Yuda Zhao

Stretchable all-solid-state supercapacitor with wavy shaped polyaniline/graphene electrode

A stretchable electronic device can retain its functionalities during high-level mechanical deformation, and stimulates the applications in the field of wearable and bio-implantable electronics. Efficient energy storage devices are an indispensable component in stretchable electronic systems. To integrate power supplies together with electronic devices that are mechanically flexible and stretchable, we demonstrate a new kind of stretchable all-solid-state supercapacitor, which consists of two slightly separated polyaniline/graphene electrodes in a wavy shape, with a phosphoric acid/polyvinyl alcohol gel as the solid-state electrolyte and separator. The as-fabricated wavy shaped supercapacitor was encapsulated in an elastomeric substrate which can be stretched to a large extent without mechanical degradation. The supercapacitor exhibited a maximum specific capacitance of 261 F g−1. Electrochemical cycling testing with the supercapacitor showed 89% capacitance retention over 1000 charge–discharge cycles at a current density of 1 mA cm−2. The bending and stretching tests showed that the supercapacitor maintained high mechanical strength and high capacitance simultaneously, even under a strain of 30%. This stretchable all-solid-state supercapacitor shows great potential as an energy storage device for stretchable electronic systems.

Extraordinarily Strong Interlayer Interaction in 2D Layered PtS2

Platinum disulfide (PtS2 ), a new member of the group-10 transition-metal dichalcogenides, is studied experimentally and theoretically. The indirect bandgap of PtS2 can be drastically tuned from 1.6 eV (monolayer) to 0.25 eV (bulk counterpart), and the interlayer mechanical coupling is almost isotropic. It can be explained by strongly interlayer interaction from the pz orbital hybridization of S atoms.

Two‐Dimensional Material Membranes: An Emerging Platform for Controllable Mass Transport Applications

Two-dimensional materials provide an ideal platform for studying the fundamental properties of atomic-level thickness systems, and are appropriate for lots of engineering applications in various fields. Although 2D materials are the thinnest membranes, they have been revealed to have high impermeability even to the smallest molecule. By the virtue of this high impermeability of the 2D materials in combination with their other unique properties, 2D materials open up a variety of applications that are impossible for conventional membranes. In this review, the latest applications based on high impermeability and selective permeation of these 2D material membranes are overviewed for different fields, including environmental control, chemical engineering, electronic devices, and biosensors. The working mechanism for each kind of application is described in detail. A summary and outlook is then provided on the challenges and new directions in this emerging research field.

Controllable Growth of Large-Size Crystalline MoS2 and Resist-Free Transfer Assisted with a Cu Thin Film.

Two-dimensional MoS2 is a promising material for future nanoelectronics and optoelectronics. It has remained a great challenge to grow large-size crystalline and high surface coverage monolayer MoS2. In this work, we investigate the controllable growth of monolayer MoS2 evolving from triangular flakes to continuous thin films by optimizing the concentration of gaseous MoS2, which has been shown a both thermodynamic and kinetic growth factor. A single-crystal monolayer MoS2 larger than 300 μm was successfully grown by suppressing the nuclei density and supplying sufficient source. Furthermore, we present a facile process of transferring the centimeter scale MoS2 assisted with a copper thin film. Our results show the absence of observable residues or wrinkles after we transfer MoS2 from the growth substrates onto flat substrates using this technique, which can be further extended to transfer other two-dimensional layered materials.

Perovskite Photovoltachromic Supercapacitor with All-Transparent Electrodes

Photovoltachromic cells (PVCCs) are of great interest for the self-powered smart windows of architectures and vehicles, which require widely tunable transmittance and automatic color change under photostimuli. Organolead halide perovskite possesses high light absorption coefficient and enables thin and semitransparent photovoltaic device. In this work, we demonstrate co-anode and co-cathode photovoltachromic supercapacitors (PVCSs) by vertically integrating a perovskite solar cell (PSC) with MoO3/Au/MoO3 transparent electrode and electrochromic supercapacitor. The PVCSs provide a seamless integration of energy harvesting/storage device, automatic and wide color tunability, and enhanced photostability of PSCs. Compared with conventional PVCC, the counter electrodes of our PVCSs provide sufficient balancing charge, eliminate the necessity of reverse bias voltage for bleaching the device, and realize reasonable in situ energy storage. The color states of PVCSs not only indicate the amount of energy stored and energy consumed in real time, but also enhance the photostability of photovoltaic component by preventing its long-time photoexposure under fully charged state of PVCSs. This work designs PVCS devices for multifunctional smart window applications commonly made of glass.

2D Layered Materials of Rare‐Earth Er‐Doped MoS2 with NIR‐to‐NIR Down‐ and Up‐Conversion Photoluminescence

A 2D system of Er-doped MoS2 layered nanosheets is developed. Structural studies indicate that the Er atoms can be substitutionally introduced into MoS2 to form stable doping. Density functional theory calculation implies that the system remains stable. Both NIR-to-NIR up-conversion and down-conversion light-emissions are observed in 2D transition metal dichalcogenides, ascribed to the energy transition from Er(3+) dopants.

High-Electron-Mobility and Air-Stable 2D Layered PtSe2 FETs

The electrical and optical measurements, in combination with density functional theory calculations, show distinct layer-dependent semiconductor-to-semimetal evolution of 2D layered PtSe2 . The high room-temperature electron mobility and near-infrared photo-response, together with much better air-stability, make PtSe2 a versatile electronic 2D layered material.

Highly impermeable and transparent graphene as an ultra-thin protection barrier for Ag thin films

Ag thin films have a wide variety of applications in optics. However, Ag is chemically unstable under atmospheric conditions, which significantly degrades its optical properties and hinders its practical applications. Conventional protective coatings retard or inhibit the corrosion of Ag, but also alter the optical properties of Ag substantially. In this work, we transfer highly impermeable and transparent monolayer graphene onto the surface of Ag thin films as an ultra-thin protection barrier. We comparatively study the morphological and spectroscopic characteristics of the Ag thin films with and without the graphene protective barrier, revealing the high corrosion-resistance of monolayer graphene to gases and liquids. The Tafel analysis shows that the corrosion rate of the Ag thin film is reduced by about 66 times by the use of a graphene protection barrier. We further demonstrate that the graphene coated Ag thin films can be used for optical applications, including optical mirrors and surface enhanced Raman spectroscopy substrates. Our results show that monolayer graphene as a protective barrier simultaneously maintains the high stability and unique optical properties of Ag thin films.

A rectification-free piezo-supercapacitor with a polyvinylidene fluoride separator and functionalized carbon cloth electrodes

The integration of energy harvesting and energy storage in this device not only enables the conversion of ambient energy into electricity, but also provides a sustainable power source for various electronic devices and systems. It is highly desirable to improve the integration level and minimize unnecessary energy loss in the power-management circuits between energy harvesting and storage devices. In our work, we integrate a PVDF film into a supercapacitor as both the separator and the energy harvester. The double-sides of the polarized PVDF films are coated with H2SO4/poly(vinyl alcohol) (PVA) gel electrolyte. Functionalized carbon cloths are assembled with H2SO4/PVA electrolyte as both anode and cathode, forming a flexible all-solid-state supercapacitor. Externally mechanical impacts establish a piezoelectric potential across the PVDF films, and drive ions in the electrolyte to migrate towards the interface of the supercapacitor electrode, storing the electricity in the form of electrochemical energy. The asymmetric output characteristic of the piezoelectric PVDF film under mechanical impact results in the effective charging of the supercapacitor without any rectification device. The integrated piezo-supercapacitor exhibits a specific capacitance of 357.6 F m−2, a power density of 49.67 mW h m−2, and an energy density of 400 mW m−2. Our hybridized energy harvesting and storage device can be further extended for providing sustainable power source of various types of sensors.

A long-term corrosion barrier with an insulating boron nitride monolayer

Graphene has been demonstrated as an ultrathin and light-weight corrosion barrier because of its high impermeability. However, it fails to prevent the Cu corrosion over a long term because the high conductivity of graphene enables the formation of a galvanic cell and promotes the electrochemical reaction. Here we theoretically and experimentally study a boron nitride (BN) monolayer as a long-term corrosion barrier for Cu. Our density functional theory calculations show that the potential barrier for O2 to pass through BN is close to that of graphene. The long-term barrier characteristics of BN and graphene are comparably evaluated by aging in an ambient environment for 160 days. Morphological and spectroscopic characterization shows that a BN monolayer has much better long-term barrier performance than graphene. X-ray photoelectron spectroscopy analysis shows that the Cu2+ percentage of the aging Cu sample with a BN barrier is reduced by around 15 times compared with that covered by graphene. The superior long-term barrier performance of a BN monolayer can be understood to be a result of its high impermeability and insulating characteristics, which suppress the galvanic corrosion under the ambient environment. These studies reveal that a BN monolayer is a more effective long-term corrosion barrier than graphene.