Yaogang Li

3D Freeze-Casting of Cellular Graphene Films for Ultrahigh-Power-Density Supercapacitors.

3D cellular graphene films with open porosity, high electrical conductivity, and good tensile strength, can be synthesized by a method combining freeze-casting and filtration. The resulting supercapacitors based on 3D porous reduced graphene oxide (RGO) film exhibit extremely high specific power densities and high energy densities. The fabrication process provides an effective means for controlling the pore size, electronic conductivity, and loading mass of the electrode materials, toward devices with high energy-storage performance.

Highly Conductive, Flexible, and Compressible All‐Graphene Passive Electronic Skin for Sensing Human Touch

A facile and passive multiply flexible thin-film sensor is demonstrated based on thermoelectric effects in graphene. The sensor is highly conductive, free-standing, flexible, and elastic. It senses heat and cold, and measures heated/cooled areas; it also discerns human touch from other pressures, locates human touch, and measures pressure levels. All of these sensing abilities are demonstrated without any internal/external power supply.

P25–graphene hydrogels: Room-temperature synthesis and application for removal of methylene blue from aqueous solution

Herein we report a room-temperature synthesis of chemically bonded TiO2 (P25)-graphene composite hydrogels and their use as high performance visible light photocatalysts. The three-dimensional (3D) TiO2-carbon composite exhibits a significant enhancement in the reaction rate in the decontamination of methylene blue, compared to the bare P25. The 3D P25-graphene hydrogel is much easier to prepare and apply as a macroscopic device, compared to the 2D P25-graphene sheets. This work could provide new insights into the room-temperature synthesis of graphene-based materials. As a kind of the novel 3D graphene-based composite, the obtained high performance P25-graphene gel could be widely used in the environmental protection issues.

High-performance flexible asymmetric supercapacitors based on 3D porous graphene/MnO2 nanorod and graphene/Ag hybrid thin-film electrodes

We demonstrate a simple method for preparing flexible, free-standing, three-dimensional porous graphene/MnO2 nanorod and graphene/Ag hybrid thin-film electrodes using a filtration assembly process. These graphene hybrid films, which accelerate ion and electron transport by providing lower ion-transport resistances and shorter diffusion-distances, exhibit high specific capacitances and power performances, and excellent mechanical flexibility. A novel asymmetric supercapacitor (SC) has been fabricated by using a graphene/MnO2 nanorod thin film as the positive electrode and a graphene/Ag thin film as the negative electrode. These devices exhibit a maximum energy density of 50.8 W h kg−1 and present a high power density of 90.3 kW kg−1, even at an energy density of 7.53 W h kg−1. The bent hybrid nanostructured asymmetric SC is connected to spin a fan, which also proved the high power density of the fabricated asymmetric SCs. These results suggest that such asymmetric graphene/MnO2 nanorod and graphene/Ag hybrid thin-film architectures are promising for next-generation high-performance flexible supercapacitors.

Origami-inspired active graphene-based paper for programmable instant self-folding walking devices

Origami-inspired self-folding graphene papers show remote control grasping, manipulation, and walking behaviors. Origami-inspired active graphene-based paper with programmed gradients in vertical and lateral directions is developed to address many of the limitations of polymer active materials including slow response and violent operation methods. Specifically, we used function-designed graphene oxide as nanoscale building blocks to fabricate an all-graphene self-folding paper that has a single-component gradient structure. A functional device composed of this graphene paper can (i) adopt predesigned shapes, (ii) walk, and (iii) turn a corner. These processes can be remote-controlled by gentle light or heating. We believe that this self-folding material holds potential for a wide range of applications such as sensing, artificial muscles, and robotics.

Morphology-tailored synthesis of vertically aligned 1D WO3 nano-structure films for highly enhanced electrochromic performance

We have demonstrated that vertically aligned WO3 nanostructure films can be fabricated on FTO-coated glass substrates using a template-free hydrothermal technique. Detailed mechanistic studies revealed that a variety of WO3 nanostructures—including nano-bricks, 1D nanorods and nanowires, and 3D nanorod-flowers—could be obtained by tuning the composition of the precursor solution, where the urea content and solvent composition played important roles in controlling the shape and size of the WO3 nanostructures, respectively. These nanostructured films exhibited enhanced electrochromic performance, and we drew a map for the correlation between the morphology and the electrochromic performance of the as-synthesized WO3 films. Due to the large tunnels in the hexagonally structured WO3, and the large active surface area available for electrochemical reactions, a large optical modulation of 66% at 632.8 nm and a potential of −2.0 V, fast switching speeds of 6.7 s and 3.4 s for coloration and bleaching, respectively, and a high coloration efficiency of 106.8 cm2 C−1 are achieved for the cylindrical nanorod array film.

A strong and stretchable self-healing film with self-activated pressure sensitivity for potential artificial skin applications

Artificial skin, which mimics the functions of natural skin, will be very important in the future for robots used by humans in daily life. However, combining skins pressure sensitivity and mechanical self-healing properties in a man-made material remains a challenging task. Here, we show that graphene and polymers can be integrated into a thin film which mimics both the mechanical self-healing and pressure sensitivity behavior of natural skin without any external power supply. Its ultimate strain and tensile strength are even two and ten times larger than the corresponding values of human skin, respectively. It also demonstrates highly stable sensitivity to a very light touch (0.02 kPa), even in bending or stretching states.

Facile growth of vertically aligned BiOCl nanosheet arrays on conductive glass substrate with high photocatalytic properties

A facile, solvothermal method was developed to grow vertically aligned BiOCl nanosheet arrays on a fluorine-doped tin oxide (FTO) substrate. The solvothermal temperature and reaction time dependence for growing the BiOCl nanostructures were examined. The formation mechanism of the BiOCl nanosheet arrays was proposed based on the morphology and structure of the BiOCl nanosheets at different reaction stages. The band gap of the as-prepared BiOCl nanosheet arrays was estimated to be about 3.38 eV. Photocatalytic experiments showed that the BiOCl nanosheet arrays exhibited excellent activity much higher than hydrothermally grown rutile TiO2 nanorod arrays, which was comparable to P25 TiO2 film, while retaining much better photocatalytic stability in durability tests. On the basis of the growth characteristics of BiOCl on FTO substrate, the photocatalysis was integrated in a microreactor for performing rapid and continuous degradation of organic compounds.

Hierarchical NiO microflake films with high coloration efficiency, cyclic stability and low power consumption for applications in a complementary electrochromic device

We have demonstrated that thin films of hierarchical NiO microflakes assembled from nanoleaves can be grown directly on FTO-coated glass substrates using a facile and template-free hydrothermal technique. This hierarchical structure holds the advantages of both nanometre-sized building blocks and microsized assemblies. Thus, the films exhibit highly enhanced electrochromic performances and cyclic stability due to their high surface area and good electrochemical stability. Moreover, a complementary electrochromic device combining the hierarchical NiO microflake film with a self-weaving WO3 nanoflake film is fabricated to further improve the electrochromic performance. As a result, the complementary electrochromic device shows a high optical modulation (73.2% at 550 nm), large coloration efficiency (146.9 cm(2) C(-1) at 550 nm by applying a low coloration voltage of -1.0 V) and fast switching responses with a coloring time of 1.8 s and a bleaching time of 3.2 s. It is also observed that there is no significant degradation of the electrochromic properties after 2000 continuous coloration/bleaching cycles, making it attractive for practical applications.

Hierarchical nanostructure of WO3 nanorods on TiO2 nanofibers and the enhanced visible light photocatalytic activity for degradation of organic pollutants

A hierarchically nanostructured TiO2/WO3 photocatalyst was synthesized via the subsequent hydrothermal treatment of electrospun TiO2 nanofibers in the presence of tungstic acid. With a uniform WO3 seed layer providing growth sites, the nucleation on the nanofibers was uniform, thus uniform WO3 nanorods could be grown. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence spectra (PL), and Brunauer–Emmett–Teller (BET) method. The results indicated that the WO3 nanorods with a diameter of about 40 nm and an average length of about 150 nm grew perpendicularly on the TiO2 nanofibers. The crystallite size and specific surface area of the bare TiO2 nanofibers were about 30 nm and 46.5 m2 g−1. The bare nanofibers are anatase phase with the average diameter of about 350 nm. The TiO2/WO3 heterostructures provide more accessible sites for both catalysis and adsorption, and the WO3 nanorods possess a single crystal structure, which facilitates the migration of the photogenerated electrons. Photocatalytic tests show that the TiO2/WO3 heterostructures exhibit a remarkably higher degradation rate of organic pollutants than that of the bare TiO2 nanofibers under visible light irradiation. The enhanced photocatalytic activity is attributed to the extended absorption in the visible light region and the effective charge separation derived from the coupling effect of TiO2 and WO3 nanocomposites.