Engineering Hierarchical Co@N-Doped Carbon Nanotubes/α-Ni(OH)2 Heterostructures on Carbon Cloth Enabling High-Performance Aqueous Nickel-Zinc Batteries.

Searching for high-performance Ni-based cathodes plays an important role in developing better aqueous nickel-zinc (Ni-Zn) batteries. For this purpose, herein, we demonstrate the design and synthesis of ultrathin α-Ni(OH)2 nanosheets branched onto metal-organic frameworks (MOFs)-derived 3D cross-linked N-doped carbon nanotubes encapsulated with tiny Co nanoparticles (denoted as Co@NCNTs/α-Ni(OH)2), which are directly supported on a flexible carbon cloth (CC). An aqueous Ni-Zn battery employing the hierarchical CC/Co@NCNTs/α-Ni(OH)2 as the binder-free cathode and a commercial Zn plate as the anode is fabricated, which displays an ultrahigh capacity (316 mAh g-1) and energy density (540.4 Wh kg-1) at 1 A g-1 as well as excellent rate capability (238 mAh g-1 at 10 A g-1) and superior cycling performance (about 84% capacity retention after 2000 cycles at 10 A g-1). The impressive electrochemical performance might benefit from the rich active sites, rapid electron transfer, cushy electrolyte access, rapid ion transport, and robust structural stability. In addition, the quasi-solid-state CC/Co@NCNTs/α-Ni(OH)2//Zn batteries are also successfully assembled with polymer electrolyte, indicating the great potential for portable and wearable electronics. This work might provide important guidance for constructing carbon-based hybrid materials directly supported on conductive substrates as high-performance electrodes for energy-related devices.

Hierarchical Nanoreactor with Multiple Adsorption and Catalytic Sites for Robust Lithium-Sulfur Batteries.

Developing high-performance cathode host materials is fundamental to solve the low utilization of sulfur, the sluggish redox kinetics, and the lithium polysulfide (LiPS) shuttle effect in lithium-sulfur batteries (LSBs). Here, a multifunctional Ag/VN@Co/NCNT nanocomposite with multiple adsorption and catalytic sites within hierarchical nanoreactors is reported as a robust sulfur host for LSB cathodes. In this hierarchical nanoreactor, heterostructured Ag/VN nanorods serve as a highly conductive backbone structure and provide internal catalytic and adsorption sites for LiPS conversion. Interconnected nitrogen-doped carbon nanotubes (NCNTs), in situ grown from the Ag/VN surface, greatly improve the overall specific surface area for sulfur dispersion and accommodate volume changes in the reaction process. Owing to their high LiPS adsorption ability, outer Co nanoparticles at the top of the NCNTs catch escaped LiPS, thus effectively suppressing the shuttle effect and enhancing kinetics. Benefiting from the multiple adsorption and catalytic sites of the developed hierarchical nanoreactors, Ag/VN@Co/NCNTs@S cathodes display outstanding electrochemical performances, including a superior rate performance of 609.7 mAh g-1 at 4 C and a good stability with a capacity decay of 0.018% per cycle after 2000 cycles at 2 C. These properties demonstrate the exceptional potential of Ag/VN@Co/NCNTs@S nanocomposites and approach LSBs closer to their real-world application.

A lightweight and low-cost electrode for lithium-ion batteries derived from paper towel supported MOF arrays.

Herein, Cu-doped Co-ZIF nanoplate arrays are uniformly grown on a commercial paper towel substrate first. After a subsequent annealing treatment, well-defined Cu-doped Co/CoO nanoparticles embedded in N-doped carbon hybrid nanoplate arrays supported on the carbon paper substrate (denoted as Cu-doped Co/CoO/NC NPAs@CP) are obtained, which exhibit excellent performance as a low-cost, lightweight and binder-free anode for lithium ion storage.

MOF-Derived Hybrid Hollow Submicrospheres of Nitrogen-Doped Carbon-Encapsulated Bimetallic Ni-Co-S Nanoparticles for Supercapacitors and Lithium Ion Batteries.

The development of bimetallic transition-metal sulfide and nitrogen-doped carbon composites with unique hollow structure is highly desirable for energy storage applications but is also challenging. In the present work, we demonstrate a facile metal-organic framework engaged strategy for synthesizing bimetallic nickel cobalt sulfide and nitrogen-doped carbon composites with hollow spherical structure (denoted as hollow Ni-Co-S- n/NC composites) and a Ni/Co molar ratio ( n value) that can be easily controlled. When evaluated as electrode materials for both supercapacitors and lithium ion batteries, it is found that the hollow Ni-Co-S-0.5/NC composite with a Ni/Co molar ratio of 0.5 exhibits optimal electrochemical performance. The hollow Ni-Co-S-0.5/NC composite exhibits a high specific capacity of 543.9 C g-1 at 1 A g-1 and maintains a capacity retention of 67.3% when the current density is increased to 20 A g-1. An asymmetric supercapacitor based on the hollow Ni-Co-S-0.5/NC composite is fabricated, which shows good electrochemical performance with a high energy density of 39.6 W h kg-1 at a power density of 808 W kg-1. For lithium storage, the hollow Ni-Co-S-0.5/NC composite manifests a high reversible discharge capacity of 755.0 mA h g-1 at 200 mA g-1 for 200 cycles as well as good rate capability. The excellent electrochemical performance could be attributed to the desirable structural, compositional, and component advantages. This work could offer new insight into the rational design and synthesis of highly efficient electrode materials for both supercapacitors and lithium ion batteries.

Resorcinol-Formaldehyde Resin-Coated Prussian Blue Core-Shell Spheres and Their Derived Unique Yolk-Shell FeS2@C Spheres for Lithium-Ion Batteries.

The practical applications of transition metal sulfides as electrode materials for lithium-ion batteries (LIBs) is greatly hindered by the fast capacity fading owing to the large volume expansion. To address this issue, construction of transition metal sulfide and carbon nanocomposites with unique yolk-shell structures is an effective strategy but also remains a great challenge. In this work, we reported a facile approach to synthesize the unique yolk-shell FeS2@carbon (FeS2@C) spheres via calcination treatment of the resorcinol-formaldehyde (RF) resin-coated Prussian blue (FeFe PB) core-shell spheres in Ar atmosphere and a subsequent sulfidation treatment. The synthetic method herein was quite simple and convenient. Such unique structure design could effectively prevent the large volume expansion and dissolution of the active materials in the electrolytes during lithiation. As expected, the yolk-shell FeS2@C spheres exhibited good electrochemical performance as anode materials for LIBs, which displayed a high discharge capacity of 560 mA h g-1 at 100 mA g-1 for 100 cycles. When the current density increased to 1000 mA g-1, a reversible discharge capacity of 269 mA h g-1 was still retained after 500 cycles. The present work demonstrated an extraordinary synthetic strategy to construct transition metal sulfide and carbon nanocomposites with unique yolk-shell structure. In addition, this RF resin coating strategy can be further extended to synthesize other RF resin-coated PB analogue (PBA) core-shell nanostructures, demonstrating the generality of this RF resin coating strategy.

Construction of MOF-derived hollow Ni-Zn-Co-S nanosword arrays as binder-free electrodes for asymmetric supercapacitors with high energy density.

Mixed transition metal sulfides with hollow structures hold great promise for energy-related applications. However, most of them are in the powder form, which should be mixed with unwanted polymer binders and conductive agents. In this study, a facile two-step strategy has been developed to grow mesoporous and hollow Ni-Zn-Co-S nanosword arrays (NSAs) on a nickel foam (NF) substrate with robust adhesion, which involves the hydrothermal growth of bimetallic Zn-Co-ZIF NSAs on NF and subsequent transformation into hollow Ni-Zn-Co-S NSAs through the sulfurization process. Benefiting from the unique structural and compositional advantages as well as directly grown conductive substrate, the Ni-Zn-Co-S-0.33 NSAs/NF electrode exhibits the best electrochemical performance when investigated as a binder-free electrode for supercapacitors. Impressively, the Ni-Zn-Co-S-0.33 NSAs/NF electrode delivers a high areal capacity of 1.11 mA h cm-2 at the current density of 10 mA cm-2, and the corresponding specific capacity is as high as 358.1 mA h g-1. Moreover, an asymmetric supercapacitor (ASC) device based on the Ni-Zn-Co-S-0.33 NSAs/NF as the positive electrode and Bi2O3/NF as the negative electrode has been successfully fabricated, and can deliver a high energy density of 91.7 W h kg-1 at a power density of 458 W kg-1 and maintain the energy density of 66.9 W h kg-1 at a high power density of 6696 W kg-1. The electrochemical results suggest that the hollow Ni-Zn-Co-S NSAs would possess great potential for applications in high-performance supercapacitors.

Bimetallic CoNiSx nanocrystallites embedded in nitrogen-doped carbon anchored on reduced graphene oxide for high-performance supercapacitors.

Exploring high-performance and low-priced electrode materials for supercapacitors is important but remains challenging. In this work, a unique sandwich-like nanocomposite of reduced graphene oxide (rGO)-supported N-doped carbon embedded with ultrasmall CoNiSx nanocrystallites (rGO/CoNiSx/N-C nanocomposite) has been successfully designed and synthesized by a simple one-step carbonization/sulfurization treatment of the rGO/Co-Ni precursor. The intriguing structural/compositional/morphological advantages endow the as-synthesized rGO/CoNiSx/N-C nanocomposite with excellent electrochemical performance as an advanced electrode material for supercapacitors. Compared with the other two rGO/CoNiOx and rGO/CoNiSx nanocomposites, the rGO/CoNiSx/N-C nanocomposite exhibits much enhanced performance, including a high specific capacitance (1028.2 F g-1 at 1 A g-1), excellent rate capability (89.3% capacitance retention at 10 A g-1) and good cycling stability (93.6% capacitance retention over 2000 cycles). In addition, an asymmetric supercapacitor (ASC) device based on the rGO/CoNiSx/N-C nanocomposite as the cathode and activated carbon (AC) as the anode is also fabricated, which can deliver a high energy density of 32.9 W h kg-1 at a power density of 229.2 W kg-1 with desirable cycling stability. These electrochemical results evidently indicate the great potential of the sandwich-like rGO/CoNiSx/N-C nanocomposite for applications in high-performance supercapacitors.

Comparison of the electrochemical performance of iron hexacyanoferrate with high and low quality as cathode materials for aqueous sodium-ion batteries.

In this work, high quality iron hexacyanoferrate nanocubes (HQ-PB NCs) were synthesized through a simple hydrothermal method and then investigated as cathode electrode materials for aqueous sodium-ion batteries (SIBs), which displayed a much enhanced electrochemical performance compared with the PB nanoparticles with low quality (LQ-PB NPs). The HQ-PB NCs could be promising cathode materials for aqueous SIBs.

Dendritic unzipped carbon nanofibers enable uniform loading of surfactant-free Pd nanoparticles for the electroanalysis of small biomolecules.

In this study, graphene nanofibers (GNF), which are a superior support material, are successfully synthesized via the dendritic unzipping of stacked-cup carbon nanofibers (SCNF). Ultrasmall Pd nanoparticles are uniformly dispersed on the GNF (Pd/GNF) via chemical reduction under mild conditions without any surfactant involved. The components and structure of Pd/GNF are evaluated via scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Raman spectra and X-ray photoelectron spectroscopy (XPS). The characterization results indicate that the Pd nanoparticles have a uniform size of 3-6 nm without significant aggregation and the overall Pd content is about 11.2 wt% in the Pd/GNF composite. Moreover, a modified electrochemical sensor based on the Pd/GNF composite is successfully fabricated. In the two investigated redox probes (IrCl6 2- and [Fe(CN)6]3-), Pd/GNF shows a superior electrochemical response compared to the Pd nanoparticles loaded on SCNF and bare glass carbon electrode. For the detection of small biomolecules, Pd/GNF could individually or simultaneously detect ascorbic acid (AA), dopamine (DA) and uric acid (UA) through differential pulse voltammetry. The linear concentration ranges of UA, DA and AA are 0.1-1200 µM, 1-180 µM and 0.1-6000 µM, respectively.

Muti-component nanocomposite of nickel and manganese oxides with enhanced stability and catalytic performance for non-enzymatic glucose sensors.

A muti-component nanocomposite of nickel and manganese oxides with a uniformly dispersed microspherical structure has been fabricated by a hydrothermal synthesis method. The as-prepared nanocomposite has been employed as a sensing material for non-enzymatic glucose detection and shown excellent electrocatalytic activity, such as high sensitivities of 82.44 µA mM(-1) cm(-2) and 27.92 µA mM(-1) cm(-2) over the linear range of 0.1-1 mM and 1-4.5 mM, respectively, a low detection limit of 0.2 µM and a fast response time of <3 s. Moreover, satisfactory specificity and excellent stability have also been achieved. The results demonstrate that a muti-component nanocomposite of nickel and manganese oxides has great potential applications as glucose sensors.

Non-enzymatic electrochemical glucose sensor based on NiMoO4 nanorods.

A non-enzymatic glucose sensor based on the NiMoO4 nanorods has been fabricated for the first time. The electrocatalytic performance of the NiMoO4 nanorods' modified electrode toward glucose oxidation was evaluated by cyclic voltammetry and amperometry. The NiMoO4 nanorods' modified electrode showed a greatly enhanced electrocatalytic property toward glucose oxidation, as well as an excellent anti-interference and a good stability. Impressively, good accuracy and high precision for detecting glucose concentration in human serum samples were obtained. These excellent sensing properties, combined with good reproducibility and low cost, indicate that NiMoO4 nanorods are a promising candidate for non-enzymatic glucose sensors.

High-performance supercapacitor electrode based on the unique ZnO@Co3O44 core/shell heterostructures on nickel foam.

Currently, tremendous attention has been paid to the rational design and synthesis of unique core/shell heterostructures for high-performance supercapacitors. In this work, the unique ZnO@Co3O4 core/shell heterostructures on nickel foam are successfully synthesized through a facile and cost-effective hydrothermal method combined with a short post annealing treatment. Mesoporous Co3O4 nanowires are multidirectional growing on the rhombus-like ZnO nanorods. In addition, the growth mechanism for such unique core/shell heterostructures is also proposed. Supercapacitor electrodes based on the ZnO@Co3O4 and Co3O4 heterostructures on nickel foam are thoroughly characterized. The ZnO@Co3O4 electrode exhibits high capacitance of 1.72 F cm(-2) (857.7 F g(-1)) at a current density of 1 A g(-1), which is higher than that of the Co3O4 electrode. Impressively, the capacitance of the ZnO@Co3O4 electrode increases gradually from 1.29 to 1.66 F cm(-2) (830.8 F g(-1)) after 6000 cycles at a high current density of 6 A g(-1), indicating good long-term cycling stability. These results indicate the unique ZnO@Co3O4 electrode would be a promising electrode for high-performance supercapacitor applications.

Enhanced sensitivity and stability of room-temperature NH3 sensors using core-shell CeO2 nanoparticles@cross-linked PANI with p-n heterojunctions.

We report a room-temperature NH3 gas sensor with high response and great long-term stability, including CeO2 NPs conformally coated by cross-linked PANI hydrogel. Such core-shell nanocomposites were prepared by in situ polymerization with different weight ratios of CeO2 NPs and aniline. At room temperature, the nanohybrids showed enhanced response (6.5 to 50 ppm of NH3), which could be attributed to p-n junctions formed by the intimate contact between these two materials. Moreover, the stability was discussed in terms of phytic acid working as a gelator, which helped the PANI sheath accommodate itself and enhance the mechanical strength and chemical stability of the sensors by avoiding "swelling effect" in high relative humidity. The sensors maintained its sensing characteristic (response of ca. 6.5 to 50 ppm of NH3) in 15 days. Herein, the obtained results could help to accelerate the development of ammonia gas sensor.

Surrounding sensitive electronic properties of Bi2Te3 nanoplates-potential sensing applications of topological insulators.

Significant efforts have been paid to exploring the fundamental properties of topological insulators (TIs) in recent years. However, the investigation of TIs as functional materials for practical device applications is still quite limited. In this work, electronic sensors based on Bi2Te3 nanoplates were fabricated and the sensing performance was investigated. On exposure to different surrounding environments, significant changes in the conducting properties were observed by direct electrical measurements. These results suggest that nanostructured TIs hold great potential for sensing applications.

Three-dimensional Co3O4@NiMoO4 core/shell nanowire arrays on Ni foam for electrochemical energy storage.

In this work, we report a facile two-step hydrothermal method to synthesize the unique three-dimensional Co3O4@NiMoO4 core/shell nanowire arrays (NWAs) on Ni foam for the first time. The Co3O4 nanowires are fully covered by ultrathin mesoporous NiMoO4 nanosheets. When evaluated as a binder-free electrode for supercapacitors in a 2 M KOH aqueous solution, the Co3O4@NiMoO4 hybrid electrode exhibits a greatly enhanced areal capacitance of 5.69 F cm(-2) at a high current density of 30 mA cm(-2), nearly 5 times that of the pristine Co3O4 electrode (1.10 F cm(-2)). The energy density of the hybrid electrode is 56.9 W h kg(-1) at a high power density of 5000 W kg(-1). In addition, the Co3O4@NiMoO4 hybrid electrode also exhibits good rate capability and cycling stability, which would hold great promise for electrochemical energy storage.

Strongly coupled hybrid nanostructures for selective hydrogen detection--understanding the role of noble metals in reducing cross-sensitivity.

Noble metal-semiconductor hybrid nanostructures can offer outperformance to gas sensors in terms of sensitivity and selectivity. In this work, a catalytically activated (CA) hydrogen sensor is realized based on strongly coupled Pt/Pd-WO3 hybrid nanostructures constructed by a galvanic replacement participated solvothermal procedure. The room-temperature operation and high selectivity distinguish this sensor from the traditional ones. It is capable of detecting dozens of parts per million (ppm) hydrogen in the presence of thousands of ppm methane gas. An insight into the role of noble metals in reducing cross-sensitivity is provided by comparing the sensing properties of this sensor with a traditional thermally activated (TA) one made from the same pristine WO3. Based on both experimental and density functional theory (DFT) calculation results, the cross-sensitivity of the TA sensor is found to have a strong dependence on the highest occupied molecular orbital (HOMO) level of the hydrocarbon molecules. The high selectivity of the CA sensor comes from the reduced impact of gas frontier orbitals on the charge transfer process by the nano-scaled metal-semiconductor (MS) interface. The methodology demonstrated in this work indicates that rational design of MS hybrid nanostructures can be a promising strategy for highly selective gas sensing applications.

Comparison of the electrochemical performance of NiMoO4 nanorods and hierarchical nanospheres for supercapacitor applications.

Much attention has been paid to exploring electrode materials with enhanced supercapacitor performance as well as relatively low cost and environmental friendliness. In this work, NiMoO4 nanospheres and nanorods were synthesized by facile hydrothermal methods. The hierarchical NiMoO4 nanospheres were about 2.5 µm in diameter and assembled from thin mesoporous nanosheets with a thickness of about 10-20 nm. The NiMoO4 nanorods were about 80 nm in diameter and about 300 nm to 1 µm in length. Their electrochemical properties were investigated for use as electrode materials for supercapacitors (SCs). The NiMoO4 nanospheres exhibited a higher specific capacitance and better cycling stability and rate capability, which were attributed to their large surface area and high electrical conductivity. The specific capacitances were 974.4, 920.8, 875.5, 859.1, and 821.4 F/g at current densities of 1, 2, 4, 6, and 10 A/g, respectively. Remarkably, the energy density was able to reach 20.1 Wh/kg at a power density of 2100 W/kg. After 2000 cycles, the NiMoO4 nanospheres still displayed a high specific capacitance of about 631.8 F/g at a current density of 5 A/g. These results implied that the hierarchical NiMoO4 nanospheres could be a promising candidate for use as high-performance SCs.

High-performance room-temperature hydrogen sensors based on combined effects of Pd decoration and Schottky barriers.

A new hydrogen sensor was fabricated by coating a Pd-decorated In2O3 film on Au electrodes. In response to 1 vol% H2 at room temperature, an ultra high sensitivity of 4.6 × 10(7) was achieved. But after an annealing treatment in vacuum, its sensitivity degenerated by 4 orders of magnitude. In addition, the response time and recovery time were also extended from 28 s and 32 s to 242 s and 108 s, respectively. It was found from contrast experiments that Pd decoration was essential to make the sensor work at room temperature and Schottky barriers played a vital role in enhancing the sensor's performance. The methodology demonstrated in this paper shows that a combination of novel sensing materials and Schottky contact is an effective approach to design high-performance gas sensors.