Mingmao Wu

A Solution‐Processed High‐Performance Phototransistor based on a Perovskite Composite with Chemically Modified Graphenes

Phototransistors with a structure of a nitrogen-doped graphene quantum dots (NGQDs)-perovskite composite layer and a mildly reduced graphene oxide (mrGO) layer are fabricated through a solution-processing method. This hybrid phototransistor exhibits broad detection range (from 365 to 940 nm), high photoresponsivity (1.92 × 104 A W-1 ), and rapid response to light on-off (≈10 ms). NGQDs offer an effective and fast path for electron transfer from the perovskite to the mrGO, resulting in the improvement of photocurrent and photoswitching characteristics. The high photoresponsivity can also be ascribed to a photogating effect in the device. In addition, the phototransistor shows good stability with poly(methyl methacrylate) encapsulation, and can maintain 85% of its initial performance for 20 d in ambient air.

Ultrahigh‐Conductivity Polymer Hydrogels with Arbitrary Structures

A poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) hydrogel is prepared by thermal treatment of a commercial PEDOT:PSS (PH1000) suspension in 0.1 mol L-1 sulfuric acid followed by partially removing its PSS component with concentrated sulfuric acid. This hydrogel has a low solid content of 4% (by weight) and an extremely high conductivity of 880 S m-1 . It can be fabricated into different shapes such as films, fibers, and columns with arbitrary sizes for practical applications. A highly conductive and mechanically strong porous fiber is prepared by drying PEDOT:PSS hydrogel fiber to fabricate a current-collector-free solid-state flexible supercapacitor. This fiber supercapacitor delivers a volumetric capacitance as high as 202 F cm-3 at 0.54 A cm-3 with an extraordinary high-rate performance. It also shows excellent electrochemical stability and high flexibility, promising for the application as wearable energy-storage devices.

A high-performance current collector-free flexible in-plane micro-supercapacitor based on a highly conductive reduced graphene oxide film

A flexible in-plane micro-supercapacitor (MSC) was fabricated by laser carving a highly conductive and mechanically robust reduced graphene oxide (rGO) film adhered to a polyethylene naphthalate (PEN) sheet, followed by electrochemical activation of its microelectrodes. The laser carved rGO film can readily produce rGO interdigital micropatterns on a flexible PEN substrate, whereas electrochemical post-treatment can efficiently exfoliate the highly stacked rGO microelectrodes into a porous three-dimensional interconnected porous microstructure, greatly enhancing the accessible surface area for the formation of electrical double layers. The resultant metal current collector-free, flexible in-plane MSC exhibited a high areal specific capacitance, superior rate capability, excellent cycling stability as well as outstanding flexibility.

Topological Design of Ultrastrong and Highly Conductive Graphene Films

Nacre-like graphene films are prepared by evaporation-induced assembly of graphene oxide dispersions containing small amounts of cellulose nanocrystal (CNC), followed by chemical reduction with hydroiodic acid. CNC induces the formation of wrinkles on graphene sheets, greatly enhancing the mechanical properties of the resultant graphene films. The graphene films deliver an ultrahigh tensile strength of 765 ± 43 MPa (up to 800 MPa in some cases), a large failure strain of 6.22 ± 0.19%, and a superior toughness of 15.64 ± 2.20 MJ m-3 , as well as a high electrical conductivity of 1105 ± 17 S cm-1 . They have a great potential for applications in flexible electronics because of their combined excellent mechanical and electrical properties.

A Chemical Approach to Ultrastiff, Strong and Environmentally Stable Graphene Films

Reduced graphene oxide (rGO) sheets prepared by a modified Hofmann method (Ho-rGO) have large graphitic domains with few structural defects, facilitating the dense packing between rGO sheets to enhance the mechanical performances of the resultant graphene films. Graphene films are fabricated by the filtration of the aqueous dispersions of Ho-rGO sheets and further treated by thermal annealing. They display high moduli (stiffness) of 54.6 ± 1.4 GPa and high tensile strengths of 521 ± 19 MPa. They also exhibit high toughness and good electrical properties. The intact structure of Ho-rGO sheets narrows the nanochannels in the film matrices, greatly reducing the water infiltration into films and providing the graphene films with excellent environmental stability. These graphene films are attractive for practical applications because of their light weights and ultrastiff and ultrastrong mechanical properties.

Tailoring the oxygenated groups of graphene hydrogels for high-performance supercapacitors with large areal mass loadings

High-performance electrodes with high areal capacitances are highly desired for the practical applications of supercapacitors. Herein, we report such electrodes prepared from hydroxyl-rich graphene hydrogels (HRGHs). The hydroxyl groups on graphene sheets contribute to pseudo-capacitance and improve the wettability of HRGHs to aqueous electrolyte, ensuring fast ion transport within the electrodes, especially for the electrodes with high mass loadings. The supercapacitor based on mechanically compressed HRGHs shows a high gravimetric capacitance (260 F g−1) and volumetric capacitance (312 F cm−3) at 1 A g−1, good rate capability (∼78% at 100 A g−1), and excellent cycling stability (∼100% after 10 000 cycles). Moreover, an ultrahigh areal capacitance of 2675 mF cm−2 at 1 mA cm−2 is achieved at the mass loading of 10 mg cm−2. Even at a high current density of 50 or 100 mA cm−2, the areal capacitance is still retained at 2140 or 1768 mF cm−2, demonstrating the outstanding scalability of the HRGH electrodes.