Sulfur Co-doped Graphene Research Articles

Enhanced oxygen reduction performance of nitrogen and sulfur Co-doped graphene oxide by immobilized ionic liquid

The development of robust metal-free catalysts for electrochemical oxygen reduction reaction (ORR) is a great challenge due to the large energy barriers for the intermediate *OO− formation. In this work, an ionic liquid (IL) modified N/S co-doped graphene oxide (IL-SNG) was synthesized and explored as a metal-free ORR catalyst in alkaline conditions. Compared to the electrode without IL modification (SNG), the onset and half-wave potentials of IL-SNG were positively shifted by 130 and 110 mV, respectively. The IL and co-doping effects enable IL-SNG a comparable activity to that of Pt/C catalyst in alkaline solution. In addition to impressive activity, IL-SNG exhibits a superior tolerance to methanol and excellent long-term stability over Pt/C under the identical conditions, enabling it a potential candidate for ORR in alkaline conditions. DFT calculation shows that IL enhances O2 adsorption and stabilizes the high-energy *OO− intermediate by forming ion pairs and therefore boosts the catalytic activity.

Degradation of Sulfamethoxazole Using Pms Activated by Cobalt Sulfides Encapsulated in Nitrogen and Sulfur Co-Doped Graphene

Degradation of Sulfamethoxazole Using Pms Activated by Cobalt Sulfides Encapsulated in Nitrogen and Sulfur Co-Doped Graphene

Electronic structure modulation of isolated Co-N4 electrocatalyst by sulfur for improved pH-universal hydrogen evolution reaction

Exploring an efficient platinum group metal (PGM) free electrocatalyst with superior activity and stability for hydrogen evolution reaction (HER) in a wide pH range is desirable for low-cost hydrogen production. Here, we report atomically dispersed cobalt on nitrogen and sulfur co-doped graphene (N-Co-S/G) for HER. Remarkably, the prepared N-Co-S/G electrocatalyst shows a small overpotential of 67.7 mV vs. reversible hydrogen electrode (RHE) at a current density of 10 mA cm−2 and exceptional durability over 100 h at 10 mA cm−2 under acidic conditions. Moreover, we found that the HER activity of N-Co-S/G is close to 20% Pt/C at all pH levels (0–14) and superior activity at high current density (>100 mA cm−2). Experimental and theoretical calculations reveal that the S atom in N-Co-S/G form Co-S bond, resulting new Co-N3S1 active site, which optimizes Gibbs free energy for hydrogen adsorption (∆GH*) close to zero, while water adsorption and dissociation enhanced by S modulation for neutral and basic media HER.

Nitrogen and Sulfur Codoped Graphene Macroassemblies as High-Performance Electrocatalysts for the Oxygen Reduction Reaction in Microbial Fuel Cells

Microbial fuel cells (MFCs) are receiving considerable attention for generating clean and sustainable electrical energy directly from wastewater. The development of highly efficient, durable, and i...

Nitrogen and sulfur co-doped graphene quantum dots/nanocellulose nanohybrid for electrochemical sensing of anti-schizophrenic drug olanzapine in pharmaceuticals and human biological fluids

A nanohybrid prepared from green source (nanocellulose, NC) and nitrogen, sulfur co-doped graphene quantum dots (N, S@GQDs) was prepared for the electrochemical detection of olanzapine (OLZ), atypical antipsychotic primarily used to treat schizophrenia and bipolar disorder. Polar groups on the surface of NC and N, S@GQDs provide more anchoring sites for adsorption of OLZ onto the electrode surface. In addition, it provides high conductivity, good mechanical strength, large surface area, and excellent electrical conductivity. The nanocomposite was characterized morphologically and electrochemically by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and square wave adsorptive stripping voltammetry (SWAdSV). Under the optimized conditions, the modified electrode has a good response in the range of 1.5–90.0 × 10−8 M with LOD of 0.5 × 10−8 M. The proposed electrode offers high sensitivity, selectivity, and reliability towards OLZ detection. The SWAdSV was used to determine OLZ in pharmaceutical tablets, human plasma and urine with good recoveries % and reasonable RSD% values.

Nitrogen and sulfur co-doped graphene composite electrode with high electrocatalytic activity for vanadium redox flow battery application

Nitrogen and sulfur co-doped graphene has been decorated on graphite felt electrode via a hydrothermal treatment using thiourea as sulfur and nitrogen sources for vanadium redox flow battery application. Our results demonstrate that the modification of sulfur and nitrogen co-doped graphene on graphite felt provides an effective way to improve surface area and introduce functional groups for vanadium redox reaction, resulting in a significant improvement in energy efficiency (85.37% at a current density of 80 mA/cm2), power density (0.4925 W/cm2), discharge capacity and capacity retention. These results reveal that the modification of nitrogen and sulfur co-doped graphene on graphite felts is a promising method for the enhancement of vanadium redox flow battery performance.

Synthesis of nitrogen and sulfur doped graphene on graphite foam for electro-catalytic phenol degradation and water splitting

A rational design of electrode materials with both high electron conductivity and abundant of catalytic sites is essential for high-performance electrochemical reactions.Herein, a nitrogen and sulfur co-doped graphene (SNG) anchored on the interconnected conductive graphite foam (GF) is fabricated via drop-casting and in situ annealing. The SNG flakes are tightly immobilized on the GF surface, which can provide fast electron transfer rate and large electrolyte/electrode interfaces. The SNG@GF composite can be directly used as a free-standing electrode for electro-catalytic degradation of organic pollutants and overall water splitting. SNG@GF significantly enhanced the electrochemical activation of peroxymonosulfate (PMS) for catalytic oxidation. During the oxygen evolution reaction (OER), the SNG@GF exhibits an initial overpotential of 330 mV vs. RHE at 10 mA cm−2 with a Tafel slope of 149 mV dec−1 in 1 M KOH, which outperforms most of the reported metal-free catalysts. The density functional theory calculations are also used to unveil the S, N dual doping effects of carbon materials and their synergy in carbocatalysis. This study dedicates to developing multi-functional carbocatalysts for environmental and energy applications, and enables insights into carbocatalysis in electrochemistry.

Coordination engineering of iridium nanocluster bifunctional electrocatalyst for highly efficient and pH-universal overall water splitting

Water electrolysis offers a promising energy conversion and storage technology for mitigating the global energy and environmental crisis, but there still lack highly efficient and pH-universal electrocatalysts to boost the sluggish kinetics for both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). Herein, we report uniformly dispersed iridium nanoclusters embedded on nitrogen and sulfur co-doped graphene as an efficient and robust electrocatalyst for both HER and OER at all pH conditions, reaching a current density of 10 mA cm−2 with only 300, 190 and 220 mV overpotential for overall water splitting in neutral, acidic and alkaline electrolyte, respectively. Based on probing experiments, operando X-ray absorption spectroscopy and theoretical calculations, we attribute the high catalytic activities to the optimum bindings to hydrogen (for HER) and oxygenated intermediate species (for OER) derived from the tunable and favorable electronic state of the iridium sites coordinated with both nitrogen and sulfur.

Increasing the heteroatoms doping percentages of graphene by porous engineering for enhanced electrocatalytic activities

Graphene based materials are considered as promising catalysts towards electro-catalytic water splitting. Heteroatoms doping and structure defects creation in graphene matrix could enhance the electro-catalytic activity effectively. In this work, a nitrogen and sulfur co-doped graphene is synthesized and then activated by KOH to involve a porous structure. The atomic ratios of doped heteroatoms are found increased surprisingly. This should be due to the better thermal stability of doped heteroatoms compared with the origin carbon atoms. More carbon atoms will be removed, thus leading to the increased heteroatoms doping percentages. The increased surface area, larger heteroatoms ratios, and abundant structure defects result in the improved catalytic activity towards electrochemical oxygen evolution reaction (OER). The overpotential for OER could achieve as early as 281 mV vs. RHE at 10 mA·cm−2 in 1 M KOH, better than most of the metal free catalysts. The obtained sample is active over a wide pH range in electrochemical hydrogen evolution reaction (HER), thus could be used as bifunctional materials for water splitting. This work provides a simple and low-cost approach to increase the ratios of doped heteroatoms, and thus should have great potential both for carbon materials synthesis and hydrogen production.

Synergetic effect of nitrogen and sulfur co-doping in mesoporous graphene for enhanced energy storage properties in supercapacitors and lithium-ion batteries

Nitrogen and sulfur co-doped mesoporous graphene (NSMG) was fabricated via a hydrothermal method followed by heat treatment utilizing graphite oxide (GO), tri-block co-polymer P123 and thiourea as the N and S source. The porous structure of the NSMG was controlled by heat treatment at 600 ​°C and 800 ​°C thus obtaining NSMG600 and NSMG800 which had specific surface areas of 966 and 1335 ​m2 ​g−1, respectively. X-ray photoelectron spectroscopy (XPS) of the NSMGs demonstrated the presence of active pyridinic-N, pyrrolic-N, graphitic-N, pyridinic N- oxide, thiophene and –SOx groups in the structure. The N and S contents and configurations were controlled by annealing temperature hence influencing the performance in supercapacitors (SC) and lithium-ion batteries (LIBs). There was improved electrolyte ion mobility and lithium-ion diffusion for both SCs and LIBs respectively. The improved performance could be attributed to the unique structural features such as plentiful defects, wrinkles, abundant pores, and N/S co-doping. NSMG600 exhibited the highest capacitance of 261 ​F ​g−1 at 0.5 ​A ​g−1 in SCs while NSMG800 showed the best performance in LIBs with a discharge capacity of 460 mAh g−1 at 100 ​mA ​g−1 with good cycling stability (440 mAh g−1) and superior rate capability. Thus NSMGs exhibit potential application in high-performance energy storage devices.

A simple, economical one-pot microwave assisted synthesis of nitrogen and sulfur co-doped graphene for high energy supercapacitors

Supercapacitors are continuously gaining popularity in the market because of their powerful ultrafast charging ability, yet their energy is still low while contrasting with batteries. In most cases, utilization of redox additive materials (either by decoration or composite creation) and the redox response in the electrolyte itself are some of the strategies for improving the poor energy density of supercapacitors. Herein, we present, a facile, fast and economical one-pot microwave-assisted synthesis, characterization and supercapacitor application of nitrogen and sulfur co-doped graphene (NSG). The characterization result shows good exfoliation and a superior amount of heteroatoms content (14.9% of Nitrogen and 4.3% of Sulfur) in the graphene. The 1:1.5NSG shows a maximum specific capacitance of 310 F/g in two electrodes symmetric configuration using 1 M H2SO4 electrolyte. In addition, the device fabrication shows a high specific capacitance of 226 F/g and 150 F/g in non-aqueous organic and ionic liquid electrolytes with an energy density of 31 Wh/kg and 32 Wh/kg, respectively. In redox additive 0.015 M HQ in H2SO4 electrolyte, the supercapacitor device exhibits enhanced specific capacitance (667 F/g) with maximum energy density of 59 Wh/kg, which is very high and comparable to lithium-ion batteries.

Study of the effect of chemical composition on the surface wettability of three-dimensional graphene foams

The chemical composition obviously affects the surface wettability of a three-dimensional (3D) graphene material apart from its surface energy and microstructure. In the hydrothermal preparation, the heteroatom doping changes the chemical composition and wettability of the 3D graphene material. To realize the controllable surface wettability of graphene materials, aminobenzene sulfonic acid (ABSA) was selected as a typical doping agent for the preparation of nitrogen and sulfur co-doped 3D graphene foam (SNGF) using a hydrothermal method. Different from using o-ABSA or p-ABSA as the dopant, SNGF with tunable surface wettability is obtained only when m-ABSA is used. This result indicates that the substituent position of -SO3H group in the benzene ring of ABSA is rather important for the tunable wettability. This work provides some theoretical foundations for dopant selection and some new insights in manipulating the properties of 3D graphene foams by adjusting the configuration of dopants.

Nitrogen, sulfur Co-doped porous graphene boosting Li4Ti5O12 anode performance for high-rate and long-life lithium ion batteries

Enhancing the electron/ion transfer ability of Li4Ti5O12 materials is very important to achieve advanced high-rate and long-life anode in lithium ion batteries (LIBs). Here, for the first time, we report Li4Ti5O12/nitrogen, sulfur co-doped porous graphene composites (LTO/N, S-PG) via one-step facile calcination and activation process by using LiOH as Li source and activating agent. Mechanisms underlying the beneficial effects of N, S co-doped graphene for LTO anode were substantiated by the Density Functional Theory (DFT) calculations, revealing that co-doped N and S atoms not only significantly facilitate Li+ adsorption, but also ameliorate Li+ diffusion in graphene. Furthermore, the synergistic effects of nanosized LTO and porous graphene endow the composites with efficient Li+ diffusion channels and electron-conductive networks. Therefore, the LTO/N, S-PG can deliver extraordinarily high rate capability (e.g. 130 ​mA ​h ​g−1 at 80 ​C and 123 ​mA ​h ​g−1 at 100 ​C), and excellent cycling stability (83.1% capacity retention after 4000 cycles at 20 ​C). In addition, their superior electrochemical performance was also demonstrated in the full cells with LiNi0.5Mn1.5O4 cathode, which displayed 89.5% capacity retention after 500 cycles at 5 ​C. These results suggest the great promise of using the LTO/N, S-PG as a novel anode material for high-rate and long-life LIBs.

Nitrogen and sulfur co-doped hierarchical graphene hydrogel for high-performance electrode materials

In this investigation, nitrogen and sulfur co-doped graphene hydrogel (N,S-GH) with well-connected hierarchical networks was prepared using a simple one-step process. The hierarchical structures provide electrically conductive channels for ion transfer, whereas N,S heteroatoms improve the chemical reactivity and pseudocapacitance of the electrode material. An optimized N,S-GH as a bind-free supercapacitor electrode demonstrates a large gravimetric capacitance (294.8 F g−1 at 1 A g−1), long lifetime (89.4% retention after 10,000 cycles), and excellent rate capability, twice as that of pure GH due to the synergistic effect of N and S doping. Therefore, a large capacitance of the optimized N,S-GH is ascribed to fast ion diffusion, large accessible area (hierarchical network), and pseudocapacitance (N and S co-doping). Furthermore, the optimized N,S-GH-based supercapacitor delivers a high energy density (8.6 Wh kg−1) at a high power density (2.4 kW kg−1). Overall, the obtained N,S-GH through this investigation presents a promising electrode material with outstanding electrochemical properties for energy storage applications.

Facile Synthesis of Bi2MoO6 Nanosheets@Nitrogen and Sulfur Codoped Graphene Composites for Sodium-ion Batteries

Recently, sodium-ion batteries gradually become the promising alternative to lithium-ion batteries because of cost considerations. In this work, a kind of Bi2MoO6 nanosheets@N,S codoped graphene composite is designed and fabricated for sodium storage applications. Detailed characterizations are employed to investigate its morphology, structure and chemical compositions. When evaluated as an anode material for sodium-ion batteries, the as-prepared composite is able to display a specific capacity of 254 mA·h/g after 50 cycles at a current density of 0.2 A/g, and 186 mA·h/g at 1.6 A/g during the rate capability test. As a result, the further morphology and structure optimization is still required for high performance sodium-ion batteries.

The synthesis of nitrogen and sulfur co-doped graphene quantum dots for fluorescence detection of cobalt(ii) ions in water

A highly sensitive and selective fluorescence sensor using N,S-GQDs for the detection of Co2+within 3 minutes.

Few-layer WS2 nanosheets with oxygen-incorporated defect-sulphur entrapped by a hierarchical N, S co-doped graphene network towards advanced long-term lithium storage performances.

Tungsten sulfide (WS2) with two-dimensional layered graphene-like structure as an anode for lithium-ion batteries (LIBs) has attracted large attention owing to its high theoretical capacity and unique S–W–S layer structure. However, it also always suffers from poor electrical conductivity and volume expansion during lithiation/delithiation process in the practical application. Herein, we demonstrate the successful synergistic regulation of both structural and electronic modulation by simultaneous oxygen incorporation in defect-sulphur WS2 nanosheets embedded into a conductive nitrogen and sulfur co-doped graphene framework (denoted as O-DS-WS2/NSG), leading to dramatically enhanced lithium storage. Such a unique structure not only increases the accessible active sites for Li+ and enhances the kinetics of ion/electron transport, but also relieves the volume effect of WS2. Furthermore, the surface defects and heteroatom incorporation can effectively regulate the electronic structure, improve the intrinsic conductivity and offer more active sites. Consequently, electrochemical performance results demonstrate that the obtained O-DS-WS2/NSG nanocomposites possess great application prospects in LIBs with high specific capacity, superior rate performance as well as excellent cycle stability.

Electrochemical synthesis of phosphorus and sulfur co-doped graphene quantum dots as efficient electrochemiluminescent immunomarkers for monitoring okadaic acid

In this study, water-dispersed, uniform-sized phosphorus and sulfur co-doped graphene quantum dots (P, S-GQDs) were prepared by the one-step electrolysis of a graphite rod in an alkaline solution containing sodium phytate and sodium sulfide. Compared with GQDs and mono-doped GQDs (P-GQDs and S-GQDs), the P, S-GQDs dramatically improved the electrochemiluminescence (ECL) performance. Therefore, they were used as bright ECL signaling markers through conjugation with a monoclonal antibody against okadaic acid (anti-OA-MAb). Moreover, as an effective matrix for OA immobilization, the carboxylated multiwall carbon nanotubes-poly(diallyldimethylammonium) chloride-Au nanocluster (CMCNT-PDDA-AuNCs) composite promoted electron transfer and enlarged the surface area. Owing to the multiple amplifications, a competitive indirect ECL immunosensor for highly sensitive quantitation of OA has been developed. Under the optimized conditions, the 50% inhibitory concentration (IC50) of the immunosensor was 0.25 ng mL−1, and its linear range was 0.01–20 ng mL−1 with a low detection limit of 0.005 ng mL−1. Finally, the proposed ECL sensor was successfully utilized to detect OA contents in mussel samples. Therefore, this study provides new insights into the designation of ECL luminophores and expands application of co-doped GQDs in fabrication of ECL immunosensors for shellfish toxin determination.

Nitrogen and sulfur co-doped graphene aerogel with hierarchically porous structure for high-performance supercapacitors

Supercapacitors with unique performance have been widely utilized in many fields. Herein, we report a nitrogen and sulfur co-doped graphene aerogel (N/S-GA-2) prepared using a low toxic precursor for high-performance supercapacitors. The as-obtained material possesses a hierarchically porous structure and a large number of electrochemical active sites. At a current density of 1 A g−1, the specific capacitance of the N/S-GA-2 for supercapacitors with the ionic liquid as the electrolyte is 169.4 F g−1, and the corresponding energy density is 84.5 Wh kg−1. At a power density of 8.9 kW kg−1, the energy density can reach up to 75.7 Wh kg−1, showing that the N/S-GA-2 has an excellent electrochemical performance. Consequently, the N/S-GA-2 can be used as a promising candidate of electrode materials for supercapacitors with high power density and high energy density.

Ni and NiO in situ grown on sulfur and phosphorus co-doped graphene as effective bifunctional catalyst for hydrogen evolution

Designing a precious-metal-free catalyst with high activity and stability is of great significance for hydrogen evolution reaction (HER). Herein, sulfur (S) and phosphorus (P) co-doped graphene (SPG) is successfully synthesized via a facile hydrothermal process using sulfuric acid and phytic acid as sulfur and phosphorus dopant. Subsequently, two types of nickel-based nanomaterials grown directly on SPG (abbreviated as Ni/SPG and NiO/SPG) are fabricated through a simple alcohol-thermal method. The as-prepared Ni/SPG electrocatalyst display unexpected HER performance with extremely small impedance (0.48 Ω), wonderful electrochemically active surface areas (32.6 m2/g), high TOF (0.0051 s−1), low initial potential (25 mV), excellent Tafel slope (79 mV decade−1) and more excellent stable cycle stability (5000 cyclic voltammetry cycles). These remarkable electrocatalytic properties are attributed to the S and P dual-doping graphene producing more exposed active sites and surface defects, which allows Ni with small crystallite size uniformly dispersed on its surface and the facilitated electron transport between them.