Scientific paper
Synthesis and Electrochemical Characterization of Graphene Nanoribbon stacks Functionalized
with Buckyballs
Bo{tjan Genorio
University of Ljubljana, Faculty of Chemistry and Chemical Technology, Ve~na pot 113, 1000 Ljubljana, Slovenia
* Corresponding author: E-mail: bostjan.genorio@fkkt.uni-lj.si Tel: +386 41 839 686
Received: 15-04-2015
Abstract
Graphene nanoribbons were prepared from commercially-available multi-walled carbon nanotubes and in situ functionalized with C60 - buckyballs. The physical properties of the synthesized functionalized material were analyzed by scanning electron microscopy, transmission electron microscopy, evolved gas analysis and Raman spectroscopy, and were compared to non-functionalized material. Further, electrochemical characterization was done to evaluate the re-dox-activity and capacity of the material in Li-ion batteries. Comparison to non-functionalized material shows improved capacity at lower current densities.
Keywords Graphene nanoribbon stacks, buckyballs, C60, functionalization, electrochemistry, Li-ion battery
1. Introduction
Carbon-based materials are one of the main components of energy conversion and storage devices. Various carbon allotropes can be found as catalyst supports in fuel cells, active materials in capacitors, and active components or conductive additives in batteries.1 Recently, grap-hene and its sub-structure graphene nanoribbons (GNRs) - both two-dimensional allotropes of carbon - have attracted attention in the field of energy storage and conversion due to their advantageous properties such as: high conductivity, high surface area and mechanical stability. High quality - low defect graphene materials are envisioned to be a main component of future electronics, however low quality graphene materials on the other hand which still features high conductivity, high surface area, mechanical stability and facile processability are already paving their way to the commercialization. There are several reports on use of graphene in Li-ion batteries and supercapaci-tors,2-4 where the addition of graphene has been shown to significantly enhance battery cycling performance and lithium storage capacity. Graphene can also effectively relieve the expansion and shrinkage of active materials during cell operation.5 The majority of the battery literature discusses graphene as either an anode intercalation mate-
rial, a volume expansion buffer, or an electron transfer medium (for both cathode and anode materials).6 There are also reports on dual-graphite cells where graphene stacks are used as both, the anode and cathode.7 Carbon materials are also well-known supercapacitor components for storing electrostatic charges on the electrode double-layer;8-10. However, the use of graphene based materials as a redox-active component of a battery system is still underexplored.
Graphene is, by itself, redox-inactive, and as a result functionalization with redox-active molecules is required. One of the redox active candidates is C60-fullerene. C60 has a rich redox chemistry, where six electrons per molecule can be exchanged at potentials (E1/2): -0.98, -1.37, -1.87, -2.35,-2.85, and -3.26 V vs ferrocene (Fc/Fc+).11 Functionalization can have a major impact on the conductivity of the material; therefore an edge functionalization is preffered.12 In order to achieve high degree of edge functionalization, high aspect ratio graphene analogues such as GNRs should be considered. Focusing on high aspect ratio GNRs, two general approaches can be applied: a) covalent functionalization, and b) non-covalent functio-nalization.13 Both approaches can be used in supercapaci-tor and Li-ion battery electrode material synthesis. The re-dox-active material most commonly used in non-covalent
functionalization approach is MnO2, which has been described in several reports.1415 Using a covalent functionalization approach, our group has previously shown that qui-none-based functional groups on GNRs can be used as an electrode material for Li-Ion batteries.16
In the present study, we explored the possibility of developing an all-carbon hybrid electrode material for Li-ion battery that is conductive and redox-active at the same time. In order to develop redox activity in an all-carbon material, we focused on functionalization with bucky-ball-C60 fullerenes. All-carbon, hybrid C60-GNR material was synthesized according to previously described, modified synthesis/functionalization method.12,17 Using commercialy available multi-walled carbon nanotube (MWCNT) starting materials, this in situ functionaliza-tion method yielded GNRs that are edge functionalized with C60. This material was characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), evolved gas analysis (EGA), and Raman spectroscopy. Further, hybrid C60-GNR material was subjected to electrochemical characterization in a Li-ion battery setup using linear scan cyclic voltammetry (CV) and galvanostatic measurements with different current rates.
2. Results and Discussion
Fullerene C60 is a well-known electrophile that can readily react with electron-rich systems.18 It has also been shown that electrophiles may functionalize graphene na-noribbons by displacing alkali metal sources on graphene nanoribbons.1217 C60 functionalized GNRs (C60-GNRs)
were synthesized using a one-pot, in situ functionalization method with MWCNTs as starting material, Na/K alloy and C60 as reagents and 1,2-dimethoxyethane (DME) as solvent (Scheme 1). In the last step, methanol was used to quench all of the residual activated carbon and excess Na/K that remained after unzipping and/or C60 addition. To serve as a reference material, non-functionalized GNRs (GNRs) were also synthesized. In this case active carbon centers were quenched by methanol and no elec-trophile was used.
Synthesized C60-GNRs were imaged by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) (Figure 1). SEM imaging (Figure 1a) revealed high yield splitting of MWCNTs to GNRs (additional large scale SEM images can be found in Supporting Information Figure S1). Furthermore, TEM imaging shows the presence of round structures on the edges of the C60-GNRs. These structures are <2nm in diameter, which is comparable to the van der Waals diameter of C60 molecules and suggests that C60 has been successfully cova-lently bound to the edge of the GNR (additional TEM images of C60-GNRs can be found in Supporting Information Figure S2). However, for a clearer confirmation of covalent functionalization, more detailed high resolution TEM studies should be conducted, as similar fullerenic structures have also been shown on raw samples of combustion-generated fullerenes.19 Regardless, according to Figure 1b the degree of possible functionalization is relatively low (for TEM images of MWCNTs and GNRs see Supporting Information Figure S3). To further explore the degree of possible functionalization, the indirect evolved gas analysis (EGA) method was used.
Scheme 1. Proposed reaction scheme for synthesis of C60-GNRs and GNRs.
a)	b)
Figure 1. Images of synthesized C60-GNRs. a) SEM image, b) TEM image
Comparing the EGAs of C60-GNRs and GNRs (Figure 2) one can see that the difference in total weight loss between two samples is 13.4 % at 900 °C. MS spectra revealed that main difference in weight loss is due to adsorbed water, which is slowly released from the materials in the range between 60 °C to 260 °C and observed to be higher for C60-GNRs. However, the most important difference between the functionalized and non-functionalized materials is the presence of a mass fragment at m/z = 64 (purple curve of Figure 2) in case of C60-GNRs. Fragmentation of C60 is a very complex process. It was previously shown that C60 decomposes to several fragments with m/z M=C60-2nm+.20 Extrapolating this formula one can assume that fragment m/z = 64 could be C163+. Further, another publication discusses plausible mechanisms for the thermal decomposition of C60.21 They discuss possible formation of complexes with trace impurities such as oxygen, carbon, and hydrogen. Consequently, one could also expect that fragment m/z 64 could be C4O+ or C5H4+. However, in order to confirm the chemical structure of the species with fragment m/z 64 extensive studies should be carried out, which is beyond the scope of this manuscript. However, above mentioned indicates possible presence of C60 moieties in the composition of functionalized C60-GNRs. Due to the limitations of the technique and the apparatus (the upper limit of detection is 100 AMU), one cannot directly observe the molecular mass of C60 with m/z 720 (C60+) or conclude whether the functionalization is covalent or non-covalent. We have shown previously that GNRs-based materials decompose with the appearance of fragment m/z 15 (blue curve of Figure 2) in the temperature region between 400 °C and 600 °C.12 This fragment can be found in both spectra, which indicates that both materials decompose in the same fashion. To estimate degree of functionalization, calculation based on EGA
data together with SEM images was applied (Supporting Information Table S4, Figure S5, Figure S6). Similar method was used in our previous publications.12'22 Following experimental data were used: a) defunctionalization of C60-GNRs is occurring in the temperature region between 380 °C and 600 °C, b) average size of the ribbon was 30,000 nm X 200 nm, c) weight loss related to C60 was
Figure 2. Evolved gas analysis. Black and red curves represent the TGA profile of GNRs and C60-GNRs respectively. Blue and purple lines represent fragments with m/z fragments that correspond to m/z 15 and m/z 64, respectively.
3.2%. Considering above mentioned the estimated degree of functionalization is 600 atomic ppm.
Raman spectroscopy of C60-GNRs was also performed to evaluate the structural quality of these materials. As shown in Figure 3, there is no noticeable difference between two spectra. They both show characteristic peaks for graphene-based materials: D at ~1352 cm-1, G at ~1583 cm-1, D' at ~1635 cm-1, 2D at ~2708 cm-1, and G+D' at ~2945 cm-1.23 The ID/IG ratio was also estimated, which is an indicator of the structural disorder in graphitic materials. In both cases ID/IG is relatively low - 0.6 -which indicates that the GNRs are of relatively high quality and that the functionalization process does not disrupt the quality of the supporting GNR material. We have previously shown that materials with similar ID/IG ratios show relatively good electronic conductivity, which is important for energy conversion and storage devices.12
Figure 3. Raman spectra comparing non-functionalized (black curve) GNRs and functionalized (red curve) C60-GNRs.
For electrochemical measurements, the so-called "coffee bag" battery setup with C60-GNRs or GNRs as a working electrode and Li foil as a counter electrode was used. It is important to emphasize that working electrodes were prepared without any added binders or conductive additives, which is critical when considering practical applications for electrode materials. Cyclic voltammetry (CV) was measured for these materials (Figure 4), and from the 1st scan two oxidation peaks at 3.6 V and 3.9 V can be seen as shoulders in the red curve of Figure 4. The-
se two peaks could represent oxidation of the C60 molecules present in the functionalized material C60-GNRs. However, instead of complementary, reversible reduction peaks in the reverse scan, only one broad reduction peak starting at 2.5 V is visible. This could indicate highly irreversible redox reaction of C60 moiety on GNRs. CV measurements also reveal that the oxidation and reduction currents slowly decrease with cycling. In contrast, non-func-tionalized GNRs show a much smaller, broad reduction peak and no oxidation peak (black curve of Figure 4). This indicates that C60 functionalization improves the electrochemical performance of GNR materials; however, the irreversibility of electrochemistry is a definite drawback for possible application in real Li-ion battery systems. Similar electrochemistry was also observed previously for the pure C60 which was used as a cathode in Li-ion battery setup. 24 The electrochemical irreversibility of C60-GNRs material could also be the result of a reaction between oxidized species and the electrolyte or due to formation of a solid-electrolyte interphase on the electrode. Nevertheless, the functionalization showed improved electrochemistry when compared to non-functionalized material.
Figure 4. Cyclovoltammograms for non-functionalized GNRs (black curve) and functionalized C60-GNRs (red curve); scan rate 0.1 mV/s.
Charge-discharge rate capability is one of the most important properties of cathode materials that can be used in lithium batteries. Galvanostatic rate capability tests for both of the materials: C60-GNRs and GNRs were performed (Figure 5), which show higher capacities for the func-tionalized C60-GNRs material. At low current densities the capacity for C60-GNRs (22 mAh/g) is twice that of the non-functionalized GNRs (12 mAh/g) (for charge-discharge curves see Supporting Information Figures S7 and S8). However, at higher current densities (800 mA/g) the capacity difference between two materials decreases until the capacities are equal (6 mAh/g). This means that rate performance for C60-GNRs is actually worse than for GNRs.
As functionalization does not noticeably increase the surface area, one can expect that the difference in capacity for low current densities is related to activity of the functional groups. Furthermore, it is possible that the slow redox kinetics of C60 or lower the conductivity of the functionali-zed material relative to non-functionalized, leading to the poor rate capability. It is known from previous reports that conductivity can decrease with functionalization.1 Different contact resistance between single C60-GNRs can also impact fast capacity drop at higher current densities. We have shown previously, that alignment of the graphene na-noribbons drastically affect the contact resistance.17 In this respect, spherical C60 functionalities might disturb favorable alignment, increase contact resistance, and consequently cause fast capacity drop at higher current densities. However, the reason for the poor rate capability of these materials remains unclear at this point.
m Alg
* • •
SO riflAJg
2D тАУд
120 m Alg
300 mA/g
t t t
800 m Alg
Figure 5. Rate capability for non-functionalized GNRs (black circles) and functionalized C60-GNRs (red squares) at 20 mA/g, 50 mA/g, 120 mA/g, 300 mA/g, and 800 mA/g current densities.
3. Conclusions
Functionalization of GNRs with electroactive moieties is an approach that could lead to novel cathode materials for a variety of battery applications. In the present study, MWCNTs were split to GNRs in situ and functio-nalized with C60 fullerenes. These functionalized C60-GNR materials were compared to non-functionalized GNRs and characterized using a variety of imaging and electrochemical techniques. SEM imaging revealed high yield splitting of MWCNTs to GNRs and TEM imaging shows the presence of spherical structures on the GNR edges that suggest the presence of attached C60. Further, EGA analysis supports the hypothesis of successful func-tionalization of these structures with C60. In particular, it reveals that the mass fragment at m/z = 64 is present only for the functionalized C60-GNRs material. As the fragment at m/z = 64 is also one of the fragments observed for pure C60, it could be an indicator of the presence of C60
functional groups. These results favor the hypothesis of successful functionalization, however, at this time it cannot be confirmed conclusively whether C60 molecules are adsorbed or covalently bound. The graphitic nature of the functionalized material was confirmed by Raman spec-troscopy, where bands typical for graphene are present. Further, a relatively small ID/IG ratio is a good indicator of low concentration of structural defects in the graphene lattice, and confirms that the functionalization with C60 does not disrupt the quality of the GNR supporting material. Electrochemical experiments, in particular CV, showed irreversible redox reaction of functionalized material in first cycles. Galvanostatic cycling was performed under various current densities for both samples - C60-GNRs and GNRs and compared. Results showed doubled capacity for C60-GNRs on one hand, but worse rate performance on the other hand. Nevertheless, the improved capacity at low current densities for functionalized GNR materials, in combination with the simple assembly method of the electrode where no binders or conductive additives are used, make these materials attractive for further investigation. These materials may also be attractive for beyond lithium systems, e.g. Mg-ion batteries, where reversible cycling of Mg with pure C60 was shown recently.25
4. Experimental
4. 1. Materials
All reactions were performed in dried glassware under an Ar atmosphere unless stated otherwise. Reagent grade 1,2-dimethoxyethane was degassed with Ar, refluxed over Na/K alloy in an Ar atmosphere and freshly distilled. Other solvents were used without further distillation. NTL - M grade MWCNTs were donated by Nanotech Labs, Inc. (5T10M10). All other commercially available reagents were used as received. Liquid Na/K alloy was prepared in a vial inside of a N2 glove box by pressing together freshly cut K (1 molar equivalent) and Na (0.22 molar equivalents) chunks using tweezers to facilitate the melting process. Amounts of liquid Na/K alloy indicated are by volume. Caution: All synthetic steps involving Na/K alloy should be carried out with extreme caution under strict exclusion of air or moisture, under inert gas and appropriate personal protection (hood, blast shields, face shield, protective and fire resistant clothing) should be used and worn at all times. C60 was obtained from Sigma-Aldrich and used as received without further purification. Milli-Q water was used during purification of the products.
4. 2. Synthesis of C60 Functionalized Graphene Nanoribbons Stacks (C60-GNRs)
To an vacuum oven-dried (200 °C) 250 mL round-bottom flask containing a magnetic stir bar were added the MWCNTs (100 mg, 8.3 mmol). The vessel was then
transferred to a Ar glove box where freshly distilled 1,2-dimethoxyethane (43 mL) and liquid Na/K alloy (0.1 mL) were added. The flask containing the suspension was then sealed with a septum and was vigorously stirred (450 RPM) at room temperature in glove-box for 3 d. The reaction suspension was then quenched by the addition of the C60 (180 mg, 0.25 mmol) and left to stir at the room temperature for an additional day. Reaction mixture was then transferred out of the glove-box where methanol (20 mL, 500 mmol) was added to quench any excess Na/K alloy and the mixture was stirred at room temperature for 10 min. For workup, the reaction mixture was filtered over a 0.2 pm pore size PTFE membrane. The filter cake was successively washed with THF (100 mL) and CS2 (100 mL) and exposed to Soxhlet extraction for 8 h to remove the unreacted C60. After extraction solid was dispersed in CS2 (50 mL) and sonicated for 1 h. Solution was then filtrated again using PTFE 0,2 pm filter pad. The filter cake was successively washed with THF (100 mL), i-PrOH (100 mL), H2O (100 mL), i-PrOH (50 mL), THF (50 mL), Et2O (50 mL) and dried under high vacuum. Mass of the dried product was 80.6 mg.
4. 3. Synthesis of Non-functionalized
Graphene Nanoribbons Stacks (GNRs)
The same procedure as described above for synthesis of C60-GNRs was followed, except that step where C60 was added was omitted.
4. 4. Electron Microscopy
Samples were dispersed in chlorobenzene and bath sonicated using an ultrasonic cleaner for 15 min for a quick dispersion. A drop was cast on a 100 nm SiO2/Si substrate and large area low resolution images were taken at 20 kV under FEI Quanta 400 ESEM FEG scanning electron microscope. For more refined images of the synthesized structure at higher resolution, a JEOL 2010 transmission electron microscope was used with the sample drop cast on a coated TEM grid.
4. 5. Evolved Gas Analysis (EGA)
Thermogravimetric measurements were performed on a Netzsch 449 F3 Jupiter® instrument under a dynamic Ar (5.0) flow with a flow rate of 60 mL/min in a temperature range from 25 °C to 900 °C. A heating rate of 10 K/min was used. About 5 mg of sample was placed in alumina (Al2O3) crucible. Simultaneously mass spectrometry was performed on MS 403C Aeolos® with detector SEM Chenneltron and system pressure of 2 x 10-5 mbar. Gasses evolved under TG heat treatment were transferred to mass spectrometer through transfer capillary: quartz ID 75 pm which was heated up to 220 °C. The upper limit of the mass spectrometer detector was 100 AMU.
4. 6. Raman Spectroscopy
The Raman spectra were acquired using a Renishaw Raman RE01 microscope with 40 x lens; 514 nm wavelength LASER was used for excitation.
4. 7. Electrochemical Tests
C60-GNRs and GNRs (~5 mg) were suspended in THF (15 mL) in an ultrasonic bath for 10 min until the suspension was homogeneous. The suspension was then filtered through a glassy fiber Whatman GF/A (battery separator) in a Millipore membrane filtration system. The diameter of the filtration disc was 25 mm. The filtration resulted in a uniformly distributed material on a glassy fiber separator, from which 12mm diameter discs were cut out. These discs were then transferred to an Ar glove-box and allowed to dry for 1 day. Modified Swagelok battery cells were assembled in the glove box (water and oxygen levels <1 ppm). For every cell, 5 drops of 1M LiPF6 in ethylene carbonate/diethyl carbonate (EC/DEC)=1:1 (vol.), purchased from Merck (LP40), were used. A lithium foil (Aldrich, 0.75mm thick) as counter electrode was rolled and cut prior to assembly.
Electrochemical measurements were performed on a VMP3 potentiostat/galvanostat (Bio-Logic, France). Batteries were cycled be- tween 4.0 and 1.3 V versus metallic Li. CV measurements were performed in a two-electrode cell with a scan rate of 0.1 mV/s. Galvanostatic cycling (rate capability) was performed at various current densities in a wide range from 20 to 800 mA/g.
5. Acknowledgements
I thank to Center of Excellence Low Carbon Technologies, Slovenia (CO NOT), Center of Excellence Advanced Materials and Technologies for the Future, Slovenia (CO NAMASTE) for financial support, Dr. Klemen Pirnat for electrochemical measurements and Dr. Barbara Novosel for EGA measurements. I also thank to Nanotech Labs, Inc. for the MWCNTs.
6. References
1.	Rao, C.; Sood, A. Graphene: Synthesis, Properties, and Phenomena; Rao, C. N. R.; Sood, A. K., Eds.; 1st ed.; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, 2013.
2.	Luo, B.; Liu, S.; Zhi, L. Small 2012, 8, 630-646. http://dx.doi.org/10.1002/smll.201101396
3.	Zhang, L. L.; Zhou, R.; Zhao, X. S. J. Mater. Chem. 2010, 20, 5983-5992. http://dx.doi.org/10.1039/c000417k
4.	Huang, Y.; Liang, J.; Chen, Y. Small 2012, 8, 1805-1834. http://dx.doi.org/10.1002/smll.201102635
5.	Liang, M.; Zhi, L. J. Mater. Chem. 2009, 19, 5871-5878. http://dx.doi.org/10.1039/b901551e
6.	Raccichini, R.; Varzi, A.; Passerini, S.; Scrosati, B. Nat. Mater. 2014, 14, 271-279. http://dx.doi.org/10.1038/nmat4170
7.	Placke, T.; Fromm, O.; Lux, S. F.; Bieker, P.; Rothermel, S.; Meyer, H.-W.; Passerini, S.; Winter, M. J. Electrochem. Soc. 2012, 159, A1755-A1765. http://dx.doi.org/10.1149/2.011211jes
8.	Zhu, Y.; Li, L.; Zhang, C.; Casillas, G.; Sun, Z.; Yan, Z.; Ruan, G.; Peng, Z.; Raji, A.-R. O.; Kittrell, C.; Hauge, R. H.; Tour, J. M. Nat. Commun. 2012, 3, 1225. http://dx.doi.org/10.1038/ncomms2234
9.	Kotal, M.; Bhowmick, A. K. J. Phys. Chem. C 2013, 117, 25865-25875. http://dx.doi.org/10.1021/jp4097265
10.	Zhang, C.; Peng, Z.; Lin, J.; Zhu, Y.; Ruan, G.; Hwang, C.C.; Lu, W.; Hauge, R. H.; Tour, J. M. ACS Nano 2013, 7, 5151-5159. http://dx.doi.org/10.1021/nn400750n
11.	Echegoyen, L.; Echegoyen, L. E. Acc. Chem. Res. 1998, 31, 593-601. http://dx.doi.org/10.1021/ar970138v
12.	Genorio, B.; Lu, W.; Dimiev, A. M.; Zhu, Y.; Raji, A.-R. O.; Novosel, B.; Alemany, L. B.; Tour, J. M. ACS Nano 2012, 6, 4231-4240. http://dx.doi.org/10.1021/nn300757t
13.	Genorio, B.; Znidarsic, A. J. Phys. D. Appl. Phys. 2014, 47, 094012. http://dx.doi.org/10.1088/0022-3727/47/9/094012
14.	Li, L.; Raji, A. R. O.; Tour, J. M. Adv. Mater. 2013, 25, 6298-6302. http://dx.doi.org/10.1002/adma.201302915
15.	Liu, M.; Tjiu, W. W.; Pan, J.; Zhang, C.; Gao, W.; Liu, T. Na-noscale 2014, 6, 4233-4242. http://dx.doi.org/10.1039/c3nr06650a
16.	Pirnat, K.; Bitenc, J.; Jerman, I.; Dominko, R.; Genorio, B. ChemElectroChem 2014, 1, 2131-2137. http://dx.doi.org/10.1002/celc.201402234
17.	Genorio, B.; Peng, Z.; Lu, W.; Hoelscher, B. K. P.; Novosel, B. J.; Tour, J. M. ACS Nano 2012, 6, 10396-10404. http://dx.doi.org/10.1021/nn304509c
18.	Wudl, F. Acc. Chem. Res. 1992, 25, 157-161. http://dx.doi.org/10.1021/ar00015a009
19.	Goel, A.; Howard, J. B.; Sande, J. B. V. Carbon N. Y. 2004, 42, 1907-1915.
http://dx.doi.org/10.1016/j.carbon.2004.03.022
20.	Baba, M. S.; Narasimhan, T. S. L.; Balasubramanian, R.; Mathews, C. K. J. Phys. Chem. 1995, 99, 3020-3032. http://dx.doi.org/10.1021/j100010a010
21.	Sundar, C. S.; Bharathi, A.; Hariharan, Y.; Janaki, J.; Sankara Sastry, V.; Radhakrishnan, T. S. Solid State Commun. 1992, 84, 823-826.
http://dx.doi.org/10.1016/0038-1098(92)90098-T
22.	Lu, W.; Ruan, G.; Genorio, B.; Zhu, Y.; Novosel, B.; Peng, Z.; Tour, J. M. ACS Nano 2013, 7, 2669-2675. http://dx.doi.org/10.1021/nn400054t
23.	Dresselhaus, M. S.; Jorio, a.; Saito, R. Annu. Rev. Condens. Matter Phys. 2010, 1, 89-108.
http://dx.doi.org/10.1146/annurev-conmatphys-070909-103919
24.	Seger, L.; Wen, L.-Q.; Schlenoff, J. B. J. Electrochem. Soc. 1991, 138, 81-82. http://dx.doi.org/10.1149/L2085516
25.	Zhang, R.; Mizuno, F.; Ling, C. Chem. Commun. 2014, 51, 1108-1111.
http://dx.doi.org/10.1039/C4CC08139K
Povzetek
Opisana je sinteza s fulereni-C60 funkcionaliziranih grafenski nanotrakov, ki so bili pripravljeni iz komercialno dostopnih večstenskih ogljikovih nanocevk po in situ postopku. Fizikalne lastnosti sintetiziranega materiala so bile analizirane z elektronsko vrstično mikroskopijo, presevno elektronsko mikroskopijo, analizo sproščenega plina in ramansko spektroskopijo. Lastnosti funkcionaliziranega materiala so bile nato primerjane z nefunkcionaliziranim. Oba materiala, tako funkcionaliziran, kot nefunkcionaliziran sta bila nato ovrednotena tudi elektrokemijsko. Določena je bila redoks ativ-nost in kapaciteta obeh v litij-ionskih baterijah. Primerjava obeh materialov je pokazala izboljšano kapaciteto funkcio-naliziranega materiala pri nizkih tokovnih gostotah.
Synthesis and Electrochemical Characterization of Graphene Nanoribbon stacks Functionalized with Buckyballs - Supporting Information
Bostjan Genorio
University of Ljubljana, Faculty of Chemistry and Chemical Technology, Večna pot 113, 1000
Ljubljana, Slovenia Corresponding author: E-mail: bostjan. genorio@fkkt.uni-lj.si Tel: +386 41 839 686
Table of Contents
Figure S1, Large scale SEM images of MWCNTs, GNRs and Cs0-GNRs, page S1
Figure S2. TEM images of C60-GNRs, page S2
Figure S3. TEM images of a) MWCNTs and b) GNRs, page S3
Table S4, Calculation of degree of Functionalization, page S4
Figure S5, Evolved gas analysis, page S5
Figure S6, Large scale C60-GNRs SEM image, page S6
Figure S7, Galvanostatic curves for GNRs and C60-GNRs, page S7
Figure S8, Charge-Discharge curves at different current densities, page S8
Figure S1. Large scale SEM images of: a) M-grade NTL MWCNTs, b) GNRs and c) Сбо-GNRs
Figure S2. TEM images of Сбо-GNRs.
Figure S3. TEM images of a) M-grade NTL MWCNTs and b) GNRs
Table S4. Calculation of degree of functionalization.
С
(D
О
-12
-12
-12
,-12
,-12
		
. \x = 380, Y = 99.85		
		X = 600, Y = 97.61
X = 380, Y = 94.60		-
■		X = 600, Y = 89.16
		-
--1-1-1-1-1—	-1---1-«-1	-i-1-1-1-1-
98
96
94 g
92 .С
ö)
90 Ъ §
88 86 84
0.0
100 200 300 400 500 600 700 800 900
TGGNRs Temperature (°C)
TG C -GNRs
60
■ m/z 64
Figure S5. Evolved gas analysis.
Figure S7. Galvanostatic curves for: a) GNRs and b) C60-GNRs.
Figure S8. Charge-Discharge curves at different current densities: a) GNRs and b) C60-GNRs