Gengzhi Sun

Hybrid Fibers Made of Molybdenum Disulfide, Reduced Graphene Oxide, and Multi‐Walled Carbon Nanotubes for Solid‐State, Flexible, Asymmetric Supercapacitors

One of challenges existing in fiber-based supercapacitors is how to achieve high energy density without compromising their rate stability. Owing to their unique physical, electronic, and electrochemical properties, two-dimensional (2D) nanomaterials, e.g., molybdenum disulfide (MoS2 ) and graphene, have attracted increasing research interest and been utilized as electrode materials in energy-related applications. Herein, by incorporating MoS2 and reduced graphene oxide (rGO) nanosheets into a well-aligned multi-walled carbon nanotube (MWCNT) sheet followed by twisting, MoS2 -rGO/MWCNT and rGO/MWCNT fibers are fabricated, which can be used as the anode and cathode, respectively, for solid-state, flexible, asymmetric supercapacitors. This fiber-based asymmetric supercapacitor can operate in a wide potential window of 1.4 V with high Coulombic efficiency, good rate and cycling stability, and improved energy density.

Self-powered, visible-light photodetector based on thermally reduced graphene oxide–ZnO (rGO–ZnO) hybrid nanostructure

Here we report a new type of self-powered, visible-light photodetector fabricated from thermally reduced rGO–ZnO hybrid nanostructure. The photocurrent generation of the photodetectors under zero-bias enables hybrid rGO–ZnO devices to work like photovoltaic cells, which could power themselves without electrical power input. The thermal treatment at elevated temperature not only reduces graphene oxide (GO) into reduced graphene oxide (rGO), but also dopes the ZnO nanoparticles with carbon atoms, enabling their visible-light photoresponse capability. The pronounced and fast photocurrent generation was attributed to the efficient charge transfer between the rGO and carbon-doped ZnO nanoparticles, which were in intimate contact. The efficient charge transfer of the rGO–ZnO hybrid nanostructures also indicates that there could be applications in other light energy harvesting devices, including solar cells, sensors and visible-light photocatalysis.

Fabrication of Ultralong Hybrid Microfibers from Nanosheets of Reduced Graphene Oxide and Transition-Metal Dichalcogenides and their Application as Supercapacitors†

Two-dimensional materials have attracted increasing research interest owing to their unique electronic, physical, optical, and mechanical properties. We thus developed a general strategy for the fabrication of ultralong hybrid microfibers from a mixture of reduced graphene oxide and transition-metal dichalcogenides (TMDs), including MoS2 , TiS2 , TaS2 , and NbSe2 . Furthermore, we prepared fiber-based solid-state supercapacitors as a proof-of-concept application. The performance of thus-prepared supercapacitors was greatly improved by the introduction of the TMDs.

Tuning Array Morphology for High‐Strength Carbon‐Nanotube Fibers

Vertically aligned carbon-nanotube arrays are synthesized by chemical vapor deposition. Carbon-nanotube fibers are directly spun from the obtained nanotube arrays and then tested mechanically. A strong correlation between the array morphologies and the mechanical properties of the fibers is observed: well-aligned arrays yield fibers with much higher performance, while wavy and entangled arrays give poor fiber properties. More importantly, such array morphologies could be controlled by introducing hydrogen or oxygen during the nanotube synthesis. By simply switching the growth condition from 150 ppm oxygen addition to 2% hydrogen addition, the nanotube array changes from the wavy morphology to the well-aligned morphology, and correspondingly the tensile strength of the resultant fibers could be increased by 4.5 times, from 0.29 GPa for the fibers spun from the oxygen-assistance-grown nanotube arrays to 1.3 GPa for the fibers spun from the hydrogen-assistance-grown nanotube arrays. The detailed effects of hydrogen and oxygen on the nanotube growth, especially on the growth rate and the array spinnability, are extensively studied. The formation mechanism of the different morphologies of the nanotube arrays and the failure mechanism of the nanotube fibers are also discussed in detail.

Achieving stable and efficient water oxidation by incorporating NiFe layered double hydroxide nanoparticles into aligned carbon nanotubes

A facile and scalable co-precipitation method is developed to prepare stable colloidal NiFe-LDH nanoparticles at room temperature. We further scrolled NiFe-LDH nanoparticles into well-aligned multi-walled carbon nanotube (MWCNT) sheets to form binder-free hybrid microfiber electrodes, which showed excellent OER activity, reaching 180 mA cm-2 at a small overpotential of 255 mV with outstanding durability.

Three-Dimensional Porous LiFePO4: Design, Architectures and High Performance for Lithium Ion Batteries

The olivine-structured lithium ion phosphate (LiFePO4) is one of the most competitive candidates of cathode materials for the sustainable lithium ion battery (LIB) systems. However, the major drawback of olivine-structured LiFePO4 is the poor intrinsic electronic and lithium ion conductivities arising from the lack of mixed valency and the one- dimensional lithium ion diffusion, which influence its high electrochemical performance, especially high rate capability. Nano-structured LiFePO4 materials offer a potential solution to enhance surface-to-volume ratio and reduce transport length for mobile charges, but they have high interfacial energy, aggregate easily and need more agglutinant in electrode, which seriously impact the electrochemical performance and practical applications of LiFePO4. Furthermore they con- tinue to experience limitations as energy and power requirements escalate with the evolution of technology. Recently, three-dimensional (3D) porous LiFePO4 architectures have been widely designed and studied. This has led to increased in- terest in the development of cathode materials and processing capabilities necessary to enable high-performance, next- generation LIB system that can deliver large amounts of energy at high rates. In this review, we focus on 3D porous LiFePO4 architectures for high power LIBs, summarize and discuss its structure, synthesis, electrochemical behaviors, mechanism, and the problems encountered in its application. The major goal is to highlight the recent progress of 3D po- rous LiFePO4 architectures with high rate capability, high energy density and application.

A modified Weibull model for tensile strength distribution of carbon nanotube fibers with strain rate and size effects

Fundamental studies on the effects of strain rate and size on the distribution of tensile strength of carbon nanotube (CNT) fibers are reported in this paper. Experimental data show that the mechanical strength of CNT fibers increases from 0.2 to 0.8 GPa as the strain rate increases from 0.00001 to 0.1 (1/s). In addition, the influence of fiber diameter at low and high strain rate conditions was investigated further with statistical analysis. A modified Weibull distribution model for characterizing the tensile strength distribution of CNT fibers taking into account the effect of strain rate and fiber diameter is proposed.

Ultra-sensitive and wide-dynamic-range sensors based on dense arrays of carbon nanotube tips

Electrochemical electrodes based on dense and vertically aligned arrays of multi-walled carbon nanotubes (MWCNTs) were produced. The open tips of individual hollow nanotubes are exposed as active sites while the entangled nanotube stems encapsulated in epoxy collectively provide multiplexed and highly conductive pathways for charge transport. This unique structure together with the extraordinary electrical and electrochemical properties of MWCNTs offers a high signal-to-noise ratio (thus high sensitivity) and a large detection range, compared with other carbon-based electrodes. Our electrodes can detect K(3)FeCN(6) and dopamine at concentrations as low as 5 nM and 10 nM, respectively, and are responsive in a large dynamic range that spans almost 5 orders of magnitude.

Clothing polymer fibers with well-aligned and high-aspect ratio carbon nanotubes

It is believed that the crucial step towards preparation of electrical conductive polymer-carbon nanotube (CNT) composites is dispersing CNTs with a high length-to-diameter aspect ratio in a well-aligned manner. However, this process is extremely challenging when dealing with long and entangled CNTs. Here in this study, a new approach is demonstrated to fabricate conductive polymer-CNT composite fibers without involving any dispersion process. Well-aligned CNT films were firstly drawn from CNT arrays, and then directly coated on polycaprolactone fibers to form polymer-CNT composite fibers. The conductivity of these composite fibers can be as high as 285 S m(-1) with only 2.5 wt% CNT loading, and reach 1549 S m(-1) when CNT loading is 13.4 wt%. As-prepared composite fibers also exhibit 82% retention of conductivity at a strain of 7%, and have improved mechanical properties.

Three-Dimensional Porous Architectures of Carbon Nanotubes and Graphene Sheets for Energy Applications

Owing to their extraordinary physicochemical, electrical, and mechanical properties, carbon nanotubes (CNTs) and graphene materials have been widely used to improve energy storage and conversion. In this article, we briefly review the latest development on fabrication of 3D porous structures of CNTs or graphene sheets or their hybrids, and their applications in various energy devices including supercapacitors, (bio-) fuel cells, and lithium ion batteries.