Core-branch Arrays Research Articles

Promoted synergy in core-branch CoP@NiFe–OH nanohybrids for efficient electrochemical-/ photovoltage-driven overall water splitting

Developing low-cost, high-performance electrocatalysts to efficiently convert intermittent solar energy into hydrogen via water splitting is the key to realize sustainable energy cycle but remain challenges. Herein, the three dimensional core-branch CoP@NiFe–OH nanohybrids supported on surface-phosphatized Ni foam (CoP@NiFe–OH/SPNF) are facilely fabricated as the high-performance bifunctional electrocatalysts for alkaline water electrolysis. Theoretical calculation and electrochemical tests manifest that hybridizing CoP with NiFe–OH engenders strong synergistic catalytic effects, leading to fast hydrogen and oxygen evolution reaction kinetics. Meanwhile, hierarchical core-branch arrays and self-supported architecture also result in CoP@NiFe–OH/SPNF with multiple exposing active sites, faster ions, electron transport behavior and superior lifespan. Owing to these typical merits, the bifunctional CoP@NiFe–OH/SPNF electrode expedites overall water splitting with affording a current density of 10, 50 and 100 mA cm−2 only at 1.53, 1.63 and 1.68 V respectively, surpassing the performance of noble (+)IrO2/C//Pt/C(−) and most bifunctional electrocatalysts. As a practical application, a portable solar energy-driven water electrolyzer equipped with the bifunctional CoP@NiFe–OH/SPNF electrode can produce hydrogen at room temperature with a high gas evolution rate of 20.83 μL s−1.

Directional construction of Cu2S branch arrays for advanced oxygen evolution reaction

Abstract Metal sulphide electrocatalyst is considered as one of the most promising low-cost candidates for oxygen evolution reaction (OER). In this work, we report a novel free-standing Cu2S branch array via a facile TiO2-induced electrodeposition-sulfurization method. Interestingly, cross-linked Cu2S nanoflake branch is strongly anchored on the TiO2 backbone forming high-quality Cu2S/TiO2/Cu2S core-branch arrays. The branch formation mechanism is also proposed. As compared to the pure Cu2S nanowire arrays, the as-prepared Cu2S/TiO2/Cu2S core-branch arrays show much better alkaline OER performance with lower overpotential (284 mV at 10 mA cm−2) and smaller Tafel slope (72 dec−1) as well as enhanced long-term durability mainly due to larger exposed area and more active electrocatalytic sites. Our work provides a new way for construction of advanced metal sulphide electrocatalysts for electrochemical energy conversion.

Carbon nanotubes branch on cobalt oxide nanowires core as enhanced high-rate cathodes of alkaline batteries

Directional synthesis of carbon/metal oxide core-branch arrays is of great importance for development of advanced high-rate alkaline batteries. In this work, we report a facile hydrothermal-chemical vapor deposition (CVD) method for controllable fabrication of Co3O4 @CNTs core-branch arrays. Interestingly, free-standing Co3O4 core nanowires are intimately decorated by cocoon-like branch CNTs with diameters of 20–30 nm, which act as a highly conductive network and structure stabilizer. The electrochemical performance of the designed Co3O4 @CNTs core-branch arrays are tested as cathodes of alkaline batteries. Arising from enhanced electrical conductivity, larger surface area and improved structural stability, the Co3O4 @CNTs arrays show superior high-rate electrochemical performance with a higher capacity (116 mAh g−1 at 2.5 A g−1), lower polarization and better cycling stability than the pure Co3O4 nanowires arrays (76 mAh g−1 at 2.5 A g−1). Our directional composite strategy can be extended to preparation of other carbon-based core-branch arrays for applications in electrochemical batteries and catalysis.

Enhancing Ultrafast Lithium Ion Storage of Li4Ti5O12 by Tailored TiC/C Core/Shell Skeleton Plus Nitrogen Doping

AbstractIt is of great importance to reinforce electronic and ionic conductivity of Li4Ti5O12 electrodes to achieve fast reaction kinetics and good high‐power capability. Herein, for the first time, a dual strategy of combing N‐doped Li4Ti5O12 (N‐LTO) with highly conductive TiC/C skeleton to realize enhanced ultrafast Li ion storage is reported. Interlinked hydrothermal‐synthesized N‐LTO nanosheets are homogeneously decorated on the chemical vapor deposition (CVD) derived TiC/C nanowires forming binder‐free N‐LTO@TiC/C core–branch arrays. Positive advantages including large surface area, strong mechanical stability, and enhanced electronic/ionic conductivity are obtained in the designed integrated arrays and rooted upon synergistic TiC/C matrix and N doping. The above appealing features can effectively boost kinetic properties throughout the N‐LTO@TiC/C electrodes to realize outstanding high‐rate capability at different working temperatures (143 mAh g−1/10 C at 25 °C and 122 mAh g−1/50 C at 50 °C) and notable cycling stability with a capacity retention of 99.3% after 10 000 cycles at 10 C. Moreover, superior high‐rate cycling life is also demonstrated for the full cells with N‐LTO@TiC/C anode and LiFePO4 cathode. The dual strategy may provoke wide interests in fast energy storage areas and motivate the further performance improvement of power‐type lithium ion batteries (LIBs).

Pine-Needle-Like Cu-Co Skeleton Composited with Li4 Ti5 O12 Forming Core-Branch Arrays for High-Rate Lithium Ion Storage.

High-performance of lithium-ion batteries (LIBs) rely largely on the scrupulous design of nanoarchitectures and smart hybridization of bespoke active materials. In this work, the pine-needle-like Cu-Co skeleton is reported to support highly active Li4 Ti5 O12 (LTO) forming Cu-Co/LTO core-branch arrays via a united hydrothermal-atomic layer deposition (ALD) method. ALD-formed LTO layer is uniformly anchored on the pine-needle-like heterostructured Cu-Co backbone, which consists of branched Co nanowires (diameters in 20 nm) and Cu nanowires (250-300 nm) core. The designed Cu-Co/LTO core-branch arrays show combined advantages of large porosity, high electrical conductivity, and good adhesion. Due to the unique positive features, the Cu-Co/LTO electrodes are demonstrated with enhanced electrochemical performance including excellent high-rate capacity (155 mAh g-1 at 20 C) and noticeable long-term cycles (144 mAh g-1 at 20 C after 3000 cycles). Additionally, the full cell assembled with activated carbon positive electrode and Cu-Co/LTO negative electrode exhibits high power/energy densities (41.6 Wh kg-1 at 7.5 kW kg-1 ). The design protocol combining binder-free characteristics and array configuration opens a new door for construction of advanced electrodes for application in high-rate electrochemical energy storage.

Hollow TiO2@Co9S8 Core-Branch Arrays as Bifunctional Electrocatalysts for Efficient Oxygen/Hydrogen Production.

Designing ever more efficient and cost‐effective bifunctional electrocatalysts for oxygen/hydrogen evolution reactions (OER/HER) is greatly vital and challenging. Here, a new type of binder‐free hollow TiO2@Co9S8 core–branch arrays is developed as highly active OER and HER electrocatalysts for stable overall water splitting. Hollow core–branch arrays of TiO2@Co9S8 are readily realized by the rational combination of crosslinked Co9S8 nanoflakes on TiO2 core via a facile and powerful sulfurization strategy. Arising from larger active surface area, richer/shorter transfer channels for ions/electrons, and reinforced structural stability, the as‐obtained TiO2@Co9S8 core–branch arrays show noticeable exceptional electrocatalytic performance, with low overpotentials of 240 and 139 mV at 10 mA cm−2 as well as low Tafel slopes of 55 and 65 mV Dec−1 for OER and HER in alkaline medium, respectively. Impressively, the electrolysis cell based on the TiO2@Co9S8 arrays as both cathode and anode exhibits a remarkably low water splitting voltage of 1.56 V at 10 mA cm−2 and long‐term durability with no decay after 10 d. The versatile fabrication protocol and smart branch‐core design provide a new way to construct other advanced metal sulfides for energy conversion and storage.

Dual Carbon Layered Tin Oxide Anode for High Energy Lithium Ion Batteries

The development of high–capacity anode materials for lithium ion batteries (LIBs) is a key step toward achieving large–scale energy storage applications for portable electronic devices, electrical vehicles, and hybrid electrical vehicles.1 Since its first discovery, the current commercial LIBs have been using graphite as anode material. Although this carbon–based anode is cheap, abundant and reliable, however it provides a limited theoretical capacity of 372 mAh/g, hence hampering the establishment of high–energy density LIBs to meet huge technological demands in the near future.2 To replace the incumbent anode, intensive research has been devoted on the alloy–based materials such as silicon, germanium, tin, and tin oxide (SnO2). Among these candidates, SnO2 is a promising anode material attributing to its low cost, nontoxicity, low operating potential (0.25 V vs. Li/Li+), high theoretical capacity (782 and 1,493 mAh/g for alloying/de–alloying and both alloying/de–alloying and conversion reaction, respectively), and easy synthesis in regard to nanostructures.3 It was widely studied that employing the pristine SnO2 anode for LIBs may face a significant barrier because of a severe volume change during the electrochemical cycle, causing pulverization and cracks and eventually the loss of electrical conduction paths. In the meantime, the new–fresh cracks that are exposed to the electrolyte may form a continuous solid electrolyte interphase (SEI)–filming process resulting in a thickened SEI layer on the surface of SnO2 anode. Consequently, the cell cannot avoid a rapid capacity fading.4 To overcome these problems, we synthesized the rational anode material consisting of hierarchical structure and dual carbon layers. The hierarchical structures of SnO2 anode are aimed at increasing the active surface area, allowing more Li ions can be stored in the spaces, thus promoting a faster Li ion diffusivity. In addition, dual carbon layers are aimed at alleviating the volume change during charge-discharge reaction, leading to mechanically keep the structure of electrode stable and enhance the ionic conductivity at the interfaces. As the results, our C@SnO2@C anode demonstrated a significant electrochemical performance such as long cycle life and high reversible capacity, hence postulating a solution for commercialization of Sn-based anode for LIBs in the market. [References] Chen, Y. M.; Lu, Z. G.; Zhou, L. M.; Mai, Y. W.; Huang, H. T. Triple–coaxial electrospun amorphous carbon nanotubes with hollow graphitic carbon nanospheres for high– performance Li ion batteries. Energy Environ. Sci. 2012, 5, 7898–7902. Ko, Y. N.; Park, S. B.; Kang, Y. C. Design and fabrication of new nanostructured SnO2–carbon composite microspheres for fast and stable lithium storage performance. Small 2014, 10, 3240–3245. Thomas, R.; Rao, G. M. SnO2 nanowire anchored graphene nanosheet matrix for the superior performance of Li–ion thin film battery anode. J Mater Chem A 2015, 3, 274–280. Zhu, C. R.; Xia, X. H.; Liu, J. L.; Fan, Z. X.; Chao, D. L.; Zhang, H. et al. TiO2 nanotube@SnO2 nanoflake core–branch arrays for lithium–ion battery anode. Nano Energy 2014, 4, 105–112.

Self-branched α-MnO2/δ-MnO2 heterojunction nanowires with enhanced pseudocapacitance

For the first time two phase MnO2 nanostructures are constructed into core-branch arrays which deliver high pseudocapacitance.

Double-Sided Carbon Covered Hierarchical Tin Oxide Anode for High Capacity Lithium-Ion Batteries

The development of high–capacity anode materials for lithium ion batteries (LIBs) is a key step toward achieving large–scale energy storage applications for portable electronic devices, electrical vehicles, and hybrid electrical vehicles.1 Since its first discovery, the current commercial LIBs have been using graphite as anode material. Although this carbon–based anode is cheap, abundant and reliable, however it provides a limited theoretical capacity of 372 mAh/g, hence hampering the establishment of high–energy density LIBs to meet huge technological demands in the near future.2 To replace the incumbent anode, intensive research has been devoted on the alloy–based materials such as silicon, germanium, tin, and tin oxide (SnO2). Among these candidates, SnO2 is a promising anode material attributing to its low cost, nontoxicity, low operating potential (0.25 V vs. Li/Li+), high theoretical capacity (782 and 1493 mAh/g for alloying/de–alloying and both alloying/de–alloying and conversion reaction, respectively), and easy synthesis in regard to nanostructures.3 It was widely studied that employing the pristine SnO2 anode for LIBs may face a significant barrier because of a severe volume change during the electrochemical cycle, causing pulverization and cracks and eventually the loss of electrical conduction paths. In the meantime, the new–fresh cracks that are exposed to the electrolyte may form a continuous solid electrolyte interphase (SEI)–filming process resulting in a thickened SEI layer on the surface of SnO2 anode. Consequently, the cell cannot avoid a rapid capacity fading.4 To overcome these problems, we synthesized the rational anode material consisting of hierarchical structure and thin double carbon layers. The hierarchical structures of SnO2 anode are aimed at increasing the active surface area, allowing more Li ions can be stored in the spaces, thus promoting a faster Li ion diffusivity. In addition, thin double carbon layers are aimed at alleviating the volume change during charge-discharge reaction, leading to mechanically keep the structure of electrode stable and enhance the ionic conductivity at the interfaces. As the results, our C@SnO2@C anode demonstrated a significant electrochemical performance such as long cycle life and high reversible capacity, hence postulating a solution for commercialization of Sn-based anode for LIBs in the market. [References] Chen, Y. M.; Lu, Z. G.; Zhou, L. M.; Mai, Y. W.; Huang, H. T. Triple–coaxial electrospun amorphous carbon nanotubes with hollow graphitic carbon nanospheres for high– performance Li ion batteries. Energy Environ. Sci. 2012, 5, 7898–7902. Ko, Y. N.; Park, S. B.; Kang, Y. C. Design and fabrication of new nanostructured SnO2–carbon composite microspheres for fast and stable lithium storage performance. Small 2014, 10, 3240–3245. Thomas, R.; Rao, G. M. SnO2 nanowire anchored graphene nanosheet matrix for the superior performance of Li–ion thin film battery anode. J Mater Chem A 2015, 3, 274–280. Zhu, C. R.; Xia, X. H.; Liu, J. L.; Fan, Z. X.; Chao, D. L.; Zhang, H. et al. TiO2 nanotube@SnO2 nanoflake core–branch arrays for lithium–ion battery anode. Nano Energy 2014, 4, 105–112.

Self-Standing 3D Thin Film Cathodes for Micobatteries

While the microelectronic industry is advancing at a rapid pace with smaller and smaller devices, the implementation of microelectro-mechanical systems (MEMS) on the market strongly depends on the availability of on-board power sources. However, traditional rechargeable batteries based on liquid electrolyte are not applicable due to the restrictions for on-chip design, size and inherent risk of leakage, which give rise to the development of all-solid-state thin film lithium-ion microbattery technology. As more energy is required in microelectronic devices, two-dimensional (2D) thin film microbatteries are no longer the ideal battery design because the limited footprint area results in a compromise between energy density and power density for the build-in power source. A move to all-solid-state three-dimensional (3D) architectures has been proposed as a promising approach to tackle this challenge and achieve both high energy and power densities within the footprint area [1]. 3D microbatteries generally require the fabrication of 3D nanoarchitectured electrodes with large capacity at high charge/discharge rates and long-term cycling capability. Without using binders or conductive additives, the direct fabrication of nanoarchitectures for the electrode materials on conductive substrates represents a new class of electrodes: 3D self-supported electrodes. Except as the key component for constructing 3D microbatteries, the 3D self-supported electrodes using flexible substrates (such as metal foil and carbon cloth) can be ideal electrodes for flexible lithium-ion batteries. Active research efforts have been devoted to the synthesis and characterization of various 3D self-supported electrodes on different conductive substrates. However, most of the previous works focused on the preparation of 3D self-supported nanoarchitectures for anode materials such as Si, Co3O4, and TiO2 [2], while very limited work has been reported on the 3D self-supported nanoarchitectures for cathode materials. The difficulty lies in the fact that the synthesis of cathode materials such as LiCoO2 and LiMn2O4 involves high temperature treatment, which is difficult for retaining the nanostructures after heat treatment. In this work, we present a new "hydrothermal lithiation" method to construct 3D LiCoO2 and LiMn2O4 nanoarrays on metal substrates [3,4]. Mesoporous low-temperature LiCoO2 nanowire arrays can be directly prepared by a two-step hydrothermal method and they can be easily converted into chain-like high-temperature LiCoO2 nanowire arrays through further calcination. The layered LiCoO2 nanowire arrays exhibit both high gravimetric capacity and areal capacity, while maintaining good cycling stability and rate capability. Similar method was used to prepare vertically aligned porous LiMn2O4 nanowall arrays, comprising highly crystallized spinel nanoparticles, on various conductive substrates without high temperature treatment. The "hydrothermal lithiation" can effectively convert Mn3O4 spinel nanowall arrays into LiMn2O4 spinel nanowall arrays without severe morphology change. The binder-free three-dimensional porous LiMn2O4 nanowall arrays exhibit high specific reversible capacity up to 131 mAh g-1 (or 0.29 mAh cm-2) as well as outstanding cycling stability and rate capability, making them promising as cathodes for both three-dimensional thin film lithium-ion microbatteries. The 3D cathode design and the effective low-temperature synthesis route will lead to new opportunities to develop high-performance microbatteries and flexible lithium-ion batteries.

Construction of cobalt sulfide/nickel core-branch arrays and their application as advanced electrodes for electrochemical energy storage

Design/fabrication of advanced electrodes with tailored functionality is critical for the development of advanced electrochemical devices. Herein, we report a powerful strategy for construction of high-quality cobalt sulfide (CoS)/Ni core-branch arrays via combined methods of hydrothermal and electro-deposition. Electrodeposited thin porous Ni branch is successfully decorated on the CoS nanowires arrays with the help of hydrothermal ZnO nanorods template. Enhanced mechanical stability and improved ion/electron transfer characteristics are achieved in this composite system. As compared to the pure CoS nanowires arrays, the CoS/Ni core-branch arrays show enhanced electrochemical performance with lower polarization, better high-rate capability and superior cycling life. A high capacity of 605mAhg−1at 2C and 371mAhg−1at 6C is obtained in the composite core-branch system, respectively. Our developed electrode design protocol can be applicable for fabrication of other advanced metal sulfides electrodes for applications in solar cells, batteries and supercapacitors.

Construction of Co/Co3O4–C ternary core-branch arrays as enhanced anode materials for lithium ion batteries

Porous hierarchical nanostructures have received wide attention in high-performance lithium ion batteries (LIBs) applications. In this work, we report a simple strategy for the fabrication of porous Co/Co3O4–C core-branch nanowire arrays. By the aid of chemical bath deposition, electro-deposition and annealing process, Co3O4–C nanoflake branch is successfully assembled on the Co core nanowires forming the aligned core-branch nanowires with diameters of about 550 nm. As anode materials for LIBs, the Co/Co3O4–C core-branch nanowire arrays exhibit high reversible capacity, improved cycle stability as well as good rate capability. A specific capacity of 608 mAh g−1 is obtained at 0.5C after 200 cycles, much higher than the unmodified Co3O4 nanoflake arrays (501 mAh g−1 at 0.5C after 200 cycles). The enhanced electrochemical properties are mainly ascribed to the porous core-branch architecture with faster ion/electron transfer path. This newly developed method can be extended to prepare other advanced core-branch nanomaterials for applications in electrochemical and optoelectronic devices.

Hierarchical TiO2-B nanowire@α-Fe2O3 nanothorn core-branch arrays as superior electrodes for lithium-ion microbatteries

This paper reports a simple yet efficient method for the synthesis of hierarchical TiO2-B nanowire@α-Fe2O3 nanothorn core-branch arrays based on a stepwise hydrothermal approach. The as-fabricated hybrid arrays show impressive performance as a high-capacity anode for lithium-ion batteries. The key design in this study is a core-branch hybrid architecture, which not only provides large surface active sites for lithium ion insertion/extraction, but also enables fast charge transport owing to the reduced diffusion paths for both electrons and lithium ions. The peculiar combination of attributes of TiO2 (good structural stability) and Fe2O3 (large specific capacity) provides the hybrid array electrodes with several desirable electrochemical features: large reversible capacity (∼800 mA·h·g−1 for specific mass capacity and ∼750 μA·h·cm−2 for specific areal capacity), good cycling stability, and high rate capability. The impressive electrochemical performance, together with the facile synthesis procedure, may provide an efficient platform to integrate the TiO2 nanowire@Fe2O3 nanothorn core-branch arrays as a three-dimensional thin film electrode for lithium-ion microbatteries.

TiO2 nanotube @ SnO2 nanoflake core–branch arrays for lithium-ion battery anode

While SnO2 is regarded as a good material for Li ion storage because of its high theoretical capacity, its microstructured powder form cannot be directly used as battery electrode because of a drastic pulverization problem and thus poor cyclic performance. Nanostructuring offers opportunities to circumvent this drawback. We report the construction of SnO2 nanoflake branches onto robust TiO2 nanotube stems. This core-branch nanostructured electrode demonstrate evidently improved Li ion storage properties compared to powders, with more stable cycling processes and higher rate capability. In this design, the TiO2 nanotube stems are realized by atomic layer deposition and offer a low-mass scaffold for the SnO2 nanoflakes and also a charge conductive path.