Vol. 21 • No. 5 • March 8 • 2011 www.afm-journal.de AADFM21-5-COVER.inddDFM21-5-COVER.indd 1 22/11/11/11/11 66:50:31:50:31 PPMM www.afm-journal.de www.MaterialsViews.com Carbide-Derived Carbons – From Porous Networks to Nanotubes and Graphene Volker Presser , Min Heon , and Yury Gogotsi * FEATURE ARTICLE FEATURE from carbides has attracted special atten- Carbide-derived carbons (CDCs) are a large family of carbon materials derived tion lately. [ 3,4 ] Carbide-derived carbons from carbide precursors that are transformed into pure carbon via physical (CDCs) encompass a large group of car- (e.g., thermal decomposition) or chemical (e.g., halogenation) processes. bons ranging from extremely disordered to highly ordered structures ( Figure 1 ). The Structurally, CDC ranges from amorphous carbon to graphite, carbon nano- carbon structure that results from removal tubes or graphene. For halogenated carbides, a high level of control over the of the metal or metalloid atom(s) from the resulting amorphous porous carbon structure is possible by changing the carbide depends on the synthesis method synthesis conditions and carbide precursor. The large number of resulting (halogenation, hydrothermal treatment, carbon structures and their tunability enables a wide range of applications, vacuum decomposition, etc.), applied tem- perature, pressure, and choice of carbide from tribological coatings for ceramics, or selective sorbents, to gas and precursor. electrical energy storage. In particular, the application of CDC in supercapac- The growing interest in this fi eld is itors has recently attracted much attention. This review paper summarizes refl ected by a rapidly increasing number key aspects of CDC synthesis, properties, and applications. It is shown that of publications and patents. A signifi cant the CDC structure and properties are sensitive to changes of the synthesis progress in CDC research has been seen in parameters. Understanding of processing–structure–properties relationships several fi elds. Various carbide precursors have been systematically studied. Studies facilitates tuning of the carbon material to the requirements of a certain on binary carbides with different grain application. sizes show the possibility of low-temper- ature carbon formation for nanopowders. Also, a better understanding of graphene 1. Introduction formation during high-temperature vacuum decomposition of silicon carbide has been achieved since SiC single crystals are In parallel with the rise of nanomaterial research and applica- now available in large sizes with extremely low defect concen- tions, interest in carbons as multipurpose materials has spiked trations and an almost atomically fl at surface fi nish. [ 8 ] in recent years. [ 1,2 ] One fi eld in particular has attracted atten- CDC applications as electrode materials in electric double tion: carbon materials for energy-related applications such as layer capacitors have attracted much attention lately. [ 9 ] The batteries, supercapacitors, fuel cells, and gas storage. [ 1 ] It is nec- unique properties of porous CDC obtained by halogenation, essary to understand the relationship between carbon structure such as a high specifi c surface area and tunable pore size with and the resulting properties to be able to tune and optimize a narrow size distribution, make it an ideal material for sorb- the carbon material to meet application requirements. With ents or supercapacitor electrodes. CDCs have been derived carbon materials existing in a variety of forms (amorphous and from many precursors (SiC, TiC, Mo C, VC, etc.) using a crystalline; sp 2 and sp 3 hybridization; porous and dense; fi lms, 2 variety of treatment conditions that lead to a broad range of particles, nanotubes, and fi bers) numerous applications are useful properties. Furthermore, graphene, [ 10 ] nanotubes, [ 11 ] possible, [ 2 ] but selecting the best material for a specifi c applica- and even nanodiamond [ 12 ] can be produced from carbide tion may be challenging. precursors. Their applications naturally differ from those of Porous carbons, fullerenes, nanotubes and, more recently, porous CDC. graphene are among the most widely studied materials. While The last comprehensive journal review on this subject was there are numerous methods of synthesizing carbon materials published about fi fteen years ago in Russian; [ 13 ] book chapters from gaseous, solid, and liquid precursors, their synthesis published later [ 3,4 , 14 ] are less accessible and require updating due to rapid progress in the fi eld over the past few years. [14] V. Presser , M. Heon , Prof. Y. Gogotsi The most recent review of CDC covers only energy-related Department of Materials Science & Engineering and A.J. Drexel applications. Therefore, a comprehensive review on the fi eld is Nanotechnology Institute long overdue. The goal of this article is to show how a variety Drexel University of carbon structures can be produced from carbides, to explain 3141 Chestnut St., Philadelphia, PA 19104, USA how those structures can be controlled on the nanometer and E-mail: [email protected] subnanometer scale, and to describe CDC properties that are DOI: 10.1002/adfm.201002094 benefi cial for a number of applications. 810 wileyonlinelibrary.com © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Funct. Mater. 2011, 21, 810–833 www.afm-journal.de www.MaterialsViews.com FEATURE ARTICLE FEATURE Volker Presser received his PhD from the Eberhard Karls Universität in Tübingen, Germany. Being awarded the Feodor Lynen Research Fellowship from the Alexander von Humboldt Foundation, he joined Drexel University, Philadelphia, as a post- doctoral researcher in 2010. As the leader of the carbide- derived carbons group, he investigates the correlation between structure and properties of carbon nanomaterials. Min Heon is a PhD student at Drexel University. He received his B.S. and M.S. degrees in Materials Science and Engineering from Pohang University of Science and Technology (POSTECH) in Korea and worked for Samsung Corning as a research engineer for eight years developing materials and devices related to LCD display technologies. His research is concerned with new devices for electric energy storage and he explores patterned carbide-derived carbon fi lms for application in micro-supercapacitors. Yury Gogotsi is Distinguished University Professor and Trustee Chair in the Department of Materials Science and Engineering at Figure 1 . Transmission electron microscopy images of various CDC Drexel University. He also structures as obtained from carbide chlorination[ 4 , 5 ] (a–g, j) and vacuum serves as director of the decomposition of SiC [ 6,7 ] (h–i). Amorphous porous carbon (a), turbos- A.J. Drexel Nanotechnology tratic carbon (b), fullerene-like carbon (c), nano-diamond (d), onion-like Institute. He received his carbon (e), carbon nano-barrels (f), mesoporous carbon (g), carbon MS (1984) and PhD (1986) nanotubes (h), epitaxial graphene (i), graphite (j). The scale bar is 5 nm. degrees from Kiev Polytechnic Reproduced with permission. [ 4 ] Copyright 2006, CRC Taylor & Francis. Reproduced with permission. [ 5–7 ] Copyright 2008-2010, Elsevier. and a DSc degree from the Ukrainian Academy of Science in 1995. His current research is focused on carbon nanomaterials. 2. Nomenclature Over the years, different terms were used for CDCs, such as “mineral carbons” [ 15 ] or “nanoporous carbons” (NPC). [ 13 ] While carbon, for example, has been referred to as SiC-CDC, [ 16 ] the former has been out of use for a long time, the latter does SiC-DC, [ 17 ] Si-CDC, [ 18 ] or SiCDC. Since the latter two, however, not refl ect the variety of carbon structures present in the CDC do not indicate the different stoichiometries of the precursor family and does not differentiate between CDC and an acti- (e.g., B4 C, TiC0.5 , or WC vs. W2 C) and are not applicable to car- vated or template carbon with nanoscale porosity. In recent bons derived from carbonitrides (e.g., SiCN) and other complex years, most studies refer to CDC using a nomenclature that compounds, they should not be used. We will use the “pre- clearly indicates the carbide precursor. Silicon carbide-derived cursor-CDC” terminology and recommend its use in future Adv. Funct. Mater. 2011, 21, 810–833 © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 811 www.afm-journal.de www.MaterialsViews.com publications as the most descriptive term. This nomenclature unlike that in activated carbon. Remaining residual chlorine or can also be used for a more general description of precursor metal chlorides can be removed by annealing, for example, in type, such as PDC-CDC (polymer-derived ceramics). For CDC hydrogen gas. From the experience of large-scale SiCl4 synthesis, derived from ordered mesoporous (OM) carbide precursors, it is clear that CDC synthesis process can be easily scaled up to [19] the nomenclature OM-CDC was introduced in analogy to manufacturing commercial quantities of carbon per year. [20] OM-SiC. In this regard, we suggest using a more specifi c For many binary carbides (e.g., M = Si, Ti, Zr), Equation 2 term, like OM-SiC-CDC, which clearly indicates the precursor yields both gaseous MCl4 and solid carbon in the temperature and not just the resulting structure. range of interest: [ 23–25 ] + → + MC(s) 2Cl2(g) MCl4(g) C(s) (2) FEATURE ARTICLE FEATURE 3. CDC Synthesis and Structure The carbon formation by selective carbide etching is possible Several chemical reactions and physical processes can be used for other binary carbides and different halogens[ 26–30 ] leading to for CDC synthesis. Halogenation and especially chlorination a more general reaction equation: has become one of the key synthetic methods for large-scale production of CDC. All CDC synthesis methods have one · + y · → + · x MC(s) 2 A2(g) MxAy(g) x C(s) (3) aspect in common: carbon is formed by selective extraction of the metal or metalloid atoms, transforming the carbide struc- where A is a gaseous halogen (F2 , Cl2 , Br2 , I2 , or mixtures ture into pure carbon. In this way, the carbon layer is formed by thereof) or a halogen-containing etchant (e.g., HCl, HF), and inward growth, usually with the retention of the original shape Mx Ay a gaseous reaction product.