Graphene-based materials for energy applications
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Introduction The development of clean and renewable energy is vital to meet ever-increasing global energy demands arising from rapid economic expansion and increasing world population, while minimizing fossil-fuel depletion, pollution, and global warming.1 Currently, new technologies for energy conversion (e.g., solar cells and fuel cells) and energy storage (e.g., supercapacitors and batteries) are under intensive research. Because the performance of these devices depends strongly on the materials employed, various emerging nanomaterials with desired nanostructures and large surface/interface areas have been developed for applications in energy-related devices.2 Of particular interest are carbon nanomaterials for energy applications. Graphene, in particular, has received considerable attention because of its unique properties, including high thermal conductivity (∼5000 W m–1 K–1), high electrical conductivity (108 S m–1), high transparency (absorbance of 2.3%), great mechanical strength (breaking strength of 42 N m–1 and Young’s modulus of 1.0 TPa), inherent flexibility, high aspect ratio, and large specific surface area (2.63 × 106 m2 kg–1).3,4 Graphene sheets of different sizes and defect contents can be prepared by various approaches, including manual mechanical cleavage of graphite with adhesive tape,3 epitaxial growth on single-crystal SiC,5 chemical vapor deposition (CVD) on metal surfaces,6 oxidation–exfoliation–reduction of graphite powder,7
exfoliation of graphite through sonication/intercalation,8 and organic coupling reactions.9 Among these approaches, oxidation– exfoliation of graphite, followed by solution reduction, can be used to achieve large-scale production of graphene.8 Graphene can also be readily doped with heteroatoms10 (e.g., nitrogen, boron) or modified with organic molecules, polymers, or inorganic components.11 The resultant soluble graphene derivatives can be processed into functional films by solution processing for many functional devices, such as sensors, actuators, fieldeffect transistors, solar cells, supercapacitors, and batteries.12–17 In this article, we summarize progress in the development of graphene-based materials for energy-conversion and -storage applications and discuss some challenges in this exciting field.
Graphene for energy conversion It is estimated that the world will need to double its energy supply by 2050,1 so it is of paramount importance to develop new types of energy sources. Compared to conventional energy materials, carbon nanomaterials exhibit unusual sizeand surface-dependent (e.g., morphological, electrical, optical, and mechanical) properties that enhance energy-conversion performance. Specifically, considerable efforts have been expended to exploit the unique properties of graphene in highperformance energy-conversion devices, including solar cells and fuel cells.
Jun Liu, Department of Macromolecular Science and Engineering, Case Western Reserve University; [email protected] Yuhua Xue, Department of Macromolecular Science and Engineering, Case Western Res
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