Shibing Ye

Deposition of Three-Dimensional Graphene Aerogel on Nickel Foam as a Binder-Free Supercapacitor Electrode

We reported a new type of graphene aerogel-nickel foam (GA@NF) hybrid material prepared through a facile two-step approach and explored its energy storage application as a binder-free supercapacitor electrode. By simple freeze-drying and the subsequent thermal annealing of graphene oxide hydrogel-NF hybrid precursor, three-dimensional graphene aerogels with high mass, hierarchical porosity, and high conductivity were deposited on a NF framework. The resulting binder-free GA@NF electrode exhibited satisfactory double-layer capacitive behavior with high rate capability, good electrochemical cyclic stability, and a high specific capacitance of 366 F g(-1) at a current density of 2 A g(-1). The versatility of this approach was further verified by the successful preparation of 3D graphene/carbon nanotube hybrid aerogel-NF as a supercapacitor electrode, also with improved electrochemical performance. With advantageous features, such a facile and versatile fabrication technique shows great promise in the preparation of various types of carbon-metal hybrid electrodes.

Self-Assembled Three-Dimensional Hierarchical Graphene/Polypyrrole Nanotube Hybrid Aerogel and Its Application for Supercapacitors

A three-dimensional hierarchical graphene/polypyrrole aerogel (GPA) has been fabricated using graphene oxide (GO) and already synthesized one-dimensional hollow polypyrrole nanotubes (PNTs) as the feedstock. The amphiphilic GO is helpful in effectively promoting the dispersion of well-defined PNTs to result in a stable, homogeneous GO/PNT complex solution, while the PNTs not only provide a large accessible surface area for fast transport of hydrate ions but also act as spacers to prevent the restacking of graphene sheets. By a simple one-step reduction self-assembly process, hierarchically structured, low-density, highly compressible GPAs are easily obtained, which favorably combine the advantages of graphene and PNTs. The supercapacitor electrodes based on such materials exhibit excellent electrochemical performance, including a high specific capacitance up to 253 F g(-1), good rate performance, and outstanding cycle stability. Moreover, this method may be feasible to prepare other graphene-based hybrid aerogels with structure-controllable nanostructures in large scale, thereby holding enormous potential in many application fields.

Highly elastic graphene oxide–epoxy composite aerogels via simple freeze-drying and subsequent routine curing

In this study, highly elastic graphene oxide–epoxy composite aerogel (GEA) was fabricated by a facile method, in which the mixed suspension of the thermoset epoxy precursors and graphene oxide sheets was freeze-dried, followed by a routine curing process. The resulting GEA with a three-dimensional network structure not only exhibits a high decomposition temperature (286 °C), excellent mechanical strength (0.231 MPa) and extremely low density (0.09 g cm−3), but also achieves high elasticity, as it recovers from a large compressive strain without significant permanent deformation. The exceptional properties of our obtained GEA provide the potential for a range of practical applications in energy-absorbing and durable insulation materials, and the convenient synthetic approach could also be utilized in the fabrication of other organic–inorganic composite aerogels with outstanding mechanical properties.

Core–shell-like structured graphene aerogel encapsulating paraffin: shape-stable phase change material for thermal energy storage

The development of energy storage materials is critical to the growth of sustainable energy infrastructures in the coming years. Here, a composite phase change material (PCM) based on graphene and paraffin was designed and prepared through a modified hydrothermal method. Graphene oxide sheets were reduced and self-assembled into three-dimensional graphene aerogels consisting of numerous hollow graphene cells, and paraffin was simultaneously encapsulated into the cells in the form of micrometer-scale droplets during the hydrothermal process. The resulting core–shell-like structured, composite PCM exhibits a high encapsulation ratio of paraffin, large phase change enthalpy, and excellent cycling performance. Due to the unique encapsulated structure and continuous graphene network in the matrix, such a composite PCM holds a good shape-stable property, which prevents the leakage of paraffin above its melting point. In addition, it inherits the intrinsic thermally and electrically conductive nature of the embedded graphene, and thus shows enhanced thermal and electrical conductivity compared to pure paraffin. This novel composite PCM can realize efficient thermal energy storage and demonstrates the potential to be directly used as an actual thermal storage device without containers.

A new insight into the in situ thermal reduction of graphene oxide dispersed in a polymer matrix

By comparing the reduction temperatures of graphene oxide dispersed in non-polar, polar and aromatic polymers, we proposed a mechanism that the interactions between graphene oxide and polymers play a key role in decreasing the reduction temperature of graphene oxide dispersed in a polymer matrix.

Temperature-dependent compatibilizing effect of graphene oxide as a compatibilizer for immiscible polymer blends

We demonstrated the compatibilizing effect of graphene oxide (GO) in the immiscible poly(methyl methacrylate)/polystyrene (PMMA/PS, 80/20) blend and showed that such a compatibilizing effect was affected by the processing temperature. For the blends prepared at a relatively low temperature (190 °C), the incorporation of 0.5 wt% of GO results in a dramatic reduction in the domain diameter of dispersed minor phase (PS), indicating that GO is an effective compatibilizer. Increasing the processing temperature decreases the dispersed phase size reduction, illustrating that the compatibilizing effect of GO is adverse to processing temperature. The characterization results including the changes in chemical composition of GO and morphologies evolution of blends at different annealing temperatures reveal that this temperature-dependent compatibilizing effect should be attributed to the in situ thermal reduction of GO during the melt processing, which breaks the hydrophilicity-hydrophobicity balance of GO and renders it more hydrophobic. A comparative experiment shows that chemically reduced GO has almost no compatibilizing effect for PMMA/PS blends, which further confirms the proposed mechanism. In addition, the GO-compatibilized blends exhibit great improvement in the mechanical properties than uncompatibilized blends.

Fracture Mechanism and Toughness Optimization of Macroscopic Thick Graphene Oxide Film

Combined high strength and toughness of film materials are rather important for their industrial applications. As a new class of films, graphene oxide films (GOFs) attract intense attention in many applications but are frequently divergent, inconsistent, and poorly reproducible in their mechanical properties. In this study, we first demonstrate that different chemical compositions and assembly structures probably are responsible for the difference in elongations between cast GOFs and filtration GOFs. Comprehensive analysis of the morphologies and mechanical properties indicates that the enhanced elongation of the thick cast GOFs is mainly attributed to the presence of a unique skin-wrinkles-skin structure, which more easily forms in cast GOFs than in filtration counterparts. On the basis of this finding, we attempt to optimize the strength-toughness performance of the cast GOFs by adjusting their structures. With an appropriate thickness of 12.5 μm, the GOFs can achieve an ultrahigh toughness up to 4.37 MJ m−3, which is even comparable to the polymer-toughening graphene/GO-based paper-like materials. Such an optimization of the mechanical properties from the perspective of skin-wrinkles-skin structure appears to be a universal approach that could be extended to a variety of other film materials.

Towards three-dimensional, multi-functional graphene-based nanocomposite aerogels by hydrophobicity-driven absorption

By skillfully taking advantage of the high oil-absorption capacity of hydrophobic graphene aerogels (GAs), a novel, facile, scalable, and versatile approach is put forward for the preparation of three-dimensional, multi-functional graphene-based nanocomposite aerogels. Through the simple hydrophobicity-driven absorption of organic solutions containing functional modifiers, high-strength GA/polymer and magnetic GA/metal oxide aerogels were obtained.

Low-Density, Mechanical Compressible, Water-Induced Self-Recoverable Graphene Aerogels for Water Treatment

Graphene aerogels (GAs) have demonstrated great promise in water treatment, acting as separation and sorbent materials, because of their high porosity, large surface area, and high hydrophobicity. In this work, we have fabricated a new series of compressible, lightweight (3.3 mg cm-3) GAs through simple cross-linking of graphene oxide (GO) and poly(vinyl alcohol) (PVA) with glutaraldehyde. It is found that the cross-linked GAs (xGAs) show an interesting water-induced self-recovery ability, which can recover to their original volume even under extremely high compression strain or after vacuum-/air drying. Importantly, the amphiphilicity of xGAs can be adjusted facilely by changing the feeding ratio of GO and PVA and it exhibits affinity from polar water to nonpolar organic liquids depended on its amphiphilicity. The hydrophobic xGAs with low feeding ratio of PVA and GO can be used as adsorbent for organic liquid, while the hydrophilic xGAs with high feeding ratio of PVA and GO can be used as the filter material to remove some water-soluble dye in the wastewater. Because of the convenience of our approach in adjusting the amphiphilicity by simply changing the PVA/GO ratio and excellent properties of the resulting xGAs, such as low density, compressive, and water-induced self-recovery, this work suggests a promising technique to prepare GAs-based materials for the water treatment in different environment with high recyclability and long life.

The effect of sonication treatment of graphene oxide on the mechanical properties of the assembled films

Graphene oxide films (GOFs) are candidates for structural materials in many applications, but their mechanical properties are frequently divergent, inconsistent, and poorly reproducible. During the fabrication of GOFs, sonication treatment of graphite oxide (GiO) has become a standard step in preparing graphene oxide (GO) solutions prior to assembly. In this work, we systematically studied the effect of sonication treatment of GiO on the mechanical properties of the final GOFs. GOF made from the initial sonication-free GiO solution has large elongation but very low fracture strength and toughness, mainly due to the inhomogeneous structures formed with the incompletely exfoliated GiO flakes. In contrast, a mild sonication within 2 min fully exfoliates the GiO flakes and simultaneously maintains a large amount of large-size GO sheets. The resulting GOF achieves a good balance of both high strength and large elongation, and hence exhibits a superior toughness (1.09 ± 0.14 MJ m−3). However, when further increasing the sonication time to 10, 30, or 60 min, the mechanical properties of GOFs gradually deteriorate, primarily attributed to the significantly reduced GO sizes under intense continuous sonication. Our study provides an insight into the relationship between the sonication time of GiO and the mechanical properties of GOFs, and this knowledge may help to devise better strategies to achieve high-performance GOFs and other GO-based materials.