Direct laser writing of micro-supercapacitors on hydrated graphite oxide films
TL;DR: This work demonstrates the scalable fabrication of a new type of all-carbon, monolithic supercapacitor by laser reduction and patterning of graphite oxide films, which show good cyclic stability, and energy storage capacities comparable to existing thin-filmsupercapacitors.
Abstract: All-carbon microscale supercapacitors can be simply and scalably fabricated by the laser patterning and reduction of graphene oxide.
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TL;DR: It is shown that graphite oxide sheets can be converted by infrared laser irradiation into porous graphene sheets that are flexible, robust, and highly conductive, and hold promise for high-power, flexible electronics.
Abstract: Although electrochemical capacitors (ECs), also known as supercapacitors or ultracapacitors, charge and discharge faster than batteries, they are still limited by low energy densities and slow rate capabilities. We used a standard LightScribe DVD optical drive to do the direct laser reduction of graphite oxide films to graphene. The produced films are mechanically robust, show high electrical conductivity (1738 siemens per meter) and specific surface area (1520 square meters per gram), and can thus be used directly as EC electrodes without the need for binders or current collectors, as is the case for conventional ECs. Devices made with these electrodes exhibit ultrahigh energy density values in different electrolytes while maintaining the high power density and excellent cycle stability of ECs. Moreover, these ECs maintain excellent electrochemical attributes under high mechanical stress and thus hold promise for high-power, flexible electronics.
3,603 citations
TL;DR: The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature, and challenges in producing high-performing electrolytes are analyzed.
Abstract: Electrolytes have been identified as some of the most influential components in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors, pseudocapacitors and hybrid supercapacitors. This paper reviews recent progress in the research and development of ES electrolytes. The electrolytes are classified into several categories, including: aqueous, organic, ionic liquids, solid-state or quasi-solid-state, as well as redox-active electrolytes. Effects of electrolyte properties on ES performance are discussed in detail. The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature. Interaction among the electrolytes, electro-active materials and inactive components (current collectors, binders, and separators) is discussed. The challenges in producing high-performing electrolytes are analyzed. Several possible research directions to overcome these challenges are proposed for future efforts, with the main aim of improving ESs' energy density without sacrificing existing advantages (e.g., a high power density and a long cycle-life) (507 references).
2,480 citations
TL;DR: This review discusses the basic principles of the electrical double-layer (EDL), especially regarding the correlation between ion size/ion solvation and the pore size of porous carbon electrodes, and summarizes the key aspects of various carbon materials synthesized for use in supercapacitors.
Abstract: Electrical energy storage (EES) is one of the most critical areas of technological research around the world. Storing and efficiently using electricity generated by intermittent sources and the transition of our transportation fleet to electric drive depend fundamentally on the development of EES systems with high energy and power densities. Supercapacitors are promising devices for highly efficient energy storage and power management, yet they still suffer from moderate energy densities compared to batteries. To establish a detailed understanding of the science and technology of carbon/carbon supercapacitors, this review discusses the basic principles of the electrical double-layer (EDL), especially regarding the correlation between ion size/ion solvation and the pore size of porous carbon electrodes. We summarize the key aspects of various carbon materials synthesized for use in supercapacitors. With the objective of improving the energy density, the last two sections are dedicated to strategies to increase the capacitance by either introducing pseudocapacitive materials or by using novel electrolytes that allow to increasing the cell voltage. In particular, advances in ionic liquids, but also in the field of organic electrolytes, are discussed and electrode mass balancing is expanded because of its importance to create higher performance asymmetric electrochemical capacitors.
2,140 citations
TL;DR: In this paper, the effect of nanostructures on the properties of supercapacitors including specific capacitance, rate capability and cycle stability is discussed, which may serve as a guideline for the next generation of super-capacitor electrode design.
Abstract: Supercapacitors have drawn considerable attention in recent years due to their high specific power, long cycle life, and ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells. Nanostructured electrode materials have demonstrated superior electrochemical properties in producing high-performance supercapacitors. In this review article, we describe the recent progress and advances in designing nanostructured supercapacitor electrode materials based on various dimensions ranging from zero to three. We highlight the effect of nanostructures on the properties of supercapacitors including specific capacitance, rate capability and cycle stability, which may serve as a guideline for the next generation of supercapacitor electrode design.
1,987 citations
TL;DR: This work demonstrates a scalable fabrication of graphene micro-supercapacitors over large areas by direct laser writing on graphite oxide films using a standard LightScribe DVD burner, which demonstrates a power density among the highest values achieved for any supercapacitor.
Abstract: Microscale supercapacitors are promising alternative energy-storage devices; however, their use has been limited by the need for complicated fabrication techniques. This work reports the scalable fabrication of graphene supercapacitors with planar geometry that achieve power densities of up to 200 W cm−3.
1,619 citations
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26,456 citations
TL;DR: CMG materials are made from 1-atom thick sheets of carbon, functionalized as needed, and here their performance in an ultracapacitor cell is demonstrated, illustrating the exciting potential for high performance, electrical energy storage devices based on this new class of carbon material.
Abstract: The surface area of a single graphene sheet is 2630 m2/g, substantially higher than values derived from BET surface area measurements of activated carbons used in current electrochemical double layer capacitors. Our group has pioneered a new carbon material that we call chemically modified graphene (CMG). CMG materials are made from 1-atom thick sheets of carbon, functionalized as needed, and here we demonstrate in an ultracapacitor cell their performance. Specific capacitances of 135 and 99 F/g in aqueous and organic electrolytes, respectively, have been measured. In addition, high electrical conductivity gives these materials consistently good performance over a wide range of voltage scan rates. These encouraging results illustrate the exciting potential for high performance, electrical energy storage devices based on this new class of carbon material.
7,505 citations
TL;DR: A solution-based method is reported that allows uniform and controllable deposition of reduced graphene oxide thin films with thicknesses ranging from a single monolayer to several layers over large areas, which could represent a route for translating the interesting fundamental properties of graphene into technologically viable devices.
Abstract: The integration of novel materials such as single-walled carbon nanotubes and nanowires into devices has been challenging, but developments in transfer printing and solution-based methods now allow these materials to be incorporated into large-area electronics1,2,3,4,5,6. Similar efforts are now being devoted to making the integration of graphene into devices technologically feasible7,8,9,10. Here, we report a solution-based method that allows uniform and controllable deposition of reduced graphene oxide thin films with thicknesses ranging from a single monolayer to several layers over large areas. The opto-electronic properties can thus be tuned over several orders of magnitude, making them potentially useful for flexible and transparent semiconductors or semi-metals. The thinnest films exhibit graphene-like ambipolar transistor characteristics, whereas thicker films behave as graphite-like semi-metals. Collectively, our deposition method could represent a route for translating the interesting fundamental properties of graphene into technologically viable devices.
4,174 citations
TL;DR: Light scattering experiments revealed that the radius of gyration had a linear dependence on the molar mass of the aggregates, which suggests that the particles are in the form of rods or ribbons, or at least some elongated structure.
Abstract: Equivalent weight (EW) is the number of grams of dry Nafion per mole of sulfonic acid groups when the material is in the acid form. This is an average EW in the sense that the comonomer sequence distribution (that is usually unknown to the investigator and largely unreported) gives a distribution in m in this formula. EW can be ascertained by acid-base titration, by analysis of atomic sulfur, and by FT-IR spectroscopy. The relationship between EW and m is EW ) 100m + 446 so that, for example, the side chains are separated by around 14 CF2 units in a membrane of 1100 EW. Common at the time of this writing are Nafion 117 films. The designation “117” refers to a film having 1100 EW and a nominal thickness of 0.007 in., although 115 and 112 films have also been available. Early-reported studies involved 1200 EW samples as well as special experimental varieties, some being rather thin. The equivalent weight is related to the property more often seen in the field of conventional ion exchange resins, namely the ion exchange capacity (IEC), by the equation IEC ) 1000/EW. The mention of the molecular weight of high equivalent weight (EW > 1000 g‚mol-1) Nafion is almost absent in the literature, although the range 105-106 Da has been mentioned. As this polymer does not form true solutions, the common methods of light scattering and gel permeation chromatography cannot be used to determine molecular weight as well as the size and shape of isolated, truly dissolved molecules. Studies of the structure of this polymer in solvent (albeit not a true solution) will be mentioned in the scattering section of this review. It should be noted that Curtin et al. performed size exclusion chromatography determinations of the molecular weight distribution in Nafion aqueous dispersions after they were heated to high temperatures (230, 250, and 270 °C).1 Before heating, there was a high molecular weight shoulder on a bimodal distribution, due to molecular aggregates, but this shoulder disappeared upon heating, which indicated that the aggregates were disrupted. The peaks for the monomodal distribution for the heated samples were all located at molecular weights slightly higher than 105 g‚mol-1. Also, light scattering experiments revealed that the radius of gyration had a linear dependence on the molar mass of the aggregates, which suggests that the particles are in the form of rods or ribbons, or at least some elongated structure. Nafion ionomers are usually derived from the thermoplastic -SO2F precursor form that can be extruded into sheets of required thickness. Strong interactions between the ionic groups are an obstacle to melt processing. This precursor does not possess the clustered morphology that will be of great concern in this article but does possess Teflon-like crystallinity which persists when the sulfonyl fluoride form is converted to, for example, the K+ form by reacting it with KOH in water and DMSO. Thereafter, the -SO3H form is achieved by soaking the film in a sufficiently concentrated aqueous acid solution. Extrusion of the sulfonyl fluoride precursor can cause microstructural orientation in the machine direction, * Address correspondence to either author. Phone: 601-266-5595/ 4480. Fax: 601-266-5635. E-mail: Kenneth.Mauritz@usm.edu; RBMoore@usm.edu. 4535 Chem. Rev. 2004, 104, 4535−4585
4,130 citations
TL;DR: In this paper, it is suggested that the molecular mechanism behind prototropic mobility involves a periodic series of isomerizations between H 9 O 4 + and H 5 O 2 +, the first trigerred by hyrdogen-bond cleavage of a second-shell water molecule and the second by the reverse, hydrogen-bonder formation process.
2,664 citations