Qinqin Zhou

Three-dimensional porous graphene/polyaniline composites for high-rate electrochemical capacitors

We report an electrochemical co-deposition method to prepare three-dimensional (3D) porous composites of reduced graphene oxide (rGO) and polyaniline (PANI) with pores vertically oriented on the surfaces of current collectors and used as an electrode material for electrochemical capacitors (ECs). These composites showed much higher areal specific capacitances and greatly improved rate capability than those of PANI. Typically, the rGO/PANI composite film with a thickness of 150 μm exhibited a high areal specific capacitance (Ca, 67.2 mF cm−2), small relaxation time constant (τ0, 316 ms) and good electrochemical stability, promising for the fabrication of a high-rate EC.

Base-Induced Liquid Crystals of Graphene Oxide for Preparing Elastic Graphene Foams with Long-Range Ordered Microstructures.

Base-induced graphene oxide (GO) liquid crystals form a highly ordered texture. This microstructure can be inherited by graphene foams prepared by hydrothermal reduction, showing a long-range ordered microstructure of graphene sheets in 3D. This provides an insightful understanding into the supramolecular chemistry of GO sheets.

Ultrasensitive and selective nitrogen dioxide sensor based on self-assembled graphene/polymer composite nanofibers.

Reduced graphene oxide (rGO) sheets were self-assembled onto the surfaces of electrospun polymer nanofibers to form an ultrathin coating. These rGO/polymer composite nanofibers were used to fabricate nitrogen dioxide (NO2) sensor. This sensor can be performed at room temperature, and it exhibited a high sensitivity of 1.03 ppm(-1) with excellent selectivity and good reversibility. Furthermore, the limit of detection was experimentally measured to be as low as 150 ppb, and this value is much lower than the threshold exposure limit proposed by American Conference of Governmental Industrial Hygienists (200 ppb).

Composite organogels of graphene and activated carbon for electrochemical capacitors

We report the preparation of composite organogels of reduced graphene oxide (rGO) and activated carbon (AC) by a solvothermal reaction and their application as electrodes of electrochemical capacitors (ECs). In these organogels, rGO sheets are assembled into a 3-dimensional (3D) framework for encapsulating AC particles. The 3D interconnected rGO network increased the electrical conductivity and the AC component provided high specific surface areas (SSAs) for the composite organogels. These composite organogels also have stable mechanical properties and can be directly used as electrodes of ECs without using any binding agent and conducting additive. In a practical two-electrode system, the specific capacitance of the ECs based on the composite organogels was tested to be 116.5 ± 2.2 F g−1 at a current density of 1 A g−1 in an organic electrolyte of propylene carbonate (PC) containing 1 M tetraethylammonium tetrafluorobromate (TEABF4). These ECs also exhibited a high energy density of 12.5 Wh kg−1 even at a high power density of 6216 W kg−1. They also showed a much larger volumetric specific capacitance compared with that of the EC based on rGO organogel and a much higher specific capacitance and rate capability than those of the AC-based EC.

An ultrahigh-rate electrochemical capacitor based on solution-processed highly conductive PEDOT:PSS films for AC line-filtering

Alternating current (AC) line-filters are widely used to attenuate the leftover AC ripples in line-powered devices. However, the commercialized aluminum electrolytic capacitors (AECs) have low specific capacitances, making them usually the largest components in the electronic circuits of miniaturized, portable and/or flexible electronics. Herein, we report a scalable wet-process to fabricate an electrochemical capacitor (EC) using sulfuric acid treated commercially available poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (AT-PEDOT:PSS) as an electrode material and graphite foil as the current collector. It exhibited high areal (994 μF cm−2) and volumetric (16.6 F cm−3) specific capacitances at 120 Hz, ultrahigh-rate frequency response (phase angle = −83.6° at 120 Hz) with a short resistor–capacitor time constant of 0.15 ms, and an excellent electrochemical stability. Therefore, it is promising to replace AECs for AC line-filtering, and their performance is superior to those of the state-of-the-art ECs for this purpose.

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.

Nitrogen-Doped Holey Graphene Film-Based Ultrafast Electrochemical Capacitors

The commercialized aluminum electrolytic capacitors (AECs) currently used for alternating current (AC) line-filtering are usually the largest components in the electronic circuits because of their low specific capacitances and bulky sizes. Herein, nitrogen-doped holey graphene (NHG) films were prepared by thermal annealing the composite films of polyvinylpyrrolidone (PVP), graphene oxide (GO), and ferric oxide (Fe2O3) nanorods followed by chemical etching with hydrochloride acid. The typical electrochemical capacitor with NHG electrodes exhibited high areal and volumetric specific capacitances of 478 μF cm(-2) and 1.2 F cm(-3) at 120 Hz, ultrafast frequency response with a phase angle of -81.2° and a resistor-capacitor time constant of 203 μs at 120 Hz, as well as excellent cycling stability. Thus, it is promising to replace conventional AEC for AC line-filtering in miniaturized electronics.

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.