Congxing Yang

Cable-type supercapacitors of three-dimensional cotton thread based multi-grade nanostructures for wearable energy storage.

A novel cable-type flexible supercapacitor with excellent performance is fabricated using 3D polypyrrole(PPy)-MnO2 -CNT-cotton thread multi-grade nanostructure-based electrodes. The multiple supercapacitors with a high areal capacitance 1.49 F cm(-2) at a scan rate of 1 mV s(-1) connected in series and in parallel can successfully drive a LED segment display. Such an excellent performance is attributed to the cumulative effect of conducting single-walled carbon nanotubes on cotton thread, active mesoporous flower-like MnO2 nanoplates, and PPy conductive wrapping layer improving the conductivity, and acting as pseudocapacitance material simultaneously.

A wire-shaped flexible asymmetric supercapacitor based on carbon fiber coated with a metal oxide and a polymer

Due to high capacitance resulting from the redox character of the MnO2–PPy–carbon and V2O5–PANI–carbon fiber composites, a flexible wire-shaped fiber asymmetric supercapacitor (WFASC) was fabricated using these materials as the positive and negative electrodes, respectively. Especially, the large work function difference between MnO2 and V2O5 help the device to exhibit a wide potential window of 2.0 V and a high areal capacitance of 0.613 F cm−2. As a result, the WFASC showed a maximum energy density of 0.340 mW h cm−2 at a power density of 1.5 mW cm−2 and a maximum power density of 30 mW cm−2 at an energy density of 0.294 mW h cm−2. Furthermore, the device exhibited a perfect stability after 5000 cycles at a current density of 30 mA cm−2, meanwhile, it could withstand the bending test and drive a LED under bending states. All of the above results prove the potential application of WFASC devices.

Inkjet printing of conductive patterns and supercapacitors using a multi-walled carbon nanotube/Ag nanoparticle based ink

A multi-walled carbon nanotube (MWCNT) and silver (Ag) nanoparticle ink for inkjet printing was prepared by dispersing MWCNTs and Ag nanoparticles in water with the assistance of sodium dodecylbenzenesulfonate (SDBS). Highly conductive patterns of Ag–MWCNTs were printed on paper using a HP Deskjet 1010 inkjet printer. The patterns showed good stability during the bending test and a low sheet resistance of ∼300 Ω sq−1 after being printed 50 times. By simply adding manganese dioxide (MnO2) nanoparticles with a diameter of 60–90 nm into the ink solution, patterned positive electrodes were prepared for asymmetric supercapacitors (ASCs) with filtrated MWCNT negative electrodes. The ASCs exhibit a wide operating potential window of 1.8 V and excellent electrochemical performances, e.g. a high energy density of 1.28 mW h cm−3 at a power density of 96 mW cm−3 and a high retention ratio of ∼96.9% of its initial capacitance after 3000 cycles. The inkjet-printing acting as a simple, low-cost, non-contact deposition method can be fully integrated with the fabrication process in current printed electronic devices and has potential applications in energy storage.

A Flexible Integrated System Containing a Microsupercapacitor, a Photodetector, and a Wireless Charging Coil

Nowadays, the integrated systems on a plane substrate containing energy harvesting, energy storing, and working units are strongly desired with the fast development of wearable and portable devices. Here, a simple, low cost, and scalable strategy involving ink printing and electrochemical deposition is proposed to fabricate a flexible integrated system on a plane substrate containing an all-solid-state asymmetric microsupercapacitor (MSC), a photoconduct-type photodetector of perovskite nanowires (NWs), and a wireless charging coil. In the asymmetric MSCs, MnO2-PPy and V2O5-PANI composites are used as positive and negative electrodes, respectively. Typical values of energy density in the range of 15-20 mWh cm-3 at power densities of 0.3-2.5 W cm-3 with an operation potential window of 1.6 V are achieved. In the system, the wireless charging coil receives energy from a wireless power transmitter, which then can be stored in the MSC to drive the photoconductive detector of perovskite NWs in sequence. The designed integrated system exhibits a stable photocurrent response comparable with the detector driven by an external power source. This research provides an important routine to fabricate integrated systems.

Freestanding and flexible graphene wrapped MnO2/MoO3 nanoparticle based asymmetric supercapacitors for high energy density and output voltage

Asymmetric supercapacitors (ASC) based on freestanding membranes with high energy density and high output voltage by a simple pre-reduced and vacuum filtering method are reported. Reduced graphene oxide (rGO) coated MnO2 nanospheres and rGO coated MoO3 nanoparticle composites are selected as the positive and the negative materials of the devices, respectively. The ASC has a high operation voltage window of 2.0 V in a hydrogen electrolyte, a high energy density of 34.6 mW h cm−3 at a power density of 100 mW cm−3, and a high volumetric capacitance of 62.7 F cm−3 at a current density of 0.1 A cm−3. Especially, the ASC exhibits an excellent cycling performance of 94.2% capacitance retention after over 3000 cycles. This strategy of designing the hybridized structure for freestanding and flexible ASC provides a promising route for next-generation supercapacitors with high energy density and high output voltage.

Fully screen printed highly conductive electrodes on various flexible substrates for asymmetric supercapacitors

Highly flexible conductive electrodes were prepared by screen printing a commercial carbon nanoparticle ink onto various substrates such as clothes, polyethylene terephthalate (PET) and paper. The flexible electrodes showed good stability during the bending test and could act as a foldable electric circuit. Multi-walled carbon nanotubes–manganese dioxide (MWCNTs–MnO2) anodes and multi-walled carbon nanotubes–molybdenum trioxide (MWCNTs–MoO3) cathodes for asymmetric supercapacitors (ASCs) were screen printed onto carbon nanoparticle electrodes, which acted as a collector. The fully screen printed supercapacitor has a wide operating potential window of 1.7 V and exhibits excellent electrochemical performance, e.g. a high energy density of 11.04 mW h cm−3 at a power density of 614.6 mW cm−3, a high retention ratio of ∼91.3% of its initial capacitance after 5000 cycles. The screen-printing acting as a simple, versatile, fast, and cost-effective printing method can be fully integrated with the fabrication process in current printed electronics and has potential applications for energy storage.

Graphene‐Skeleton Heat‐Coordinated and Nanoamorphous‐Surface‐State Controlled Pseudo‐Negative‐Photoconductivity of Tiny SnO2 Nanoparticles

SnO2 nanoparticles display a pseudo-negative-photoconductivity (PsdNPC) effect, which shows that their resistance increases under light irradiation via a heating effect. The PsdNPC originates from intensive electron scattering of the nanoamorphous surface state of the SnO2 nanoparticles, resulting in a small inner current and a large absorption of moisture, leading to a large surface current. Graphene as the inner skeleton can shorten the response and recovery times.

Multicolour electroluminescence from light emitting diode based on ZnO:Cu/p-GaN heterojunction at positive and reverse bias voltage

Incorporation of Cu atoms in ZnO can arouse Cu-related defect, which will influence electroluminescence (EL) light of light emitting diode (LED) based on ZnO:Cu/p-GaN heterojunction. ZnO:Cu nanobushes were grown on p-GaN film by simple chemical vapour deposition (CVD) method. Ultraviolet (UV) photoluminescence (PL) peak of ZnO:Cu had a redshift compared with that of pure ZnO, and low temperature (5 K) PL spectrum exhibited a structured green emission, indicating the substitutional incorporation of Cu atoms in ZnO crystal lattice. The LED based on ZnO:Cu/p-GaN heterojunction emitted blue-greenish EL light at p-GaN site at the positive bias voltage, and green EL peak gradually overtook the blue EL peak with the increase of positive bias voltage. At reverse bias voltage, this LED not only exhibited yellow-green EL light at ZnO:Cu site, but also emitted from orange to yellow EL light at p-GaN site with the increase of reverse bias voltage. The origins of EL light at positive and reverse bias voltage were explained using PL spectra and energy band diagram of ZnO:Cu/p-GaN structure.

A flexible and highly sensitive pressure sensor based on elastic carbon foam

In this paper, we fabricate a flexible elastic carbon foam (ECF)-based pressure sensor by direct carbonization of melamine foams (MF) at 800 °C without using any metal catalyst. The carbonized ECF is composed of a unique 3D interconnected concave triangular carbon network with a fraction of cracked carbon microfibers, and displays abundant micro and meso-porosity. We select the ECF as a sensing material due to its conductive and elastic features, and make a piezoresistive sensor with ultrahigh sensitivity (100.29 kPa−1) and reproducible sensing (11 000 cycles) characteristics. Moreover, the pressure sensor is able to distinguish a large pressure range from as low as 3 Pa to 10 kPa. The cheap raw materials, simple fabrication process and satisfactory performance of the pressure sensor make it a promising device for electronic monitoring systems in industrial detection, human motion monitoring and so on.

In situ synthesis of MoS2/graphene nanosheets as free-standing and flexible electrode paper for high-efficiency hydrogen evolution reaction

In this article, an exquisite flexible hybrid MoS2/graphene free-standing electrocatalyst paper was fabricated by a one-step in situ solvothermal process. The assembled MoS2/graphene catalysts exhibit significantly enhanced electrocatalytic activity and cycling stability towards the splitting of water in acidic solution. Furthermore, a strategic balance of abundant active sites at the edge of the S–Mo–S layers with efficient electron transfer in the MoS2/graphene hybrid catalyst plays a key role in controlling the electrochemical performance of the MoS2 nanosheets. Most importantly, the hybrid MoS2/graphene nanosheet paper shows excellent flexibility and high electrocatalytic performance under the various bending states. This work demonstrates an opportunity for the development of flexible electrocatalysts, which have potential applications in renewable energy conversion and energy storage systems.