Nanosheet Networks Research Articles

On the relationship between morphology and conductivity in nanosheet networks

It is well-known that the morphology of nanostructured networks is closely linked to network properties. However, controlling and characterizing the morphology of networks of 2D nanosheets has not been explored. In this work, we use networks of liquid-exfoliated graphene nanosheets as a model system to examine the relationship between network morphology and conductivity in nanosheet networks. We use a combination of heat and pressure to controllably alter the morphology of the network, resulting in the annihilation of large pores (>40 nm) and improved nanosheet alignment within the sample. Such compression can result in a tenfold increase in network conductivity. Analysis shows both in-plane and out-of-plane conductivities to scale with porosity in line with percolation theory. The conductivity anisotropy was ∼3000 at low-porosity and was projected to fall to 1 in the limit of high porosity. Computational studies link the conductivity increase to an increase in network connectivity and a reduction in junction resistance as the porosity is decreased.

In Situ Formation of Prussian Blue Analogue Nanoparticles Decorated with Three-Dimensional Carbon Nanosheet Networks for Superior Hybrid Capacitive Deionization Performance.

Capacitive deionization (CDI) is considered to be an alternative water purification technology because of its low cost and low driven energy. However, the desalination performance of traditional CDI still cannot meet the requirement of actual operations, which is the limited adsorption capacity of carbon electrodes. Here, we report a feasible and simple strategy for the synthesis of a three-dimensional hierarchical composite with homogeneous Prussian blue analogue nanoparticles, decorating hierarchical porous carbon nanosheet networks (NiHCF@3DC-2) as a redox-active intercalation electrode material for hybrid capacitive deionization (HCDI). The interconnected network structure, accompanied by its unique porous characteristic and uniform NiHCF nanoparticles, endows the prepared NiHCF@3DC-2 with enough straining space for alleviating the effect of volume change upon the regeneration process and guarantees fast transmission kinetics for both electrons and salt ions. As a consequence, an HCDI cell with NiHCF@3DC-2 and activated carbon showed superior desalination ability with a high ion removal capacity of 47.8 mg g-1 (107.5 mg g-1 NiHCF@3DC-2) and good cyclic regenerative performance. Moreover, the Na+ ions storage mechanism and the interfacial synergy of the NiHCF@3DC-2 were also explored by structure and electrochemistry analyses during the CDI process. Our work provides a promising redox-active intercalation electrode material to highly efficient hybrid capacitive deionization for brine.

Fabrication of Nonmetal-Modulated Dual Metal-Organic Platform for Overall Water Splitting and Rechargeable Zinc-Air Batteries.

The fast development of portable water-splitting devices has led to a great deal of work on rechargeable metal-air batteries or solar cells; however, the lack of affordable multifunctional electrocatalysts still hampers their widespread applications. Herein, a well-aligned ternary metal (oxy)hydroxide nanostructure is a sacrificial pseudomorphic transformation template of an integrated metal-organic network on the carbon cloth (CC) surface, that is, the Fe-doped metal-organic framework (MOF) ZnNiCoSe@CC nanosheet network, exhibiting powerful and efficient multifunctional electrocatalysts such as the oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction in alkaline media combined with desirable electrode kinetics. As a proof-of-concept observational study, the nanostructured Fe-doped MOF ZnNiCoSe@CC could be used as air-cathode materials in the rechargeable metal-air battery. The fabricated device delivered higher open-circuit voltage, higher capacity, and peak power density, excellent discharge-charge performance, and long cycle life. Thus, our research creates a unique perspective on the development of highly portable air electrodes with a favorable electrocatalytic application of overall water-splitting reaction.

Nitrogen-doped mesoporous carbon nanosheet network entrapped nickel nanoparticles as an efficient catalyst for electro-oxidation of glycerol

The design and synthesis of nitrogen-doped (N-doped) carbon nanosheets network offer a tremendous electro-catalytic activity due to their high surface area and tunable porous structures for the development of direct alcohol fuel cells (DAFCs). In this work, nickel (Ni) nanoparticles entrapped onto the N-doped mesoporous carbon nanosheets network such as Ni–C-1, Ni–C-2, and Ni–C-3 are fabricated and characterized using SEM, TEM, XRD, XPS, and electrochemical methods. The physicochemical characterization of synthesized nanocomposite material confirmed that sodium chloride (NaCl) plays a major role in the formation of porous nanostructure during carbonization process. Under optimized conditions, all the above carbon samples are tested as potential electro-catalyst towards the electro-oxidation of glycerol for DAFCs application. Among them, the Ni–C-2 catalyst displays enhanced catalytic current density (~2.6 mA) and low onset oxidation potential (0.11 V) for electro-oxidation of glycerol than the Ni–C-1, and Ni–C-3 catalysts in alkaline electrolyte. In addition, the mesoporous carbon network structure containing Ni nanoparticles delivers substantial longer durability/robustness when compared to the conventional Pt/C-catalyst towards stable- and efficient electro-oxidation of glycerol for the first time. Thus, the obtained electro-catalytic performance revealed that Ni–C-2 is considered as a promising earth abundant non-noble low-cost catalyst material for DAFCs application.

Development of hydrogels with thermal-healing properties using a network of polyvinyl alcohol and boron nitride composites.

The biocompatibility, flexibility, and tissue-like mechanical properties of hydrogels suggest they are promising materials for wearable devices. However, the production of smart, self-healing hydrogels is limited by the unstable structure of load-bearing stressors and the need for long-term healing capacity. An important goal when developing such hydrogels is to improve their mechanical characteristics and rapid ability to self-repair in physiological environments. In this study, we aimed to create a thermo-responsive hydrogel that possessed thermal-healing and enhanced mechanical properties, without losing its self-healing capabilities, by employing two interpenetrating cross-linked networks of polyvinyl alcohol (PVA) and boron nitride nanosheets (BNNSs). We observed that addition of BNNSs significantly increased the glass transition temperature (Tg) and temperature-dependent swelling of PVA hydrogels, indicating a high compatibility between these two materials and a high thermal response to external stimuli. Our results suggest that PVA hydrogels combined with BNNSs outperform single-network PVA hydrogels in terms of thermal-healing capacity. As above Tg, the thermal energy gained during moisture loss leads to an increase in the thermal mobility of the polymer chains and in the free volume available for new hydrogen bonds at the fracture surface. This unique structure increases water content and confers better mechanical properties. Interestingly, this structure of the second network benefits the first PVA network during deformation by effectively dissipating energy and bearing force, and contrarily to single-network PVA hydrogels. Taken together, our results show that combining PVA and BNNSs to create a hybrid structure, exerts a synergistic effect and successfully improves the thermal-healing performance of wet hydrogels.

Self-supporting Co0.85Se nanosheets anchored on Co plate as highly efficient electrocatalyst for hydrogen evolution reaction in both acidic and alkaline media

Electrocatalytic water splitting via hydrogen evolution reaction (HER) represents one of promising strategies to gain hydrogen energy. In current work, self-supporting Co0.85Se nanosheets network anchored on Co plate (Co0.85Se NSs@Co) is fabricated by employing easily tailorable Co metal plate as the source conductive substrate. The scalable dealloying and hydrothermal selenization strategy was employed to build one layer of three dimensional interlinking Co0.85Se nanosheets network on the surface of Co plate. Benefiting from bulky integrated architecture and rich active sites, the as-made Co0.85Se NSs@Co exhibits superior electrocatalytic activity and long-term catalytic durability toward HER. It only requires lower overpotentials of 121 and 162 mV to drive the current density of 10 mA·cm−2 for hydrogen evolution in 0.5 M H2SO4 and 1 M KOH solution. Especially, no evident activity decay occurs upon 1,500 cycles or continuous test for 20 h at 10 mA·cm−2 in both acidic and alkaline electrolytes. With the merits of exceptional performances, scalable production, and low cost, the self-supporting Co0.85Se NSs@Co holds prospective application potential as stable and binder-free electrocatalysts for hydrogen generation in a wide range of electrolyte.

Ultrathin MoS2 anchored on 3D carbon skeleton containing SnS quantum dots as a high-performance anode for advanced lithium ion batteries

Transition metal sulfides have high abundance and large theoretical capacities are considered to be an effective candidate for advanced electrodes of lithium ion batteries (LIBs). Here, a large-scale and controllable method was used in synthesizing ultrathin MoS2 nanosheets anchored on 3D hierarchical nanohybrids with SnS quantum dots, which are decorated on a carbon nanosheet network (MoS2@SnS-QDs/CNN). The 3D cross-linked carbon nanosheet not only could prevent SnS from being directly exposed to the electrolyte but also retained the structural stability of the electrode. Moreover, the MoS2 nanosheets exposed active sites to carry lithium ions. A heterojunction was formed at the interface owing to the close contact between molybdenum disulfide and SnS and greatly increased charge carrying and lithium storage capacities. Benefiting from these structural advantages, the MoS2@SnS-QDs/CNN electrodes showed outstanding electrochemical and long-term cycling performance owing to their unique structures and amazing synergies. As a half-cell anode material, MoS2@SnS-QDs/CNN-2 provided a reversible capacity of 713 mAh g−1 after 1000 cycles at a current density of 2 A g−1. When assembled into a full battery, it still provided 491 mAh g−1 at a current density of 1 A g−1 after 100 cycles. At the same time, a small LED bulb was lit for a while. This advanced material has great potential in other applications, such as supercapacitors, catalysis, and sensors.

Interconnected two-dimensional MnO2 nanosheets anchored on three-dimensional porous Cu skeleton as a high-performance cathode for energy storage

Interconnected two-dimensional (2D) MnO2 nanosheet network anchored on 3D nanoporous Cu skeleton (named as NPC@MnO2) was easily prepared by utilizing the redox reaction between KMnO4 and Cu. The as-prepared trans-dimensional NPC@MnO2 composite, which combined the advantages of high surface area MnO2 nanosheets and 3D integrated conductive NPC skeleton, is equipped with abundant multilevel pore voids, rich active sites and channels for smooth ion and electron delivery. The NPC@MnO2 exhibits decent specific capacitance, admirable cycling and rate capability. At a high current density of 10 A g−1, the NPC@MnO2 can be durably cycled for more than 10,000 loops with 91.6% capacitance retention. An asymmetric supercapacitor was constructed with NPC@MnO2 and active carbon, and delivered a high energy density of 10.9 Wh kg−1 (at a power density of 4260 W kg−1) and a high capacitance retention of 93.4% over 10,000 cycles at 10 A g−1. With the merits of easy preparation and superior energy storage performances, NPC@MnO2 holds promising application prospect as a candidate for high performance supercapacitors.

Carbon Coated Core-Shell FeSiCr/Fe3C Embedded in Carbon Nanosheets Network Nanocomposites for Improving Microwave Absorption Performance

Development of microwave absorbing materials with tunable thickness and bandwidth is particularly important for practical applications, but its realization remains a great challenge. Here, we report carbon coated core-shell FeSiCr/Fe3C embedded in two-dimensional carbon nanosheets network (FeSiCr/Fe3C@C/C) nanocomposites fabricated by plasma arc-discharging method. FeSiCr/Fe3C@C/C has the best microwave absorption properties in which the minimum calculated reflection loss (RL) can reach [Formula: see text][Formula: see text]dB at 11.5[Formula: see text]GHz with a coating thickness of 2.4[Formula: see text]mm and the efficient absorption bandwidth (RL[Formula: see text][Formula: see text]dB) almost covers 4.5–18[Formula: see text]GHz range by adjusting the coating thicknesses from 1.3 to 5.0[Formula: see text]mm. The improved microwave absorption properties could be ascribed to the optimized impedance matching and enhanced polarization loss, conduction loss and internal reflections of the propagated microwave.

Effect of the Gate Volume on the Performance of Printed Nanosheet Network-Based Transistors

Demonstration of high-performance, all-printed transistors fabricated only from networks of two-dimensional nanosheets would represent a significant advance in printed electronics. However, such de...

Cobalt nanoparticles intercalated nitrogen-doped mesoporous carbon nanosheet network as potential catalyst for electro-oxidation of hydrazine

Developing an efficient low-cost and high performance electrocatalyst for electro-oxidation of hydrazine is one of the key challenges in the prospect of direct hydrazine fuel cell (DHFC) application. In this work, a series of nitrogen doped three-dimensional porous Co3O4/carbon nanosheet network catalysts are synthesized (Co-NPC NNs-x), and simultaneously characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and electrochemical methods. Among them, Co-NPC NNs-2 is found to be a potential electrocatalyst towards highly efficient electro-oxidation of hydrazine. The electrochemical results clearly display that Co-NPC NNs-2 catalyst shows enhanced electro-oxidation (low-onset oxidation potential, higher catalytic current response), and higher cycling stability (catalytic response retained even after 120 successive cycles) toward hydrazine when compared to Co-NPC NNs-1, Co-NPC NNs-3, and NPC NNs catalysts modified electrodes. The existence of large active surface area, higher active catalytic sites, and synergetic activity between NPC NNs and Co3O4 NPs (Co-NPC NNs-2) are vital factors mainly attributes to the superior electro-oxidation response of hydrazine. Further, the Co-NPC NNs-2 catalyst demonstrated longer durability towards the electro-oxidation of hydrazine, which is highly comparable with commercially available Pt/C catalyst. Such an efficient low-cost electrocatalyst nanomaterial can enable the use of hydrazine as a promising energy carrier for DHFCs, which increases its practicality for upcoming energy storage and conversion applications.

Monodispersed FeS nanoparticles confined in 3D interconnected carbon nanosheets network as an anode for high-performance lithium-ion batteries

Transition metal sulfides as the most prominent candidates with high theoretical capacities; however, serious agglomeration and enormous volumetric variation limit its application in lithium-ion batteries. Herein, a chemical blowing strategy for the synthesis of FeS nanoparticles encapsulated into 3D porous carbon framework via chemical vapor deposition method and subsequent sulfidation process. In the constructed architecture, the monodispersed FeS nanoparticles are fully encapsulated in graphitic carbon, simultaneously, confined in 3D architecture composed of 2D graphitic carbon nanosheets. The unique architecture provides a facilitated transport pathway, enhances electron conductivity and buffers the volumetric expansion of FeS. Consequently, the composite delivers a high reversible capacity of 1084.2 mAh g−1 at 0.1 A g−1, excellent rate capability (723.5 mAh g−1 at 1 A g−1), and outstanding cycling stability (a specific capacity of 848.3 mAh g−1 without decay is achieved at 0.5 A g−1). Therefore, the present work suggests that the novel design of 3D FeS/C material provides a strategy for achieving high-performance anodes in lithium-ion batteries. Uniformly monodispersed FeS nanoparticles confined in 3D interconnected carbon network was synthesized by using chemical vapor deposition method and subsequent sulfidation process. The hybrid electrode exhibits excellent performance with a reversible capacity of 1084.2 mAh g−1 at 0.1 A g−1 as well as outstanding cycling stability performance of 848.3 mAh g−1 at 0.5 A g−1 after 170 cycles.

Facile Preparation of a Ni/Mn-LDH Nanosheet @Graphene Foam Hierarchical Structure for High-performance Flexible Supercapacitors

In this study, a novel Ni/Mn-LDH nanosheets array @graphene foam nanocomposite is fabricated via an in-situ self-assembled strategy through the facile hypothermal chemical coprecipitation, which can work at relatively low temperature (55 °C) and atmospheric pressure distinct from common hydrothermal process. Neither surfactant nor stabilizer is employed to produce the three-dimensional hierarchical architecture, which is composed of interconnected nanosheets network encapsulating graphene foam. The prepared mechanism is ascribed to stepwise reaction of nanoparticles growing to nanopetals and then assembling into nanosheets-network. Benefiting from the special configuration, the electrode demonstrates favorable electrochemical properties with a capacitance of 2380 F·g−1 (1 A·g−1) and 1315 F·g−1 reserved even at 20 A·g−1. The derivative all-solid-state asymmetric supercapacitor displays high energy density and power density of 134.83 Wh·kg-1 and 1.01 kW·kg-1 with cycling stability of 94.9% remaining after 1000 cycles. That performance makes it be of great prospects of the application in future wearable devices.

Cu2S decorated MoSe2 nanosheets as counter electrode for quantum dot sensitized solar cells

The power conversion efficiency of quantum dot sensitized solar cells (QDSCs) is limited by poor redox activity of the sulfide/polysulfide electrolyte toward the counter electrodes. Here, we demonstrate the use of MoSe2-Cu2S nanoheterostructures as an efficient counter electrode in QDSCs. The QDSC based on MoSe2-Cu2S counter electrode displays an efficiency of 3.6%, which is ∼17% higher as compared to Cu2S counter electrode. The improvement is resulting from the efficient shuttling of charge carriers across the two dimensional network of MoSe2 nanosheets owing to the decrease of charge transfer resistance.

Effect of Synthesis Temperature on the Morphologies, Optical and Electrical Properties of MgO Nanostructures.

Herein, we report the effect of synthesis temperature on the morphologies, optical and electronic properties of magnesium oxide (MgO) nanostructures. The MgO nanostructures were synthesized at different temperatures, i.e., 100 °C, 300 °C, and 600 °C by simple chemical reaction process and their morphology, particle size, optical, and electrical properties were examined by different techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and UV-Vis. spectroscopy. The morphological investigations revealed that various morphologies of MgO nanostructures, i.e., nanoparticles, nanosheet networks, and nanoneedles were synthesized at 100 °C, 300 °C, and 600 °C. The XRD results confirmed that with increasing the synthesis temperature, the crystallinity of the synthesized nanostructures increases. Further, the dielectric properties and AC conductivity at various frequencies for MgO nanostructures were studied which revealed that the dielectric losses decrease with increase in frequency and temperature. In addition, the observed band gap decreases from 4.89 eV to 4.438 eV (100 °C to 600 °C) representing its increase in the conductivity.

Influence of annealing temperature on the sensitivity of nickel oxide nanosheet films in humidity sensing applications

Nickel oxide (NiO) nanosheet films were successfully grown onto NiO seed-coated glass substrates at different annealing temperatures for humidity sensing applications. NiO seed layers and NiO nanosheet films were prepared using a sol-gel spin coating and sonicated sol-gel immersion techniques, respectively. The properties of NiO nanosheet films at as-deposited, 300 ℃, and 500 ℃-annealed were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultraviolet-visible (UV-vis) spectroscopy, and humidity sensor measurement system. The XRD patterns demonstrate that the grown NiO films have crystalline cubic structures at temperature of 300 ℃ and 500 ℃. The FESEM images show that the large porous nanosheet network spread over the layers as the annealing temperature increased. The UV-vis spectra revealed that all the nanosheet films have the average transmittance below than 50% in the visible region, with absorption edges ~ 350 nm. The optical band gap energy was evaluated in ranges of 3.39 to 3.61 eV. From the obtained humidity sensing results, it shows that 500 ℃-annealed film exhibited the best sensitivity of 257, as well as the slowest response time, and the fastest recovery time compared with others.

Highly thermally conductive PVDF-based ternary dielectric composites via engineering hybrid filler networks

Thermally conductive ternary poly (vinylidene fluoride) (PVDF)-based dielectric materials were fabricated via engineering the filler networks using hexagonal boron nitride (hBN) nanosheets and surface functionalized silicon carbide (f-SiC) nanowires. The hBN nanosheets and f-SiC nanowires synergistically improved the thermal conductivity of the composites, in a way that parallelly oriented f-SiC nanowires bridged by the hBN nanosheet networks. The ternary composites with 20 wt% hBN nanosheets and 26 wt% f-SiC nanowires exhibited a high thermal conductivity of 1.41 W/mK, about 5.9 times of that of neat PVDF. In addition, the ternary composites showed superior dielectric permittivity, while maintaining a low loss at 1 kHz. The presence of f-SiC nanowires contributed to the interfacial polarization between the fillers and PVDF matrix, resulting in the increased dielectric permittivity. Meanwhile, low dielectric loss could be maintained due to the isolation of f-SiC nanowires by insulating hBN nanosheets and PVDF matrix.

N,S dual-doped carbon nanosheet networks with hierarchical porosity derived from biomass of Allium cepa as efficient catalysts for oxygen reduction and Zn–air batteries

Efficient metal-free electrocatalysts for oxygen reduction reactions (ORR) have been actively pursued in recent years to promote the application of fuel cells and metal–air batteries. In this work, hierarchically porous nitrogen and sulfur dual-doped carbon nanosheet networks (N,S-HPC) were facilely synthesized by pyrolysis of Allium cepa chips impregnated with thiourea and KOH. The as-prepared N,S-HPC featured high content of N and S dopants (5.32 at.% for N and 2.23 at.% for S, respectively), abundant catalytically active sites, unique hierarchically porous architecture, large surface area (1859 m2 g−1) and exhibited remarkable electrocatalytic activity toward ORR with positive onset/half-wave potential and large limiting diffusion current. In addition, N,S-HPC showed much better long-time stability and resistance to methanol crossover than Pt/C did. When used as the cathodic catalysts of Zn–air battery, N,S-HPC outperformed Pt/C in terms of the open-circuit potential, discharge current density, peak power density, specific capacity and rate performance, showing promise as an alternative to Pt/C for application in fuel cells and metal–air batteries.

Highly Efficient Three-Dimensional Gas Barrier Network for Biodegradable Nanocomposite Films at Extremely Low Loading Levels of Graphene Oxide Nanosheets

A simple and facile method was proposed to successfully build a three-dimensional (3D) gas barrier network of graphene oxide nanosheets (GONSs) in the biodegradable poly(lactic acid) (PLA) matrix, in which GONSs were first self-assembled on the surface of PLA microspheres and then preferentially distributed at the interface of PLA domains. Polyethylene oxide was introduced as a flow accelerator and interfacial adhesive for favorable interfaces. As a result, the as-prepared PLA nanocomposite films exhibited a significant enhancement in barrier performance with ∼78.6% reduction in the O₂ permeability coefficient at a low GONS loading of 0.0344 vol %. The modified Bharadwaj model by introducing an effective stacking factor indicated an efficient assembly of GONSs in the form of “edge-to-edge” stacking. The new insight into the relationship between the stacking efficiency of nanoplatelets and barrier performance provides a valuable clue in developing high-barrier polymer nanocomposite films.

Homologous NiCoP/CoP hetero-nanosheets supported on N-doped carbon nanotubes for high-rate hybrid supercapacitors

Rational design of highly active electrode materials made of low-cost and earth-abundant transition metal phosphides is essential to boost the energy density and overall performance of electrochemical capacitors. In this work, homologous 3D NiCoP/CoP hetero-nanosheets network supported on N-doped carbon nanotubes are synthesized through one-step phosphorization of nickel cobalt hydroxide. The synergistic effects between NiCoP and CoP in the heterointerface are studied systematically through tuning the molar ratio of original Ni/Co. As a result, the optimized N-CNTs@NiCoP/CoP (with the Ni/Co ratio of 1:2) reveals a remarkable specific capacity of 152 mAh g−1 at 1 A g−1 and a superior rate capability with a capacity retention of 61% even at 30 A g−1. A hybrid supercapacitor assembled with N-CNTs@NiCoP/CoP cathode and ZIF-67-derived porous carbon anode exhibits a high energy density of 45.5 Wh kg−1 at power density of 784 W kg−1 and excellent stability of 87% retention after 10,000 cycles at 12 A g−1. Such excellent electrochemical performance of N-CNTs@NiCoP/CoP is mainly ascribed to the strong synergistic effect between NiCoP and CoP in their heterojunctions, enlarged surface area and active sites due to the 3D nanosheets network and conductive N-CNTs support.