Weijie Liu

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.

Ultrathin and Lightweight 3D Free-Standing Ni@NiO Nanowire Membrane Electrode for a Supercapacitor with Excellent Capacitance Retention at High Rates

A free-standing binder-free 3D Ni@NiO nanowire membrane is fabricated by a simple filtration method followed by thermal annealing. With an appropriate annealing temperature, the functional nanowires can keep their rough and echinate surface, and the conductive network composed of welded nickel nanowire cores is well-preserved without isolation (0.53 Ω/sq). The unique 3D multigrade mesporous structure not only accelerates the intercalation and deintercalation velocity of electrolyte ions but also provides numerous electroactive sites for the Faraday reaction. As a result, the supercapacitor electrode can preserve a capacitance retention of 96.1% (36.9 F/cm(3)) with a high discharge current density, indicating its wonderful rate capability. The fabricated membrane electrode exhibits high volumetric capacitance, stable cycling life, and remarkable retention of the capacitance at high rate, energy, and power density, making it a promising candidate for application in portable electronic products.

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.

Highly Self-Healable 3D Microsupercapacitor with MXene–Graphene Composite Aerogel

High-performance microsupercapacitors (MSCs) with three-dimensional (3D) structure provide an effective approach to improve the ability of energy storage. Because the electrodes with 3D structure are generally easily destroyed under mechanical deformation in practical applications, we fabricated a self-healable 3D MSC consisting of MXene (Ti3C2T x)-graphene (reduced graphene oxide, rGO) composite aerogel electrode by wrapping it with a self-healing polyurethane as an outer shell. The MXene-rGO composite aerogel combining large specific surface area of rGO and high conductivity of the MXene can not only prevent the self-restacking of the lamella structure but also resist the poor oxidization of MXene to a degree. The MSC based on a 3D MXene-rGO aerogel delivers a large area specific capacitance of 34.6 mF cm-2 at a scan rate of 1 mV s-1 and an outstanding cycling performance with a capacitance retention up to 91% over 15 000 cycles. The 3D MSC presents an excellent self-healing ability with specific capacitance retention of 81.7% after the fifth healing. The preparation of this self-healable 3D MSC can provide a method for designing and manufacturing next-generation long-life multifunctional electronic devices further to meet the requirements of sustainable development.

Piezoresistive Pressure Sensor Based on Synergistical Innerconnect Polyvinyl Alcohol Nanowires/Wrinkled Graphene Film

Piezoresistive sensor is a promising pressure sensor due to its attractive advantages including uncomplicated signal collection, simple manufacture, economical and practical characteristics. Here, a flexible and highly sensitive pressure sensor based on wrinkled graphene film (WGF)/innerconnected polyvinyl alcohol (PVA) nanowires/interdigital electrodes is fabricated. Due to the synergistic effect between WGF and innerconnected PVA nanowires, the as-prepared pressure sensor realizes a high sensitivity of 28.34 kPa-1 . In addition, the device is able to discern lightweight rice about 22.4 mg (≈2.24 Pa) and shows excellent durability and reliability after 6000 repeated loading and unloading cycles. What is more, the device can detect subtle pulse beat and monitor various human movement behaviors in real-time.

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.