Facile Sulfurization Research Articles

Built-in electric field boosted exciton dissociation in sulfur doped BiOCl with abundant oxygen vacancies for transforming the pathway of molecular oxygen activation

The reactive oxygen species (ROS) generated by photoinduced molecular oxygen (O2) activation has attracted great attention in environmental remediation and pollution control. Herein, we establish a facile sulfur doping strategy that promotes the activation of molecular oxygen over BiOCl for rapid and continuous degradation of organic pollutants. In this work, we demonstrate that the significantly enhanced built-in electric field (BIEF) induced by the heterogeneous introduction of S atoms not only multiplies the electron concentration in the BiOCl matrix, but also accelerates the rapid separation/transfer of charge carriers and inhibits recombination. Driven by this, the exciton behavior in the BOC undergoes a transformation. The electrons generated through exciton dissociation activate the adsorbed O2 on the surface into superoxide radicals (•O2–). Benefited from the superior O2 activation efficiency, the degradation rate constant of ciprofloxacin (CIP) the fabricated S-doped BiOCl increased by 8.8 times, under visible light. This work proposes a strategy to promote the photocatalytic O2 activation via tuning BIEF and manipulating excitonic effects, which affords new perspective for understanding the reaction mechanisms related to charge transfer in photocatalytic systems.

Selective and smart dual-channel colorimetric sulfur ion sensing readout platform

It is in urgent to develop a facile sulfur ion (S2-) detection platform with good selectivity, sensitivity and portability, since the abnormal concentration of S2- poses a serious threat to human health and environment. Nanozymes are expected as promising colorimetric probe for visual assays, but the selectivity is challenged since the mostly typical nanozymes are oxidoreductase-like ones while various analytes possess equivalent redox capacity. Herein, one-platform-two-channels detection method with both excellent selectivity and sensitivity was constructed based on the bifunctions of tin telluride (SnTe) nanobelts. On one hand, SnTe and S2- can react rapidly to form a special brown product SnS to assure the selectivity; On the other hand, SnTe with peroxidase-like activity can oxidize 3,3’,5,5’-tetramethylbenzidine (TMB) to blue ox-TMB in the presence of H2O2, while strong reducing S2- could inversely convert the solution from blue to colorless and then brown, enabling a wider range of S2- detection (10 nM-900 μM) and low detection limit of 7.1 nM. In addition, this detection platform could still show excellent specificity against 19 other interfering substances in sulfur soaps with complex components. With the assistance of the color-to-value conversion function of a smartphone, a portable signal reading-out platform was established, which can successfully achieve the accurate visualization of the S2− in 10 min

Morphology-controlled Co0.5Ni0.5S2-C double-shell porous microspheres for the construction of high-performance asymmetric supercapacitors

In this research, we develop a facile sulfuration treatment approach to synthesize the carbon doped double-shell porous cobalt nickel sulfide microspheres (Co0.5Ni0.5S2-C DSPMs) using CoNi-MOF yolk-shell microspheres (CoNi-MOF YSMs) as the precursor. The obtained Co0.5Ni0.5S2-C DSPMs exhibits a maximum specific capacity of 2011.3 F g − 1 at 1 A g − 1 due to the unique double-shell porous structure and amorphous carbon. The density functional theory (DFT) shows that cobalt nickel sulfide with the same molar ratio of cobalt and nickel possesses good absorbability and stability toward OH− ion on the thermodynamics, which significantly improves their electrochemical performance. Furthermore, an asymmetric supercapacitor (ASC) device is fabricated by using Co0.5Ni0.5S2C DSPMs as the cathode and the activated carbon (AC) as the anode. The ASC device exhibits a supreme specific capacity of 182.4 F g − 1 at 1 A g − 1, a high energy density of 64.85 Wh kg−1 at the power density of 800 W kg−1, and excellent cycle stability with 92.78% capacitance retention rate at the current density of 8 A g − 1 over 5000 cycles. This research pave the way for the development of next-generation energy storage devices using micro/nanocomposite with double-shell porous structure.

Electrochemical hydroxidation of sulfide for preparing sulfur-doped NiFe (oxy) hydroxide towards efficient oxygen evolution reaction

The well-known NiFe hydroxides show tremendous promise as low-cost oxygen evolution reaction (OER) catalysts, which however suffer from the rapid decline of activity at current densities exceeding 100 mAcm−2. Herein, we constructed a sulfur-doped OER electrode ((Ni7Fe3)OOH-S) by facile sulfurization and anodic displacement processes. The as-prepared (Ni7Fe3)OOH-S electrode shows an overpotential of 238 mV at 10 mA cm−2 in 1 M KOH at 25 °C, which is due to the high intrinsic catalytic activity, the super hydrophilic nature of the electrode for the S dopant. DFT calculations reveal that the S dopant changes the electronic structure and charge density (NiFe)OOH, thereby optimizing the OER rate-determining step, improving the binding energy for OER intermediates, which ensures the high intrinsic catalytic activity. In addition, the long-term stability (e.g., 200 h) at industrial-level current density (399 mV at 500 mA cm−2) holds the promise for the real application of the (Ni7Fe3)OOH-S electrode. Furthermore, a solar-powered electrolyzer consisting of the (Ni7Fe3)OOH-S anode and a 20 % Pt/C@CC cathode operates successfully at a low voltage of 1.46 V(10 mA cm−2) in 10 M KOH at 75 °C. Overall, the combined sulfidation and anodic displacement approach could be a general approach to prepare efficient and durable catalysts for water electrolyzers.

Mo-Doped Cu2S Multilayer Nanosheets Grown In Situ on Copper Foam for Efficient Hydrogen Evolution Reaction.

Metal sulfide electrocatalyst is developed as a cost-effective and promising candidate for hydrogen evolution reaction (HER). In this work, we report a novel Mo-doped Cu2S self-supported electrocatalyst grown in situ on three-dimensional copper foam via a facile sulfurization treatment method. Interestingly, Mo-Cu2S nanosheet structure increases the electrochemically active area, and the large fleecy multilayer flower structure assembled by small nanosheet facilitates the flow of electrolyte in and out. More broadly, the introduction of Mo can adjust the electronic structure, significantly increase the volmer step rate, and accelerate the reaction kinetics. As compared to the pure Cu2S self-supported electrocatalyst, the Mo-Cu2S/CF show much better alkaline HER performance with lower overpotential (18 mV at 10 mA cm−2, 322 mV at 100 mA cm−2) and long-term durability. Our work constructs a novel copper based in-situ metal sulfide electrocatalysts and provides a new idea to adjust the morphology and electronic structure by doping for promoting HER performance.

Optimized NiFe-Based Coordination Polymer Catalysts: Sulfur-Tuning and Operando Monitoring of Water Oxidation.

In-depth insights into the structure-activity relationships and complex reaction mechanisms of oxygen evolution reaction (OER) electrocatalysts are indispensable to efficiently generate clean hydrogen through water electrolysis. We introduce a convenient and effective sulfur heteroatom tuning strategy to optimize the performance of active Ni and Fe centers embedded into coordination polymer (CP) catalysts. Operando monitoring then provided the mechanistic understanding as to how exactly our facile sulfur engineering of Ni/Fe-CPs optimizes the local electronic structure of their active centers to facilitate dioxygen formation. The high OER activity of our optimized S-R-NiFe-CPs outperforms the most recent NiFe-based OER electrocatalysts. Specifically, we start from oxygen-deprived Od-R-NiFe-CPs and transform them into highly active Ni/Fe-CPs with tailored sulfur coordination environments and anionic deficiencies. Our operando X-ray absorption spectroscopy analyses reveal that sulfur introduction into our designed S-R-NiFe-CPs facilitates the formation of crucial highly oxidized Ni4+ and Fe4+ species, which generate oxygen-bridged NiIV-O-FeIV moieties that act as the true OER active intermediates. The advantage of our sulfur-doping strategy for enhanced OER is evident from comparison with sulfur-free Od-R-NiFe-CPs, where the formation of essential high-valent OER intermediates is hindered. Moreover, we propose a dual-site mechanism pathway, which is backed up with a combination of pH-dependent performance data and DFT calculations. Computational results support the benefits of sulfur modulation, where a lower energy barrier enables O-O bond formation atop the S-NiIV-O-FeIV-O moieties. Our convenient anionic tuning strategy facilitates the formation of active oxygen-bridged metal motifs and can thus promote the design of flexible and low-cost OER electrocatalysts.

Facile Sulfuration Route to Enhance the Supercapacitor Performance of 3D Petal‐like NiV‐Layered Double Hydroxide

The charge conductivity properties and ionic delivery of pseudocapacitive materials are important factors for the charge storage process. Herein, the new petal‐like S‐NiV‐layered double hydroxide (LDH) materials are successfully synthesized by a presynthetic solvothermal reaction and a sulfidation modification procedure. The specific capacitance of the new petal‐like S‐NiV‐LDHs electrode reaches 1403 F g−1 when the current density is 1 A g−1, and this is attributed to Ni3S2 formed on the surface of NiV‐LDHs. When the current density is up to 20 A g−1, the rate performance of the new petal‐like S‐NiV‐LDHs electrode is 65.04%. It can be seen that the comprehensive electrochemical performance of the new petal‐like S‐NiV‐LDHs is better than the petal‐like NiV‐LDHs before modification. When the power density of the S‐NiV‐LDHs//activated carbon asymmetric supercapacitor cell is 2278.48 W kg−1, its energy density is 20 Wh kg−1. The innovation of this work lies in that, based on the microstructure of petal‐like NiV‐LDHs with rich mesoporous structure, the surface of petal‐like NiV‐LDHs is slightly sulfurized, which makes the new petal‐like S‐NiV‐LDHs electrode material have smaller electrochemical impedance, richer oxidation states, richer chemical active sites, better energy storage, and cycle stability.

Amorphous FeCoNi-S as efficient bifunctional electrocatalysts for overall water splitting reaction

Developing bifunctional electrocatalysts for overall water splitting reaction is still highly desired but with large challenges. Herein, an amorphous FeCoNi-S electrocatalyst was developed using thioacetamide for the sulfuration of FeCoNi hydroxide during the hydrothermal process. The obtained catalyst exhibited an amorphous structure with hybrid bonds of metal-S bond and metal-O bonds in the catalyst system. The optimized catalyst showed a largely improved bifunctional catalytic ability to drive water splitting reaction in the alkaline electrolyte compared to the FeCoNi hydroxide. It required an overpotential of 280 mV and 80 mV (No-IR correction) to offer 10 mA/cm2 for water oxidation and reduction respectively; a low cell voltage of 1.55 V was required to reach 10 mA/cm2 for the water electrolysis with good stability for 12 h. Moreover, this catalyst system showed high catalytic stability, catalytic kinetics, and Faraday efficiency for water splitting reactions. Considering the very low intrinsic activity of FeCoNi hydroxide, the efficient bifunctional catalytic ability should result from the newly formed hybrid active sites of metallic metal-S species and the high valence state of metal oxide species. This work is effective in the bifunctional catalytic ability boosting for the transition metal materials by facile sulfuration in the hydrothermal approach.

Regeneration of well-performed anode material for sodium ion battery from waste lithium cobalt oxide via a facile sulfuration process

More attentions have been paid to the increasing expired spent lithium ion batteries due to the contained precious metals, especially Li and Co. However, the recycling systems at present have their limitations, such as unsatisfied recovery rate for pyrometallurgical process. In this study, a facile and efficient recovery method is proposed to simultaneously achieve the selective separation of metals and material regeneration. Based on the thermodynamic equilibrium diagrams and practical experiments, the product of recovery process, as expected, consists of soluble lithium salt and insoluble cobalt sulfide. Almost all of Co is recycled and transformed into regenerated material, while 89.76% Li is recycled separately. Moreover, the regenerated material exhibits excellent sodium storage performance (500 mAh/g at the current density of 2 A/g in 500 cycles), which is on a par with the similar reported materials synthesized by pure reagents. This study may provide a different perspective with potential values for the future large-scale recycling of spent lithium ion batteries.

Sulfur Compensation: A Promising Strategy against Capacity Decay in Li-S Batteries.

Drastic capacity decay as a result of active sulfur loss caused by the severe shuttle effect of dissolved polysulfides is the main obstacle in the commercial application of Li-S batteries. Various methods have been developed to suppress the active sulfur loss, but the results are far from ideal. Herein, we propose a facile sulfur compensation strategy to improve the cyclic stability of Li-S batteries. The strategy is to compensate sulfur to the cathode by chemical reactions between additional sulfur and lithium polysulfides diffusing away from the cathode. The compensatory sulfur can effectively mitigate the loss of active sulfur in the cathode side caused by the shuttle effect and thus maintain the high capacity of the battery during charging and discharging for long life cycle assessments. Using this strategy, the specific capacity of the assembled Li-S batteries was maintained at >700 mA h g-1 for more than 500 cycles at 1 C and >1000 mA h g-1 for ∼100 cycles at 0.1 C, while the capacity of control batteries rapidly decreased to <200 mA h g-1 under the same conditions.

Facile Sulfurization under Ambient Condition with Na2S to Fabricate Nanostructured Copper Sulfide.

The sulfurization reaction was investigated as a promising fabrication method for preparing metal sulfide nanomaterials. Traditional sulfurization processes generally require high vacuum systems, high reaction temperatures, and toxic chemicals, utilizing complicated procedures with poor composition and morphology controllability. Herein, a facile method is reported for synthesizing nanostructured copper sulfide using a sulfurization reaction with Na2S at room temperature under non-vacuum conditions. Moreover, we demonstrate that the morphology, composition, and optical properties of nanostructured copper sulfides could be controlled by the Na2S solution concentration and the reaction time. Nanostructured copper sulfides were synthesized in nanospheres, nanoplates, and nanoplate-based complex morphologies with various oxidation states. Furthermore, by comparing the optical properties of nanostructured copper sulfides with different oxidation states, we determined that reflectivity in the near infrared (NIR) region decreases with increasing oxidation states. These results reveal that the Na2S solution concentration and reaction time are key factors for designing nanostructured copper sulfides, providing new insights for synthesis methods of metal sulfide nanomaterials.

Tuning the electrochemical properties of nanostructured CoMoO4 and NiMoO4 via a facile sulfurization process for overall water splitting and supercapacitors

In contemporary society, there are many different ways that energy is used in daily life. From applications that require a high energy density to long-term storage in a stable manner, the requirements for energy usage are diverse. Therefore, the greater the number of uses a designed material exhibits, the more practical it may be for wide-scale manufacture. Two areas of particular interest for energy applications are fuel cells (to generate energy) and supercapacitors (to store energy). To provide cheaper and more durable alternatives for energy storage, electrodes containing CoMoO4, NiMoO4, CoMoS4, and NiMoS4 were synthesized. The electrodes were synthesized through a hydrothermal method using Ni-foam as the substrate then tested as electrocatalysts for water splitting and electrodes for supercapacitor. As an electrocatalyst for hydrogen evolution reaction, NiMoS4 displayed the lowest overpotential of 148 mV with a Tafel slope of 159 mV/dec. On the other hand, CoMoS4 showed the lowest overpotential of 189 mV with a Tafel slope of 78 mV/dec among all four samples for oxygen evolution reactions. In terms of energy storage, the CoMoO4 had the highest specific capacitance of 2652 F/g at a current density of 0.5 A/g with an averaged charge retention of 91% and a Coulombic efficiency of 99% after 10,000 cycles.

Phase Engineering of Metal Oxides for Enhanced Energy Application

A recent ongoing technological breakthrough in numerous fields including eco-friendly energy, electronics, transportation, defense, and security, etc. is immensely challenged by the inadequate capability of energy devices. Deliberate efforts in researches that could lead to obtaining reliable energy devices are being carried out applying diverse approaches. In this study, the structure of the materials has been considered and examine its impact on electrocatalysis and hence its green fuel production capability. The porous NiFe-oxide nanocubes (NCs) system is generated from a NiFe Prussian analog metal-organic framework. In 1M KOH, the nanocubes demonstrate overpotentials of 54 mV and 298 mV for HER and OER, respectively to deliver a current of 10 mA/cm2 whereas the spherical NiFe-oxide nanoparticles (NPs) of similar composition showed respective overpotentials of 187 mV and 258 mV for HER and OER. The incredible catalytic performance of NiFe-NCs is attributed to the exposure of active sites at the edges and vertices of NCs. Moreover, both the NPs and NCs showed interesting property changes after being sulfurized. Sulfurized nanocubes (NCs-S) demonstrated overpotentials of 177 mV and 241 mV whilst sulfurized nanoparticles (NPs-S) showed overpotentials of 152 mV and 216 mV for HER and OER, respectively. On top of that, the electrochemical measurements in 3M KOH showed the increase of the specific capacitances of NCs and NPs after sulfurization from 69 to 604 F/g and from 185 to 514F/g, respectively, at a current density of 1 A/g. Our study suggests that a facile sulfurization process could significantly improve catalytic activities of metal oxides.

Multi-dimensional hierarchical CoS2@MXene as trifunctional electrocatalysts for zinc-air batteries and overall water splitting

The demanding all-in-one electrocatalyst system for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in zinc-air batteries or water splitting requires elaborate material manufacturing, which is usually complicated and time-consuming. Efficient interface engineering between MXene and highly active electrocatalytic species (CoS2) is, herein, achieved by an in situ hydrothermal growth and facile sulfurization process. The CoS2@MXene electrocatalyst is composed by one-dimensional CoS2 nanowires and two-dimensional MXene nanosheets, which lead to a hierarchical structure (large specific surface area and abundant active sites), a spatial electron redistribution (high intrinsic activity), and high anchoring strength (superior performance stability). Therefore, the electrocatalyst achieves enhanced catalytic activity and long-time stability for ORR (a half-wave potential of 0.80 V), OER (an overpotential of 270 mV at 10 mA cm−2, i.e., η10 = 270 mV) and HER (η10 = 175 mV). Furthermore, the asymmetry water splitting system based on the CoS2@MXene composites delivers a low overall voltage of 1.63 V at 10 mA cm−2. The solid-state zinc-air batteries using CoS2@MXene as the air cathode display a small charge-discharge voltage gap (0.53 V at 1 mA cm−2) and superior stability (60 circles and 20-h continuous test). The energy interconversion between the chemical energy and electricity can be achieved by a self-powered system via integrating the water splitting system and quasi-solid-state zinc-air batteries. Supported by in situ Raman analyses, the formation of cobalt oxyhydroxide species provides the active sites for water oxidation. This study paves a promising avenue for the design and application of multifunctional nanocatalysts.

The fabrication of hierarchical MoO2@MoS2/rGO composite as high reversible anode material for lithium ion batteries

Although nanometer-sized MoO2 materials demonstrate enhanced electrochemical performance for lithium ion batteries (LIBs), they are suffering from new issues, like low initial Coulombic efficiency (ICE) and volumetric energy density. Herein, submicrometer-sized hierarchical MoO2@MoS2/rGO composites are fabricated through facile sulfuration treatment and subsequent hydrothermal reaction. When tested as anode for LIB, the optimum sample delivers an initial reversible capacity of 833 mAh g−1 with ICE of 80.6% and improved cycling stability (733 mAh g−1) after 80 cycles at 200 mA g−1 compared to bare sample (409 mAh g−1). Excellent rate performance with a capacity of 645 mAh g−1 at 4 A g−1 is also demonstrated. The high ICE should be attributed to the optimized interface, on which the large interlayer spacing of MoS2 and the high conductivity of MoO2 and rGO significantly facilitate the transfer of Li+/e−, improving the reversibility of lithiation/delithiation process. Moreover, the low specific surface area of 1.53 m2 g−1 for MoO2@MoS2/rGO efficiently suppress the decomposition of electrolyte. The tentatively assembled full cell (MoO2@MoS2/rGO//LiCoO2) maintains a reversible capacity of 694 mAh g−1 at 200 mA g−1 after 40 cycles. This work is expected to inspire the design of low cost and high-performance MoO2-based electrode materials for energy storage application.

(Gold triangular nanoplate core)@(silver shell) nanostructures as highly sensitive and selective plasmonic nanoprobes for hydrogen sulfide detection.

Hydrogen sulfide plays a significant role in living beings, while its abnormal concentration is related to many diseases. Besides, H2S gas is harmful to human beings and the environment. The detection of H2S has therefore attracted much attention in the past several decades. Herein, highly sensitive and selective H2S plasmonic nanoprobes (gold triangular nanoplate core)@(silver shell) (AuTNP@Ag) are reported. By virtue of the high refractive index sensitivity of Au TNPs to the surrounding medium and facile sulfurization of silver by sulfur ions, AuTNP@Ag exhibits great sensitivity to both sulfur ions and H2S gas. The shifts of the plasmon peak are as large as 16 nm for the ventilation of 1 ppm hydrogen sulfide. AuTNP@Ag nanoprobes also exhibit very good sensing linearity at low concentrations of sulfur ions. Moreover, excellent sensing selectivity for sulfur ions is obtained. A type of test gel, which can produce a naked-eye observable color change when exposed to 1-100 ppm hydrogen sulfide gas, is developed using AuTNP@Ag nanoprobes. Owing to the high sensitivity, linearity, and selectivity of the Au TNP@Ag nanoprobes for hydrogen sulfide sensing, this work paves the way for the plasmonic detection of hydrogen sulfide in both biological and environmental applications.

Stepwise Conversion from GeO2 to [MGe4S10]n3n- (M = Cu, Ag) Polymer via Isolatable [Ge2S6]4- and [Ge4S10]4- Anions by Virtue of Templating Technique.

Rational synthesis of inorganic matter remains a great challenge encountered with modern synthetic chemistry. Here we reported the stepwise solvothermal conversion from GeO2 to [MGe4S10]n3n- (M = Cu, Ag) polymer via isolatable [Ge2S6]4- and [Ge4S10]4- anions by virtue of templating technique. The facile sulfuration of GeO2 resulted in the methylammonium-templated dimeric thiogermanate [CH3NH3]4Ge2S6 (1). This was used subsequently as a precursor for the formation of adamantane-like [Ge4S10]4- cluster, which was isolated as a mixed methylammonium/ethylammonium salt [CH3CH2NH3]3[CH3NH3]Ge4S10 (2). Compound 2 was then successfully used as a precursor to react with Cu+ and Ag+ cations in the presence of tetraethylammonium, resulting in alternating copolymeric products [(CH3CH2)4N]3MGe4S10 (M = Cu (3), Ag (4)), whose anionic moieties feature a novel zigzag chainlike structure constructed by [Ge4S10]4- clusters via two-coordinate Cu+/Ag+ linkers. Mixed amine/ethanol or deep eutectic solvents were applied as media for the syntheses of 1-4, and all the products were characterized in the solid state and solution. Crystal structural analysis of the title compounds revealed significant templating roles of the alkylammonium cations as both space-filling agents and hydrogen-bonding donors, suggesting the structure-directing mechanism for the species formation and crystal growth. The design and optimization of multistep structural conversion upon templating effects would be beneficial for drawing rational, predictable pathways for inorganic synthesis.

A multi-functional sulfurized polyacrylonitrile interlayer for lithium sulfur batteries

Abstract Functional interlayers applied in lithium sulfur batteries have been widely investigated due to its high reutilization of the diffused polysulfides and good cycle stability. However, the functional layer on the modified separator will indirectly decrease the sulfur content, which is harmful to the energy density of the whole cell. Herein, we report sulfurized polyacrylonitrile (SPAN) modified functional separator which can deliver quite a lot reversible capacity to overcome the shortage of traditional interlayer. Meanwhile, S and N dual dopants can offer abundant adsorptive sites and have strong chemisorption to polysulfides. Thus, with this modified separator, a facile sulfur cathode can deliver a high initial discharge capacity of 1338 mAh/g and merely 0.178% capacity fade per cycle over 200 cycles at 1 C. The results indicate that SPAN is a promising material for functional interlayer between cathode and separator.

Zinc cobalt sulfide nanoparticles as high performance electrode material for asymmetric supercapacitor

Zinc cobalt sulfide (ZCS) is a promising and high performance electrode material for pseudocapacitors due to its good electrical conductivity, abundant active sites and rich valence states. In this work, zinc cobalt oxide (ZCO) nanoparticles are firstly synthesized via a hydrothermal method assisted by hexadecyltrimethyl ammonium bromide (CTAB), and then transformed into zinc cobalt sulfide nanoparticles (ZCS NPs) using a facile sulfuration process. The average diameter of ZCS NPs is estimated to be about 15 nm, which is beneficial for Faradaic redox reactions in energy storage process due to their numerous active surfaces. The ZCS NPs are then coated onto a nickel foam to form the working electrode of supercapacitors. Because the ZCS electrode has lower series and charge transfer resistance, and also higher ion diffusion rate than that of the ZCO electrode, it achieves a large specific capacitance of 1269.1 F g−1 at 0.5 A g−1 in 2 M KOH electrolyte, which is four times more than that of the ZCO electrode (e.g., 295.8 F g−1 at 0.5 A g−1). In addition, an asymmetric supercapacitor using the ZCS NPs as the positive electrode and activated carbon as the negative electrode is assembled, which delivers a high energy density of 45.4 Wh kg−1 at a power density of 805.0 W kg−1, with an excellent cycling stability (91.6% retention of the initial capacitance over 5000 cycles).

Highly tunable Raman scattering and transport in layered magnetic Cr2S3 nanoplates grown by sulfurization

The recent discovery of intrinsic two-dimensional (2D) ferromagnetism has sparked growing interests in the search for new 2D magnets with diverse and tunable properties for both fundamental scientific advances and novel spintronic applications. Here we report on the synthesis of layered chromium sulfide (Cr2S3) nanoplates via a facile sulfurization approach and the studies of their highly tunable Raman and (magneto-)transport properties. Depending on the specific growth conditions, we have achieved both epitaxial (and hence strained) and non-epitaxial nanoplates of Cr2S3 on the c-cut sapphire substrates. Via Raman scattering and density functional theory (DFT) calculations, we determined both types of nanoplates to be a rhombohedral R3 phase whose bulk counterpart exhibits weak ferromagnetism below a metal–insulator transition (MIT) temperature of ~120 K. Compressive strain from the lattice-mismatched substrate yields a red-shift of up to 8 cm−1 in Raman peaks in comparison to the strain-free nanoplates obtained from the non-epitaxial growth. The strain-free nanoplate shows a variable-range-hopping type of insulating behavior, while the strained nanoplates exhibit an enhanced MIT up to ~275 K in comparison to 120 K in bulk samples. The room temperature resistivity values of the two types of nanoplates differ by 2 to 3 orders of magnitude. The distinct transport properties can be understood qualitatively based on the electronic band structures calculated by DFT.