Nanosheet Networks Research Articles

One-step synthesis of Fe-Ni hydroxide nanosheets derived from bimetallic foam for efficient electrocatalytic oxygen evolution and overall water splitting

The research of superior water oxidation electrodes is essential for the green energy in the form of hydrogen by way of electrolytic water splitting, and still remains challenging. Based upon dealloying foam, Fe-Ni hydroxide nanosheets network structure is designed on the surface of Fe-Ni alloy foam. The ratio of Ni/Fe elements was adjusted to realize the optimal catalytic activities for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The obtained electrode of Fe-Ni hydroxide nanosheets/Fe-Ni alloy foam-60% Fe (FN LDH/FNF-60, 60 is the percentage of Fe content) possess low overpotential of 261 mV to reach 10 mA/cm2, small Tafel slope (85.5 mV/dec), and superior long-term stability (remaining 10 mA/cm2 for over 14 h without attenuation) toward OER in 1.0 mol/L KOH. Moreover, an alkaline water electrolyzer is constructed with the FN LDH/FNF-60 as anode and Ni(OH)2/Fe-Ni alloy foam-25% Fe (Ni(OH)2/FNF-25) as cathode, which displays superior electrolytic performance (affording 10 mA/cm2 at 1.62 V) and lasting durability.

Facile preparation of robust porous MoS2/C nanosheet networks as anode material for sodium ion batteries

Developing advanced MoS2 anode material for sodium ion battery is still a big challenge since it is hindered by poor cycling stability and rate capability owing to huge volume variation during charge/discharge processes and low conductivity. In this work, three-dimensional porous networks consisting of several-layered MoS2/C nanosheets are synthesized via a facile freeze-drying approach using NaCl as template. MoS2/C nanosheet networks demonstrate a high reversible capacity of 389 mAh g−1 and maintain 370 mAh g−1 after 100 cycles at 100 mA g−1, indicating excellent cycling stability. Good rate properties are also achieved with reversible capacities of 292, 256, 223, 174 mAh g−1 at 1, 2, 4, 6 A g−1, respectively. The excellent electrochemical performance can be ascribed to the unique three-dimensional networks consisting of few-layered MoS2 nanosheets, which facilitates sodium ion diffusion via near-surface reaction. Moreover, the robust three-dimensional carbon matrix can not only provide a conductive network, but also buffer the strain and maintain the electrode integrity during repeated sodiation/desodiation process. This strategy presents a new path for fabricating low-cost and high-yield three-dimensional metal sulfide (phosphide)/carbon composites for applications in energy-related fields and beyond.

Crystalline‐Water/Coordination Induced Formation of 3D Highly Porous Heteroatom‐Doped Ultrathin Carbon Nanosheet Networks for Oxygen Reduction Reaction

AbstractDevelopment of highly efficient electrocatalysts with low cost for oxygen reduction reaction (ORR) is crucial for their application in fuel cells and metal‐air batteries. In this work, we report a synthesis of 3D heteroatom‐doped ultrathin carbon nanosheet networks directly starting from solid raw materials. This method represents an operationally simple, general, and sustainable strategy to various ultrathin carbon nanosheet networks. Evaporation of crystalline water and coordination interaction are proposed to be responsible for the formation of the 3D carbon nanosheet networks. The carbon nanosheet networks possess high surface area with micro‐ and macropores, large pore volume, ultrathin nanosheet structure, and effective N/S‐co‐doping. The as‐prepared materials show outstanding electrocatalytic ORR performance with more positive onset potential and half‐wave potential, good methanol tolerance, and excellent stability, compared with those of the porous carbons derived from the ZIF counterpart and commercial Pt/C. This work not only provides highly active ORR electrocatalysts via an operationally simple and green process and also demonstrates a general method to prepare 3D ultrathin carbon nanosheet networks without any additional template and solvent.

Mesoporous NiO nanosheet network as efficient hole transporting layer for stable inverted perovskite solar cells

Hole transporting layer (HTL) plays an important role in device stability and charge transport for inverted perovskite solar cells (PSCs). Here, a novel HTL consisted of mesoporous NiO nanosheet (NS) was fabricated via simple hydrothermal method. The contract region of HTL/perovskite was increased by using the mesoporous NiO NS network structure, resulting in the good interface contract and rapid charge transfer. Therefore, the corresponding devices exhibit an optimal power conversion efficiency of >12%, with hysteresis-less. Besides, the developed PSCs still maintain 75% efficiency after 500 h, implying its good stability. In a word, this mesoporous NiO NS structure can be a promising candidate for HTL of inverted PSCs.

Fe3O4 nanoparticle/graphene aerogel composite with enhanced lithium storage performance

Fe3O4 nanoparticle/graphene aerogel (Fe3O4/GA) composite is fabricated by a simple one-step liquid phase precipitation method without further heat-treatment. The reduction of graphene oxide, deposition of Fe3O4 nanoparticle and formation of 3D graphene nanosheet network can happen simultaneously during preparation process, guaranteeing the uniform distribution of Fe3O4 nanoparticles on the surface of graphene nanosheets. The influence of the graphene amount in the Fe3O4/GA composites on electrochemical performance is investigated. The as-prepared Fe3O4/GA composite with a graphene content of 25% displays good electrochemical lithium storage performance (a high reversible capacity of 985 mAh g−1 at a current density of 0.1 A g−1 after 100 cycles) and good rate capability (434 mAh g−1 at the current density as high as 2 A g−1). Moreover, the contribution of the pseudocapacitance capacity can explicate the origin of good rate capability of the Fe3O4/GA composite. This work demonstrates the great potential of Fe3O4/GA composite as an alternative anode material for the low-cost and high-performance lithium ion batteries.

NiCo2S4 nanosheets network supported on Ni foam as an electrode for hybrid supercapacitors

In this work, we report the synthesis of NiCo2S4 nanosheets network and its application as electrode material for hybrid supercapacitors. The synthesis involves two-steps. Firstly, a precursor nanowires array is synthesized by a hydrothermal process. Then, the reaction between precursor and sodium sulfide through a vapor-phase diffusion process under hydrothermal condition leads to NiCo2S4 nanosheets network. The unique network structure can prevent NiCo2S4 nanosheets from aggregation and overlap. When act as an electrode material for supercapacitors, the NiCo2S4 nanosheets network exhibits specific capacitances of 1956 F g−1 at 1 A g−1 and 1622 F g−1 at 20 A g−1. Cycling test shows 91.6% capacitance retention after 5000 charge–discharge cycles. The specific capacitance and rate capability of the NiCo2S4 nanosheets network are higher than that of the NiCo2S4 nanotubes array which was obtained from the direct reaction of precursor and sodium sulfide in solution. In addition, a hybrid supercapacitor device is assembled by using the NiCo2S4 nanosheets network as positive electrode and porous carbon as negative electrode. The device exhibits an energy density of 27.5 W h kg−1 at a power density of 0.747 kW kg−1, and a power density of 6.03 kW kg−1 at an energy density of 18.75 W h kg−1. The results indicate that the NiCo2S4 nanosheets network is an excellent electrode material candidate for high-performance supercapacitors.

3D interconnected Bi2S3 nanosheets network directly grown on nickel foam as advanced performance binder-free electrode for hybrid asymmetric supercapacitor

In this paper, we report the successful synthesis of “rock-candy” shape Bi2S3 nanocrystals and 3D interconnected Bi2S3 nanosheets network on Ni foam by a facile hydrothermal method. The structure and composition of the as-synthesized products were characterized by XRD, XPS, SEM and SEM analyses. The unique structure makes them have high electrochemical properties. At current density of 0.5 A g−1, the binder-free Bi2S3/Ni foam working electrode with high specific area possesses high specific capacity (500.8 mAh g−1) compared to pristine Bi2S3 (245.5 mAh g−1). In the actual application of Bi2S3/Ni foam, the assembled Bi2S3/Ni foam//AC hybrid asymmetric supercapacitor exhibits excellent supercapacitive performances, such as high specific capacitance (148.7 F g-1 at 1 A g−1), high energy density (45.1 Wh Kg−1 at 3202 W Kg−1), excellent cycling stability (capacitance retention is about 98.7% after 2000 cycles at a current density of 3 A g−1) and low Warburg and charge transfer resistances.

3D MoS2-rGO@Mo nanohybrids for enhanced hydrogen evolution: The importance of the synergy on the Volmer reaction

Hydrogen evolution reaction (HER) through electrocatalytic water splitting is regarded as a promising route to produce hydrogen in a large scale. Molybdenum disulfide (MoS2) has been reported as a transition metal electrocatalysts, but generally with a poor activity, e.g. 540 mV overpotential at 10 mA cm−2 and Tafel slope value of 84 mV dec−1. A 3D MoS2-rGO@Mo nanohybrids, a three-dimensional MoS2 nanosheets network coated with reduced graphene oxide (rGO) on molybdenum mesh, is demonstrated as one of the best MoS2-based electrocatalysts. It delivers a benchmark current density of 10 mA cm−2 under a small overpotential (∼123 mV) with a low Tafel slope (∼62 mV dec−1), and an excellent stability performance. Its excellent performance can be attributed to the synergy between the 3D MoS2 and rGO with abundant active sites and high conductivity which leads to a faster water dissociation on the surface in the Volmer step.

Ultralong Fe3O4 nanowires embedded graphene aerogel composite anodes for lithium ion batteries

Fe3O4 nanowires/graphene aerogel composite is prepared for the first time via a simple two-step method, including a hydrothermal and self-assembly water-bath l-ascorbic acid reduction process. Structural and morphological characterizations confirm that the ultralong Fe3O4 nanowires are embedded into the networks of graphene nanosheets. When exploited as an anode material for lithium ion batteries, Fe3O4 nanowires/graphene aerogel composite exhibits good rate capability (557 mAh g−1 at a current density 2000 mA g−1) and excellent cycling performance (900 mAh g−1 at a current density of 200 mA g−1 after 100 cycles) together with good rate performance. This work offers a simple and large-scale preparation process for Fe3O4 nanowires/graphene aerogel composite as an advanced anode material for lithium ion batteries.

Thin Film Tin Selenide (SnSe) Thermoelectric Generators Exhibiting Ultralow Thermal Conductivity

Tin selenide (SnSe) has attracted much attention in the field of thermoelectrics since the discovery of the record figure of merit (ZT) of 2.6 ± 0.3 along the b-axis of the material. The record ZT is attributed to an ultralow thermal conductivity that arises from anharmonicity in bonding. While it is known that nanostructuring offers the prospect of enhanced thermoelectric performance, there have been minimal studies in the literature to date of the thermoelectric performance of thin films of SnSe. In this work, preferentially orientated porous networks of thin film SnSe nanosheets are fabricated using a simple thermal evaporation method, which exhibits an unprecedentedly low thermal conductivity of 0.08 W m-1 K-1 between 375 and 450 K. In addition, the first known example of a working SnSe thermoelectric generator is presented and characterized.

Preparation of three-dimensional vanadium nitride porous nanoribbon/graphene composite as an efficient electrode material for supercapacitors

Three-dimensional vanadium nitride porous nanoribbons/graphene composite with hierarchical porosity was prepared and investigated as the electrode material for supercapacitors. Morphology characterization of vanadium nitride porous nanoribbons/graphene composite indicates that vanadium nitride porous nanoribbons incorporate with graphene nanosheets to from a stable three-dimensional architecture with hierarchical porosity. This unique three-dimensional architecture and the combining effect of vanadium nitride porous nanoribbons and graphene nanosheets network make vanadium nitride porous nanoribbons/graphene composite a high-performance electrode material for supercapacitors. At a current density of 0.3 A g−1, vanadium nitride porous nanoribbons/graphene electrode displays a specific capacitance of 164.4 F g−1, which is much higher than that of pure vanadium nitride electrode. In addition, vanadium nitride porous nanoribbons/graphene composite shows high capacitance retention rate (82% capacitance retention at the current density up to 10 A g−1) and good long-term cycling stability (97.5% capacitance retention over 2500 cycles).

Reduced graphene oxide/strontium titanate heterostructured nanocomposite as sunlight driven photocatalyst for degradation of organic dye pollutants

Reduced graphene oxide/Strontium titanate (RGO/SrTiO3) heterostructured nanocomposite was synthesized by coupling Hummer's synthesized graphene oxide (GO) with hydrothermally synthesized SrTiO3 nanoparticles (SrTiO3) through a facile and unique high energy ultrasonication technique using triple solvents. XRD result confirmed the successful formation of pure, single phase and primitive cubic crystal structure RGO/SrTiO3 heterostructured nanocomposite. SEM result confirmed the successful intercalation of SrTiO3 nanoparticles over the two dimensional networks of RGO nanosheets. The synergistic and beneficial interactions between SrTiO3 and RGO resulted in smaller crystallite size (53 nm), reduced band gap (2.87 eV) and larger specific surface area (31 m2/g) than that of as prepared pure SrTiO3 nanoparticles. RGO strongly influenced the photocatalytic activity of SrTiO3 and hence RGO/SrTiO3 heterostructured nanocomposite exhibited greater efficiency in degrading Rhodamine B (RhB) and Rose Bengal (RB) organic dye pollutants under natural sunlight irradiation than that of pure SrTiO3 nanoparticles.

Construction of vertically aligned PPy nanosheets networks anchored on MnCo2O4 nanobelts for high-performance asymmetric supercapacitor

Three-dimensional self-assemble polypyrrole@MnCo2O4 nanoarchitectures on graphite foam are fabricated via hydrothermal method and in situ polymerization process. During polymerization, the dopant p-toluenesulfonic acid can partially etch the MnCo2O4 nanobelts, while the dissociated Mn/Co ions may lead to the formation of metal-N bond in the polypyrrole nanosheets. The vertically aligned conductive polypyrrole nanosheets can facilitate the electrons transfer, while the porous structure can store electrolyte and increase the active materials utilization efficiency. Therefore, the polypyrrole@MnCo2O4/graphite foam composite exhibits a specific capacitance of 2364 F g−1 (328 mA h g−1 when normalized to specific capacity), with good rate performance and cycling stability. An asymmetric supercapacitor is assembled with the composite and activated microwave exfoliated graphite oxide as the positive and negative electrode, respectively. A highest energy density of 25.7 Wh kg−1 and power density of 16.1 kW kg−1 are obtained, which is comparable to most of the high-end supercapacitor electrodes. Furthermore, a capacitance retention of 85.5% is obtained after 10000 cycles.

Melamine foam-supported 3D interconnected boron nitride nanosheets network encapsulated in epoxy to achieve significant thermal conductivity enhancement at an ultralow filler loading

Realizing high-efficiency thermal conductivity enhancement at low filler loading has a great significance for thermally conductive composite. Herein, three-dimensional (3D) boron nitride nanosheets (BNNSs) wrapped melamine foams (MF@BNNS) were first fabricated by repeated layer-by-layer (L-B-L) assembly using melamine skeleton as substrate and BNNSs as building blocks. The resultant MF@BNNS scaffold with order and interconnected BNNS layer, as a thermally conductive network, was further infiltrated with epoxy resin. As a consequence, a relatively high thermal conductivity of 0.6 W m−1 K−1 was achieved at an ultralow BNNS loading of ∼1.1 vol%, which is equivalent to a thermal conductivity enhancement of 233% compared to epoxy resin. Besides, the obtained epoxy composite also possesses a good mechanical property and excellent electrical insulativity. This method can be further extended to construct 3D filler network of other 2D layered materials on the melamine foam for high-performance composite.

Ni2P2O7Nanoarrays with Decorated C3N4Nanosheets as Efficient Electrode for Supercapacitors

Ni2P2O7-based composites grown on conductive substrate can efficiently promote the electrical transport during the electrochemical reactions in supercapacitors. However, Ni2P2O7 nanoarrays are easily peeled off from the substrate upon repeated electrochemical reaction. Herein, Ni2P2O7 nanoarrays grown on Ni foam with surficially decorated C3N4 thin nanosheets are achieved by a hydrothermal and in situ calcination strategy. The decorated C3N4 nanosheet network on the surface fully covers both Ni2P2O7 and Ni foam and efficiently prevents Ni2P2O7 nanoarrays from peeling off during the charge and discharge cycles. The optimized composites exhibit high pseudocapacitance and greatly enhanced cycling stability. The assembled asymmetric supercapacitor shows favorable specific capacitance and stability as energy storage devices. Such a strategy for fabricating C3N4-modified Ni2P2O7 nanoarrays is feasible and efficient, and can be therefore extended for constructing other electrodes with high capacitance and excell...

ZnO/AAO photocatalytic membranes for efficient water disinfection: Synthesis, characterization and antibacterial assay

Novel type of ZnO/AAO photocatalytic membranes were fabricated by growing highly dense and porous network of ZnO nanosheets on nanoporous anodic aluminum oxide (AAO) using the facile hydrothermal approach. The structural properties of the membranes were investigated by field emission gun scanning electron microscopy (FEG-SEM) and X-ray diffraction spectroscopy (XRD). The ZnO nanosheet networks were found polycrystalline, showing mainly (100) and (002) ZnO reflections. The XRD results suggested that the ZnO-AAO interface promotes lattice disorder mainly along the polar-axis while the nonpolar plane remains less defective. The energy dispersive X-ray spectrometry (EDX) confirmed the formation of pure ZnO. In addition, Fourier transform infrared spectroscopy (FTIR) indicated an intense absorption band in the range of 661–780 cm−1 for stretching vibrations of Zn–O bond and also specified the presence of intrinsic crystal defects. The diffuse reflectance spectroscopy (DRS) revealed an optical absorption edge of 401 nm and a band gap of 3.09 eV for grown ZnO nanosheet mesh. Moreover, the DRS studies also substantiated the existence of crystal defects by recognizing a red shift in the band gap, and a trail of low energy absorptions in the reflectance spectrum in the range of 400–800 nm. Due to the corrugated surface morphology and hierarchical porosity of ZnO scaffolds on porous AAO substrates, the membranes possess a great deal of catalytic surface and demonstrated a strong antibacterial activity against water-borne bacteria Escherichia coli (E. coli) under dark and UV light conditions. Our results showed that fabricated ZnO/AAO membranes have great potency for photocatalytic disinfection of contaminated water on account of their large catalytic surface and inherent porosity which can facilitate the mass transfer and diffusion of oxygen species and Zn+2 ions during the disinfection process. This morphology-function relationship is highly effective for designing cost effective, efficient, environment-friendly, and self-antifouling photocatalytic disinfectants.

Heteromorphic NiCo2S4/Ni3S2/Ni Foam as a Self-Standing Electrode for Hydrogen Evolution Reaction in Alkaline Solution.

Considerable works have been devoted on developing high-efficiency nonplatinum electrocatalysts for hydrogen evolution reaction (HER). Herein, 3D heteromorphic NiCo2S4/Ni3S2 nanosheets network has been constructed on Ni foam (denoted as NiCo2S4/Ni3S2/NF) serving as a self-standing electrocatalyst through directly thermal sulfurization of a single-source NiCo-layered double hydroxide precursor. The resultant NiCo2S4/Ni3S2/NF electrode exhibits outstanding electrocatalytic HER performance with an extremely low onset overpotential of 15 mV and long-term durability in alkaline solution. Such enhanced HER performance can be credited to (1) the massive exposed active sites provided by mixed transition metal chalcogenides (NiCo2S4 and Ni3S2), (2) the strong interfacial interaction at NiCo2S4/Ni3S2 heterojunction interfaces with the strengthened H binding, and (3) the porous highly conductive Ni foam substrate with accelerated electron transfer. This work opens up a new direction to fabricate effective and non-noble-metal electrodes for water splitting and hydrogen generation.

Effect of graphene oxide nanosheets on visible light-assisted antibacterial activity of vertically-aligned copper oxide nanowire arrays

In the present work, the effect of graphene oxide (GO) nanosheets on the antibacterial activity of CuO nanowire arrays under visible light irradiation is shown. A combined thermal oxidation/electrophoretic deposition technique was employed to prepare three-dimensional networks of graphene oxide nanosheets hybridized with vertically aligned CuO nanowires. With the help of standard antibacterial assays and X-ray photoelectron spectroscopy, it is shown that the light-activated antibacterial response of the hybrid material against gram-negative Escherichia coli is significantly improved as the oxide functional groups of the GO nanosheets are reduced. In order to explore the physicochemical mechanism behind this behavior, ab-initio simulations based on density functional theory were performed and the effect of surface functional groups and hybridization were elucidated. Supported by the experiments, a three-step photo-antibacterial based mechanism is suggested: (i) injection of an electron from CuO into rGO, (ii) localization of the excess electron on rGO functional groups, and (iii) release of reactive oxygen species lethal to bacteria. Activation of new photoactive and physical mechanisms in the hybrid system makes rGO-modified CuO nanowire coatings as promising nanostructure devices for antimicrobial applications in particular for dry environments.

Specific capacitance, energy and power density coherence in electrochemically synthesized polyaniline-nickel oxide hybrid electrode

Abstract In the present manuscript, polyaniline (PAni), nickel oxide (NiO), and a fine nanosheet-type network of PAni-NiO hybrid film electrodes are prepared using electrodeposition technique and envisaged as electrode materials in electrochemical capacitor application. Furthermore, these film electrodes are characterized for their structural and morphological studies with the help of X-ray diffraction and scanning electron microscopy measurements, respectively. Atomic force microscopy revelation affords the roughnesses of electrode surfaces. Contact angle elucidation explodes the hydrophilic nature of PAni, NiO and PAni-NiO hybrid electrode surfaces. Electrochemical measurements confirm that the PAni-NiO hybrid electrode shows synergic effect as its specific capacitance measured at a scan rate of 5 mV/s in 1 M Na 2 SO 4 electrolyte is noticeably higher (936.36 F/g) than the PAni and NiO electrodes (601 and 263.5 F/g). All these electrodes exhibit remarkable capacity retention performance after 2000 cycles. The nanosheet network of PAni-NiO hybrid electrode offer a great reaction surface area for rapid ion and electron transfer with good stability as well, which all are advantageous for enhancing the electrochemical capacitance performance.

Hierarchically Porous Multilayered Carbon Barriers for High-Performance Li-S Batteries.

As one of the most promising energy storage devices, the practical application of lithium-sulfur batteries is limited by the low electrical conductivity of sulfur and the notable "shuttle effects" of sulfur-based electrodes. In this work, we describe a hierarchically porous N-doped zeolitic imidazolate framework-8 (ZIF-8)-derived carbon nanosphere (N-ZDC) with an outer shell and an inner honeycomb-like interconnected nanosheet network as sulfur host material for high-performance and long-term lithium-sulfur batteries. The N-ZDC serves as multilayered barrier against the dissolution of lithium polysulfides. The porously inner interconnected carbon network of the N-ZDC facilitates the electron and ion transportation, ensures a high sulfur loading, and accommodates a volume expansion of the sulfur species. As a result, the optimized N-ZDC4 /S electrodes displayed high initial specific capacities of 1343, 1182, and 698 mAh g-1 at 0.5, 1, and 2 C, respectively, and an ultraslow capacity decay of only 0.048 % per cycle at 2 C over 800 cycles. Even with a high sulfur loading of 3.1 mg cm-2 , N-ZDC4 /S still delivered a reversible capacity of 956 mAh g-1 and stabilizes at 544 mAh g-1 after 500 cycles at 0.5 C, revealing the great potential of the novel carbon nanospheres for energy storage application.