Aqueous dispersions of graphene oxide (GO) have been found to emit a structured, strongly pH-dependent visible fluorescence. Based on experimental results and model computations, this is proposed to arise from quasi-molecular fluorophores, similar to polycyclic aromatic compounds, formed by the electronic coupling of carboxylic acid groups with nearby carbon atoms of graphene. Sharp and structured emission and excitation features resembling the spectra of molecular fluorophores are present near 500 nm in basic conditions. The GO emission reversibly broadens and red-shifts to ca. 680 nm in acidic conditions, while the excitation spectra remain very similar in shape and position, consistent with excited state protonation of the emitting species in acidic media. The sharp and structured emission and excitation features suggest that the effective fluorophore size in the GO samples is remarkably well defined.

Graphene oxide (GO) has drawn tremendous interest as a tunable precursor in numerous areas, due to its readily manipulable surface. However, its inhomogeneous and nonstoichiometric structure makes achieving chemical control a major challenge. Here, we present a room-temperature based, controlled method for the stepwise reduction of GO, with evidence of sequential removal of each organic moiety. By analyzing signature infrared absorption frequencies, we identify the carbonyl group as the first to be reduced, while the tertiary alcohol takes the longest to be completely removed from the GO surface. Controlled reduction allows for progressive tuning of the optical gap from 3.5 eV down to 1 eV, while XPS spectra show a concurrent increase in the C/O ratio. This study is the first step toward selectively enhancing the chemical homogeneity of GO, thus providing greater control over its structure, and elucidating the order of removal of functional groups and hydrazine-vapor reduction.

all need to be used in conjugation with an energy storage system to provide smooth power leveling. Currently, electrochemical energy storage systems are by far the most optimal solutions for powering a broad range of technologies, expanding from compact and light-weighted portable electronic devices to stationary gridscale energy storage applications. [3][4][5][6] These energy storage devices (batteries and supercapacitors) store the available electrical energy in the form of chemical energy and release it whenever needed, by simply reversing the electrochemical reaction. [7][8][9][10][11] Among various available battery chemistries, lithium batteries and supercapacitors are the most promising technologies. [ 7,[9][10][11][12][13][14][15][16][17][18][19][20] Ever since the realization of the fi rst electrochemical energy storage cell by Alessandro Volta (end of 17th century), the working principle and its function has changed very little. [ 21,22 ] Basically, two redox couples (or charge storage electrodes), electrically and physically separated, are bridged by an ion conducting medium to constitute an electrochemical cell. This holds true also for modern Li-ion batteries, although the chemistry involved is much more complex. During operation, the electrons are transferred through an external circuit while ions shuttle through the electrolyte to counterbalance the depleted charge at the electrodes. [ 23 ] So far, much of the effort has been directed towards improvement of the energy and power characteristics by downsizing the active components, re-engineering the current collectors and separators, as well as fi ne-tuning the Batteries have become fundamental building blocks for the mobility of modern society. Continuous development of novel battery chemistries and electrode materials has nourished progress in building better batteries. Simultaneously, novel device form factors and designs with multi-functional components have been proposed, requiring batteries to not only integrate seamlessly to these devices, but to also be a multi-functional component for a multitude of applications. Thus, in the past decade, along with developments in the component materials, the focus has been shifting more and more towards novel fabrication processes, unconventional confi gurations, and additional functionalities. This work attempts to critically review the developments with respect to emerging electrochemical energy storage confi gurations, including, amongst others, paintable, transparent, fl exible, wire or cable shaped, ultra-thin and ultra-thick confi gurations, as well as hybrid energy storage-conversion, or graphene-incorporated batteries and supercapacitors. The performance requirements are elaborated together with the advantages, but also the limitations, with respect to established electrochemical energy storage technologies. Finally, challenges in developing novel materials with tailored properties that would allow such confi gurations, and in designing easier manufacturing techniques that can be widely adopted ar...

Graphene has attracted a great deal of attention because of its unique band structure and electronic properties that make it promising for applications in next-generation electronic devices, transparent flexible conducting electrodes, and sensors. Here, we report the substrate selective growth of centimeter size (∼3.5 cm  1.5 cm), uniform, and continuous single and few-layer graphene films employing chemical vapor deposition technique on polycrystalline Cu foils using liquid precursor hexane. Structural characterizations suggest that as-grown graphene films are mostly single and few layers over large areas. We have demonstrated that these graphene films can be easily transferred to any desired substrate without damage. A liquid-precursor-based synthesis route opens up a new window for simple and inexpensive growth of pristine as well as doped graphene films using various organic liquids containing the dopant atoms.