Reduced graphene oxide aerogel with high-rate supercapacitive performance in aqueous electrolytes
- Weijiang Si†1,
- Xiaozhong Wu†1,
- Jin Zhou1,
- Feifei Guo1,
- Shuping Zhuo1Email author,
- Hongyou Cui1 and
- Wei Xing2Email author
© Si et al.; licensee Springer. 2013
Received: 6 April 2013
Accepted: 7 May 2013
Published: 21 May 2013
Reduced graphene oxide aerogel (RGOA) is synthesized successfully through a simultaneous self-assembly and reduction process using hypophosphorous acid and I2 as reductant. Nitrogen sorption analysis shows that the Brunauer-Emmett-Teller surface area of RGOA could reach as high as 830 m2 g−1, which is the largest value ever reported for graphene-based aerogels obtained through the simultaneous self-assembly and reduction strategy. The as-prepared RGOA is characterized by a variety of means such as scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Electrochemical tests show that RGOA exhibits a high-rate supercapacitive performance in aqueous electrolytes. The specific capacitance of RGOA is calculated to be 211.8 and 278.6 F g−1 in KOH and H2SO4 electrolytes, respectively. The perfect supercapacitive performance of RGOA is ascribed to its three-dimensional structure and the existence of oxygen-containing groups.
KeywordsSupercapacitor Reduced graphene oxide aerogel Current density Cyclic voltammetry
As a novel energy storage device that bridges the gap between conventional capacitors and batteries, supercapacitor has attracted much attention for its high power density and long cyclic life . The studies about supercapacitor mainly focus on the electrode materials such as transition metal oxides, conducting polymers, and particularly carbon materials that are perfect electrode materials because of their good conductivity, cyclic stability, and large specific surface area [2–4]. Carbon materials with different structures such as carbon nanotubes, carbon nanofibers, hierarchical porous carbons, and ordered mesoporous carbons are widely studied in recent years [5–8]. Apart from these carbon materials, graphene and graphene-based materials have also been widely studied as electrode materials of supercapacitor [9–13]. Graphene is a two-dimensional sheet of sp2-hybridized carbon, which possesses many remarkable properties such as high surface area, excellent mechanical strength, and low electrical resistivity [14, 15]. However, the practical preparation (chemical reduction process) of graphene-based material is often accompanied by the sacrifice of graphene surface area because the graphene layers are easy to restack through a π-π interaction during the chemical reduction process.
In order to obtain graphene-based material with high specific surface area, many researchers have prepared graphene-based materials with three-dimensional architecture. As a typical three-dimensional graphene-based material that has attracted much attention of researchers, graphene aerogel is often synthesized mainly through two strategies currently: self-assembly during reduction process [16–20] and post-reduction process after self-assembly [21–24]. Employing the first method, Xu et al. prepared graphene aerogel via self-assembly of graphene oxide during a hydrothermal reduction process at 180°C . Chen synthesized graphene aerogel using various reductants such as NaHSO3, Na2S, vitamin C, and HI . The specific surface area of the as-prepared graphene aerogels could only reach up to 512 m2 g−1 because the reduction of graphene oxide was accompanied by the elimination of oxygen-containing groups in aqueous solution. This could lead to the hydrophobility increase of reduced graphene oxide, thus resulting in the restacking of graphene sheets. Adopting the second method, we prepared the graphene aerogel with a superhigh C/O molar ratio by hydrogen reduction . Worsley et al. synthesized a graphene aerogel through the self-assembly process in a basic solution followed by thermal reduction under nitrogen atmosphere. The Brunauer-Emmett-Teller (BET) surface area of the as-prepared graphene aerogel could reach as high as 1,300 m2 g−1, which is the largest value ever reported in the literatures . Although the graphene aerogels possess large BET surface area when employing the second strategy, the preparation procedure is complex due to the separated self-assembly and reduction processes. It usually takes 72 h to finish the separate self-assembly process . How to produce graphene aerogel with high surface area in a simple way is still a challenge currently.
Apart from the high surface area, the surface properties should also be taken into consideration while graphene-based material is used as electrode material in supercapacitor. The existence of surface functional groups is the characteristic surface properties of graphene-based materials made by Hummers' method. Graphene materials with functional surface often have a better dispersibility in aqueous electrolyte. Moreover, these functional groups may also generate pseudocapacitance in aqueous electrolytes. Xu's study indicates that graphene oxide is more suitable for supercapacitor application than graphene due to the existence of pseudocapacitance generated from the oxygen-containing groups . Our previous work also shows that graphene oxide aerogel possesses a higher specific capacitance than graphene aerogel at low current densities in KOH electrolyte . Thus, it would be promising to prepare high surface area graphene-based aerogels with functional surface for supercapacitor applications.
Herein, we synthesize a partially reduced graphene oxide aerogel (RGOA) through a simultaneous self-assembly and reduction process using hypophosphorous acid (HPA) and I2 as the reductants. Nitrogen sorption analysis shows that the specific surface area of the as-prepared RGOA could reach as high as 830 m2 g−1, which is the largest specific surface area ever reported for graphene aerogels obtained through the simultaneous self-assembly and reduction strategy. Electrochemical tests show that RGOA exhibits a high-rate supercapacitive performance in aqueous electrolytes. The specific capacitance of the RGOA can reach 211.8 and 278.6 F g−1 in KOH and H2SO4 electrolytes, respectively.
Graphite powder was purchased from Qingdao Ruisheng Graphite Co., Ltd. (Shandong, China). All other chemicals were purchased from Shanghai Chemical Reagents Company (Shanghai, China) and used directly without further purification. Graphite oxide was prepared according to Hummers' method . Graphene oxide solution (5 mg mL−1) was acquired by dispersing graphite oxide in deionized water under ultrasonication. The reduced graphene oxide hydrogel was prepared according to Phams' method . In a typical experiment, 5 g I2 was dissolved in 100 g HPA solution (50 wt.%), and then a 100-mL graphene oxide solution was added and sonicated for 5 min before transferred into an oven and aged at 90°C for 12 h. The obtained product was washed twice with acetone in a Soxhlet extractor (ISOPAD, Heidelberg, Germany) for 12 h to get reduced graphene oxide gels. The wet gels were dried with supercritical CO2 to obtain reduced graphene oxide aerogel, which was labeled as RGOA.
The microstructure of the samples was characterized by X-ray diffraction (XRD, D8 Advance, Bruker Optik Gmbh, Ettlingen, Germany) and Raman spectroscopy (RM2000, Renishaw, Gloucestershire, UK). The thickness of graphite oxide sheet was examined using an atomic force microscope (AFM, Multimode NS3A, Veeco Instruments Inc., Plainview, NY, USA). The microscopic morphology of the samples was observed using a scanning electron microscope (SEM, FEI, Eindhoven, The Netherlands) and a transmission electron microscope (TEM, JEOL2010, Akishima, Tokyo, Japan). The surface properties of the samples were characterized by X-ray photoelectron spectroscopy (XPS, Escalab 250, Thermo VG Scientific, Waltham, MA, USA) and Fourier transform infrared spectroscopy (FT-IR, Nicolet 5700, Thermo Electron Corporation, Waltham, MA, USA). Nitrogen sorption measurement was performed with an ASAP 2020M analyzer (Micromeritics, Norcross, GA, USA) to obtain the specific surface area and pore structure parameters of the sample.
Working electrodes were made by pressing RGOA onto the nickel foam and titanium mesh for 6 M KOH and 1 M H2SO4 electrolytes, respectively. The mass of active materials in each electrode was about 2 mg. In order to ensure that the electrode materials were thoroughly wetted with the electrolyte, the working electrodes were vacuum-impregnated with the electrolytes before electrochemical tests. The electrochemical capacitive performances of the sample were studied on a CHI660D electrochemical workstation. Electrochemical measurements including cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS) were performed in a three-electrode system using a platinum film as a counter electrode and a saturated calomel electrode (SCE) as a reference electrode. Potential windows of −1 ~ 0 V and 0 ~ 1 V vs. SCE reference electrode were applied to the electrochemical measurements in KOH and H2SO4 electrolytes, respectively. In addition, the electrochemical performance of RGOA was also evaluated using a two-electrode system in H2SO4 electrolyte with a potential window of 0 ~ 1.2 V.
Results and discussion
Evolution of surface properties
Electrochemical capacitive performances
In addition, the current density at each scan rate in H2SO4 electrolyte is higher than that in KOH electrolyte, which indicates that oxygen-containing groups exhibit more pseudocapacitance in acid electrolyte. Therefore, as shown in Figure 4b, the specific capacitance calculated from CV curves displays that RGOA possesses larger capacitance in H2SO4 electrolyte when the scan rates are lower than 100 mV s−1. However, RGOA maintains a higher capacitance in KOH electrolyte when the scan rates exceed 100 mV s−1, which is probably due to the higher ionic concentration of KOH electrolyte than that of H2SO4 electrolyte. The galvanostatic charge–discharge curves of RGOA in different electrolytes are composed of two parts: the first part is within the potential window of 0.0 ~ −0.3 V in KOH electrolyte and 0.6 ~ 1.0 V in H2SO4 electrolyte, which is attributed to the electric double-layer capacitance. The other part exhibits a longer duration time, indicating the existence of pseudocapacitance besides the electric double-layer capacitance. As shown in Figure 4d, capacitance retention ratios of RGOA remain 74% and 63% in KOH and H2SO4 electrolytes when current density increases from 0.2 to 20 A g−1, exhibiting a high-rate capacitive performance. This high-rate performance is mainly attributed to the three-dimensional structure, which is beneficial for the ionic diffusion of electrolyte to the inner pores of bulk material. As shown in Figure 4d, the specific capacitances are calculated to be 211.8 and 278.6 F g−1 in KOH and H2SO4 electrolytes at the current density of 0.2 A g−1. The specific capacitances per surface area are calculated to be 25.5 and 33.6 μF cm−2 in KOH and H2SO4 electrolytes, respectively, indicating more pseudocapacitance in H2SO4 electrolyte. These results coincide well with the cyclic voltammetry measurements.
A simultaneous self-assembly and reduction method is adopted to successfully synthesize the reduced graphene oxide aerogel with the specific surface area of 830 m2 g−1, which is the largest value ever reported for graphene-based aerogels obtained through the simultaneous self-assembly and reduction strategy. Systematic characterizations suggest that the as-prepared RGOA is a three-dimensional mesoporous material with functionalized surface. Electrochemical tests show that RGOA exhibits high-rate supercapacitive performance. Its specific capacitances reach as high as 211.8 and 278.6 F g−1 in KOH and H2SO4 electrolytes, respectively. The perfect supercapacitive performance of RGOA is ascribed to its three-dimensional structure and the existence of oxygen-containing groups.
This work was financially supported by the Natural Science Foundation of China (51107076), Distinguished Young Scientist Foundation of Shandong Province (JQ201215), China University of Petroleum (13CX02004A), Outstanding Young Scientist Foundation of Shandong Province (BS2009NJ014), and Key Sci-Tech Development Project of Shandong Province (2009GG10007006).
- Conway BE: Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications. New York: Kluwer-Plenum; 1999.View ArticleGoogle Scholar
- Karandikar PB, Talange DB, Mhaskar UP, Bansal R: Development, modeling and characterization of aqueous metal oxide based supercapacitor. Energy 2012, 40: 131–138. 10.1016/j.energy.2012.02.020View ArticleGoogle Scholar
- Nishihara H, Kyotani T: Templated nanocarbons for energy storage. Adv Mater 2012, 24: 4473–4498. 10.1002/adma.201201715View ArticleGoogle Scholar
- Snook GA, Kao P, Best AS: Conducting-polymer-based supercapacitor devices and electrodes. J Power Sources 2011, 196: 1–12. 10.1016/j.jpowsour.2010.06.084View ArticleGoogle Scholar
- Kim C, Choi Y-O, Lee W-J, Yang K-S: Supercapacitor performances of activated carbon fiber webs prepared by electrospinning of PMDA-ODA poly(amic acid) solutions. Electrochim Acta 2004, 50: 883–887. 10.1016/j.electacta.2004.02.072View ArticleGoogle Scholar
- Sivakkumar SR, Ko JM, Kim DY, Kim BC, Wallace GG: Performance evaluation of CNT/polypyrrole/MnO2 composite electrodes for electrochemical capacitors. Electrochim Acta 2007, 52: 7377–7385. 10.1016/j.electacta.2007.06.023View ArticleGoogle Scholar
- Xing W, Huang CC, Zhuo SP, Yuan X, Wang GQ, Hulicova-Jurcakova D, Yan ZF, Lu GQ: Hierarchical porous carbons with high performance for supercapacitor electrodes. Carbon 2009, 47: 1715–1722. 10.1016/j.carbon.2009.02.024View ArticleGoogle Scholar
- Xing W, Qiao SZ, Ding RG, Li F, Lu GQ, Yan ZF, Cheng HM: Superior electric double layer capacitors using ordered mesoporous carbons. Carbon 2006, 44: 216–224. 10.1016/j.carbon.2005.07.029View ArticleGoogle Scholar
- Bai Y, Rakhi RB, Chen W, Alshareef HN: Effect of pH-induced chemical modification of hydrothermally reduced graphene oxide on supercapacitor performance. J Power Sources 2013, 233: 313–319.View ArticleGoogle Scholar
- Li Y, van Zijll M, Chiang S, Pan N: KOH modified graphene nanosheets for supercapacitor electrodes. J Power Sources 2011, 196: 6003–6006. 10.1016/j.jpowsour.2011.02.092View ArticleGoogle Scholar
- Liu C, Yu Z, Neff D, Zhamu A, Jang BZ: Graphene-based supercapacitor with an ultrahigh energy density. Nano Lett 2010, 10: 4863–4868. 10.1021/nl102661qView ArticleGoogle Scholar
- Liu Y, Zhang Y, Ma G, Wang Z, Liu K, Liu H: Ethylene glycol reduced graphene oxide/polypyrrole composite for supercapacitor. Electrochim Acta 2013, 88: 519–525.View ArticleGoogle Scholar
- Sun D, Yan X, Lang J, Xue Q: High performance supercapacitor electrode based on graphene paper via flame-induced reduction of graphene oxide paper. J Power Sources 2013, 222: 52–58.View ArticleGoogle Scholar
- Balandin AA, Ghosh S, Bao W, Calizo I, Teweldebrhan D, Miao F, Lau CN: Superior thermal conductivity of single-layer graphene. Nano Lett 2008, 8: 902–907. 10.1021/nl0731872View ArticleGoogle Scholar
- Lee C, Wei X, Kysar JW, Hone J: Measurement of the elastic properties and intrinsic strength of monolayer graphene. Science 2008, 321: 385–388. 10.1126/science.1157996View ArticleGoogle Scholar
- Xu Y, Sheng K, Li C, Shi G: Self-assembled graphene hydrogel via a one-step hydrothermal process. ACS Nano 2010, 4: 4324–4330. 10.1021/nn101187zView ArticleGoogle Scholar
- Chen W, Yan L: In situ self-assembly of mild chemical reduction graphene for three-dimensional architectures. Nanoscale 2011, 3: 3132–3137. 10.1039/c1nr10355eView ArticleGoogle Scholar
- Pham HD, Pham VH, Cuong TV, Nguyen-Phan T-D, Chung JS, Shin EW, Kim S: Synthesis of the chemically converted graphene xerogel with superior electrical conductivity. Chem Commun 2011, 47: 9672–9674. 10.1039/c1cc13329bView ArticleGoogle Scholar
- Wang J, Shi Z, Fan J, Ge Y, Yin J, Hu G: Self-assembly of graphene into three-dimensional structures promoted by natural phenolic acids. J Mater Chem 2012, 22: 22459–22466. 10.1039/c2jm35024fView ArticleGoogle Scholar
- Zhang X, Sui Z, Xu B, Yue S, Luo Y, Zhan W, Liu B: Mechanically strong and highly conductive graphene aerogel and its use as electrodes for electrochemical power sources. J Mater Chem 2011, 21: 6494–6497. 10.1039/c1jm10239gView ArticleGoogle Scholar
- Wu X, Zhou J, Xing W, Wang G, Cui H, Zhuo S, Xue Q, Yan Z, Qiao SZ: High-rate capacitive performance of graphene aerogel with a superhigh C/O molar ratio. J Mater Chem 2012, 22: 23186–23193. 10.1039/c2jm35278hView ArticleGoogle Scholar
- Worsley MA, Kucheyev SO, Mason HE, Merrill MD, Mayer BP, Lewicki J, Valdez CA, Suss ME, Stadermann M, Pauzauskie PJ, Satcher JH Jr, Biener J, Baumann TF: Mechanically robust 3D graphene macroassembly with high surface area. Chem Commun 2012, 48: 8428–8430. 10.1039/c2cc33979jView ArticleGoogle Scholar
- Worsley MA, Pauzauskie PJ, Olson TY, Biener J, Satcher JH, Baumann TF: Synthesis of graphene aerogel with high electrical conductivity. J Am Chem Soc 2010, 132: 14067–14069. 10.1021/ja1072299View ArticleGoogle Scholar
- Worsley MA, Olson TY, Lee JRI, Willey TM, Nielsen MH, Roberts SK, Pauzauskie PJ, Biener J, Satcher JH, Baumann TF: High surface area, sp2-cross-linked three-dimensional graphene monoliths. J Phys Chem Lett 2011, 2: 921–925. 10.1021/jz200223xView ArticleGoogle Scholar
- Xu B, Yue S, Sui Z, Zhang X, Hou S, Cao G, Yang Y: What is the choice for supercapacitors: graphene or graphene oxide? Energy & Environmental Science 2011, 4: 2826–2830. 10.1039/c1ee01198gView ArticleGoogle Scholar
- Hummers WS, Offeman RE: Preparation of graphitic oxide. J Am Chem Soc 1958, 80: 1339. 10.1021/ja01539a017View ArticleGoogle Scholar
- Park S-H, Bak S-M, Kim K-H, Jegal J-P, Lee S-I, Lee J, Kim K-B: Solid-state microwave irradiation synthesis of high quality graphene nanosheets under hydrogen containing atmosphere. J Mater Chem 2011, 21: 680–686. 10.1039/c0jm01007cView ArticleGoogle Scholar
- Wu Z-S, Ren W, Gao L, Zhao J, Chen Z, Liu B, Tang D, Yu B, Jiang C, Cheng H-M: Synthesis of graphene sheets with high electrical conductivity and good thermal stability by hydrogen arc discharge exfoliation. ACS Nano 2009, 3: 411–417. 10.1021/nn900020uView ArticleGoogle Scholar
- Ferrari AC, Robertson J: Raman spectroscopy of amorphous, nanostructured, diamond-like carbon, and nanodiamond. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 2004, 362: 2477–2512. 10.1098/rsta.2004.1452View ArticleGoogle Scholar
- Su C-Y, Xu Y, Zhang W, Zhao J, Tang X, Tsai C-H, Li L-J: Electrical and spectroscopic characterizations of ultra-large reduced graphene oxide monolayers. Chem Mater 2009, 21: 5674–5680. 10.1021/cm902182yView ArticleGoogle Scholar
- Gao J, Liu F, Liu Y, Ma N, Wang Z, Zhang X: Environment-friendly method to produce graphene that employs vitamin C and amino acid. Chem Mater 2010, 22: 2213–2218. 10.1021/cm902635jView ArticleGoogle Scholar
- Shin H-J, Kim KK, Benayad A, Yoon S-M, Park HK, Jung I-S, Jin MH, Jeong H-K, Kim JM, Choi J-Y, Lee YH: Efficient reduction of graphite oxide by sodium borohydride and its effect on electrical conductance. Adv Funct Mater 2009, 19: 1987–1992. 10.1002/adfm.200900167View ArticleGoogle Scholar
- Stankovich S, Dikin DA, Piner RD, Kohlhaas KA, Kleinhammes A, Jia Y, Wu Y, Nguyen ST, Ruoff RS: Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide. Carbon 2007, 45: 1558–1565. 10.1016/j.carbon.2007.02.034View ArticleGoogle Scholar
- Fan X, Peng W, Li Y, Li X, Wang S, Zhang G, Zhang F: Deoxygenation of exfoliated graphite oxide under alkaline conditions: a green route to graphene preparation. Adv Mater 2008, 20: 4490–4493. 10.1002/adma.200801306View ArticleGoogle Scholar
- Gao W, Alemany LB, Ci L, Ajayan PM: New insights into the structure and reduction of graphite oxide. Nat Chem 2009, 1: 403–408. 10.1038/nchem.281View ArticleGoogle Scholar
- Fernández-Merino MJ, Guardia L, Paredes JI, Villar-Rodil S, Solís-Fernández P, Maertínez-Alonso A, Tascón MD: Vitamin C is an ideal substitute for hydrazine in the reduction of graphene oxide suspensions. J Phys Chem C 2010, 114: 6426–6432. 10.1021/jp100603hView ArticleGoogle Scholar
- Sun G, Long D, Liu X, Qiao W, Zhan L, Liang X, Ling L: Asymmetric capacitance response from the chemical characteristics of activated carbons in KOH electrolyte. J Electroanal Chem 2011, 659: 161–167. 10.1016/j.jelechem.2011.05.017View ArticleGoogle Scholar
- Frackowiak E, Metenier K, Bertagna V, Beguin F: Supercapacitor electrodes from multiwalled carbon nanotubes. Appl Phys Lett 2000, 77: 2421–2423. 10.1063/1.1290146View ArticleGoogle Scholar
- Pan H, Poh CK, Feng YP, Lin J: Supercapacitor electrodes from tubes-in-tube carbon nanostructures. Chem Mater 2007, 19: 6120–6125. 10.1021/cm071527eView ArticleGoogle Scholar
- Stoller MD, Park S, Zhu Y, An J, Ruoff RS: Graphene-based ultracapacitors. Nano Lett 2008, 8: 3498–3502. 10.1021/nl802558yView ArticleGoogle Scholar
- Meher SK, Justin P, Rao GR: Pine-cone morphology and pseudocapacitive behavior of nanoporous nickel oxide. Electrochim Acta 2010, 55: 8388–8396. 10.1016/j.electacta.2010.07.042View ArticleGoogle Scholar
- Zhang J, Jiang J, Li H, Zhao XS: A high-performance asymmetric supercapacitor fabricated with graphene-based electrodes. Energy & Environmental Science 2011, 4: 4009–4015. 10.1039/c1ee01354hView ArticleGoogle Scholar
- He Y, Chen W, Li X, Zhang Z, Fu J, Zhao C, Xie E: Freestanding three-dimensional graphene/MnO2 composite networks as ultralight and flexible supercapacitor electrodes. ACS Nano 2013, 7: 174–182. 10.1021/nn304833sView ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.