of S-doped LiFePO4 nanoparticles synthesized by a solvothermal method using thioacetamide as a sulfur source. S-doping into the LiFePO4 matrix expands the lattice due to the larger ionic radius of S2− than that of O2−. The lattice parameters a and b increase by around 0.2% with sulfur content, while that of c remains almost unchanged with only 0.03% increase. The S-doping also contributes to the suppression of antisite defects (Fe occupying Li sites), which facilitates the easy migration of Li in the diffusion channels without blockage. Owing to these effects of S-doping, the S-doped LiFePO4 nanoparticles show enhanced electrochemical properties with a high discharge capacity of ∼113 mA h g−1 even at a high rate of 10C.

S-doping effects on optical properties and highly enhanced photocatalytic performance of Cu3Se2 nanoparticles under solar-light irradiation

Undoped and S-doped Cu3Se2 nanostructures (NSs) with different sulfur concentrations were synthesized by a green, simple, and cost-effective co-precipitation method in ambient conditions. X-ray diffraction patterns (XRD) of the samples indicated that, all samples had a tetragonal phase of Cu3Se2. Fourier transform infrared spectroscopy (FTIR) results revealed that, some vibration modes were appeared by sulfur. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that, sulfur had a significant role to change of morphology of the products. UV–vis and Photoluminescence (PL) results showed that, the band gap value of the pristine sample was 1.72–1.85 eV, while S-doped (4%) sample had a band-gap value between 1.61 eV and 1.67 eV. On the other hand, further increase of sulfur up to 6% caused band gap value increase in compared to the 4% sulfur doped. In addition, the PL results revealed that, the products had surface-trap states (STS) energy as well as different intrinsic defects such as Cu-vacancy. Furthermore, the PL spectrum of the S-doped sample showed that, sulfur ions caused increase natural donor-acceptor (D°→A°) recombination energy intensity. Finally, photocatalytic measurements showed that, the photocatalytic performance of the samples under solar-light irradiation was enhanced by an increase of sulfur concentration up to 4%.

Effects of S-doping on the electronic transition, band gap, and optical absorption of GaSe1−xSx single crystals

The intrinsic evolutions of electronic transition and the band gap of GaSe1−xSx solid solution single crystals (x = 0, 0.133, and 0.439) grown for nonlinear optical applications have been systemically investigated by using spectroscopic ellipsometry and first-principle calculations. Five interband electronic transitions E1, E2, E3, E4, and E5 have been obtained by fitting the second derivatives of the complex dielectric functions and the physical origins were explained with the aid of theoretical calculations. It is found that the interband electronic transition energy E2, E3, and E4 show a blueshift trend from 3.457 eV, 3.736 eV, and 4.810 eV at x = 0 to 3.786 eV, 4.628 eV, and 5.086 eV at x = 0.439, respectively. This is because the larger Se atoms are replaced by smaller S atoms in GaSe1−xSx. The experimental band gap of GaSe1−xSx is increased from 1.908 eV at x = 0 to 2.081 eV at x = 0.439. Moreover, in order to verify the influences of S-doping on the band gap of GaSe1-xSx, we performed the first-principle calculations based on the density-functional theory. The theoretical results also confirm that the band gap energy increases from 2.085 eV at x = 0 to 2.15 eV at x = 0.439, which is in good agreement with the experiment results.

Photoconductivity in nanostructured sulfur-doped V2O5 thin films

In this paper, S-doped vanadium oxide thin films with doping levels up to 40 at.% are prepared via spray pyrolysis method on glass substrates, and the effect of S-doping on the structural and photoconductivity related properties of [Formula: see text]-V2O5 thin films is studied. The results show that most of the films have been grown in the tetragonal [Formula: see text]-V2O5 phase structure with the preferred orientation along [200]. With increasing the doping level, the samples tend to be amorphous. The structure of the samples reveals to be nanobelt-shaped whose width decreases from nearly 100 nm to 40 nm with S concentration. The photoconductivity measurements show that by increasing the S-doping level, the photosensitivity increases, which is due to the prolonged electron’s lifetime as a result of enhanced defect states acting as trap levels.

Facile Synthesis and Electrocatalytic Activity of Sulfur Doped Carbon for Oxygen Reduction

Fuel cells and metal-air batteries have attracted much attention over the past few years due to their high energy density and the potential to reduce the negative impact of climate change [1,2]. However, the sluggish oxygen reduction reaction (ORR) at the cathode, which requires highly efficient and low cost electrocatalysts, is one of the important factors that restrict the wide application of fuel cells [3-5]. Exploring low-cost and sustainable electrocatalysts with high efficiency to alternate the platinum-based noble electrocatalysts for the ORR is critical for the development of fuel cells and metal-air batteries [6-8]. Heteroatom-doped carbon materials have emerged as promising alternative electrocatalyts for the ORR due to its low price, high catalytic activity and environmental friendliness [6-13]. The heteroatom doped in carbon is usually N, S, B, F and P et al., which can modify the electronic structure (like charge and/or spin density redistribution) of carbon and create the active sites favorable for the adsorption of O2 molecule and facilitate the ORR process [9-13]. Considerable efforts have been devoted to the study of N-doped carbon catalysts for the ORR[14-17]. Sulfur doping is also convinced to be a valid method in promoting the catalytic activity of carbon towards ORR. Sulfur has an electronegativity of 2.58, which is similar to carbon’s (2.55) [12]. In contrast, the electronegativity of N(3.04) is higher than that of carbon. Therefore the modification of structure and the catalytic activity of carbon resulting from N doping and S doping is different. S-doped graphene has been reported to show improved electrocatalytic activity for ORR [11,18]. Nevertheless, there have been few reports about the ORR activity of S-doped porous carbon. It’s known that porous carbon can provide effective triple phase (solid-liquid-gas) region for the mass transfer of reactants and products during the ORR. To better understand the effect of S-doping on the structure and ORR activity of carbon, we developed a facile method to synthesize the S-doped porous carbon via a hydrothermal method with sucrose and benzyl disulfide (BDS) as the carbon and sulfur sources, respectively. The influence of S doping on the electrocatalytic activity of the carbon for the ORR in alkaline media was investigated. The pyrolysis temperature has a significant impact on the structure and texture of the S-doped carbon, which further affects the ORR activity and durability of S-doped carbon as shown in Figure 1. Acknowledgements This work is supported by National Natural Science Foundation of China (Nos.51272167 and 21206101 ).

Cobalt sulfide/N,S codoped porous carbon core-shell nanocomposites as superior bifunctional electrocatalysts for oxygen reduction and evolution reactions.

Exploring highly-efficient and low-cost bifunctional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) in the renewable energy area has gained momentum but still remains a significant challenge. Here we present a simple but efficient method that utilizes ZIF-67 as the precursor and template for the one-step generation of homogeneous dispersed cobalt sulfide/N,S-codoped porous carbon nanocomposites as high-performance electrocatalysts. Due to the favourable molecular-like structural features and uniform dispersed active sites in the precursor, the resulting nanocomposites, possessing a unique core-shell structure, high porosity, homogeneous dispersion of active components together with N and S-doping effects, not only show excellent electrocatalytic activity towards ORR with the high onset potential (around -0.04 V vs.-0.02 V for the benchmark Pt/C catalyst) and four-electron pathway and OER with a small overpotential of 0.47 V for 10 mA cm(-2) current density, but also exhibit superior stability (92%) to the commercial Pt/C catalyst (74%) in ORR and promising OER stability (80%) with good methanol tolerance. Our findings suggest that the transition metal sulfide-porous carbon nanocomposites derived from the one-step simultaneous sulfurization and carbonization of zeolitic imidazolate frameworks are excellent alternative bifunctional electrocatalysts towards ORR and OER in the next generation of energy storage and conversion technologies.

Thermoelectric study of crossroads material MnTe via sulfur doping

Here, we report thermoelectric study of crossroads material MnTe via iso-electronic doping S on the Te-site. MnTe1-xSx samples with nominal S content of x = 0.00, 0.05, and 0.10 were prepared using a melt-quench method followed by pulverization and spark plasma sintering. The X-ray powder diffraction, scanning electron microscopy, and ZAF-corrected compositional analysis confirmed that S uniformly substitutes Te up to slightly over 2%. A higher content of S in the starting materials led to the formation of secondary phases. The thermoelectric properties of MnTe1-xSx samples were characterized by means of Seebeck coefficient, electrical conductivity, and thermal conductivity measurements from 300 K to 773 K. Furthermore, Hall coefficient measurements and a single parabolic band model were used to help gain insights on the effects of S-doping on the scattering mechanism and the carrier effective mass. As expected, S doping not only introduced hole charge carriers but also created short-range defects that effectively scatter heat-carrying phonons at elevated temperatures. On the other hand, we found that S doping degraded the effective mass. As a result, the ZT of MnTe0.9S0.1 was substantially enhanced over the pristine sample near 400 K, while the improvement of ZT became marginal at elevated temperatures. A ZT ∼ 0.65 at 773 K was obtained in all three samples.

Effect of S-doping on structural, optical and electrochemical properties of vanadium oxide thin films prepared by spray pyrolysis

In this research, S-doped vanadium oxide thin films, with doping levels from 0 to 40 at.%, are prepared by spray pyrolysis technique on glass substrates. For electrochemical measurements, the films were deposited on florin–tin oxide coated glass substrates. The effect of S-doping on structural, electrical, optical and electrochemical properties of vanadium oxide thin films was studied. The x-ray diffractometer analysis indicated that most of the samples have cubic β-V2O5 phase structure with preferred orientation along [200]. With increase in the doping levels, the structure of the samples tends to be amorphous. The scanning electron microscopy images show that the structure of the samples is nanobelt-shaped and the width of the nanobelts decreases from nearly 100 to 40 nm with increase in the S concentration. With increase in the S-doping level, the sheet resistance and the optical band gap increase from 940 to 4015 kΩ/square and 2.41 to 2.7 eV, respectively. The cyclic voltammogram results obtained for different samples show that the undoped sample is expanded and the sample prepared at 20 at.% S-doping level has sharper anodic and cathodic peaks.