Liangti Qu

Nitrogen-Doped Graphene as Efficient Metal-Free Electrocatalyst for Oxygen Reduction in Fuel Cells

Nitrogen-doped graphene (N-graphene) was synthesized by chemical vapor deposition of methane in the presence of ammonia. The resultant N-graphene was demonstrated to act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction via a four-electron pathway in alkaline fuel cells. To the best of our knowledge, this is the first report on the use of graphene and its derivatives as metal-free catalysts for oxygen reduction. The important role of N-doping to oxygen reduction reaction (ORR) can be applied to various carbon materials for the development of other metal-free efficient ORR catalysts for fuel cell applications, even new catalytic materials for applications beyond fuel cells.

Nitrogen-Doped Graphene Quantum Dots with Oxygen-Rich Functional Groups

Graphene quantum dots (GQDs) represent a new class of quantum dots with unique properties. Doping GQDs with heteroatoms provides an attractive means of effectively tuning their intrinsic properties and exploiting new phenomena for advanced device applications. Herein we report a simple electrochemical approach to luminescent and electrocatalytically active nitrogen-doped GQDs (N-GQDs) with oxygen-rich functional groups. Unlike their N-free counterparts, the newly produced N-GQDs with a N/C atomic ratio of ca. 4.3% emit blue luminescence and possess an electrocatalytic activity comparable to that of a commercially available Pt/C catalyst for the oxygen reduction reaction (ORR) in an alkaline medium. In addition to their use as metal-free ORR catalysts in fuel cells, the superior luminescence characteristic of N-GQDs allows them to be used for biomedical imaging and other optoelectronic applications.

An Electrochemical Avenue to Green‐Luminescent Graphene Quantum Dots as Potential Electron‐Acceptors for Photovoltaics

Graphene, the two-dimensional (2D) single-atom carbon sheet, has attracted tremendous research interest due to its large surface area, high carrier transport mobility, superior mechanical fl exibility and excellent thermal/chemical stability. [ 1 ] In particular, its high transport mobility [ 2 , 3 ] and environmentally friendly nature meet important requirements in the fabrication of optoelectronic devices. Apart from the conducting fi lm [ 4 , 5 ] and transparent anode [ 6 ] developed previously, its high mobility renders it a promising alternative as an electron-accepting material for photovoltaic device applications. However, the easy aggregation and the poor dispersion of 2D graphene sheets in common solvents limit its application in such devices. Although effort has been made to prepare solution-processable functionalized graphenes (SPFGs), [ 7 ] the non-uniform size and shape, on a scale of several hundred nanometers and even micrometers of SPFGs, remain big challenges for the fabrication of highperformance photovoltaic cells with active layer thicknesses of only nanometer scale. To facilitate the application of graphene in nanodevices and to effectively tune the bandgap of graphenes, a promising approach is to convert the 2D graphene sheets into 0D graphene quantum dots (GQDs). Apart from unique electron transportation properties, [ 8 ] new phenomena from GQDs associated with quantum confi nement and edge effects are expected. [ 9 ] QDs are important for various applications in bioimaging, [ 10 ] lasing, [ 11 ]

Metal-Free Catalysts for Oxygen Reduction Reaction

Liming Dai,*,†,‡ Yuhua Xue,†,‡ Liangti Qu,* Hyun-Jung Choi, and Jong-Beom Baek* †Center of Advanced Science and Engineering for Carbon (Case4Carbon), Department of Macromolecular Science and Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States Key Laboratory of Cluster Science, Ministry of Education of China, Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Department of Chemistry, School of Science, Beijing Institute of Technology, Beijing 100081, People’s Republic of China School of Energy and Chemical Engineering/Center for Dimension-Controllable Covalent Organic Frameworks, Ulsan National Institute of Science and Technology (UNIST), 100 Banyeon, Ulsan, 689-798, South Korea

All‐Graphene Core‐Sheath Microfibers for All‐Solid‐State, Stretchable Fibriform Supercapacitors and Wearable Electronic Textiles

Flexible graphene fi ber (GF) stands for a new type of fi ber of practical importance, which integrates such unique properties as high strength, electrical and thermal conductivities of individual graphene sheets into the useful, macroscopic ensembles. GFs possess the common characteristics of fi bers like the mechanical fl exibility for textiles, while maintaining the uniqueness such as low cost, light weight, and ease of functionalization in comparison with conventional carbon fi bers. [ 1–3 ] Due to the extraordinary challenge to assemble two-dimensional (2D) microcosmic graphene sheets with irregular size and shape into macroscopic fi brillar confi guration, however, the success in fabrication of neat graphene fi bers only comes true recently. [ 1–4 ]

A Versatile, Ultralight, Nitrogen‐Doped Graphene Framework

Graphene lite: a density of (2.1 ± 0.3) mg cm(-3), the lowest to date for a graphene framework architecture, is achieved by preparing an ultralight, N-doped, 3D graphene framework (see photo of a block of the material balancing on a dandelion). Its adsorption capacity for oils and organic solvents is much higher than that of the best carbonaceous sorbents, and it is a promising electrode material for supercapacitors (484 F g(-1)) and as a metal-free catalyst for the oxygen reduction reaction.

Carbon Nanotube Arrays with Strong Shear Binding-On and Easy Normal Lifting-Off

The ability of gecko lizards to adhere to a vertical solid surface comes from their remarkable feet with aligned microscopic elastic hairs. By using carbon nanotube arrays that are dominated by a straight body segment but with curly entangled top, we have created gecko-foot–mimetic dry adhesives that show macroscopic adhesive forces of ∼100 newtons per square centimeter, almost 10 times that of a gecko foot, and a much stronger shear adhesion force than the normal adhesion force, to ensure strong binding along the shear direction and easy lifting in the normal direction. This anisotropic force distribution is due to the shear-induced alignments of the curly segments of the nanotubes. The mimetic adhesives can be alternatively binding-on and lifting-off over various substrates for simulating the walking of a living gecko.

Highly compression-tolerant supercapacitor based on polypyrrole-mediated graphene foam electrodes.

Deformation-tolerant devices are vital for the development of high-tech electronics of unconventional forms. In this study, a highly compressible supercapacitor has been fabricated by using newly developed polypyrrole-mediated graphene foam as electrode. The assembled supercapacitor performs based on the unique and robust foam electrodes achieves superb compression tolerance without significant variation of capacitances under long-term compressive loading and unloading processes.

Graphene quantum dots: an emerging material for energy-related applications and beyond

In this perspective, we focus on a new type of quantum dots, graphene quantum dots (GQDs). Due to quantum confinement and edge effects, GQDs have presented extraordinary properties, attracting extensive attention from scientists in the fields of chemistry, physics, materials, biology, and other interdisciplinary sciences. Herein, we summarize the significant advances achieved by us and other groups in the past few years on both the experimental and theoretical fronts. Synthetic strategies, unique optical and electronic properties, and the promise of GQDs in energy-related devices, such as photovoltaic devices, fuel cells, and light-emitting diodes, are systematically discussed.

Facile Fabrication of Light, Flexible and Multifunctional Graphene Fibers

Macroscopic graphene fibers with strength comparable to carbon nanotube yarns have been fabricated with a facile dimensionally-confined hydrothermal strategy from low-cost, aqueous graphite oxide suspensions, which is shapable, weavable, and has a density of less than 1/7 conventional carbon fibers. In combination with the easy in situ and post-synthesis functionalization, the highly flexible graphene fibers can be woven into smart textiles.