Zheye Zhang

One-Pot Self-Assembled Three-Dimensional TiO2-Graphene Hydrogel with Improved Adsorption Capacities and Photocatalytic and Electrochemical Activities

We reported the development of a new type of multifunctional titanium dioxide (TiO2)-graphene nanocomposite hydrogel (TGH) by a facile one-pot hydrothermal approach and explored its environmental and energy applications as photocatalyst, reusable adsorbents, and supercapacitor. During the hydrothermal reaction, the graphene nanosheets and TiO2 nanoparticles self-assembled into three-dimensional (3D) interconnected networks, in which the spherical nanostructured TiO2 nanoparticles with uniform size were densely anchored onto the graphene nanosheets. We have shown that the resultant TGH displayed the synergistic effects of the assembled graphene nanosheets and TiO2 nanoparticles and therefore exhibited a unique collection of physical and chemical properties such as increased adsorption capacities, enhanced photocatalytic activities, and improved electrochemical capacitive performance in comparison with pristine graphene hydrogel and TiO2 nanoparticles. These features collectively demonstrated the potential of 3D TGH as an attractive macroscopic device for versatile applications in environmental and energy storage issues.

Freestanding Graphene Paper Supported Three-Dimensional Porous Graphene–Polyaniline Nanocomposite Synthesized by Inkjet Printing and in Flexible All-Solid-State Supercapacitor

Freestanding paper-like electrode materials have trigged significant research interest for their practical application in flexible and lightweight energy storage devices. In this work, we reported a new type of flexible nanohybrid paper electrode based on full inkjet printing synthesis of a freestanding graphene paper (GP) supported three-dimensional (3D) porous graphene hydrogel (GH)-polyaniline (PANI) nanocomposite, and explored its practical application in flexible all-solid-state supercapacitor (SC). The utilization of 3D porous GH scaffold to load nanostructured PANI dramatically enhances the electrical conductivity, the specific capacitance and the cycle stability of the GH-PANI nanocomposite. Additionally, GP can intimately interact with GH-PANI through π-π stacking to form a unique freestanding GP supported GH-PANI nanocomposite (GH-PANI/GP) with distinguishing mechanical, electrochemical and capacitive properties. These exceptional attributes, coupled with the merits of full inkjet printing strategy, lead to the formation of a high-performance binder-free paper electrode for flexible and lightweight SC application. The flexible all-solid-state symmetric SC based on GH-PANI/GP electrode and gel electrolyte exhibits remarkable mechanical flexibility, high cycling performance and acceptable energy density of 24.02 Wh kg(-1) at a power density of 400.33 W kg(-1). More importantly, the proposed simple and scale-up full inkjet printing procedure for the preparation of freestanding GP supported 3D porous GH-PANI nanocomposite is a modular approach to fabricate other graphene-based nanohybrid papers with tailorable properties and optimal components.

Facile and Green Synthesis of Palladium Nanoparticles-Graphene-Carbon Nanotube Material with High Catalytic Activity

We report a facile and green method to synthesize a new type of catalyst by coating Pd nanoparticles (NPs) on reduced graphene oxide (rGO)-carbon nanotube (CNT) nanocomposite. An rGO–CNT nanocomposite with three-dimensional microstructures was obtained by hydrothermal treatment of an aqueous dispersion of graphene oxide (GO) and CNTs. After the rGO–CNT composites have been dipped in K2PdCl4 solution, the spontaneous redox reaction between the GO–CNT and PdCl42− led to the formation of nanohybrid materials consisting rGO–CNT decorated with 4 nm Pd NPs, which exhibited excellent and stable catalytic activity: the reduction of 4-nitrophenol to 4-aminophenol using NaBH4 as a catalyst was completed in only 20 s at room temperature, even when the Pd content of the catalyst was 1.12 wt%. This method does not require rigorous conditions or toxic agents and thus is a rapid, efficient, and green approach to the fabrication of highly active catalysts.

Hierarchically structured MnO2/graphene/carbon fiber and porous graphene hydrogel wrapped copper wire for fiber-based flexible all-solid-state asymmetric supercapacitors

Recent progress in fiber-based supercapacitors has attracted tremendous attention due to the tiny volume, high flexibility and weavability of the fibers, which are required for the development of high-performance fiber electrodes. In this work, we report for the first time, the design and fabrication of two types of core–shell fiber-based electrodes, i.e. hierarchically structured manganese dioxide (MnO2)/graphene/carbon fiber (CF) and three-dimensional (3D) porous graphene hydrogel (GH) wrapped copper wire (CW), and their practical application in a fiber-architectured flexible all-solid-state supercapacitor. Taking advantage of the synergistic effects of the different components in the hierarchically structured nanohybrid fiber electrodes and the merits of the proposed synthesis strategies, the assembled asymmetric supercapacitor device using MnO2/graphene/CF as the positive electrode and GH/CW as the negative electrode could be cycled reversibly in a high-voltage region of 0–1.6 V, delivering a high areal energy density of 18.1 μW h cm−2 and volumetric energy density of 0.9 mW h cm−3. Furthermore, our fiber-based flexible supercapacitor also shows a good rate capability, excellent flexibility and high long term cyclability, which makes it a promising power source for flexible energy-related devices.

Scalable Synthesis of Freestanding Sandwich-structured Graphene/Polyaniline/Graphene Nanocomposite Paper for Flexible All-Solid-State Supercapacitor

We reported a scalable and modular method to prepare a new type of sandwich-structured graphene-based nanohybrid paper and explore its practical application as high-performance electrode in flexible supercapacitor. The freestanding and flexible graphene paper was firstly fabricated by highly reproducible printing technique and bubbling delamination method, by which the area and thickness of the graphene paper can be freely adjusted in a wide range. The as-prepared graphene paper possesses a collection of unique properties of highly electrical conductivity (340 S cm−1), light weight (1 mg cm−2) and excellent mechanical properties. In order to improve its supercapacitive properties, we have prepared a unique sandwich-structured graphene/polyaniline/graphene paper by in situ electropolymerization of porous polyaniline nanomaterials on graphene paper, followed by wrapping an ultrathin graphene layer on its surface. This unique design strategy not only circumvents the low energy storage capacity resulting from the double-layer capacitor of graphene paper, but also enhances the rate performance and cycling stability of porous polyaniline. The as-obtained all-solid-state symmetric supercapacitor exhibits high energy density, high power density, excellent cycling stability and exceptional mechanical flexibility, demonstrative of its extensive potential applications for flexible energy-related devices and wearable electronics.

Encapsulating Pd nanoparticles in double-shelled graphene@carbon hollow spheres for excellent chemical catalytic property.

Double-shelled hollow carbon spheres with reduced graphene oxide (RGO) as inner shell and carbon (C) layer as outer shell have been successfully designed and prepared. This tailor-making structure acts as an excellent capsule for encapsulating with ultrafine Pd nanoparticles (Pd NPs), which could effectively prevent Pd NPs from aggregation and leaching. As a result, the as-obtained RGO@Pd@C nanohybid exhibits superior and stable catalytic performance. With the aid of RGO@Pd@C, the reduction reaction of 4-nitrophenol (4-NP) to 4-aminophenol with NaBH4 as reducing agent can be finished within only 30 s, even the content of Pd is as low as 0.28 wt%. As far as we know, RGO@Pd@C is one of the most effective catalyst for 4-NP reducing reaction up to now.

Advanced solid-state asymmetric supercapacitors based on 3D graphene/MnO2 and graphene/polypyrrole hybrid architectures

A three-dimensional graphene wrapped nickel foam (Ni/GF) architecture has been prepared by a facile yet effective and scalable interfacial reduction method. Inspired by the porous and conductive network structures of Ni/GF, we have deposited manganese dioxide (MnO2) and polypyrrole (PPy) nanostructures on the Ni/GF substrates and successfully fabricated a flexible solid-state asymmetric supercapacitor assembled with Ni/GF/MnO2 as the positive electrode and Ni/GF/PPy as the negative electrode in a gel electrolyte. Benefiting from the high capacitance and fast ion transport properties of our hierarchically porous electrodes, the optimized asymmetric supercapacitor exhibits an excellent stability in a high-voltage region of 1.8 V and remarkable cycling stability with only 9.8% decrease of capacitance after 10 000 cycles. Moreover, the device can deliver a high energy density of 1.23 mW h cm−3, which is substantially enhanced compared to most of the reported solid-state supercapacitors. The impressive results presented here may pave the way for promising applications in future energy storage systems.

Bifunctional Nanocatalyst Based on Three-Dimensional Carbon Nanotube–Graphene Hydrogel Supported Pd Nanoparticles: One-Pot Synthesis and Its Catalytic Properties

We reported the development of a new type of bifunctional nanocatalyst based on three-dimensional (3D) macroscopic carbon nanotube (CNT)-graphene hydrogel (GH) supported Pd nanoparticles (i.e., Pd-CNT-GH) and explored its practical application in catalytic reduction of p-nitrophenol to p-aminophenol. The 3D Pd-CNT-GH was synthesized by a facile one-pot self-assembled approach through hydrothermal treatment of a mixed aqueous precursor solution of PdCl4(2-), CNT, and graphene oxide (GO). Under the appropriate condition, the spontaneous redox reaction between precursor PdCl4(2-) and CNT-GO as well as the self-assembly of macroscopic CNT-GH occurs simultaneously, leading to the formation of 3D Pd-CNT-GH. Because of the unique structural and functional properties of different components in the nanocatalyst and the synergistic effect between them, the as-prepared Pd-CNT-GH exhibits superior catalytic performance toward the reduction of p-nitrophenol to p-aminophenol, with 100% conversion within 30 s, even when the content of Pd in it is as low as 2.98 wt %. Moreover, after 20 successive cycles of reactions, the reaction time still keeps within 46 s. Therefore, the rational design of 3D macroscopic graphene-based nanohybrid material supported highly catalytically active nanoparticles, combined with the facile one-pot self-assembled strategy, provide a universal platform to fabricate desired 3D multifunctional nanomaterials that can be used in a broad range of catalysis, environmental protection, energy storage and conversation, drug delivery, chemical and biological sensing, and so forth.

Functionalized carbonaceous fibers for high performance flexible all-solid-state asymmetric supercapacitors

Fiber based supercapacitors are promising energy storage devices for flexible electronics because of their integration of lightweight, high flexibility and tiny volume. Here, a facile yet effective method is developed to synthesize two types of functionalized carbonaceous fibers, i.e., carbon fiber@reduced graphene oxide@manganese dioxide (CF@RGO@MnO2) and CF@thick RGO (CF@TRGO), by dip coating and subsequent electrochemical strategies. The assembled asymmetric supercapacitor device using CF@RGO@MnO2 as the positive electrode and CF@TRGO as the negative electrode can be operated with a high voltage region of 1.6 V and exhibits a high volumetric energy density of 1.23 mW h cm−3. Additionally, our device has an excellent long-term cycling stability with more than 91% retention after 10 000 cycles. To demonstrate potential applications of our prepared fiber based all-solid-state asymmetric supercapacitors, we successfully use them to power a flexible integrated copper phthalocyanine (CuPc) photodetector and a light-emitting diode.

Fiber-based multifunctional nickel phosphide electrodes for flexible energy conversion and storage

A fiber-based multifunctional nickel phosphide (NiPx) electrode has been successfully prepared by facile electrodeposition of nickel nanoparticle arrays on a commercial carbon fiber (CF) followed by low-temperature phosphidation. As a result of the synergistic effect from the 3D porous structure, enhanced conductivity, and the two active components Ni2+ and Pδ− with rich valences, the resulting vertically aligned NiPx nanoflakes grown on the CF (CF@NiPx) electrode exhibit superior bifunctional electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance in an alkaline electrolyte as well as an ultrahigh specific volumetric capacitance of 817 F cm−3 at a current density of 2 mA cm−2. For practical applications, an efficient CF@NiPx-based alkaline water electrolyzer, with strong durability, can achieve 10 mA cm−2 water-splitting current at a cell voltage of only 1.61 V (iR uncorrected). Besides, a fiber-based flexible solid-state asymmetric supercapacitor device with CF@NiPx as the cathode and reduced graphene oxide attached on CF@Ni (CF@Ni@RGO) as the anode was observed to achieve a remarkable volumetric energy density of 8.97 mW h cm−3, excellent flexibility and superior long term cycling stability. All these results render our fiber-based CF@NiPx electrodes as an ideal platform for electrocatalysis and flexible electrochemical energy storage applications.