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This article can be cited before page numbers have been issued, to do this please use: J. N. Wang, B. Zou, X. X. Wang and X. X. Huang, Chem. Commun., 2014, DOI: 10.1039/C4CC08197H.
This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
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Continuous synthesis of graphene sheets by spray pyrolysis and their uses as catalysts for fuel cells† Biao Zou, Xiao Xia Wang, Xin Xin Huang, Jian Nong Wang*
Graphene sheets (GNS) were synthesized continuously by spray pyrolysis of iron carbonyl and pyridine. The Pt catalyst supported on GNS exhibited an excellent durability for oxygen reduction reaction (ORR). The GNS, when used as a metal-free catalyst for ORR, showed a performance even better than the commercial Pt/C catalyst. Graphene, a single-atom-thick sheet with a two dimensional hexagonal structure, has attracted tremendous attentions, due to its special physical and chemical properties, such as the outstanding electronic transport capability, thermal conductivity, mechanical strength and specific surface area.1-4 To date, many methods have been developed to prepare graphene. Mechanical exfoliation has been proved to be a good approach to prepare graphene with high quality.5 Moreover, monolayer graphene could be exfoliated from graphite in some solvents by ultrasonication.6 But the yield of graphene by this physical exfoliation was extremely low and also affected by the solvent used. To address this issue, chemical methods have been proposed. A typical example is the reduction of graphene oxide (GO), which can be used to achieve mass production of graphene sheets (GNS).7 Unfortunately, the prepared GNS had a large amount of structural defects, resulting in a poor graphitic structure and thus poor electrical and chemical properties.8,9 Chemical vapor deposition (CVD) has been used to prepare largearea GNS. This is based on the deposition on an immovable substrate, such as Ni, Ru, Ir, Cu, Pt, and SiC.10-15 It was found to be difficult to control the thickness of GNS and remove the substrate, and the size was limited by the size of the substrate used. Apparently, the preparation of GNS with a well-developed graphitic structure, particularly in a continuous mode which is essential for large scale production, is still lacking and thus needs investigations. In this communication, we report a novel strategy to continuously prepare high-quality GNS with a well-developed graphitic structure. This was achieved by spray pyrolysis of a mixture of iron pentacarbonyl (Fe(CO)5) and pyridine (C5H5N). Iron nanoparticles from Fe(CO)5 served as substrates for the deposition of carbon atoms from C5H5N. Carbonyl and pyridine were mixed at different volume ratios and pyrolysized at different temperatures. Typical experiments are listed as G1 (100:1, 900 °C), G2 (50:1, 900 °C), G3 (25:1, 900 °C), and G4 (100:1, 1000 °C). Nano-X Research Center, School of Mechanical and Power Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, P. R. China. * E-mail for Jian Nong Wang: [email protected] †Electronic Supplementary Information (ESI) available: Experimental procedures and characterization. See DOI: 10.1039/c000000x/
This journal is © The Royal Society of Chemistry 2014
The reaction solutions were supplied from the top of a quartz reactor, and samples were continuously collected at the bottom. After the removal of Fe substrates, GNS with several graphitic layers were obtained. (See ESI† for experimental details and Fig. S1.) (a)
(b)
5 nm
(c)
(d)
100 nm
Fig. 1. TEM images of G1 (a, b) and G2 (c, d). Transmission electron microscopy (TEM, JEM-2100) was employed to characterize the morphologies of the samples. Samples G1 (Fig. 1a,b) and G2 (Fig. 1c,d) exhibited a thin sheet structure. The sheets had a thickness of about 1.4 nm, corresponding to several graphitic layers. Except for such GNS, no iron particles were observed. As to the sample of G2, atomic force microscope (AFM, Veeco/DI) characterization further demonstrated that the sample possessed a flake-like structure and the thickness of the GNS (Fig. S2, ESI†) was ~2.0 nm. This result also suggests that the GNS consisted of several graphitic layers. Raman spectroscopy was used to investigate the graphitic structure of GNS. The Raman spectrum for G2 (Fig. S3, ESI†) shows three strong peaks at 1350, 1578 and 2703 cm–1, which are designated as D, G, and 2D peaks, respectively. The D peak is related to the amount of defects, while the G peak to the amount of sp2 hybrid carbon atoms. Therefore, the ratio between the intensities of G and D peaks is often used to estimate the graphitization of carbon materials.16 Based on the Raman spectrum shown in Fig. S3, this ratio was calculated to be 2.8, which is much
J. Name., 2014, 00, 1-3 | 1
ChemComm Accepted Manuscript
Published on 19 November 2014. Downloaded by Rice University on 20/11/2014 08:06:27.
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Intensity (a.u.)
This journal is © The Royal Society of Chemistry 2014
ChemComm Accepted Manuscript
Published on 19 November 2014. Downloaded by Rice University on 20/11/2014 08:06:27.
Intensity (a.u.)
larger than that for chemically reduced graphene oxides.7,9 This N type Relative peak area [%] C1s (a) (b) Sample G2 Pyridinic N 21.97 result indicates that the GNS obtained by our method had a good C (at.%) 92.69 Pyrrolic N 15.59 Graphitic N 62.44 graphitic structure. 2D and G bands indicate the key features of GNS. O (at.%) 3.19 Pyridinic N N (at.%) 3.42 The 2D band peak at 2702 cm-1 is ascribed to the highest optical branch phonons near the K point at the Brillouin zone boundary and Graphitic N the G band peak at 1575 cm-1 is due to the two-fold degenerate E2g Pyrrolic N O1s N1s mode at the Γ-point. The relative intensity ratio of I2D/IG can be used to estimate the number of layers of GNS. The integrity intensity ratios I2D/IG of >2, 1–2, and
ChemComm Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: J. N. Wang, B. Zou, X. X. Wang and X. X. Huang, Chem. Commun., 2014, DOI: 10.1039/C4CC08197H.
This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
www.rsc.org/chemcomm
Page 1 of 4
View Article Online
ChemComm
Journal Name
DOI: 10.1039/C4CC08197H
RSCPublishing
Cite this: DOI: 10.1039/x0xx00000x
Continuous synthesis of graphene sheets by spray pyrolysis and their uses as catalysts for fuel cells† Biao Zou, Xiao Xia Wang, Xin Xin Huang, Jian Nong Wang*
Graphene sheets (GNS) were synthesized continuously by spray pyrolysis of iron carbonyl and pyridine. The Pt catalyst supported on GNS exhibited an excellent durability for oxygen reduction reaction (ORR). The GNS, when used as a metal-free catalyst for ORR, showed a performance even better than the commercial Pt/C catalyst. Graphene, a single-atom-thick sheet with a two dimensional hexagonal structure, has attracted tremendous attentions, due to its special physical and chemical properties, such as the outstanding electronic transport capability, thermal conductivity, mechanical strength and specific surface area.1-4 To date, many methods have been developed to prepare graphene. Mechanical exfoliation has been proved to be a good approach to prepare graphene with high quality.5 Moreover, monolayer graphene could be exfoliated from graphite in some solvents by ultrasonication.6 But the yield of graphene by this physical exfoliation was extremely low and also affected by the solvent used. To address this issue, chemical methods have been proposed. A typical example is the reduction of graphene oxide (GO), which can be used to achieve mass production of graphene sheets (GNS).7 Unfortunately, the prepared GNS had a large amount of structural defects, resulting in a poor graphitic structure and thus poor electrical and chemical properties.8,9 Chemical vapor deposition (CVD) has been used to prepare largearea GNS. This is based on the deposition on an immovable substrate, such as Ni, Ru, Ir, Cu, Pt, and SiC.10-15 It was found to be difficult to control the thickness of GNS and remove the substrate, and the size was limited by the size of the substrate used. Apparently, the preparation of GNS with a well-developed graphitic structure, particularly in a continuous mode which is essential for large scale production, is still lacking and thus needs investigations. In this communication, we report a novel strategy to continuously prepare high-quality GNS with a well-developed graphitic structure. This was achieved by spray pyrolysis of a mixture of iron pentacarbonyl (Fe(CO)5) and pyridine (C5H5N). Iron nanoparticles from Fe(CO)5 served as substrates for the deposition of carbon atoms from C5H5N. Carbonyl and pyridine were mixed at different volume ratios and pyrolysized at different temperatures. Typical experiments are listed as G1 (100:1, 900 °C), G2 (50:1, 900 °C), G3 (25:1, 900 °C), and G4 (100:1, 1000 °C). Nano-X Research Center, School of Mechanical and Power Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, P. R. China. * E-mail for Jian Nong Wang: [email protected] †Electronic Supplementary Information (ESI) available: Experimental procedures and characterization. See DOI: 10.1039/c000000x/
This journal is © The Royal Society of Chemistry 2014
The reaction solutions were supplied from the top of a quartz reactor, and samples were continuously collected at the bottom. After the removal of Fe substrates, GNS with several graphitic layers were obtained. (See ESI† for experimental details and Fig. S1.) (a)
(b)
5 nm
(c)
(d)
100 nm
Fig. 1. TEM images of G1 (a, b) and G2 (c, d). Transmission electron microscopy (TEM, JEM-2100) was employed to characterize the morphologies of the samples. Samples G1 (Fig. 1a,b) and G2 (Fig. 1c,d) exhibited a thin sheet structure. The sheets had a thickness of about 1.4 nm, corresponding to several graphitic layers. Except for such GNS, no iron particles were observed. As to the sample of G2, atomic force microscope (AFM, Veeco/DI) characterization further demonstrated that the sample possessed a flake-like structure and the thickness of the GNS (Fig. S2, ESI†) was ~2.0 nm. This result also suggests that the GNS consisted of several graphitic layers. Raman spectroscopy was used to investigate the graphitic structure of GNS. The Raman spectrum for G2 (Fig. S3, ESI†) shows three strong peaks at 1350, 1578 and 2703 cm–1, which are designated as D, G, and 2D peaks, respectively. The D peak is related to the amount of defects, while the G peak to the amount of sp2 hybrid carbon atoms. Therefore, the ratio between the intensities of G and D peaks is often used to estimate the graphitization of carbon materials.16 Based on the Raman spectrum shown in Fig. S3, this ratio was calculated to be 2.8, which is much
J. Name., 2014, 00, 1-3 | 1
ChemComm Accepted Manuscript
Published on 19 November 2014. Downloaded by Rice University on 20/11/2014 08:06:27.
COMMUNICATION
View Article Online
ChemComm
Page 2 of 4
DOI: 10.1039/C4CC08197H
COMMUNICATION
Journal Name
2 | J. Name., 2014, 00, 1-3
Intensity (a.u.)
This journal is © The Royal Society of Chemistry 2014
ChemComm Accepted Manuscript
Published on 19 November 2014. Downloaded by Rice University on 20/11/2014 08:06:27.
Intensity (a.u.)
larger than that for chemically reduced graphene oxides.7,9 This N type Relative peak area [%] C1s (a) (b) Sample G2 Pyridinic N 21.97 result indicates that the GNS obtained by our method had a good C (at.%) 92.69 Pyrrolic N 15.59 Graphitic N 62.44 graphitic structure. 2D and G bands indicate the key features of GNS. O (at.%) 3.19 Pyridinic N N (at.%) 3.42 The 2D band peak at 2702 cm-1 is ascribed to the highest optical branch phonons near the K point at the Brillouin zone boundary and Graphitic N the G band peak at 1575 cm-1 is due to the two-fold degenerate E2g Pyrrolic N O1s N1s mode at the Γ-point. The relative intensity ratio of I2D/IG can be used to estimate the number of layers of GNS. The integrity intensity ratios I2D/IG of >2, 1–2, and
