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.

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 ] photovoltaics [ 12 , 13 ] and light emitting diodes. [ 14 , 15 ] The development of new types of QD will allow control of the fundamental properties of materials through size/shape effects, which will further allow new devices to be developed with extraordinary properties and functions for numerous applications. Nowadays, the study of 2D graphene nanosheets [ 16 ] and 1D nanoribbons [ 17 ] has been on the high-speed track. However, the development of 0D GQDs remains inchoate and synthesis is only a recent effort. Pan and co-workers presented a hydrothermal method for cutting preoxidized graphene sheets into GQDs (approximately 10 nm in size) with blue emissions due to the large edge effect of GQDs. [ 18 ] Interestingly, graphene moieties containing certain conjugated carbon atoms have also been synthesized through solution chemistry by Müllen and Li, [ 19 , 20 ] which were demonstrated to be attractive for effi cient light harvesting in photovoltaics. [ 21 ] Herein, we report an alternative electrochemical approach for direct preparation of functional GQDs with a uniform size of 3-5 nm, which present a green luminescence and can be retained stably in water for several months without any changes. Polymer photovoltaic devices using GQDs as novel electronacceptor materials are also demonstrated. Although without device optimization in this primary study, a power conversion effi ciency of 1.28% was achieved. We expect our endeavor may further the advancement of less-developed graphenebased QDs.The ...

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][2][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][2][3][4] In this regard, we have devised a facile one-step dimensionallyconfi ned strategy to fabricate the neat GFs by directly hydrothermally assembling graphene within glass pipeline. [ 2 , 5 ] The as-produced GFs have a density of 0.23 g/cm 3 , 7 times and 85 times lower than that of conventional carbon fi bers ( > 1.7 g/cm 3 ) and Au wire (ca. 20 g/cm 3 ), while remaining strong, fl exible, conductive, weavable and shapeable, and their engineered structures with multifunctionalities can be done readily in an in situ or post-synthesis fashion. [ 2 ] These remarkable features of GFs endow them with prominent advantages over common carbon fi ber and metal wires [ 6 ] for development of unconventional, lightweight, fl exible devices, especially in fi ber shape for wearable electronics.The fl ourishing progress of electronics in the unconventional forms has opened a new prospect of future electronics such as smart skins, human friendly devices, and fl exible/stretchable circuitries and energy devices. [7][8][9][10][11][12][13][14][15][16] This new class of electronics can conformably deform into complex, non-planar shapes under bending, stretching, compressing, twisting process while maintaining good performance, reliability and integration. Flexible energy-storage devices have attracted tremendous attentions in recent years due to their promise in integration into stretchable and wearable electronics. [ 7 , 17-23 ] In particular, supercapacitors are of signifi cant interest as energy storage devices associated with their high power density, long cycling life, and short charging time. [ 24 , 25 ] Conventional supercapacitors are heavy and bulky, targeting for the applications in electric or hybrid vehicles, and auxiliary power sources. However, the development of high-effi ciency miniaturized supercapacitor devices compatible with the fl exible and wearable electronics lags except from several recent paradigms. [26][27][28][29][30] 3D graphene structures possess notable features including highly-exposed surface areas, high electrical conductivity, and good chemical stability, and therefore they have been widely explored as electrode materials for supercapacitor applications. [31][32][33][34][35] Herein, we design and fabricate a unique allgraphene core-sheath f...

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 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.