Conference Return Seminar- NANO2014,Moscow State University,Moscow,Russia Date:13-1818 th July 2014 An electrochemical method for the synthesis of single and few layers graphene sheets for high temperature applications Dr. Pitamber Mahanandia Department of Physics, National Institute of Technology, Rourkela-769008,Odisha, India E-mail:pitam@nitrkl.ac.in 1
ABSTRACT An electrochemical technique for the large scale synthesis of high quality few layer graphene sheets (FLGS) directly from graphite using oxalic acid (a weak acid) as electrolyte is demonstrated. Oneof the interesting observations is that the FLGS are stable at least up to 800 0 C which has potential application in solid oxide fuel cell as gas diffusion layer. Key Words: Graphene, method, properties, characterization 2
Discovery of different carbon allotropes a short history 1564 Discovery of graphite (plumbago) 1962 HOPG (graphite monocrystal) 1960-1980 Graphite intercalation compounds 1985 Fullerenes [Kroto, Curl, Smalley] 1991-1993 Carbon nanotubes [Iijima] 1992-1993 few layers graphite on metal substrate 2004 Graphene by Novoselov et al Science 306, 666 Graphene is the first truely 2D crystal ever observed in nature. This is remarkable because the existence of 2D crystals has often been doubted d in the past, namely due to a theorem (Mermin-Wagner theorem) which states that a 2D crystal looses its long-range order, and thus melts, at any small but non-zero temperature, due to thermal fluctuations. 10/28/2014 3
Why is graphene interesting? Graphene = 2D honeycomb lattice 2 atoms per unit cell(1/3x6 sites of hexagon) Peculiar band structure: Gap less semiconductor. Electrons are massless Dirac fermions and chiral. The most popular description of graphene band structure is the tight binding one, first done by P.R Wallace, Phys. Rev. 71,622-634(1947). 634(1947). 10/28/2014 4
Physical properties of graphene Graphene is an exciting material: *large theoretical specific surface area (2630 m 2 g 1 * High intrinsic mobility (200 000 cm 2 v 1 s 1 ), * High Young s modulus ( 1.0 TPa) * Thermal conductivity ( 5000 Wm 1 K 1 ), * Optical transmittance ( 97.7%) AND Recent report 3754 m 2 g 1 ), *G Good electrical lconductivity i capacity ~ 10 9 A/cm 2. Massless Dirac Fermion quasiparticles, shows ballistic transport up to room temperature, mean free path ~1μm 10/28/2014 5
Graphene: Approaches & Applications Graphene is a sheet, the atom-thick single layer of sp 2 bonded carbon. Approaches to prepare p graphene 1. Mechanical exfoliation from graphite-single sheet at a time- Not Scalable 2. Epitaxial growth-defects and not scalable 3. CVD- Single sheet (even larger in size) grain boundaries- not scalable 4. Solution method- Large quantity-defects-functional groups Predicted applications: FET Ultrasensitive sensors Transparent electrodes Novel nanocomposites etc.. Supercapacitor Li-Ion bateries 6 AND many more. Yet to be explored
Problems & Motivation Graphene sheets prepared by are heavily oxygenated with hydroxyl and epoxide functional groups on the surface and at the edges. Graphene prepared by micromechanical exfoliation is just meant for fundamental physical properties p study.large scale can not be prepared. p There has been efforts to prepare grephene directly from graphite without functional groups. The essential requirement of graphene is to prepare large scale directly from graphite for many commercial applications in science and technology. Bi Being motivated, t here a new technique has been developed d to prepare btt better single and few layers graphene sheets directly from graphite. 7
The Experimental Technique Few layer graphene sheets (FLGS) were prepared by electrolysis within a cooled oxalic acid cell directly from graphite as shown in Figure 1(a). Fig. 1. Schematic diagram of (a) the electrochemical setup for the synthesis of FLGS and (b) the corroded graphite electrode. Two high-purity graphite rods as electrodes and oxalic acid as electrolytes have been used. Static potential of 40 V was applied to the two electrodes about 5 h in a 0.3 M oxalic acid [H 2 C 2 O 4 C 2 O 4 H + H + ] solution maintained at 0 C. Initially first few minutes, it is believed that the bias voltage helps in getting wet the graphite electrodes and very likelyl causesgentle interaction ti of C 2 O 4 H to the grain boundary of graphite After few minutes of this bias, the graphite rods get corroded and starts dissociating into small pieces resulting a homogeneous solution. The solution was filtered to recover the graphene flakes and driedinanovenfor24hat100 o C. Fig. 2. Photographs of (a) dried FLGS and (b) homogeneous dispersion of FLGS in DMF. 8
Preparation of graphene oxide(go) Hummers method(hummers W, Offeman R. Preparation of graphitic oxide. J Am Chem Soc 1958;80:1339) 1.0gm of expanded graphite and 0.5 gm of NaNO 3 was introduced in 23 ml of H 2 SO 4 Under continuous stirring in an ice-bath. 3.0gm of KMnO 4 was added under stirring below 20 O C. The mixture was the maintained at 35 OC and stirred for 4 Hours. 115 ml deionized water was slowly added to the mixture followed by stirring the mixture at 98 O C for 20 minutes. Then the material was further diluted by adding about 350 ml of water and stirred for 30 minutes. Thenthereactionwasterminatedbyadding4mLofHO terminated adding ml of 2 2. Multiple washing with de-ionized water and the final product was obtained by drying at 100 O C for 24 hours. 10/28/2014 9
Preparation of reduced graphene oxide(rgo) 1. Graphene oxide is treated under stirring in hydrazine monohydrate(n 2 H 4 ) to get rid off oxygen. 2. Multiple wash in de-ionized water till the solution reaches PH=7 3. The reduced graphene is obtained by filtering followed by centrifugation 4. Then the final product graphene sheets is obtained by drying at 100 O C for 24 hours. 10/28/2014 10
Schematic illustration From graphite graphene oxide reduced graphene oxide KMnO 4 +H 2 SO 4 NaNO 3 carbonyl and car boxyl groups at t he edges Basal planes decorated mostly with epoxide and hydroxyl Sonicated in distilled water hydrazine hydrate (N 2 H 4. H 2 O) 100 O C 10/28/2014 11
(a) Results (b) () (c) (d) Figures: (a) SEM,(b) TEM,(c) HRTEM and (d) SAED of GO 12
(a) Results (b) (c) (d) Figures:(a) SEM,(b) TEM,(c) HRTEM and (d) SAED of RGO 13
Results RGO GO e(a.u) Absorbanc (b) (a) RGO GO 500 1000 1500 2000 2500 3000 3500 4000 Wave number(cm -1 ) Figures : (a) XRD of GO and RGO,(b) FTIR of GO and RGO 14
(a) (b) (c) (d) Fig. 5. (a) UV-Vis Vi spectra of GO (lower) & RGO (upper) (b) Raman of GO (lower) )& RGO( (upper) (c) TGA of GO(lower) & RGO(upper) (d) I-V characteristics of GO(red) & RGO(black) 15
Results Figures: (a) SEM,(b) TEM,(c) HRTEM and (d) SAED of FLGS by electrolysis method 16
(A) Results (B) (c) (D) Figures(A) HRTEM and (B) SAED of single layer graphene.(c) HRTEM image of double layer graphene and (D) respective SAED pattern 17
Results (a) (b) (c) (d) Fig. 4. (a) XRD pattern, (b) Raman, (c), FTIR and (d) UV-Vis of FLGS 18
Results (a) (b) Fig. 6. (a) TGA and (b) I-V characteristics of FLGS. 19
(a) (b) (c) Fig.7. XPS results (a) GO (b) RGO (c) FLGS 20
Conclusion Here, we demonstrate a facile green electrochemical method for the large scale synthesis of FLGS directly from graphite. The electrical properties and other spectroscopic characterization of FLGS show better in quality as compared to reported RGO. Our experimental results further suggest that FLGS can be used for high temperature applications such the support for the catalysts in solid oxide fuel cells. It is also possible to synthesize different oxides such as ZnO, CuO, etc. on FLGS by vapour phase transport technique. Mahanandia et al,chemical Communications, 50, 4613-4615(2014) Mahanandiaet al, RSc Advances,3, 12621-12624(2013) 12624(2013) Cover stories by Nanotechweb.org credited to Mahanandia et al on following site http://nanotechweb.org/cws/article/yournews/56776 21
Future Work 1.Study grain boundaries of graphene sheets 2.Detail study of transport bproperties for obtaining the better physical properties. Practical applications (a) Solar cell (b) Supercapacitor p (c)electrodes (d) Composites 22