Heterostructural composite of few-layered MoS2/hexagonal MoO2 particles/graphene as anode material for highly reversible lithium/sodium storage

The heterostructural construction of metal disulfide/oxide is essential in the electrochemical performance as anode material for lithium- and sodium-ion batteries (LIBs and SIBs). In this work, an integrated composite of molybdenum disulfide (MoS₂) and hexagonal molybdenum dioxide (MoO₂) together enwrapped in reduced graphene oxide (rGO) is synthesized under hydrothermal condition. In the pelletizing MoS₂-MoO₂/rGO composite, rGO as substrate effectively prevents the restacking and pulverization of MoS₂-MoO₂ during a long cycling process. Meanwhile, the synergistic effect among the MoS₂, MoO₂, and rGO components are responsible for abundant active sites and shorten ionic transport channels. When evaluating as anode material for LIB, MoS₂-MoO₂/rGO sample presents excellent cyclic performance and still delivers a high capacity of 1062.3 mA h g⁻¹ after 120 cycles at 0.2 A g⁻¹; evaluating in a SIB at 0.04 A g⁻¹, it presents excellent cyclic performance and delivers 430 mA h g⁻¹ at the 80th cycle. The heterostructural composite MoS₂-MoO₂/rGO is one of the candidate anode materials for high-performance LIB and SIB.     

A free-standing electrode based on 2D SnS2 nanoplates@3D carbon foam for high performance supercapacitors

A reasonable formation of an electrode material with three-dimensional (3D) microstructure for supercapacitors was proposed. Two-dimensional (2D) SnS₂ nanoplates were uniformly in situ grown on 3D carbon foam (CF) through a controllable strategy. The composite displayed excellent electrochemical performance due to the synergistic effect of SnS₂ and CF. The SnS₂@CF-2 composite containing 23.92 wt% of SnS₂ has a superior specific capacitance of 283.6 F g⁻¹ at the current density of 1 A g⁻¹. Moreover, a symmetric supercapacitor based on SnS₂@CF-2 composite has a capacitance of 82.5 F g⁻¹ at 1 A g⁻¹ and a high energy density of 13.9 Wh kg⁻¹ at the power density of 551.7 W kg⁻¹.     

Flexible all-solid-state asymmetric supercapacitor based on three-dimensional MoS2/Ketjen black nanoflower arrays

High electrochemical properties of negative electrode materials are highly desirable for flexible asymmetric supercapacitors (ASCs). Although benefiting from the unique structure and broad operation potential, molybdenum disulfide (MoS₂) has caused concern as a negative electrode material because its low electrochemical stability and poor conductivity hinder the exploitation of its application in flexible ASCs. Here we investigated a facile two-step hydrothermal approach to fabricate MoS₂/Ketjen black (KB) composites on flexible carbon cloth. Following the construction of flower-like MoS₂ on carbon cloth, KB nanospheres were embedded in MoS₂ via a secondary hydrothermal route. The as-prepared MoS₂/KB electrode presents a high capacitance of 429 F g⁻¹ at a current specific of 1 A g¹. In addition, the hybrid ASC device of NiCo₂O₄//MoS₂/KB was built, which delivers a high energy density of 25.7 Wh kg⁻¹ and power density of 16 kW kg⁻¹. These results are ascribed to the favorable structure of MoS₂ and inherently superior conductivity of KB, which improves wettability, structural stability and electronic conductivity. In brief, the proposed all-solid-state ASC device offers potential application in future portable electronics and flexible energy storage devices.     

Highly efficient Bi2O3/MoS2 p-n heterojunction photocatalyst for H2 evolution from water splitting

The design of p-n heterojunction photocatalysts to overcome the drawbacks of low photocatalytic activity that results from the recombination of charge carriers and narrow photo-response range is promising technique for future energy. Here, we demonstrate the facile hydrothermal synthesis for the preparation of Bi₂O₃/MoS₂ p-n heterojunction photocatalysts with tunable loading amount of Bi₂O₃ (0–15 wt%). The structure, surface morphology, composition and optical properties of heterostructures were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–visible absorption spectroscopy, Brunauer-Emmett-Teller (BET) surface area, photoluminescence (PL), electrochemical impedance spectroscopy (EIS). Compare to pure Bi₂O₃ and MoS_2, the Bi₂O₃/MoS₂ heterostructures displayed significantly superior performance for photocatalytic hydrogen (H₂) production using visible photo-irradiation. The maximum performance for hydrogen evolution was achieved over Bi₂O₃/MoS₂ photocatalyst (10 μmol h⁻¹g⁻¹) with Bi₂O₃ content of 11 wt%, which was approximately ten times higher than pure Bi₂O₃ (1.1 μmol h⁻¹g⁻¹) and MoS₂ (1.2 μmol h⁻¹g⁻¹) photocatalyst. The superior performance was attributed to the robust light harvesting ability, enhanced charge carrier separation via gradual charge transferred pathway. Moreover, the increased efficiency of Bi₂O₃/MoS₂ heterostructure photocatalyst is discussed through proposed mechanism based on observed performance, band gap and band position calculations, PL and EIS data.     

Cobalt-doped layered lithium nickel oxide as a three-in-one electrode for lithium-ion and sodium-ion batteries and supercapacitor applications

Layered LiNi_0.94Co_0.06O₂ (LNCO) was prepared and explored as an energy-storage material for Li-ion (LIBs), Na-ion (SIBs) batteries as well as supercapacitor application for the first time. All the physical and morphological characterizations were studied for the sample LNCO. The result displays good thermal stability, phase purity in the crystal structure, appreciable Brunauer-Emmett-Teller (BET) surface area (5.53 m² g⁻¹) and possesses cubic morphology. The cobalt was identified in lithium nickel oxide with binding energies at 794.02, 779.04 and 784.30 eV, respectively. In the case of LIBs, LNCO exists with a minimal difference of 5 mAh g⁻¹, even when cycled from 2C to 0.1C. After 200 cycles, the specific capacity, 247 mAh g⁻¹, is obtained for the cell with retention of 97.8% (efficiency 99.8%) at 0.1C. In SIBs, at 0.1C, the discharge capacity of 182 mAh g⁻¹ was restored even when cycled after 2C. After 200 cycles, a discharge capacity of 204 mAh g⁻¹ is ensured with retention of 96.6% (efficiency of 99.4% at 0.1C). In supercapacitor, the electrode, LNCO, delivered a specific capacity of 300 F g⁻¹ at 0.5 A g⁻¹. Therefore, LNCO is highly recommended as a suitable electrode material for fulfilling the requirement of energy-storage applications.     

Hierarchitecture Co2(OH)3Cl@FeCo2O4 composite as a novel and high-performance electrode material applied in supercapacitor

One-step hydrothermal reaction has successfully been used to prepared three-dimensional hierarchitecture Co₂(OH)₃Cl@FeCo₂O₄ composite without any annealing treatment. The samples are investigated to confirm the crystal structure, elemental composition, morphology structure and electrochemical performance. The results show the sample has a three-dimensional hierarchitecture that nanoblocks are assembled with nanoparticles. And the specific surface area is 87.5 m² g⁻¹ and the total pore volume is 0.17 cm³ g⁻¹. Meanwhile, the composite shows a high specific capacitance of 1110.0 F·g⁻¹ at 1 A·g⁻¹ and great cycling stability with 98.8% capacitance retention after 3000 cycles. To evaluate the electrochemical performances, the results are used to compare with the Co₂(OH)₃Cl and FeCo₂O₄ nanomaterials, indicating a higher capacitance and longer cycle stability shown by the as-synthesized sample. The as-synthesized Co₂(OH)₃Cl@FeCo₂O₄ composite has an outstanding electrochemical performance, predicting an enormous potential and promising future as a novel electrode material applied in supercapacitor.     

Improving hydrogen evolution reaction and capacitive properties on CoS/MoS2 decorated carbon fibers

We report a facile method to transform abundantly dumped banana stem fibers into carbon fibers (CFs) useful for energy applications. The CFs surface area is increased by varying the quantity of KOH activation to 488 m²g^-1. The solvothermal method is used to synthesize CoS, CoS/MoS₂ and also grown on the activated carbon fibers (ACFs). Nano nodules of CoS arranged into sheets and layers of MoS₂ stacked together were found in FESEM analysis. The morphology of the CoS/MoS₂ differs when grown on ACFs. The growth of CoS/MoS₂ along the ACFs length prevents any stacking of the pseudocapacitance materials. The ternary composite ACFs/CoS/MoS₂ exhibits superior supercapacitor behavior as well as hydrogen evolution reaction (HER) due to the synergetic effect of the conducting ACF surface and redox active CoS/MoS₂. A maximum specific capacitance of 733 Fg^-1, energy and power density of 33 WhKg⁻¹ and 999 WKg^-1 respectively are obtained. A low Tafel slope value of 61 mVdec⁻¹ is obtained for the ACFs/CoS/MoS₂ ternary composite electrode. The present work therefore offers a fresh insight into the effective conversion of waste materials into electrode material for energy storage and conversion applications.     

Fabrication of direct Z-scheme MoO3/N–MoS2 photocatalyst for synergistically enhanced H2 production

A novel visible-light active MoO₃/N–MoS₂ heterostructure photocatalyst was fabricated via hydrothermal process. The structure, morphology and optical characteristics were studied using X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), UV–visible and photoluminescence (PL) spectroscopies. The results indicated that loading pf MoO₃ and nitrogen doping played main influence role in advancing the morphology and optical characteristics. Upon visible photo-illumination, the MoO₃/N–MoS₂ sample displayed superior photocatalytic H₂-production activity (118 μ mol h⁻¹g⁻¹), which was about four-time higher than that of pure MoS₂ (30 μ mol h⁻¹g⁻¹). The enhancement in photocatalytic performance of MoO₃/N–MoS₂ photocatalyst can be ascribed to the development of direct Z-scheme heterostructure, which promoted the photo-excited electrons/holes transfer and separation. The recycling experiment verified that the MoO₃/N–MoS₂ photocatalyst had superior cyclic activity and stability, implying promising applications in energy field.     

Layered molybdenum disulfide coated carbon hollow spheres synthesized through supramolecular self-assembly applied to supercapacitors

Through supramolecular assembly method, molybdenum disulfide (MoS₂) is uniformly anchored on the mesoporous hollow carbon spheres (HCS), which are obtained by hard template method. The introduction of HCS can prevent the agglomeration of MoS₂ and decrease the electric resistance of the compound material MoS₂@HCS. The composite of MoS₂@HCS-17 also owns a specific surface area of 119.0 m² g⁻¹. For MoS₂@HCS-17, SEM and TEM results exhibit that flaky MoS₂ is uniformly covered on hollow carbon spheres and possesses an expanded layered structure. Electrochemical test results show that MoS₂@HCS-17 can reach 314.5F g⁻¹ at 1A g⁻¹. When tested at a scan speed of 50 mV s⁻¹_, there is still 87% specific capacity retention for MoS₂@HCS-17 after 4000 cycles. Moreover, the assembled MnO₂//MoS₂@HCS asymmetric supercapacitor manifests 34.0 Wh kg⁻¹ at 611.6 W kg⁻¹. Bending by 180°, our assembled device still keeps stable capacitive performance. This asymmetric supercapacitor also keeps almost 93% capacity maintained after 2000 cycles.     

Well-dispersed Sb2O3 nanoparticles encapsulated in multi-channel-carbon nanofibers as high-performance anode materials for Li/dual-ion batteries

Reasonable design and construction of electrode materials with high-performance and low-cost are essential for Li-ion batteries (LIBs) and dual-ion batteries (DIBs). Herein, an eco-friendly and facile strategy is proposed to encapsulate Sb₂O₃ nanoparticles in one-dimensional (1D) multi-nanochannel-containing carbon nanofibers (Sb₂O₃@MCNF) using the electrospinning method as well as the subsequent calcination. Such unique construction not only effectively reduces the large volume variation during cycling, but also achieves the fast Li⁺/e^? transportation. As a result, the optimized sample with the precursor triphenylantimony (III) content of 0.35 g (Sb₂O₃@MCNF-0.35) exhibits superior electrochemical performance as anode materials for LIBs and Li-based DIBs (LDIBs), including high reversible capacity (~333.5 mAh g^?1 at 1 A g^?1 for LIBs and 233.5 mAh g^?1 at 0.2 A g^?1 for LDIBs) and favorable cycling stability (over 800 cycles for LIBs and 100 cycles for LDIBs). These results demonstrate that the well-designed Sb₂O₃@MCNF-0.35 can availably boost the electrochemical performance, which provides vast potential for applications in the field of high-performance energy storage equipment.     

Morphology and electrochemical behaviour of ruthenium oxide thin film deposited on carbon paper

In order to improve the efficiency of ruthenium dioxide, RuO₂, as an electrochemical capacitor electrode, a RuO₂ thin film is deposited on carbon paper and its structure and properties are evaluated. This new composite material is prepared via solution dip-coating of a Ru-ethoxide precursor and heat conversion. The coating thickness is easily controlled by varying the number of repetitions of the preparation process. The resulting structure consists of a by homogeneously coated RuO₂ film on carbon paper which has a porous graphite matrix. Extensive electrochemical studies have been performed in 1 M H₂SO₄ electrolyte in order to evaluate the properties of the composite as an electrode in an electrochemical capacitor. The composite material shows not only high specific capacitance (620 F g⁻¹) but also good power characteristics.     

Metal doped black phosphorus/molybdenum disulfide (BP/MoS2–Y (Y: Ni,Co)) heterojunctions for the photocatalytic hydrogen evolution and electrochemical nitrite sensing applications

Recently, 2D semiconductor-based heterojunctions emerge as a focal point of intensive research owing to their unique properties, including efficient charge separation and large interface areas. Herein, Ni or Co-doped black phosphorus/molybdenum disulfide (BP/MoS₂–Y (Y: Ni, Co)) heterojunctions fabricate for photocatalytic H₂ evolution and electrochemical nitrite sensor. Compared to the BP/MoS₂, the BP/MoS₂–Ni and BP/MoS₂–Co exhibit enhanced H₂ performance, as 6.4139 mmol h⁻¹ g⁻¹ and 7.4282 mmol h⁻¹ g⁻¹, respectively, in the presence of Eosin-Y (λ ≥ 420 nm). Furthermore, BP/MoS₂–Co applies as an electrocatalyst on a GCE for the electrochemical detection of nitrite. To optimize the nitrite sensing performance of BP/MoS₂–Co, the effect of the pH, amount of material, scan rates, and other conditions study in detail. The BP/MoS₂–Co displays a linear response within the range of 100–2000 μM with a detection limit of 4.1 μM for DPV. This work can offer an opportunity for hydrogen systems as well as electrochemical sensor applications.     

Synthesis of nickel hydroxide/reduced graphene oxide composite thin films for water splitting application

Facile synthesis of highly efficient and low-cost electrocatalyst for oxygen evolution reaction (OER) is important for large-scale hydrogen production. Herein, nickel hydroxide/reduced graphene oxide (Ni(OH)₂/rGO) composite thin film was fabricated using dip-coating followed by electrodeposition method on Ni foam substrate at room temperature. The deposited composite film shows amorphous nature with ultra-thin Ni(OH)₂ nanosheets vertically coated on rGO surface, which provides large electrochemical surface area and abundant catalytically active sites. It exhibits a low overpotential of 260 mV @10 mA cm⁻² as compared to the pristine electrodes and excellent long-term stability up to 20 hours in 1 M KOH solution. The electrochemical active surface area and Tafel slope of the composite electrode are 20.2 mF cm⁻² and 35 mV dec⁻¹, respectively. The superior water oxidation performance is a result of high catalytically active sites and improved conductivity of the composite electrode.     

Hydrogen generation by photocatalytic reforming of glucose with heterostructured CdS/MoS2 composites under visible light irradiation

A binary heterostructured CdS/MoS₂ flowerlike composite photocatalysts was synthesized via a simple one-pot hydrothermal method. This photocatalyst demonstrated higher photocatalytic hydrogen production activity than pure MoS₂. The heterojunction formed between MoS₂ and CdS seems to promote interfacial charge transfer (IFCT), suppress the recombination of photogenerated electron–hole pairs, and enhance the hydrogen generation. Based on the good match between the conduction band (CB) edge of CdS and that of MoS₂, electrons in the CB of CdS can be transferred to MoS₂ easily through the heterojunction between them, which prevents the accumulation of electrons in the CB of CdS, inhibiting photocorrosion itself and greatly enhancing stability of catalyst. Hydrogen evolution reaction (HER) using Na₂S/Na₂SO₃ or glucose as sacrificial agents in aqueous solution was investigated. The ratio between CdS and MoS₂ plays an important role in the photocatalytic hydrogen generation. When the ratio between CdS and MoS₂ reaches 40 wt%, the photocatalyst showed a superior H₂ evolution rate of 55.0 mmol g⁻¹ h⁻¹ with glucose as sacrificial agent under visible light, which is 1.2 times higher than using Na₂S/Na₂SO₃ as sacrificial agent. Our experimental results demonstrate that MoS₂-based binary heterostructured composites are promising for photocorrosion inhibition and highly efficient H₂ generation.     

Bio-enzymatic synthesis of nitrogen-doped porous carbon/SnO2/carbon microspheres as high-performance composite materials for lithium-ion and sodium-ion batteries

In this study, a nitrogen-doped 3D porous starch-derived carbon/SnO₂/carbon (PSC/SnO₂/C) composite is synthesized with porous starch as a carbon source by biological enzymatic hydrolysis. Compared with the traditional complex acid-base reagent method, the biological enzymatic method is more environmentally friendly and economical, and it can also naturally introduce nitrogen sources and dope the carbon layer. Many mesoporous nanostructures provide enough buffer space and promote the ions' and electrons’ transmission rate. The formation of the Sn–O–C bond between SnO₂ and carbon ensures the stability of the structure. As a result, the PSC/SnO₂/C composite exhibits a high initial discharge capacity (1802 mAhg⁻¹ at 0.2 A g⁻¹ for LIBs and 549 mAh g⁻¹ at 0.1 A g⁻¹ for SIBs) and good cycle stability (701 mAh g⁻¹ at 0.2 A g⁻¹ after 100 cycles for LIBs and 271 mAh g⁻¹ at 0.1 A g⁻¹ after 100 cycles for SIBs). This synthesis method can prepare other energy storage systems such as fuel cells, supercapacitors, and metal ion batteries.     

Improved potassium ion storage performance of graphite by atomic layer deposition of aluminum oxide coatings

In the context of large scale and low-cost energy storage, the emerging potassium-ion batteries (PIBs) are one potential energy storage system. Graphite, a commercial anode material widely used in lithium-ion batteries (LIBs), can be directly applied to PIBs through forming the stage I graphite intercalation compound (KC₈). However, the dramatic volume expansion during the formation of KC₈ can result in poor cycling performance. In this work, one Al₂O₃ atomic layer coated on the surface of graphite via atomic layer deposition (ALD) process, aiming to construct a stable solid electrode interface and enhance the performance of graphite anode in PIBs. The electrochemical performance analysis shows that the 20 cycles Al₂O₃ deposited graphite have improved cycle stability of 223 mAh g⁻¹ at 50 mA g⁻¹ after 50 cycles compared with the raw graphite anode of 92 mAh g⁻¹.     

Novel carbon nanofiber-cobalt oxide composites for lithium storage with large capacity and high reversibility

Carbon nanofiber (CNF)-Co₃O₄ composites were prepared by the calcination of CNF-Co(OH)₂ composite precursors under argon atmosphere. SEM and TEM observations revealed that Co₃O₄ particles in the size of ca. 30–50 nm were highly dispersed and attached on the surface of the reticular CNF and all around. As for electrode materials, the CNF-Co₃O₄ composite demonstrated very high reversible capacity (more than 900 mAh g⁻¹ in the initial 50 cycles) and excellent electrochemical cycling stability. The improved cycle performance of the CNF-Co₃O₄ composite can be attributed to its unique reticular and morphology-stable composite texture with high dispersion of Co₃O₄ nanoparticles on the CNF that provides excellent electronic and ionic conduction pathway for the electrochemical processes.     

MoS2 supported on hydrogenated TiO2 heterostructure film as photocathode for photoelectrochemical hydrogen production

The substitution of noble metal platinum catalyst is one of the important research contents for sustainable development and is also the key to the practical application of photoelectrochemical (PEC) hydrogen production. In this work, we loaded the 1T-2H mixed phase MoS₂ on the hydrogenated anatase/rutile heterophase TiO₂ (A-H-RTNA) by hydrothermal method to prepare a new MoS₂/A-H-RTNA electrode material. The prepared material exhibited higher carrier density, lower PL intensity and higher conductivity than Pt/A-H-RTNA because 1T-MoS₂ has more active sites and lower charge transfer resistance than Pt. With the bias voltage of −0.4 V, the optimized 16MoS₂/A-H-RTNA as photocathode shows the largest PEC hydrogen production rate of 1840 mmol m⁻² h⁻¹, which is 2.9 and 2.2 times higher than those of A-H-RTNA (625 mmol m⁻² h⁻¹) and Pt/A-H-RTNA (848 mmol m⁻² h⁻¹), respectively. We innovatively used the prepared 16MoS₂/A-H-RTNA film as counter electrode instead of Pt electrode to construct a PEC system without any noble-metal. The result demonstrates that the noble-metal-free MoS₂ loaded on TiO₂ electrode as counter electrode has 75% PEC activity of noble metal Pt electrode. This study develops a PEC method for hydrogen evolution, which no longer depends on precious metal platinum as cathode.     

Optically active polymer nanocomposite composed of polyaniline,polyacrylonitrile and green-synthesized graphene quantum dot for supercapacitor application

Development of stable and optically active composite film that can show efficient supercapacitor activity is a challenging research interest in material science. A polymer nanocomposite film composed of a green synthesised graphene quantum dot (GQD, G) doped polyacrylonitrile (PAN) and polyaniline (PANI) systems, designated as PAN-PANI@G, have been prepared. The critical loading concentration of prepared composite and its effect on the physicochemical, optical and electrical analysis were systematically studied in detail. PAN-PANI@G composite showed an appreciable electrical conductivity (2.362 × 10⁻⁶ S m⁻¹) and optical absorbance at λ_max ~270 nm. Physicochemical characterizations by XRD, FTIR and TEM analysis reveal chemical interaction between the individual components via intermolecular hydrogen bonding. Analysed particle size of GQD in the polymer membrane was found to be about two times lesser than that of the pure GQD highlighting synergic interaction between the individual GQD and PAN/PANI matrix. A specific capacitance value of the polymer composites that have been modified on screen-printed carbon electrode were tested by cyclic voltammetric and galvanostatic charge-discharge techniques in 0.1 M H₂SO₄ solution. Calculated supercapacitor values at an applied current density, 670 mA g⁻¹ are in a range of 105–587 F g⁻¹ cm⁻² which are approximately 2–1300 times higher than the values reported for polypyrrole and polyaniline based polymer composite film in the literature. As a preliminary extension of this study, the optimal PAN/PANI@G nanocomposite of GQD loading, 1.5 wt% was extended to prototype supercapacitor cell application in combination with a dilute solution of NaCl along with suitable conducting plates. When 3 V DC power was supplied for 4 min, the prototype cell produced an operating voltage of 1.4 V for 1 h of operating time.     

α-Fe2O3 hollow microspheres assembled by ultra-thin nanoflakes exposed with (241) high-index facet: Solvothermal synthesis,lithium storage performance,and superparamagnetic property

Hierarchical α-Fe₂O₃ hollow microspheres are synthesized through a convenient and effective solvothermal method. The α-Fe₂O₃ hollow microspheres have a mean diameter of 1 μm and they are composed of ultra-thin nanoflakes with an average thickness of only 5 nm. More importantly, the primary α-Fe₂O₃ nanoflakes are preferentially enclosed by (241) high-index facet. When the α-Fe₂O₃ hollow microspheres are served as anodes for lithium-ion batteries, their first discharge capacities is 1749.1 mAh g⁻¹ at 0.1 A g⁻¹, and the corresponding values are 914.0, 628.7, and 420.5 mAh g⁻¹ at high current densities of 0.2, 0.5, and 1 A g⁻¹, respectively. The improved electrochemical performance can be attributed to the synergistic effect of the hierarchical hollow microstructure, exposed high-index (241) facet, and thin primary nanoflakes. Additionally, the α-Fe₂O₃ hollow microspheres have superparamagnetic properties due to the ultra-thin thickness of the primary α-Fe₂O₃ nanoflakes.