Ziyin Lin

Low-Cost High-Performance Solid-State Asymmetric Supercapacitors Based on MnO2 Nanowires and Fe2O3 Nanotubes

A low-cost high-performance solid-state flexible asymmetric supercapacitor (ASC) with α-MnO2 nanowires and amorphous Fe2O3 nanotubes grown on flexible carbon fabric is first designed and fabricated. The assembled novel flexible ASC device with an extended operating voltage window of 1.6 V exhibits excellent performance such as a high energy density of 0.55 mWh/cm(3) and good rate capability. The ASC devices can find numerous applications as effective power sources, such as powering color-switchable sun glasses and smart windows.

Hydrogenated ZnO Core–Shell Nanocables for Flexible Supercapacitors and Self-Powered Systems

Although MnO2 is a promising material for supercapacitors (SCs) due to its excellent electrochemical performance and natural abundance, its wide application is limited by poor electrical conductivity. Inspired by our results that the electrochemical activity and electrical conductivity of ZnO nanowires were greatly improved after hydrogenation, we designed and fabricated hydrogenated single-crystal ZnO@amorphous ZnO-doped MnO2 core-shell nanocables (HZM) on carbon cloth as SC electrodes, showing excellent performance such as areal capacitance of 138.7 mF/cm(2) and specific capacitance of 1260.9 F/g. Highly flexible all-solid-state SCs were subsequently assembled with these novel HZM electrodes using polyvinyl alcohol/LiCl electrolyte. The working devices achieved very high total areal capacitance of 26 mF/cm(2) and retained 87.5% of the original capacitance even after 10 000 charge/discharge cycles. An integrated power pack incorporating series-wound SCs and dye-sensitized solar cells was demonstrated for stand-alone self-powered systems.

Large-scale production of two-dimensional nanosheets

Two-dimensional (2D) nanomaterials such as graphene, boron nitride (BN), and molybdenum disulfide (MoS2) have been attracting increasing research interest in the past few years due to their unique material properties. However, the lack of a reliable large-scale production method is an inhibiting issue for their practical applications. Here we report a facile, efficient, and scalable method for the fabrication of monolayer and few-layer BN, MoS2, and graphene using combined low-energy ball milling and sonication. Ball milling generates two forces on layered materials, shear force and compression force, which can cleave layered materials into 2D nanosheets from the top/bottom surfaces, and the edge of layered materials. Subsequent sonication would further break larger crystallites into smaller crystallites. These fabricated 2D nanosheets can be well dispersed in aqueous solutions at high concentrations, 1.2 mg mL−1 for BN, 0.8 mg mL−1 for MoS2, and 0.9 mg mL−1 for graphene, which are highly advantageous over other methods. These advantages render great potential in the construction of high-performance 2D material-based devices at low cost. For example, a prototype gas sensor is demonstrated in our study using graphene and MoS2, respectively, which can detect several ppm of ammonia gas.

Scalable fabrication of MnO2 nanostructure deposited on free-standing Ni nanocone arrays for ultrathin, flexible, high-performance micro-supercapacitor

Ultrathin and flexible power sources are essential for the rapid development of portable and wearable electronics. The deployment of 3-dimensional (3-D) nanostructured materials on the current collectors has recently emerged as a promising strategy for preparing high-performance supercapacitors. Additionally, it is equally important to develop an appropriate device packaging technique, so as to maximize the improvement of the electrode performance characteristic. Herein, we develop a simple and efficient method for fabricating ultrathin and flexible supercapacitor electrodes containing a manganese dioxide (MnO2) nanostructure deposited onto 3-D nickel nanocone arrays (NCAs). The MnO2-NCAs electrode was prepared by an electro-deposition technology, which involves the cathode deposition of NCAs on a titanium carrier film as the current collector and subsequent anode deposited from the MnO2 nanostructures as the active material. The electrode can be peeled off from the carrier film and thus the resulting freestanding electrode is as thin as 3 μm, and exhibits outstanding mechanical robustness, high specific capacitance (632 F g−1), enhanced energy density (52.2 W h kg−1) and excellent cycle performance (95.3% retention after 20000 cycles). We further fabricated ultrathin supercapacitors with a total thickness of ∼27 μm, which achieved unprecedented features including superior energy density by volume (2.7 × 10−3 W h cm−3), superior flexibility and reliability. We demonstrated the application of the MnO2-NCAs supercapacitor as an ultrathin power source such as driving a LED indicator. This technology may find vast applications in future wearable electronics.

Magnetic Alignment of Hexagonal Boron Nitride Platelets in Polymer Matrix: Toward High Performance Anisotropic Polymer Composites for Electronic Encapsulation

We report magnetic alignment of hexagonal boron nitride (hBN) platelets and the outstanding material properties of its polymer composite. The magnetically responsive hBN is produced by surface modification of iron oxide, and their orientations can be controlled by applying an external magnetic field during polymer curing. Owing to the anisotropic properties of hBN, the epoxy composite with aligned hBN platelets shows interesting properties along the alignment direction, including significantly reduced coefficient of thermal expansion, reaching ∼28.7 ppm/°C, and enhanced thermal conductivity, 104% higher than that of unaligned counterpart, both of which are observed at a low filler loading of 20 wt %. Our modeling suggests the filler alignment is the major reason for these intriguing material properties. Finite element analysis reveals promising applications for the magnetically aligned hBN-based composites in modern microelectronic packaging.

Facile fabrication of superhydrophobic octadecylamine-functionalized graphite oxide film.

We demonstrated a facile strategy of producing superhydrophobic octadecylamine (ODA)-functionalized graphite oxide (GO) films. ODA was chemically grafted on GO sheets by the nucleophilic substitution reaction of amine groups with epoxy groups. The long hydrocarbon chain in ODA reduces the surface energy of the GO sheet. The fabricated ODA-functionalized GO film exhibited a high contact angle (163.2°) and low hysteresis (3.1°). This method is promising in terms of low-cost and large-scale superhydrophobic coatings and has potential applications for surface modification of GO paper or other GO-based composite materials.

Ultrafast, dry microwave synthesis of graphene sheets

Through direct absorption of microwave irradiation by GO film, we developed a rapid, dry approach to synthesize reduced graphene.

Worm-like amorphous MnO2 nanowires grown on textiles for high-performance flexible supercapacitors

A novel class of amorphous MnO2 nanowires with a worm-like (WL) nanostructure was prepared by electrodeposition and a possible formation mechanism was proposed. The specific capacitance of WL amorphous MnO2 was 2–3 times larger than that of its crystalline cotton-like MnO2 counterpart. The unique WL amorphous nanostructure is believed to significantly facilitate the electrochemical performance of MnO2. Flexible solid-state symmetric supercapacitors assembled with WL-MnO2 electrodes exhibited a high energy density of 6.3 W h kg−1. These results demonstrate that the amorphous WL nanostructure grown on carbon fabric can serve as a promising electrode material for flexible and portable energy storage devices.

Silicon-Based Hybrid Energy Cell for Self-Powered Electrodegradation and Personal Electronics

Silicon (Si)-based solar cell is by far the most established solar cell technology. The surface of a Si solar cell is usually covered by a layer of transparent material to protect the device from corrosion, contamination and mechanical damage. Here, we replaced this protection layer by a thin layer film of polydimethysiloxane nanowires. Based on this layer and using the conductive layer on the surface of the wavy Si, we have fabricated a triboelectric nanogenerator (TENG). The solar cell and the TENG form a hybrid energy cell for simultaneously harvesting solar and mechanical energies. The hybrid energy cell can be directly used for self-powered electrodegradation of rhodamine B, where the degradation percentage is up to 98% in 10 min. Moreover, the produced energy can also be stored in the Li-ion batteries for driving some personal electronics such as a red laser diode and a commercial cell phone.

Reversible superhydrophobic-superhydrophilic transition of ZnO nanorod/epoxy composite films.

Tuning the surface wettability is of great interest for both scientific research and practical applications. We demonstrated reversible transition between superhydrophobicity and superhydrophilicity on a ZnO nanorod/epoxy composite film. The epoxy resin serves as an adhesion and stress relief layer. The ZnO nanorods were exposed after oxygen reactive ion etching of the epoxy matrix. A subsequent chemcial treatment with fluoroalkyl and alkyl silanes resulted in a superhydrophobic surface with a water contact angle up to 158.4° and a hysteresis as low as 1.3°. Under UV irradiation, the water contact angle decreased gradually, and the surface eventually became superhydrophilic because of UV induced decomposition of alkyl silanes and hydroxyl absorption on ZnO surfaces. A reversible transition of surface wettability was realized by alternation of UV illumination and surface treatment. Such ZnO nanocomposite surface also showed improved mechanical robustness.