Hierarchical Nanosheet Arrays Research Articles

Hierarchical NiCoP nanosheet arrays with enhanced electrochemical properties for high-performance wearable hybrid capacitors

Transition metal phosphides (TMPs) are battery-typed materials with superior conductivity and redox activity, thereby making them promising in fiber-shaped hybrid capacitors (FSHCs). Yet designed synthesis of nanostructured TMPs on conductive fiber substrate as binder-free electrode is essential to improve their electrochemical performance. This work proposes an efficient strategy to directly grow hierarchical NiCoP nanosheet arrays (NSAs) on carbon nanotube fibers (CNTFs) by using a hydrothermal process and subsequent gas-solid phosphorization. Benefiting from the ordered nanosheet structure, the NiCoP/CNTF electrode exhibits a specific capacity of 0.711 mAh cm−2 at a current density of 1 mA cm−2. Matching this electrode with a negative electrode of CNTF supported vanadium nitride (VN) NSAs, we fabricated a high-performance twisted FSHC with a maximum operating voltage of 1.6 V. Owing to the ultrahigh electrochemical performance of the hybrid fiber electrodes, the FSHC device delivers a high specific capacitance of 325.6 mF cm−2 (108.53 F cm−3) at the current density of 1 mA cm−2, and achieves an energy density of 115.78 μWh cm−2. Moreover, it displays excellent flexibility with negligible capacitance loss after 5000 bending cycles. Thus, this work elucidates a feasible route to construct NiCoP-based fiber electrodes for wearable energy storage devices.

Iron-Incorporated α-Ni(OH)2 Hierarchical Nanosheet Arrays for Electrocatalytic Urea Oxidation.

An iron-incorporated α-Ni(OH)2 nanosheet array catalyst characterized by hierarchical surface nanobelts and robust urea oxidation performance are reported. The unique single-crystalline belt-on-sheet hierarchical nanostructure was identified and it endows more reactive edges for the Ni2+ -to-Ni3+ pre-oxidation process to boost the generation of active high-valence species for the urea oxidation reaction (UOR). Benefitting from the optimal Fe concentration, the UOR activity was further optimized owing to the favorable reaction kinetics. With the synergistic benefits of the increased surface areas, improved charge transfer behavior, favorable reaction kinetics and excellent structural stability, the iron-incorporated α-Ni(OH)2 hierarchical nanosheet array catalyst displays significantly improved UOR performance with both high activity and outstanding operational stability. This work could guide the design of advanced UOR catalysts for wastewater treatment and clean energy production in the future.

Core–shell NiCo2O4@ZnWO4 nanosheets arrays electrode material deposited at carbon-cloth for flexible electrochemical supercapacitors

Three dimensional (3D) hierarchical NiCo2O4 nanosheet arrays (NSAs)@ZnWO4 nanoflakes (NFs) core–shell structures have been successfully grown on a carbon cloth (CC) using two-step hydrothermal approach, following a heat treatment route. Compared with the pure CC@NiCo2O4 NSAs electrode, the binder-free CC@NiCo2O4@ZnWO4 hybrid system gives rise to a higher specific capacitance of 872.0 Fg−1 at a low current density of 1 Ag−1 and 791.1 Fg−1 at a quite high current density of 20 Ag−1, and retains ~ 92.9% of the initial capacitance even after 5000 cycles of charge and discharge. The excellent electrochemical performance of CC@NiCo2O4@ZnWO4 electrode is attributed to its high specific surface area of the 3D structures, fast electron transport property of NiCo2O4 material as the skeleton, and the synergistic effect between NiCo2O4 and ZnWO4 materials, demonstrating that CC supported NiCo2O4 NSAs@ZnWO4 NFs composite as the high-performance electrode materials are highly desirable for the application of flexible supercapacitors.

Self-Supported Bi2MoO6 Nanosheet Arrays as Advanced Integrated Electrodes for Li-Ion Batteries with Super High Capacity and Long Cycle Life

Hierarchical Bi2MoO6 nanosheet arrays (BNAs) growing on three-dimensional (3D) Ni foam are synthesized by one-step template-free route. The obtained BNAs are used as binder-free integrated electrode for Li-ion batteries (LIBs) directly. The electrode exhibits a super high reversible discharge capacity of 2311.7[Formula: see text][Formula: see text]Ah[Formula: see text]cm[Formula: see text] (1741.4[Formula: see text]mAh[Formula: see text]g[Formula: see text]), and an excellent cycle stability. The outstanding electrochemical properties are reasonable from the self-supported integrated electrode in which the electrolyte is easy to infiltrate active materials, electrons and ions are readily transported along the 3D conductive substrate and the stable electrode structure.

Superaerophobic P-doped Ni(OH)2/NiMoO4 hierarchical nanosheet arrays grown on Ni foam for electrocatalytic overall water splitting.

Transition metal (TM) oxides and hydroxides are one of the important candidates for the development of durable and low-cost electrocatalysts towards water splitting. The key issue is exploring effective methods to improve their electrocatalytic activity. Herein, we report a new type of P-doped Ni(OH)2/NiMoO4 hierarchical nanosheet array (abbr. P-Ni(OH)2/NiMoO4) grown on Ni foam (NF), which can act as a highly efficient electrocatalyst towards overall water splitting. Such a composite was obtained by a three-step preparation process. In the first two hydrothermal reactions, the crystalline Ni(OH)2 hierarchical nanosheet arrays were grown on NF and then the low crystallinity NiMoO4 was grafted on the Ni(OH)2 nanosheets. In the third phosphorization step, P element was doped into the composite Ni(OH)2/NiMoO4. Electrocatalytic experiments show that P-Ni(OH)2/NiMoO4 possesses a smaller overpotential (60 mV) and lower Tafel slope (130 mV dec-1) toward HER in 1 M KOH. When it was employed as an integrated water splitting catalyst, only a potential of 1.55 V was required to achieve a current density of 10 mA cm-2. This catalytic activity is even better than those of electrolyzers constructed with noble metals Pt/C∥IrO2. The superior electrocatalytic performance of P-Ni(OH)2/NiMoO4 can be attributed to the high quality of crystalline Ni(OH)2 nanosheet arrays grown on NF, which dramatically improve the conductivity. Furthermore, the hierarchical structure not only increases the surface area and exposes more catalytically active sites, but also provides a superaerophobic surface, which helps to accelerate the release of generated bubbles. Moreover, the synergistic effects between P-Ni(OH)2 and P-NiMoO4 efficiently promote the HER and OER processes also. This work may suggest new a way to explore TM oxide/hydroxide-based durable electrocatalysts with highly efficient electrocatalytic activities towards overall water splitting.

Vanadium dioxide-anchored porous carbon nanofibers as a Na+ intercalation pseudocapacitance material for development of flexible and super light electrochemical energy storage systems

The development of a flexible binder free electrode based on 3D vanadium dioxide (VO2) nano-architectures has materialized as an effective strategy for fabrication of advanced wearable, portable, and stretchable electronic devices. However, most of the stretchable energy storage devices based on VO2 suffer from a relatively low operating voltage, high weight, low specific capacitance, and thus low energy density. Here, a novel binder free supercapacitor electrode composed of hierarchical VO2 nanosheet arrays grown on porous carbon nanofibers (VO2@PCNFs) is designed using a simple hydrothermal method followed by annealing treatment. The electrochemical evaluation confirmed that the energy storage mechanism of the prepared VO2@PCNFs is based on the intercalation pseudocapacitance properties. The resulting VO2@PCNFs electrode displays a wide operation voltage (−1.0 to 1.1V in three electrode systems), maximum specific capacitance of 778Fg−1 (at 1Ag–1), and excellent rate capability. Moreover, a novel all-solid-state asymmetric supercapacitor with good flexibility is assembled in a neutral Na2SO4− poly(vinyl alcohol) (Na2SO4/PVA) gel electrolyte using the VO2@PCNFs film as a positive electrode and PCNFs as a negative electrode. Due to the high capacitances and excellent rate performances of VO2@PCNFs and PCNFs, as well as the synergistic effects of the two electrodes, such asymmetric cell could be cycled reversibly in the voltage range of 0–1.7V, and presents maximum energy density of 75.06Whkg−1, and excellent cycling durability, with 92.4% retaining in its specific capacitance even after 4000 cycles. These encouraging results confirm a great potential of our proposed electrode in developing energy storage devices based on VO2 electrode materials with superior performances for practical applications.

Hierarchical Li4Ti5O12 nanosheet arrays anchoring on carbon fiber cloth as ultra-stable free-standing anode of Li-ion battery

A flexible, free-standing composite anode with Li4Ti5O12 nanosheet arrays anchoring on plain-weaved carbon fiber cloth (LTO@CC) is prepared by a hydrothermal and post-annealing process assisted by a TiO2 seed layer. The LTO@CC anode free from polymeric binder and conducting agent exhibited much higher lithium storage capacity and cycling stability than the conventional slurry-processed electrode using the dandelion-like Li4Ti5O12 microspheres prepared by the same hydrothermal process. A high specific capacity of 128.8mAhg−1 was obtained at a current rate of 30C (1C = 175mAg−1), and almost negligible capacity loses was observed when the cell was cycled at 10, 20 and 30C each for 100 cycles. The carbon fiber matrix contributed to Li storage at low current rate, but the LTO nanosheet arrays have played the dominant role on the excellent rate capability. The improved electrochemical performance can be attributed to the synergetic effect between the hierarchical Li4Ti5O12 nanosheet arrays and the carbon fiber matrix, which integrated short Li+ diffusion length, three-dimensional conductive architecture and well preserved structural integrity during the high rate and repeated charge-discharge measurements.

Ni0.85Se@MoSe2 Nanosheet Arrays as the Electrode for High-Performance Supercapacitors

In this study, we report novel Ni0.85Se@MoSe2 nanosheet arrays prepared by a facile one-step hydrothermal method through nickel (Ni) foam as Ni precursor and the framework of MoSe2. Owing to the unique interconnection and hierarchical porous nanosheet array architecture, the Ni0.85Se@MoSe2 nanosheet arrays exhibit a high specific capacitance of 774 F g-1 at the current density of 1 A g-1, which is almost 2 times higher than that (401 F g-1) of the Ni0.85Se matrix and about 7 times greater than that (113 F g-1) of the MoSe2 nanoparticles. Moreover, we report an asymmetric supercapacitor (ASC), which is fabricated by using the Ni0.85Se@MoSe2 nanosheet arrays as the positive electrode and the graphene nanosheets (GNS) as the negative electrode, with aqueous KOH as the electrolyte. The Ni0.85Se@MoSe2//GNS ASC possesses an output voltage of 1.6 V, an energy density of 25.5 Wh kg-1 at a power density of 420 W kg-1, and a cycling stability of 88% capacitance retention after 5000 cycles. These results indicate that the Ni0.85Se@MoSe2 nanosheet arrays are a good electrode for supercapacitors.

Flexible textile electrode with high areal capacity from hierarchical V2O5 nanosheet arrays

The search for an appropriate flexible cathode is pivotal to expediting the development of flexible and foldable lithium-ion batteries (LIBs). Herein, we demonstrate a simple and scalable synthesis of hierarchical V2O5 nanosheet arrays on polydopamine (PDA)-decorated carbon cloth with strong combination between them, which then directly applied as flexible cathode for LIBs. We found this flexible cathode with a loading mass of 2.1 mg cm−2 can deliver a high specific capacity of 120 mAh g−1 even at 15C (1C = 300 mA g−1) and maintain a long-term cycling stability, i.e. simply 0.30% capacity loss per cycle at 2C for 100 cycles without morphology change. More importantly, the corresponding areal capacity can reach as high as 560 μAh cm−2 at 210 μA cm−2, favorably comparing with the-state-of-art flexible cathode reported to date. Additionally, a flexible LIBs full cell has been assembled, exhibiting high mechanical strength and superior electrochemical performances.

Understanding the role of Co3O4 on stability between active hierarchies and scaffolds: An insight into NiMoO4 composites for supercapacitors

It is often reported that pseudocapacitive electrodes’ mechanical stability seriously limited their cycling performances in supercapacitors due to their quick fall off the electrode matrix during frequent fast charge/discharge process. In this work, we have demonstrated the mechanical enhancement in hierarchical NiMoO4 nanosheet arrays (NSAs) on free-standing substrates after introducing Co3O4 hierarchies. Under sonication vibration environment, the mechanical stability of Co3O4@NiMoO4 NSAs was enhanced by ∼70% compared to that of the pure NiMoO4 ones. Moreover, the Co3O4@NiMoO4 NSAs can display a high specific capacitance of 1476Fg−1 at the current density of 1Ag−1, and an excellent rate capability (keeping 81% at 20Ag−1). And after 2000 cycles, high capacitance retention of 96% was achieved for the Co3O4@NiMoO4 core/shell NSAs, while only 70% for the pure NiMoO4 ones.

Robust wire-based supercapacitors based on hierarchical α-MoO3 nanosheet arrays with well-aligned laminated structure

Due to their high pseudocapacitance and laminated structure, α-MoO3 nanosheets have been considered as one of the promising electrode materials of energy storage devices. In this work, hierarchical α-MoO3 nanosheet arrays have been in-situ grown on Mo wires (MoO3-Mo wires) via one-step calcination in air. The obtained MoO3-Mo wires possess well aligned laminated structure, which will benefit intercalation of Li-ion into the electrodes. Thus, a type of Li-ion electrolyte was applied in the assembled wire-based supercapacitors (WSCs). Electrochemical tests showed that the MoO3-Mo single wire electrodes can exhibit high capacitance (7.68mFcm−1 at 2mVs−1) and excellent cycling stability (nearly 100% after 4000 cycles). Moreover, series of optimization tries indicated that the laminated structure of MoO3 nanosheet arrays can be well tuned by calcination temperature and time, accordingly resulting in the optimized electrochemical performance. Furthermore, the assembled all-solid state symmetrical WSCs based on MoO3-Mo wires showed high energy density (∼1.04mWhcm−3), high cycling stability, and good flexibility.

Hierarchical three-dimensional FeCo2O4@MnO2 core-shell nanosheet arrays on nickel foam for high-performance supercapacitor

Developing supercapacitors with high energy density, good rate capability, and superior cycle life is crucial to the ever-increasing energy storage devices. However, how to design and develop a new type of faradaic electrode material with large surface area, low resistance, and stable microstructures is still a challenge work. Herein, we have successfully realized a high-energy and long-life supercapacitor by developing nickel foam—hierarchical three-dimensional iron cobaltate nanosheet arrays framework, and covering the surface with thin nanosheets of manganese dioxide (Ni@FeCo2O4@MnO2). The free-standing supercapacitor device based on this structure gives rise to a high energy density of 22.2Whkg−1 at a power density of 978.3Wkg−1, and ∼87.2% of the capacitance can be retained after 5000 cycles of charge-discharge. These performance features are excellent among those reported for iron cobaltate based supercapacitors, making it a promising candidate for high-performance electrochemical energy storage.

Electrodeposition of Hierarchical Nanosheet Arrays of NiCo2S4 onto a Polymer Substrate: A New High Power Flexible Battery Electrode

A simple and facile fabrication of hierarchical nanosheet arrays of a ternary system comprising of NiCo2S4 deposited onto conductive copper coated flexible polymer (overhead projector; OHP) electrodes by using electrodeposition (ED) is reported. Such electrochemically modified flexible electrodes show typical faradaic redox reactions consistent with battery-type materials and exhibit higher capacity along with excellent rate performance. Structural morphology and composition of these flexible electrodes are analyzed using spectroscopic and microscopic characterization techniques. Interfacial electrochemical characteristics are investigated by using cyclic voltammetry and electrochemical impedance spectroscopic studies. Effects of several parameters associated with ED process including the concentration, applied cathodic voltage and time duration on the structural morphology of resultant NiCo2S4 deposits and on their charge transfer properties are also analyzed. From these studies it has been found that the optimized electrode, namely Ni-Co-S-1/Cu/OHP shows well defined hierarchical nanosheet arrays of NiCo2S4 grown onto Cu deposited flexible OHP strip electrodes. This particular electrode possesses higher surface roughness, porosity and shows superior electrochemical characteristics as a positive electrode for flexible battery applications. A very high specific capacity of 218.1 mAh g−1 at a current density of 2 A g−1 and capacity retention of 86.7% at 10 A g−1 after 2000 cycles are determined. All these experimental results illustrate the hierarchical nanosheet arrays deposited onto flexible copper coated OHP strip alters the interfacial capacity and could be used as a promising positive electrode for low-cost flexible energy storage devices.

Hierarchical CoNi-Sulfide Nanosheet Arrays Derived from Layered Double Hydroxides toward Efficient Hydrazine Electrooxidation.

A hierarchical CoNi-sulfide nanosheet array is fabricated via an in situ reduction of CoNi-layered double hydroxide (LDH) nanosheets, then a vulcanization process. The material inherits the morphology of the LDH precursor, consisting of well-distributed CoNi-alloy@CoNi-sulfide nanoparticles with a core-shell structure, and demonstrates promising performance toward hydrazine electrooxidation.

Hierarchical 3-dimensional nickel–iron nanosheet arrays on carbon fiber paper as a novel electrode for non-enzymatic glucose sensing

Three-dimensional nickel-iron (3-D/Ni-Fe) nanostructures are exciting candidates for various applications because they produce more reaction-active sites than 1-D and 2-D nanostructured materials and exhibit attractive optical, electrical and catalytic properties. In this work, freestanding 3-D/Ni-Fe interconnected hierarchical nanosheets, hierarchical nanospheres, and porous nanospheres are directly grown on a flexible carbon fiber paper (CFP) substrate by a single-step hydrothermal process. Among the nanostructures, 3-D/Ni-Fe interconnected hierarchical nanosheets show excellent electrochemical properties because of its high conductivity, large specific active surface area, and mesopores on its walls (vide infra). The 3-D/Ni-Fe hierarchical nanosheet array modified CFP substrate is further explored as a novel electrode for electrochemical non-enzymatic glucose sensor application. The 3-D/Ni-Fe hierarchical nanosheet arrays exhibit significant catalytic activity towards the electrochemical oxidation of glucose, as compared to the 3-D/Ni-Fe hierarchical nanospheres, and porous nanospheres. The 3-D/Ni-Fe hierarchical nanosheet arrays can access a large amount of glucose molecules on their surface (mesopore walls) for an efficient electrocatalytic oxidation process. Moreover, 3-D/Ni-Fe hierarchical nanosheet arrays showed higher sensitivity (7.90 μA μM(-1) cm(-2)) with wide linear glucose concentration ranging from 0.05 μM to 0.2 mM, and the low detection limit (LOD) of 0.031 μM (S/N = 3) is achieved by the amperometry method. Further, the 3-D/Ni-Fe hierarchical nanosheet array modified CFP electrode can be demonstrated to have excellent selectivity towards the detection of glucose in the presence of 500-fold excess of major important interferents. All these results indicate that 3-D/Ni-Fe hierarchical nanosheet arrays are promising candidates for non-enzymatic glucose sensing.

Designed Synthesis of SnO2 Nanosheet Arrays with Superior Performance for Lithium and Sodium Storage

Room-temperature rechargeable sodium-ion batteries (SIBs) are receiving increasing attention for upcoming large-scale applications in smart grid and electric vehicles due to the earth abundance and low cost of sodium.1, 2 However, Na ion has a larger radius of 1.02 Å (~55% larger than Li+, 0.76 Å) and three times heavier than lithium (23 g mol-1 compared with 6.9 g mol-1), which directly affects the Na+ insertion/deinsertion in electrochemical process, leading to low reversible capacity, poor cycling stability, inferior rate capability.3 Although reversible sodium intercalation into commercial graphite anodes was demonstrated by using diglyme-based electrolyte or chemically modified graphite recently, the specific capacity is still lower than that of lithium ion batteries.4, 5Therefore, it is highly promising to develop high capacity anode materials based new storage mechanisms toward practical application of SIBs. Fig. 1 (a) XRD pattern, (b-d) SEM images of SnO2 nanosheet arrays grown on the carbon fiber paper. Herein, we report a simple solution-based hydrothermal approach to construct hybrid architectures by growing 2D hierarchical SnO2 nanosheet arrays on conductive flexible carbon substrates as the anode for Na-ion and Li-ion batteries. Fig. 1a shows the X-ray diffraction (XRD) pattern of the SnO2 nanosheet arrays, and all the diffraction peaks can be readily indexed to the tetragonal phase of SnO2 (JCPDS Card no.71-0652). Two peaks at around 26.2° and 43.1° marked with asterisk originate from the carbon textiles.6 Scanning electron microscopy (SEM) images shown in Fig1b-d clearly display ultrathin SnO2 nanosheet arrays uniformly cover carbon substrates and interconnect with each other to form highly open and porous structure. Taking merits of the ultrathin and highly conductive nature of SnO2 nanosheets as well as the porous interconnected three-dimensional nanoarchitectures, the binder-free flexible SnO2electrodes exhibit high specific capacity with enhanced cycling stability, making it a promising anode material for electrochemical energy storage devices application. Acknowledgements The authors are grateful for financial support from the National Program on Key Basic Research Project of China (973 Program, no. 2014CB239701), National Natural Science Foundation of China (no. 21173120, 51372116), Natural Science Foundations of Jiangsu Province (no.BK2011030), Funding for Outstanding Doctoral Dissertation in NUAA (no.BCXJ14-12), Founding of Graduate Innovation Center in NUAA (no. kfjj201438), and Funding of Jiangsu Innovation Program for Graduate Education (no.KYLX_0254) and the Fundamental Research Funds for the Central Universities.

3D core/shell hierarchies of MnOOH ultrathin nanosheets grown on NiO nanosheet arrays for high-performance supercapacitors

As the most promising electrode material for supercapacitors, core/shell hybrid material will enhance the electrochemical performance comparing with single component constituent, thus has recently drawn our research. Herein, we have designed and synthesized 3D hierarchical heterostructures of dense MnOOH ultrathin nanosheets grown on porous hierarchical NiO nanosheet arrays by facial and rational process. In this configuration, porous hierarchical NiO nanosheet arrays serve as fast ion and electron transport model and dense MnOOH ultrathin nanosheets enhance the contact surface area and assist ions penetrate into the core region to realize the release of potential electrochemical properties of NiO nanosheet arrays, and thus these heterostructures provide intense needed critical function for efficient use of metal oxide and hydroxide in energy storage. As an electrode, the as-fabricated 3D NiO@MnOOH core/shell nanosheet hierarchies exhibited favorable electrochemical performances, i.e., high specific capacitance of 1625.3F/g at a current density of 4A/g with a remarkable rate capability and excellent energy density (80.0Wh/kg), as well as good cycling stability (105.7% of the initial capacitance after 5000 cycles). It suggests that they should have a promising potential for the next generation energy conversion–storage devices.