Taotao Li

Large-Scale Self-Assembly of 3D Flower-like Hierarchical Ni/Co-LDHs Microspheres for High-Performance Flexible Asymmetric Supercapacitors

In this study, a facile and inexpensive and self-assembled strategy to massively fabricate Ni/Co layered double hydroxides (LDHs) is developed under mild reaction conditions (55 °C). The resulting composite material displays a special three-dimensional hierarchical microsphere structure with well-defined flower-like configuration. The fabrication mechanism can be ascribed to stepwise and regular reaction process of nanoparticles and nanosheets gradually growing to nanopetals and then assembling into flower-like microspheres, based on the systematically investigation of various reaction factors including the Ni:Co feeding ratio, the reaction time and the initial pH-value. Because of its large surface, ultrathin feature and synergetic results of this Ni/Co LDHs nanosheets (20 nm), these Ni/Co-LDHs microspheres deliver an excellent capacitance value about 2228 F·g(-1) (1 A·g(-1)). An all-solid-state flexible asymmetric supercapacitor is designed and assembled by exploiting this Ni/Co-LDHs as the positive materials, which exhibits energy density of 165.51 Wh·kg(1-) at 1.53 KW·kg(1-). It may have vast potential significance in personal wearable equipment. Moreover, this monolithic design provides a promising approach for large scale fabrication of other LDHs materials.

Wafer-scale transfer of vertically aligned carbon nanotube arrays.

The first critical step in making vertically aligned carbon nanotube (VACNT)-based thermal interface materials is to transfer the VACNTs on a large scale. Although VACNTs have been transferred by several methods, they were only transferred inadvertently in most cases. Here we report well-controlled weak-oxidation-assisted transfer of VACNTs. Specifically, after a short time of weak oxidation, we found that VACNTs could be easily detached from the native growth substrates, and thus, a freestanding VACNT film was obtained. Then the VACNTs could be assembled onto specific substrates for its real applications. More importantly, the repeated growth-transfer synthesis of VACNT arrays can be realized in one batch by introducing an additional process of weak oxidation in chemical vapor deposition, which makes the strategy more effective. Surprisingly, no degradation in the quality was observed before and after the weak oxidation according to thermogravimetric analysis and Raman spectra of VACNTs. Enhanced thermal and mechanical properties were achieved after reactive ion etching (RIE) and subsequent metallization of the surfaces of the VACNTs, and this might be due to the removal of impurities such as amorphous carbon and entangled CNTs by RIE. These findings provide an efficient approach for transferring VACNTs, which is important for the application of VACNTs in thermal management.

Freestanding Boron Nitride Nanosheet Films for Ultrafast Oil/Water Separation.

Freestanding boron nitride nanosheet (BNNS) films with designed structures are first fabricated by chemical vapor deposition (CVD) methods. As-prepared freestanding BNNS films exhibit outstanding hydrophobicity and lipophilicity properties. Such brilliant behaviors make them applicable in oil/water separation with very high fluxes up to 1 200 000 L m-2 h-1 bar-1 and excellent separation efficiencies (ppm level in terms of the water content in the filtrate).

Electrical property enhancement of electrically conductive adhesives through Ag-coated-Cu surface treatment by terephthalaldehyde and iodine

One of the largest obstacles for Ag based electrically conductive adhesives (ECAs), as an alternative for Pb-containing solders in electronic packaging, is that the conductivity of ECAs is lower than that of solders due to the limited physical contact area between/among conductive fillers and the insulated organic lubricant and metal oxide layers on the surface of the conductive fillers. What’s more, the high cost of Ag fillers is also restricting the wide use of Ag based ECAs. In this study, Ag-coated-Cu flakes were chosen as a substitute for Ag flakes to reduce the cost. At the same time, the coating of Cu with an Ag layer could protect the Cu-based fillers from oxidation and corrosion. A mixture of weak reducing agents and substituting agents was selected to treat the Ag-coated-Cu flakes to increase the conductivity of the Ag-coated-Cu based ECAs. During the treatment process, the weak reducing agents can reduce the metal oxides on the filler surfaces, enabling more metallic contacts. Meanwhile, the substituting agents can partially remove or replace the long chain fatty acid lubricants on the metal flakes, improving the electron tunneling between/among neighboring flakes. As such, the multiple effects of the reducing agents and substituting agents can improve the conductivity of the ECAs. By using an appropriate amount of terephthalaldehyde and iodine treated Ag-coated-Cu flakes, the resistivity was reduced to as low as 1.28 × 10−4 Ω cm for the ECA with 75 wt% content of treated fillers, which is comparable to that of commercially available Ag-filled ECAs (×10−4 Ω cm). This work suggests that a surface chemical method can enhance the electrical conductivity of metal filler based ECAs.

Controlled growth of MoS2 nanopetals and their hydrogen evolution performance

Edge-oriented MoS2 nanopetals complexed with basal-oriented MoS2 thin films have been mildly grown through a simple atmospheric pressure chemical vapor deposition (APCVD) process with the reaction of MoO3 and S. Dense nanopetals with hexagonal structures exposed numerous chemically reactive edge sites. The roles of growth temperature, time and S/MoO3 mass ratio have been carefully investigated to tune the morphology and density of the as-grown products. Importantly, the carbon nanotube (CNT) films were used as substrates for growing MoS2 nanopetals. The MoS2/CNT composites, used directly as working electrodes, showed remarkable and stable electrocatalytic activity in the hydrogen evolution reaction (HER), as manifested with a low onset overpotential of ∼100 mV and a small Tafel slope of 49.5 mV per decade. The development of the MoS2/CNT electrode provides a promising way to fabricate other multifunctional electrodes.

Transfer of vertically aligned carbon nanotube arrays onto flexible substrates for gecko-inspired dry adhesive application

The geckos extraordinary climbing ability has inspired scientists to develop synthetic dry adhesives that mimic the structure and function of gecko feet. The vertically aligned carbon nanotube (VACNT) array has been considered a potential candidate for developing gecko-inspired dry adhesive materials due to its outstanding structural and mechanical properties. However, the limited choices of growth substrates and poor interfacial bonding between VACNTs and growth substrates have restricted their application as gecko-inspired dry adhesive materials. Here, we report a versatile transfer method for transferring VACNT arrays onto flexible polymer substrates using a thermal oxidation process. This transfer method mainly focused on using the VACNT array as a gecko-inspired dry adhesive. Using the transfer method developed in our study, VACNT array-based gecko-inspired dry adhesive materials with improved adhesion property, structural stability, and self-cleaning ability can be developed. A thermal oxidation process was used to obtain free-standing VACNT arrays, resulting in the production of top-transferred and bottom-transferred structural VACNT array-based dry adhesive materials. The shear adhesive strength of the transferred VACNT array was enhanced using this method. The interfacial bonding strength of the transferred VACNT array increased nearly 15 times according to nanoscratch tests. The flexible structure of the transferred VACNT array exhibited better antifouling properties by mimicking digital hyperextension (DH) motion, which is a natural peeling motion of the gecko foot with a unique dynamic self-cleaning mechanism. These findings show that our method is an efficient method for transferring VACNT arrays and an important process for fabricating gecko-inspired VACNT array-based dry adhesive materials with high structural stability, self-cleaning ability, and high adhesive strength.

Hydrothermal deposition of a zinc oxide nanorod array on a carbon nanotube film as a piezoelectric generator

Piezoelectric generators based on zinc oxide (ZnO) nanowires/nanorods require not only an aligned assembly morphology but also Schottky contacts between ZnO and electrodes to rectify the piezoelectric signals. Here we demonstrate that two-dimensional carbon nanotube (CNT) assembly films can serve as highly efficient electrode materials to meet these two requirements. The flexibility, porosity and pore size distribution, and intimate contact with ZnO of CNT films have advantages in controllable hydrothermal deposition to generate highly aligned ZnO nanorods with high crystallinity at a high density. Due to the Schottky characteristics between ZnO and CNT, aluminum and titanium are suggested to serve as the negative electrode of a piezoelectric energy supply, by using their ohmic contacts with ZnO. The three-layered piezoelectric generator outputs a signal of 50–60 mV by using bending deformations, one order of magnitude larger than the signal generated by fast pressing deformations. This study presents a method to design ZnO-based piezoelectric generators without using precious metals or rare earth elements.

Chemical vapor deposition growth of few-layer graphene for transparent conductive films

The layer numbers of graphene for graphene based transparent conductive films are crucial. An appropriate number of graphene layers would provide excellent electrical conductivity along with high transparency. Herein, we demonstrated a facile and scalable technique to grow graphene with controllable layers on copper foil substrates using the etching effect of H2 in atmospheric pressure chemical vapor deposition (APCVD), and studied the influence of H2 etching on the properties of graphene transparent conductive films. The etching of formed multi-layer graphene (MLG, 12–14 layers) for Cu substrates assists the formation of few-layer graphene (FLG, 2–3 layers). These as-obtained graphene can be used as high performance transparent conductors, which show improved tradeoff between conductivity and transparency: the transmittance of 96.4% at 550 nm with sheet resistance of ∼360 Ω sq−1, and the transmittance of 86.7% at 550 nm with sheet resistance of ∼142 Ω sq−1. They could be used as high performance transparent conductors in the future.

In Situ Generation of Photosensitive Silver Halide for Improving the Conductivity of Electrically Conductive Adhesives

Electrically conductive adhesives (ECAs) can be regarded as one of the most promising materials to replace tin/lead solder. However, relatively low conductivity seriously restricts their applications. In the present study, we develop an effective method to decrease the bulk electrical resistivity of ECAs. KI or KBr is added to replace the lubricant and silver oxide layers on silver flakes and to form photosensitive silver halide. After exposure to sunlight, silver halide can photodecompose into silver nanoparticles that will sinter and form metallic bonding between/among flakes during the curing process of ECAs, which would remarkably reduce the resistivity. The modified micro silver flakes play a crucial role in decreasing the electrical resistivity of the corresponding ECAs, exhibiting the lowest resistivity of 7.6 × 10-5 Ω·cm for 70 wt % loaded ECAs. The obtained ECAs can have wide applications in the electronics industry, where high conductance is required.