Nanoflake Arrays Research Articles

Chemical Immobilization and Conversion of Active Polysulfides Directly by Copper Current Collector: A New Approach to Enabling Stable Room‐Temperature Li‐S and Na‐S Batteries

AbstractRoom‐temperature Li/Na‐S batteries are promising energy storage solutions, but unfortunately suffer from serious cycling problems rooted in their polysulfide intermediates. The conventional strategy to tackle this issue is to design host materials for trapping polysulfides via weak physical confinement and interfacial chemical interactions. Even though beneficial, their capability for the polysulfide immobilization is still limited. Herein, the unique sulfiphilic nature of metallic Cu is revisited. Upon the exposure to polysulfide in aqueous or aprotic solution, the surface sulfidization rapidly takes place, resulting in the formation of Cu2S nanoflake arrays with tunable texture. When the sulfidized Cu current collector is directly used as the sulfur‐equivalent cathode, it enables high‐performance Li/Na‐S batteries at room temperature with reasonable high sulfur loading. Specific capacities up to ≈1200 mAh g−1 for Li‐S and ≈400 mAh g−1 for Na‐S are measured when normalized to the amount of equivalent sulfur, and can be readily sustained for >1000 cycles.

Water Splitting: A Hierarchical MoP Nanoflake Array Supported on Ni Foam: A Bifunctional Electrocatalyst for Overall Water Splitting (Small Methods 5/2018)

Water Splitting: A Hierarchical MoP Nanoflake Array Supported on Ni Foam: A Bifunctional Electrocatalyst for Overall Water Splitting (Small Methods 5/2018)

Nanoengineering of 2D tin sulfide nanoflake arrays incorporated on polyaniline nanofibers with boosted capacitive behavior

Nanoscale engineering plays an important role in designing novel electrode architecture and boosting energy storage in supercapacitors. Herein, we demonstrate the fabrication of freestanding tin sulfide based supercapacitor electrode using facile nucleation substrate control, i.e. polyaniline network. This is the first time that tin sulfide based material is fabricated as a binder-free electrode for supercapacitors. The first combination of tin sulfide and polyaniline also evokes synergistic effect to enhance the performance as the polyaniline nanofibers facilitate the growth of tin sulfide flakes in nanosize which is further proved helpful for improving the capacity and stability of the electrode. The as-obtained electrode of tin sulfide nanoflake arrays incorporated on polyaniline nanofibers (365 F g−1 at 10 mV s−1) exhibits superior electrochemical performance compared with micro-scaled tin sulfide (32 F g−1 at 10 mV s−1). The significantly improved pseudocapacitive and diffusive contributions of polyaniline nanofibers incorporated electrode are identified by quantitative kinetics analysis due to greatly decreased particle size and introduced mesopores, nanoclusters, and exposed edges. Profited from effective nanostructure engineering, a Na+ intercalation mechanism is also pointed out in boosting the electrochemical performance.

WO3 nanoflakes decorated with CuO clusters for enhanced photoelectrochemical water splitting

The low quantum efficiency arising from poor charges transfer and insufficient light absorption is one of the critical challenges toward achieving highly efficient water splitting in photoelectrochemical cells. Three dimensions (3D) structures and heterojunctions have received intensive research interests recent years due to their excellent ability to separate photo-generated charges as well as the enhanced light harvesting property. Herein, 3D CuO/WO3 structure was fabricated through a facile solvothermal method followed by chemical bath deposition. The loading of CuO clusters on WO3 nanoflake arrays results in a much improved photocurrent density compared with that of pristine WO3 nanoflake arrays, which reaches 1.8 mA/cm2 at 1.23 V vs. the reversible hydrogen electrode. The electrochemical impedance spectroscopy measurement demonstrates that the improved performance of CuO/WO3 electrode is attributed to the accelerated charge transfer kinetics as a result of the desirable band alignment in CuO/WO3 heterojunction. This work demonstrates a facile strategy to construct superior WO3 electrode, which will ultimately allow for efficient storage of solar energy into hydrogen.

A Hierarchical MoP Nanoflake Array Supported on Ni Foam: A Bifunctional Electrocatalyst for Overall Water Splitting

AbstractThe search for an inexpensive bifunctional electrocatalyst for overall water splitting has attracted considerable research interest during the past years. Herein, self‐supported hierarchical electrodes comprising nickel foam (NF) and porous molybdenum phosphide (MoP) nanoflakes are fabricated by first growing MoO2 nanoflakes on Ni foam and then further phosphorization treatment. Remarkably, serving as both anode and cathode catalysts in a two‐electrode alkaline water‐electrolysis system, the designed electrodes only require a potential of 1.62 V to deliver a current density of 10 mA cm−2. This performance is close to that of the noble‐metal‐based electrodes, that is, integrated RuO2/Ni foam and Ni foam supported Pt/C electrodes. The low cost, facile preparation method, and desirable performance make this MoP/NF electrode a potential electrocatalyst for overall water splitting.

Mesoporous Fe–Ni–Co ternary oxide nanoflake arrays on Ni foam for high-performance supercapacitor applications

A new 3D binder-free ternary Fe–Ni–Co oxide nanoflake arrays on Ni foam was synthesized using a simple facile two-step process. The as-prepared supercapacitor electrode showed excellent electrochemical performance, such as a high specific capacitance of 867Fg−1 and excellent cycling stability (92.3% capacitance retention after 10,000 charge–discharge cycles). In addition, an aqueous hybrid asymmetric supercapacitor device based on this material exhibited high energy density of 40Whkg−1 and excellent capacitance retention of 87.4% after 5000 cycles. This outstanding electrochemical performance highlights the potential of this 3D mesoporous ternary mixed-metal oxide electrode in commercial high performance supercapacitors.

Preparation and supercapacitive property of molybdenum disulfide (MoS2) nanoflake arrays- tungsten trioxide (WO3) nanorod arrays composite heterojunction: A synergistic effect of one-dimensional and two-dimensional nanomaterials

We first report a composite of molybdenum disulfide (MoS2) nanoflake arrays (MNFs) and tungsten trioxide (WO3) nanorod arrays (WNRs) directly grown on a copper (Cu) substrate. This composite is characterized in detail by scanning and transmission electron microscopes (SEM/TEM), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). All of the evidences indicate that the obtained composite is a heterojunction. The supercapacitive properties of MNFs-WNRs composite heterojunction are measured systematically by using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques. The heterojunction exhibits a high specific capacitance of 522 F g−1 at 0.5 A g−1, a high capacitance retention (95%) after 5000 cycles and a low charge transfer resistance (1.0 Ω). And this kind of heterojunction has advantages of both MoS2 and WO3, which can be a better candidate for supercapacitive electrode material.

Disposable photoelectrochemical sensing strip for highly sensitive determination of perfluorooctane sulfonyl fluoride on functionalized screen-printed carbon electrode

Owing to the lack of chromophores and ionizable functional groups, it is a significant challenge to determine perfluorooctane sulfonyl fluoride (PFOSF) by traditional high-performance liquid chromatography or liquid chromatography/mass spectrometry, especially at a low concentration. In this work a unique photoelectrochemical (PEC) sensing strip has been developed for the first time for the detection of PFOSF. The sensing strip is cost effective and disposable, whereby BiOI nanoflake arrays are fabricated on a home-made screen-printed electrode through a facile one-step in-situ electrodeposition process, and then the molecule tags (i.e., molecularly imprinted polymers) for PFOSF are subsequently grafted on the surface. Benefitting from a three-dimensional interconnected framework, the as-fabricated sensing strip has a rapid response to the interfacial steric hindrance effect between the sensing platform and the target analyte of PFOSF. The elaborated PEC sensor exhibits a outstanding linear response to a concentration of PFOSF ranging from 0.05 to 500.0 ppb and a detection limit down to 0.01 ppb (S/N = 3) Furthermore, our low-cost and highly sensitive sensor has been further explored to detect PFOSF in real water samples, showing satisfactory results.

Open hollow Co–Pt clusters embedded in carbon nanoflake arrays for highly efficient alkaline water splitting

Water splitting provides a clean and renewable way to produce high-purity hydrogen; the current bottlenecks of which are the slow kinetics and poor stability of the available electrocatalysts.

Reduced graphene oxide nanosheet modified NiMn-LDH nanoflake arrays for high-performance supercapacitors.

Reduced graphene oxide (rGO) nanosheets are exploited as a modification layer on a Ni foam-supported NiMn-LDH nanoflake array electrode via a facile dip-coating method. rGO serves as a second electron collector, which promotes rapid charge transport and improves electrochemical reaction kinetics. Asymmetric supercapacitors are also assembled exhibiting excellent electrochemical performance.

Free-standing single-crystalline NiFe-hydroxide nanoflake arrays: a self-activated and robust electrocatalyst for oxygen evolution.

Free-standing single-crystalline NiFe-hydroxide nanoflake arrays grown in situ on nickel foam are synthesized using a simple hydrothermal method and they exhibit remarkable activity and durability for oxygen evolution in 1.0 M KOH, achieving a decreased overpotential of 235 mV to produce 10 mA cm-2 current density after long-term operation up to 100 h.

Two-dimensional porous ZnCo2O4 thin sheets assembled by 3D nanoflake array with enhanced performance for aqueous asymmetric supercapacitor

As a promising electrode material for supercapacitor, two dimensional (2D) porous cobaltite with spinel structure shows high specific capacitance, long cycle life and especially high energy density, which have great potential in electrochemical energy storage. In the present work, we demonstrated for the first synthesis of 2D porous ZnCo2O4 thin sheets (CQU-Chen-Zn-Co-O-2) with micro-mesoporous structure and high specific surface area of 89.63, 151.65 and 63.72 m2·g–1 through simple hydrothermal treatment of a mixed aqueous solution containing two kinds of transition metal nitrates (zinc nitrate (Zn(NO3)2) and cobalt nitrate (Co(NO3)2)) and benzoic acid (C6H5COOH, BA) at 180, 200 and 220 °C for 12 h. The 3D nanoflake array assembled nanostructures of the ZnCo2O4 thin sheets facilitate the transmission of ions and electrons throughout the electrochemical testing process, which yield a higher specific capacitance of 3.07 F·cm–2 at 1.04 mA·cm–2 in a three-electrode system and a high energy density of 36.31 Wh·kg–1 at a power density of 850 W·kg–1 in an aqueous asymmetric supercapacitor (ZnCo2O4 thin sheets//active carbon (AC)). The results indicate that the 2D ZnCo2O4 thin sheets exhibt superior supercapacitor performance.

Wearable Fabrics with Self-Branched Bimetallic Layered Double Hydroxide Coaxial Nanostructures for Hybrid Supercapacitors.

We report a flexible battery-type electrode based on binder-free nickel cobalt layered double hydroxide nanosheets adhered to nickel cobalt layered double hydroxide nanoflake arrays on nickel fabric (NC LDH NFAs@NSs/Ni fabric) using facile and eco-friendly synthesis methods. Herein, we utilized discarded polyester fabric as a cost-effective substrate for in situ electroless deposition of Ni, which exhibited good flexibility, light weight, and high conductivity. Subsequently, the vertically aligned NC LDH NFAs were grown on Ni fabric by means of a hot-air oven-based method, and fluffy-like NC LDH NS branches are further decorated on NC LDH NFAs by a simple electrochemical deposition method. The as-prepared core-shell-like nanoarchitectures improve the specific surface area and electrochemical activity, which provides the ideal pathways for electrolyte diffusion and charge transportation. When the electrochemical performance was tested in 1 M KOH aqueous solution, the core-shell-like NC LDH NFAs@NSs/Ni fabric electrode liberated a maximum areal capacity of 536.96 μAh/cm2 at a current density of 2 mA/cm2 and excellent rate capability of 78.3% at 30 mA/cm2 (420.5 μAh/cm2) with a good cycling stability. Moreover, a fabric-based hybrid supercapacitor (SC) was assembled, which achieves a stable operational potential window of 1.6 V, a large areal capacitance of 1147.23 mF/cm2 at 3 mA/cm2, and a high energy density of 0.392 mWh/cm2 at a power density of 2.353 mW/cm2. Utilizing such high energy storage abilities and flexible properties, the fabricated hybrid SC operated the wearable digital watch and electric motor fan for real-time applications.

Free-standing Two-dimensional Mesoporous ZnCo2O4 Thin Sheets Consisting of 3D Ultrathin Nanoflake Array Frameworks for High Performance Asymmetric Supercapacitor

For developing high performance supercapacitors (SCs), it is critical to fabricate advanced electrode materials with porous nanostructures and high surface area to facilitate the transport of ions and electrons and impede the volumetric variation during cycling. Herein, we reported the fabrication of free-standing two dimensional (2D) mesoporous ZnCo2O4 thin sheets (CQU-Chen-Zn-Co-O-1) consisting of 3D ultrathin nanoflake array frameworks by facile decomposition of a mixed aqueous solution of zinc ion (Zn2+), cobalt ion (Co2+) and acetic acid (CH3COOH, AA) under hydrothermal condition without any additive agent. The resulting CQU-Chen-Zn-Co-O-1 delivers a high capacitance of 2.72Fcm−2 at 2.02mAcm−2 and high rate capability of 59.76% from 1.01 to 10.1mAcm−2 and superior cycling performance of 3.5% loss after 5,000 cycles. Furthermore, an assembled asymmetric supercapacitor (CQU-Chen-Zn-Co-O-1//active carbon (AC)) device exhibits high energy density of 33.98 and 9.78 Wh kg−1 at power density of 8 and 0.8kWkg−1, respectively, as well as good cycling performance of 6.7% loss after 10,000 cycles. These results show that the ZnCo2O4 thin sheets display great potential in energy storage applications.

Visible light assisted NO2 sensing at room temperature by CdS nanoflake array

A Highly ordered CdS nanoflake array was fabricated by CVD, and its gas sensing characteristics were investigated. The sensor exhibited high response (resistance ratio) of 89% to 5 part per million (ppm) nitrogen dioxide (NO2) under green LED illumination (wavelength 500–540 nm, irradiance 21 W/m2) with excellent selectivity and little interference by humidity. Moreover, the sensor showed promising potential for operating under fluorescent lamp and natural solar light, which can be used for medical diagnosis and indoor/outdoor environment monitoring. This performance is attributed to the low band gap energy (2.4 eV) of CdS and the unique morphology of nanoflake array which can enhance both the light absorption and conductivity.

Freestanding two-dimensional Ni(OH)2 thin sheets assembled by 3D nanoflake array as basic building units for supercapacitor electrode materials

Freestanding two dimensional (2D) porous nanostructures have great potential in electrical energy storage. In the present work, we reported the first synthesis of two-dimensional (2D) β-Ni(OH)2 thin sheets (CQU-Chen-Ni-O-H-1) assembled by 3D nanoflake array as basic building units under acid condition by direct hydrothermal decomposition of the mixed solution of nickel nitrate (Ni(NO3)2) and acetic acid (CH3COOH, AA). The unique 3D nanoflake array assembled mesoporous 2D structures endow the thin sheets with a high specific capacitance of 1.78Fcm−2 (1747.5Fg−1) at the current density of 1.02mAcm−2 and good rate capability of 67.4% retain from 1.02 to 10.2mAcm−2. The corresponding assembled asymmetric supercapacitor (ASC) achieves (CQU-Chen-Ni-O-H-1//active carbon (AC)) a high voltage of 1.8V and an energy density of 23.45Whkg−1 with a maximum power density of 9kWkg−1, as well as cycability with 93.6% capacitance retention after 10,000 cycles. These results show the mesoporous thin sheets have great potential for SCs and other energy storage devices.

3D porous NiMoO4 nanoflakes arrays for advanced supercapacitor electrodes

In recent years, supercapacitors have been considered as one of the auspicious energy storage devices. In this work, two different kinds of mixed metal oxide NiMoO4 nanoflakes arrays were directly grown on 3D Ni foam. The electrode exhibited high specific capacitance of 2004 F/g at the current density of 2 A/g in 6 M KOH electrolyte. Additionally, it also exhibited low equivalent series resistance of 0.62 Ω and excellent cycling stability (80% capacitance retention after 1000 cycles). With these extraordinary electrochemical properties, the electrode material can be considered as potential candidate for supercapacitor applications.

Optimized K+ pre-intercalation in layered manganese dioxide nanoflake arrays with high intercalation pseudocapacitance

Abstract Intercalation pseudocapacitance is emerging as a highly promising mechanism for high rate energy storage applications. However, it is still debatable how the alkali metal ion pre-intercalation in layered metal oxides affects the intercalation pseudocapacitance. Herein，the layered birnessite-MnO 2 nanoflakes with K + pre-intercalation were in- situ fabricated on the graphene foam via a one-step facile hydrothermal method. The amount of pre-intercalated K + can be controlled by adjusting the reaction parameter. The electrochemical tests indicate that the amount of pre-intercalated ions has the optimal value and intercalated slight or excessive amount of ions may lead to the pseudocapacitance decline. The K 0.19 MnO 2 /graphene foam electrode shows a high pseudocapaitance of 344 F g −1 (based on the mass of the whole electrode) at a scan rate of 2 mV s −1 , which is the best among the as-prepared samples. Cycling tests demonstrate that the pre-intercalated K + can greatly improve the cycling stability of layered birnessite-MnO 2 nanoflakes. This work provides new insights on understanding the role of pre-intercalation ions and brings new strategies to further improve the performance of layered metal oxide electrodes.

Localized Defects on Copper Sulfide Surface for Enhanced Plasmon Resonance and Water Splitting.

Surficial defects in semiconductor can induce high density of carriers and cause localized surface plasmon resonance which is prone to light harvesting and energy conversion, while internal defects may cause serious recombination of electrons and holes. Thus, it is significant to precisely control the distribution of defects, although there are few successful examples. Herein, an effective strategy to confine abundant defects within the surface layer of Cu1.94 S nanoflake arrays (NFAs) is reported, leaving a perfect internal structure. The Cu1.94 S NFAs are then applied in photoelectrochemical (PEC) water splitting. As expected, the surficial defects give rise to strong LSPR effect and quick charge separation near the surface; meanwhile, they provide active sites for catalyzing hydrogen evolution. As a result, the NFAs achieve the top PEC properties ever reported for Cux S-based photocathodes.

Chemical Synthesis of 3D Graphene‐Like Cages for Sodium‐Ion Batteries Applications

AbstractSodium (Na) super ion conductor structured Na3V2(PO4)3 (NVP) is extensively explored as cathode material for sodium‐ion batteries (SIBs) due to its large interstitial channels for Na+ migration. The synthesis of 3D graphene‐like structure coated on NVP nanoflakes arrays via a one‐pot, solid‐state reaction in molten hydrocarbon is reported. The NVP nanoflakes are uniformly coated by the in situ generated 3D graphene‐like layers with the thickness of 3 nm. As a cathode material, graphene covered NVP nanoflakes exhibit excellent electrochemical performances, including close to theoretical reversible capacity (115.2 mA h g−1 at 1 C), superior rate capability (75.9 mA h g−1 at 200 C), and excellent cyclic stability (62.5% of capacity retention over 30000 cycles at 50 C). Furthermore, the 3D graphene‐like cages after removing NVP also serve as a good anode material and deliver a specific capacity of 242.5 mA h g−1 at 0.1 A g−1. The full SIB using these two cathode and anode materials delivers a high specific capacity (109.2 mA h g−1 at 0.1 A g−1) and good cycling stability (77.1% capacity retention over 200 cycles at 0.1 A g−1).