Porous Functionalized Self-Standing Carbon Fiber Paper Electrodes

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Porous Functionalized Self-Standing Carbon Fiber Paper Electrode for High Performance Capacitive Energy Storage Yuanyuan Zhu, Shuang Cheng, Weijia Zhou, Jin Jia, Lufeng Yang, Minghai Yao, Mengkun Wang, Peng Wu, Haowei Luo, and Meilin Liu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b01210 • Publication Date (Web): 29 Mar 2017 Downloaded from http://pubs.acs.org on March 29, 2017

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ACS Applied Materials & Interfaces

Porous Functionalized Self-Standing Carbon Fiber Paper Electrode for High Performance Capacitive Energy Storage Yuanyuan Zhu,a Shuang Cheng,*a Weijia Zhou,a Jin Jia,a Lufeng Yang,a Minghai Yao,a Mengkun Wang,a Peng Wu,a Haowei Luo,a and Meilin Liu*ab a

Guanzhou Key Laboratory for Surface Chemistry of Energy Materials, New Energy

Research Institute, School of Environment and Energy, South China University of Technology, Guangzhou, 510006, China b

School of Materials Science and Engineering, Georgia Institute of Technology,

Atlanta, GA 30332-0245, USA ABSTRACT: A facile and cost-efficient approach to functionalize raw carbon fiber paper (CFP) used for self-standing capacitive electrode has been proposed here. Benefit by improved specific surface area and surface functional groups, the functionalized CFP (F-CFP) emerged much enhanced capacitive performance, three orders of magnitude higher than the raw CFP. It delivered the areal capacitance of 1275 mF cm-2 at 5 mA cm-2 with a rather wide voltage window of 1.4 V (-0.4 ~ 1 V vs Ag/AgCl) in 0.5 M H2SO4. While, in neutral 1 M Na2SO4 aqueous solution, though the areal capacitance of 1115 mF cm-2 at 3 mA cm-2 is slightly smaller, the potential window is much wider (2 V, -1 ~ 1 V vs Ag/AgCl), indicating high overpotential of hydrogen evolution. The areal capacitance was still as high as 722 mF cm-2 at very fast charge-discharge current density of 50 mA cm-2, and about 66 % of the initial capacitance (at 3 mA cm-2) was remained in Na2SO4, indicating considerable rate capability. KEYWORDS: carbon fiber paper, functionalize, wide potential window, high

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capacity, supercapacitors 1. INTRODUCTION Supercapacitors (SCs), as fast and high energy storage systems, have attracted tremendous attention since its advent.1-5 With the rapid developing of portable electronic equipments, energy storage equipments for wind, hybrid electric vehicles and so on, human’ expecting to SCs with good performance is fast growing.6 Scientists are lining up to explore advanced materials or techniques for new generation SCs with fast, high, sustainable and safe energy storage abilities. Besides, cost and green are also important assessment indicators. From now on and in the near future, it will be a protracted war for scientists to develop such energy storage sets to meet all these requirements. To realize low cost, high safety, fast charge/discharge ability, high cycling stability and green, aqueous solution based electrolyte is always the best choice with only one shortage, relative low energy storage density (E), which is concerned with specific capacity (C) and voltage window (V, E=1/2CV2).7-8 Consequently, the development and research of electrode materials with wide potential window and high capacity in aqueous solution have become important target that needs the scientists to go all out. At present, carbon-based materials with excellent conductivity, great surface area and impressive chemical stability,9 including carbon nanotubes,10-12 carbon aerogel,13-15 graphene16-18 and carbon nanofibers,19-22 have been widely considered as electrode materials for SCs. However, their widely commercial applications in high energy density fields have been hindered by the low capacity due to their intrinsic energy 2


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storage mechanism, electric double-layer (EDL) process. In recently years, transition metal based compounds or their composites with carbon have been becoming new favorites due to their superimposed energy storage ability from both EDL and Faradic reactions. However, though the specific capacitance of some composites can achieve a very high value, such as Co3O4@MnO2 with 1693.2 F g-1 at 1 A g-1, 23 Ni(OH)2 with 2064 F g-1 at 2 A g-1,24 MnCo2O4 @Ni(OH) with 2154 F g-1 at 5 A g-1,25 the limited mass loading of these active materials on current collector is still a problem that hard can be resolved. Besides, the potential window of most of the transition metal based composites is always as narrow as ~0.6V in aqueous electrolyte.26-29 The limited mass loading of active materials can be alleviated in some degree by the improvement of their conductivity through doping or composition, or by the construction of nano-scaled current collectors, e.g. carbon nanofiber paper,30-33 filmed graphene34-35 and filmed carbon nanotubes.36-38 While the issue of narrow potential window can be sugar-coated by the design of asymmetrical cells,39-41 which will come down to another challenge, the searching of suitable anode materials. In general, it is quite short of solutions to develop new SCs with high energy density (in weight and in volume) for the whole cell in aqueous based electrolyte. Construction of carbon based self-standing films without current collector or any other additives to optimize the mass of the whole electrode is an effective way to enhance the weight energy density of the whole cell. Various of such type of electrodes has been studied, including activated carbon cloth (88 mF cm-2 at 10 mV s-1),42 activated porous-carbon (42 mF cm-2 at 1 mA cm-2),43 as well as 3D hierarchical 3



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porous carbon fibers44-46 and Hierarchical Porous Graphene Films (71 mF cm-2 at 1 mA cm-2).47 These electrodes all exhibited impressive areal capacitances. Very recently, Lu et al30 developed a very facile approach to facilitate the capacity of CFP and a relative large areal capacitance of 1.56 F cm-2 at 5 mA cm-2 was obtained. However, the conductivity of the electrode is poor speculated from the poor capacitance retention at fast scan rate, also the potential window is only 1 V (0 ~ 1.0 V vs SCE) in 1 M H2SO4. In this work, self-standing capacitive F-CFP electrodes with high electrochemical performance were obtained through a rather facile and cost-efficient two-step treatment to raw CFP, including thermal oxidation in air and chemical oxidation by ultrasound in a mixed H2SO4 and HNO3 solution. After treatment, the specific surface area of the CFP was greatly improved and abundant functional groups were established on the surface. The functionalized CFP (F-CFP), as a final electrode without any other additives, emerged much enhanced capacitive performance. It delivered the areal capacitance of 1275 mF cm-2 at 5 mA cm-2 with a wide voltage window of 1.4 V (-0.4 ~ 1 V vs Ag/AgCl) in 0.5 M H2SO4. While, in 1 M Na2SO4 aqueous solution, though the obtained areal capacitance of 1115 mF cm-2 at 3 mA cm-2 is slightly smaller, the potential window is much wider (2 V, -1~1 V vs Ag/AgCl), indicating high overpotential of hydrogen evolution. The areal capacitance was still as high as 722 mF cm-2 at very high current density of 50 mA cm-2, and about 66 % of the initial capacitance (at 3 mA cm-2) was remained in Na2SO4, indicating high rate capability. The volume capacity of a single electrode can achieve 4


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about 56 F cm-3 at 3 mA cm-2 with a thickness of about 0.2 mm and an energy density of 31 mWh cm-3, which is comparable with the commercial used SCs, but much lower cost and higher safety. 2. EXPERIMENTAL SECTION 2.1. Preparation of porous F-CFP electrode The raw CFPs (0.2 mm thick) used were purchased from Shanghai Hesen Electric. Co. Ltd. in China. Before treatment, pieces of CFPs were cleaned with alcohol and deionized water by soaking in a sonic bath for five to ten minutes and dried in an oven for 1 h at 60 °C. The washed raw/original CFPs (denoted as O-CFPs) which were calcined at 300~600 °C under static air for 0.5~5 h in a muffle furnace. Then the calcined CFPs (denoted as C-CFPs) were dipped in a mixed H2SO4 and HNO3 in a ratio of 1:3 sonicated for 2 h, cleaned with a mass of deionized water, dried in an oven at 60 °C for 24 h and weighed, denoted as F-CFPs. The concentrated acid treatment process is actually a chemical oxidation process to the CFP, which can introduce amount oxygen-containing functional groups and make the CFP hydrophilic. The original and treated CFPs were directly used as working electrodes without any other additives. Additionally, if no particular explanation, C-CFP stands for the sample calcined at 500 °C. 2.2. Characterization Morphologies of the sample were observed by a Field Emission Scanning Electron Microscope (FESEM, MERLIN Compact, Carl Zeiss). X-ray photoelectron spectroscopic (XPS) measurement was performed using a PHI X-tool instrument 5



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(Ulvac-Phi). Raman spectra were obtained by a LabRAM HR800 spectrometer (Horiba Jobin Yvon, FR.) equiped with an Ar laser (wavelength = 514.5 nm) and a long working distance 50× objective lens. Brunauer-Emmet-Teller (BET) surface area was determined using a Quantachrome Autosorb-iQ2 instrument with nitrogen adsorption at 77 K. Pore size distribution (PSD) was evaluated by the quenched solid density functional theory (QSDFT). 2.3. Electrochemical measurements The electrochemical performances of the treated F-CFPs were characterized by both three-electrode and two-electrode systems. In a three-electrode system, CFPs with a geometric area of about 1 cm2 (14 mg) were used directly as working electrode without conductive additives or binders. A platinum (Pt) mesh of 1 cm2 and an Ag/AgCl (in saturated KCl) were served as counter and reference electrode, respectively. Symmetric cell was assembled with two same pieces of face-to-face F-CFPs, separated by a glass microfiber filter in a CR 2032 coin cell. Aqueous solution of 1 M Na2SO4 or 0.5 M H2SO4 were used as electrolyte. The electrochemical measurements, including cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and the long cycle life, were carried out on a CHI 660E electrochemical workstation. 3. RESULTS AND DISCUSSION

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Figure 1. SEM images of O-CFPs (a, d), C-CFPs (b, e) and F-CFPs (c, f) enlarged at different part (a-c, carbon microwires; and d-f, carbon blocks among the wires).

Morphology changes of the CFPs before and after treated were investigated by FESEM first, as presented in Figure 1. For O-CFP, the surface of its micron wires is relative smooth though there are some carbon particles attached on (Figure 1a). While, after calcination and the following acid treatment, it is clear to see that the surface of wires (Figures 1b, c) changed to be rough and porous, even abundant small pores can be recognized after calcination which are more opening after acid treatment. Except the cross-linked micron wires in the CFP, there are a lot large blocks distributed in Figure S1, some of which were splitted to thin flakes after treatment (Figures 1e, f). The obvious morphology change would lead to higher specific surface area, and hence larger electronic double layer capacity.

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Figure 2. N2 sorption isotherms at 77 K (a) and pore size distributions (b) of O-CFP, C-CFP and F-CFP.

To clearly demonstrate the origin of high electrochemical performance of the treated CFPs, specific surface areas of the CFPs at different stages were characterized by nitrogen sorption analysis (Figure 2). All the three samples exhibited typical Type-IV isotherms with upward tails at P/P0 ≈ 1.0, demonstrating the existence of macropores in these materials. Besides, hysteresis loops can be found clearly from the C-CFP and F-CFP samples, implying the presence of mesopores. While, at low pressure, these two samples display considerable N2 adsorption, which can be ascribed to the presence of micropores. Detailed pore size distributions on the base of the QSDFT are shown in Figure 2b. Results show that there are almost no pore structures in O-CFP, while treated C-CFP and F-CFP have broader pore size distributions from micropores to larger mesopores. The pore widths of the C-CFP mainly focus on ~0.9 nm, ~2.5 nm and ~4 nm. After further acid treatment, the pores were amplified to be ~1.1 nm, ~3.2 nm and 6.2 nm, following with specific surface area change, which was slightly reduced to be 97 m2 g-1 from 110 m2 g-1, markedly larger than that of O-CFP with 3 m2 g-1, calculated from the nitrogen sorption results with the Brunauer-Emmett-Teller 8


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(BET) theory.

Figure 3. (a) C 1s spectra fitting into C chemical groups for XPS spectrum recorded for F-CFP; (b) Raman spectra of the O-CFP, C-CFP and F-CFP captured from the microfibers.

For carbon base electrodes, except surface area, surface functional groups are also vital to the energy storage ability. Therefore, surface oxygen-containing functional groups were detected by X-ray photoelectron spectroscopy elemental analysis, as shown in Figure 3a and Figure S2. Compared with O-CFP, C 1s peak of F-CFP exhibits a clearly blue shift and emerges a binding energy shoulder, which is ascribed to the occurrence of oxygen-containing functionalities, as presented in Figure S2. Detailed C 1s peak information recorded for F-CFP was obtained using a Gaussian-Lorentzian (GL80) functions fitting and a Shirley background subtraction, shown in Figure 3a. The main binding energy peak centered at 284.5 eV corresponding to the C-C banding in-plane. While, the other peaks splitted at 285.8 eV, 287.6 eV, 288.9 eV can be addressed to the hydroxyl group (C-OH), carbonyl group (C=O) and carboxyl group (COOH),48-49 respectively, indicating the existence of 9



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corresponding oxygenated carbon species on the surface. The ratio of C 1s and O 1s peak intensities displays that the O/C ratio increases from 3.18 % for O-CFP to 23.78 % for F-CFP, clearly suggesting that abundant oxygen-containing functional groups were introduced along with oxidation treatments (Table S1). To further confirm the surface structure change, Raman spectra were captured from microfibers of the CFP, which display the characteristic D, G, and 2D bands of carbonaceous materials at ~1347, ~1596 and ~2706 cm-1, respectively, as presented in Figure 3b. Calculated ID/IG and I2D/IG ratios based on the corresponding bands were summarized in Table S1. The ID/IG of F-CFP increased while the I2D/IG ratios decreased compared with the O-CFP, implying that more defects were introduced into the graphite planes (higher surface disorder and fewer in-plane sp2-hybrid carbon domains), which is in accordance with the XPS results (abundant oxygen-containing groups were introduced after two-step oxidation treatment).

Figure 4. CV curves of O-CFP, C-CFP and F-CFP at a scan rate of 50 mV s-1 in (a) 1 M Na2SO4 and (b) 0.5 M H2SO4 electrolyte aqueous solution.

Electrochemical performances of the samples were investigated in a three-electrode testing system with 1 M Na2SO4 and 0.5 M H2SO4 electrolyte. The parameters of first 10


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step oxidation, calcination, were optimized through detecting the performance change along with calcination temperatures and durations in 1 M Na2SO4 at a scan rate of 50 mV s-1 (Figure S3) and 500 °C for 4 h was fixed with the best performance. CV area of the O-CFP was largely enhanced after calcinations and was further improved to be about twice after acid treatment. Surprisingly, the curves exhibited not only an ideal capacitive response with rectangular shapes, but a very wide voltage window from -1 to 1 V vs Ag/AgCl, signifying the sample is suitable for both anode and cathode for SCs in aqueous electrolyte. The areal capacitance of C-CFP was determined to be 399 mF cm-2, revealing more than 130 times higher with respect to the O-CFP (below 3 mF cm-2) as shown in Figure 4a, which can be mainly ascribed to the surface area increase that benefits for the EDL capacity. The areal capacitance can achieve as high as 786 mF cm-2 after acid oxidation and an obvious redox pair emerged in the CV curve. According to the above XPS analysis, the further increased capacitance should be attributed to the pseudocapacitive contribution aroused from the oxygen-containing functional groups of F-CFP (surface redox reaction). Furthermore, CV profiles of the electrodes in acid electrolyte (0.5 M H2SO4 aqueous solution) were also recorded, as presented in Figure 4b. As expected, areal capacitance of the F-CFP is as high as 928 mF cm-2 calculated from the CV curve at high scan rate of 50 mV s-1, much higher than that of the other electrodes and that of F-CFP itself in Na2SO4 aqueous solution. Moreover, in acid electrolyte, the redox peaks became more pronounced, indicating enhanced Faradaic reactions at the electrode surface. The capacity difference originated from different electrolyte is always concerned with electrolyte cations’ size 11



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and diffusion rate. In this case, the concentration of the hydronium should devote the main contribution to the improved capacity due to the proton involved Faradic reactions with the surface function groups, which were prior proposed as following:50-51 − COOH ⇔ COO + H+ + e−, ˃ C – OH ⇔ ˃ C = O + H+ + e−, ˃ C = O + e− ⇔ ˃ C – O−. Two types of hydroxyl group’ Faradic reaction are concerned with H+’ adsorption and release. Hence, higher pseudocapacitance could be expectable in acidic solutions compared to neutral electrolytes, yet narrower potential window.

Figure 5. Electrochemical characterizations of F-CFP electrode with an aqueous solution of 1 M Na2SO4 as electrolyte. (a) CV and (b) GCD curves at various scan 12


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rates and current densities with a voltage window from -1 to 1 V (vs Ag/AgCl); (c) Corresponding areal capacitances based on CV curves (black curve) and GCD curves (red curve); (d) Cycling stability and coulombic efficiency measured by galvanostatic charge/discharge at 50 mA cm-2.

Detailed electrochemical properties of the F-CFP electrode were inspected with CV and GCD measurements in 1 M Na2SO4, as shown in Figure 5. CV profiles keep near-rectangular shapes even at a high scan rate of 100 mV s-1 and contain a weak redox pair with a rather large half width (Figure 5a). No oxygen or hydrogen evolution reaction concerned irreversible tails can be observed from the CV curve in the wide voltage window from -1 V to 1 V vs Ag/AgCl. Moreover, GCD profiles are close to linear shape and no obvious voltage drop in the GCD curves can be observed (Figure 5b). Corresponding areal capacities calculated from the CV and GCD results were shown in Figure 5c (detailed calculation method was described in supporting information (SI)). As scan rate varies from 5 to 100 mV s-1, the areal capacitance decreased from 1138 to 673 mF cm-2, similar values with those obtained from GCD results at different discharge currents, which is 1115 mF cm-2 at 3 mA cm-2, still as high as 722 mF cm-2 even at a high current density of 50 mA cm-2. About 66% of the initial capacity (at 3 mA cm-2) was remained when the current density increased ~17 times, suggesting good rate capability and high power density. Furthermore, stability test of the F-CFP was performed with galvanostatic charge/discharge cycling at a high current density of 50 mA cm-2. As shown in Figure 5d, about 95 % of the capacitance was retained after 10, 000 consecutive cycles with a slight decrease of surface 13



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functional groups (Figure S4 and Table S2) and kept unchanged after that during another round long-time-cycling (Figure S5). It's worth noting that the coulombic efficiency remained approximately at 100% during the cycling process. The cycling stability of the electrode in 0.5 M H2SO4 electrolyte is even better though the potential window is narrower (Figure S6). These results demonstrate that the F-CFP electrode possesses an excellent long-term electrochemical stability.

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Figure 6. Electrochemical characterizations of F-CFP symmetric supercapacitor with an aqueous solution of 1 M Na2SO4 as electrolyte. (a) CV curves at varied scan voltage windows; (b) CV and (c) GCD curves at various scan rates and current densities with the maximum potential window of 2.0 V; (d) Corresponding areal

capacitances based on the CV and GCD results; (e) Ragone plot for the relation of energy density and power density; (f) Cycle performance measured at a current density of 20 mA cm-2.

The electrode of F-CFP exhibits good electrochemical performance with a rather wide potential window in a three-electrode system as demonstrated above, similar with its behavior in a narrower potential window/within water decomposition potential (Figure S7 and S8), which emerged a much higher potential for practical application than most reported anode materials in aqueous electrolyte. Besides, the electrode is also suitable to be assembled as a full symmetrical cell with a considerable energy storage ability. The corresponding performance of a symmetric cell is elaborated in Figure 6. As shown in Figure 6a, the cell demonstrates a well capacitive CV profiles at different potential windows from 1 V to 2 V at scan rate of 50 mV s-1 without obvious energy consumption from oxygen or hydrogen evolution. With the rising of scan rates, rectangle shape of CV curves was kept even at high scan rate of 200 mV s-1, consisting with the linear GCD shapes at various current densities, implying high charge/discharge ability (Figures 6b, c). For the symmetric cell running in a potential range of 2 V, calculated capacitance can achieve 370 mF cm-2 at 1 mA cm-2 and 263 mF cm-2 at 50 mA cm-2, exhibiting high capacity maintainability. For a whole 15



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symmetric capacitive cell, the energy density can achieve 0.2 mWh cm-2 (Figure 6e), and 5 mWh cm-3 with a thickness of about 0.4 mm, and 86% of the initial capacitance was remained after 10, 000 cycles test at 20 mA cm-2 (Figure 6f), which is comparable with the commercial supercapacitors but much safer due to the aqueous electrolyte used here. Moreover, if other cathode materials with higher capacity is used for an asymmetric cell, high energy density will be obtained, such as MnO2 based cathode in Na2SO4. Performance of a symmetric cell in H2SO4 aqueous solution was also investigated and presented in Figure S9. Which showed higher capacitance about 425 mF cm-2 at 1 mA cm-2 and 350 mF cm-2 at 50 mA cm-2, and better cycling stability of only about 5 % loss after 10, 000 cycles. 4. CONCLUSIONS In the work here, a rather facile and cost-efficient method was explored to prepare a self-standing capacitive electrode with considerable energy density and power density via functionalizing commercial used carbon fiber paper (CFP) directly. The raw CFP, composed of micron sized wires and large blocks bonding on, is functionalized by heat treatment in air atmosphere and further oxidation in acid. After treatment, the specific surface area of the CFP was greatly improved and abundant functional groups were constructed on the electrode surface. The functionalized CFP (F-CFP), as a final electrode without any additions, emerged much enhanced capacitive performance. It delivered the areal capacitance of 1275 mF cm-2 at 5 mA cm-2 with a rather wide potential window of 1.4 V (-0.4 ~ 1 V vs Ag/AgCl) in 0.5 M H2SO4. While, in 1 M Na2SO4 aqueous solution, though the areal capacitance of 1115 mF cm-2 at 3 mA cm-2 16


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is slightly smaller, the potential window is much wider (2 V, -1 ~ 1 V vs Ag/AgCl), indicating high overpotential of hydrogen evolution. The areal capacitance was still as high as 722 mF cm-2 at a very high current density of 50 mA cm-2, and about 66 % of the initial capacitance (at 3 mA cm-2) was remained in 1 M Na2SO4, indicating high rate capability. The volume capacity of a whole symmetric cell is ~10 F cm-3 with a thickness of about 0.4 mm and energy density is ~5 mWh cm-3 in neutral Na2SO4 aqueous electrolyte, which is comparable with the commercial used SCs, but much lower cost and higher safety, implying high potential for commercial application. ASSOCIATED CONTENT Supporting Information Supplementary results and discussion, including low magnification SEM images of O-CFP, C-CFP and F-CFP; ID/IG and I2D/IG ratios based on the Raman spectra and surface element ratios of C and O from the XPS results of O-CFP, C-CFP and F-CFP; C 1s X-ray photoelectron spectra of O-CFP, C-CFP and F-CFP; CV curves of O-CFP at different calcination temperature and time; Electrochemical characterizations of F-CFP single electrode and symmetric supercapacitor; And calculation methods of single Electrode and symmetric supercapacitor device. AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] *E-mail: [email protected] 17



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Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS The research was supported by National Science Foundation for Young Scientists of China (no. 21403073), the Fundamental Research Funds for Central Universities of SCUT, China (no. 2015ZZ118) and Guangdong Innovative and Entrepreneurial Research Team Program (2014ZT05N200). REFERENCES (1) Simon, P.; Gogotsi, Y., Materials for Electrochemical Capacitors. Nat. Mater. 2008, 7, 845-854. (2) Xia, X.; Zhang, Y.; Fan, Z.; Chao, D.; Xiong, Q.; Tu, J.; Zhang, H.; Fan, H. J., Novel Metal@Carbon Spheres Core-Shell Arrays by Controlled Self-Assembly of Carbon Nanospheres: A Stable and Flexible Supercapacitor Electrode. Adv. Energy Mater. 2015, 5, 1401709. (3) Cheng, S.; Yang, L.; Chen, D.; Ji, X.; Jiang, Z.-j.; Ding, D.; Liu, M., Phase Evolution of an Alpha MnO2-Based Electrode for Pseudo-capacitors Probed by in Operando Raman Spectroscopy. Nano Energy 2014, 9, 161-167. (4) Zhi, M.; Xiang, C.; Li, J.; Li, M.; Wu, N., Nanostructured Carbon-Metal Oxide Composite Electrodes for Supercapacitors: a review. Nanoscale 2013, 5, 72-88. (5) Yang, P.; Mai, W., Flexible Solid-State Electrochemical Supercapacitors. Nano Energy 2014, 8, 274-290. (6) El-Kady, M. F.; Strong, V.; Dubin, S.; Kaner, R. B., Laser Scribing of High-Performance and Flexible Graphene-based Electrochemical Capacitors. Science 2012, 335, 1326-1330. (7) Lu, X.; Yu, M.; Wang, G.; Zhai, T.; Xie, S.; Ling, Y.; Tong, Y.; Li, Y., H-TiO2@MnO2//H-TiO2@C Core-shell Nanowires for High Performance and 18


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Flexible Asymmetric Supercapacitors. Adv. Mater. 2013, 25, 267-272. (8) Fan, Z.; Yan, J.; Wei, T.; Zhi, L.; Ning, G.; Li, T.; Wei, F., Asymmetric Supercapacitors Based on Graphene/MnO2 and Activated Carbon Nanofiber Electrodes with High Power and Energy Density. Adv. Funct. Mater. 2011, 21, 2366-2375. (9) Lin, T.; Chen, I. W.; Liu, F.; Yang, C.; Bi, H.; Xu, F.; Huang, F., Nitrogen-Doped Mesoporous Carbon of Extraordinary Capacitance for Electrochemical Energy Storage. Science 2015, 350, 1508-1513. (10) Wang, Z.; Luan, D.; Madhavi, S.; Hu, Y.; Lou, X. W. D., Assembling Carbon-Coated α-Fe2O3 Hollow Nanohorns on the CNT Backbone for Superior Lithium Storage Capability. Energy Environ. Sci. 2012, 5, 5252-5256. (11) Yu, J.; Lu, W.; Pei, S.; Gong, K.; Wang, L.; Meng, L.; Huang, Y.; Smith, J. P.; Booksh, K. S.; Li, Q.; Byun, J. H.; Oh, Y.; Yan, Y.; Chou, T. W., Omnidirectionally Stretchable High-Performance Supercapacitor Based on Isotropic Buckled Carbon Nanotube Films. ACS Nano 2016, 10, 5204-5211. (12) Jiang, L.; Sheng, L.; Long, C.; Fan, Z., Densely Packed Graphene Nanomesh-Carbon Nanotube Hybrid Film for Ultra-High Volumetric Performance Supercapacitors. Nano Energy 2015, 11, 471-480. (13) Hao, P.; Zhao, Z.; Tian, J.; Li, H.; Sang, Y.; Yu, G.; Cai, H.; Liu, H.; Wong, C. P.; Umar, A., Hierarchical Porous Carbon Aerogel Derived from Bagasse for High Performance Supercapacitor Electrode. Nanoscale 2014, 6, 12120-12129. (14) Hao, P.; Zhao, Z.; Leng, Y.; Tian, J.; Sang, Y.; Boughton, R. I.; Wong, C. P.; Liu, H.; Yang, B., Graphene-Based Nitrogen Self-Doped Hierarchical Porous Carbon Aerogels Derived from Chitosan for High Performance Supercapacitors. Nano Energy 2015, 15, 9-23. (15) Kim, C. H. J.; Zhao, D.; Lee, G.; Liu, J., Strong, Machinable Carbon Aerogels for High Performance Supercapacitors. Adv. Funct.Mater. 2016, 26, 4976-4983. (16) Parvez, K.; Li, R.; Puniredd, S. R.; Hernandez, Y.; Hinkel, F.; Wang, S.; Feng, X.; Müllen, K., Electrochemically Exfoliated Graphene as Solution-Processable, Highly Conductive Electrodes for Organic Electronics. ACS nano 2013, 7, 3598-3606. 19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(17) Bonaccorso, F.; Colombo, L.; Yu, G.; Stoller, M.; Tozzini, V.; Ferrari, A. C.; Ruoff, R. S.; Pellegrini, V., 2D materials. Graphene, Related Two-Dimensional Crystals, and Hybrid Systems for Energy Conversion and Storage. Science 2015, 347, 1246501. (18) Kim, H.-K.; Bak, S.-M.; Lee, S. W.; Kim, M.-S.; Park, B.; Lee, S. C.; Choi, Y. J.; Jun, S. C.; Han, J. T.; Nam, K.-W.; Chung, K. Y.; Wang, J.; Zhou, J.; Yang, X.-Q.; Roh, K. C.; Kim, K.-B., Scalable Fabrication of Micron-Scale Graphene Nanomeshes for High-performance Supercapacitor Applications. Energy Environ. Sci. 2016, 9, 1270-1281. (19) Chen, L.-F.; Zhang, X.-D.; Liang, H.-W.; Kong, M.; Guan, Q.-F.; Chen, P.; Wu, Z.-Y.; Yu, S.-H., Synthesis of Nitrogen-Doped Porous Carbon Nanofibers as an Efficient Electrode Material for Supercapacitors. ACS nano 2012, 6, 7092-7102. (20) Ma, C.; Song, Y.; Shi, J.; Zhang, D.; Zhai, X.; Zhong, M.; Guo, Q.; Liu, L., Preparation and One-Step Activation of Microporous Carbon Nanofibers for Use as Supercapacitor Electrodes. Carbon 2013, 51, 290-300. (21) Kim, C. H.; Wee, J.-H.; Kim, Y. A.; Yang, K. S.; Yang, C.-M., Tailoring the Pore Structure

of

Carbon

Nanofibers

for

Achieving

Ultrahigh-Energy-Density

Supercapacitors Using Ionic Liquids as Electrolytes. J. Mater. Chem. A 2016, 4, 4763-4770. (22) Magana, J. R.; Kolen'ko, Y. V.; Deepak, F. L.; Solans, C.; Shrestha, R. G.; Hill, J. P.; Ariga, K.; Shrestha, L. K.; Rodriguez-Abreu, C., From Chromonic Self-Assembly to Hollow Carbon Nanofibers: Efficient Materials in Supercapacitor and Vapor-Sensing Applications. ACS Appl. Mater. Interfaces 2016, 8, 31231-31238. (23) Kong, D.; Luo, J.; Wang, Y.; Ren, W.; Yu, T.; Luo, Y.; Yang, Y.; Cheng, C., Three-Dimensional Co3O4@MnO2 Hierarchical Nanoneedle Arrays: Morphology Control and Electrochemical Energy Storage. Adv. Funct. Mater. 2014, 24, 3815-3826. (24) Sun, W.; Rui, X.; Ulaganathan, M.; Madhavi, S.; Yan, Q., Few-Layered Ni(OH)2 Nanosheets for High-Performance Supercapacitors. J. Power Sources 2015, 295, 323-328. 20


Page 20 of 25

Page 21 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(25) Zhao, Y.; Hu, L.; Zhao, S.; Wu, L., Preparation of MnCo2O4@Ni(OH)2 Core-Shell Flowers for Asymmetric Supercapacitor Materials with Ultrahigh Specific Capacitance. Adv. Funct. Mater. 2016, 26, 4085-4093. (26) Zhou, W.; Cao, X.; Zeng, Z.; Shi, W.; Zhu, Y.; Yan, Q.; Liu, H.; Wang, J.; Zhang, H., One-Step Synthesis of Ni3S2 Nanorod@Ni(OH)2 Nanosheet Core-Shell Nanostructures on a Three-Dimensional Graphene Network for High-Performance Supercapacitors. Energy Environ. Sci. 2013, 6, 2216-2221. (27) Wang, L.; Dong, Z. H.; Wang, Z. G.; Zhang, F. X.; Jin, J., Layered α-Co(OH)2 Nanocones as Electrode Materials for Pseudocapacitors: Understanding the Effect of Interlayer Space on Electrochemical Activity. Adv. Funct. Mater. 2013, 23, 2758-2764. (28) Boota, M.; Anasori, B.; Voigt, C.; Zhao, M. Q.; Barsoum, M. W.; Gogotsi, Y., Pseudocapacitive Electrodes Produced by Oxidant-Free Polymerization of Pyrrole between the Layers of 2D Titanium Carbide (MXene). Adv. Mater. 2016, 28, 1517-1522. (29) Guan, Q.; Cheng, J.; Wang, B.; Ni, W.; Gu, G.; Li, X.; Huang, L.; Yang, G.; Nie, F., Needle-Like Co3O4 Anchored on the Graphene with Enhanced Electrochemical Performance for Aqueous Supercapacitors. ACS Appl. Mater. Interfaces 2014, 6, 7626-7632. (30) Wang, Z.; Han, Y.; Zeng, Y.; Qie, Y.; Wang, Y.; Zheng, D.; Lu, X.; Tong, Y., Activated Carbon Fiber Paper with Exceptional Capacitive Performance as a Robust Electrode for Supercapacitors. J. Mater. Chem. A 2016, 4, 5828-5833. (31) Xiao, J.; Wan, L.; Yang, S.; Xiao, F.; Wang, S., Design Hierarchical Electrodes with Highly Conductive NiCo2S4 Nanotube Arrays Grown on Carbon Fiber Paper for High-Performance Pseudocapacitors. Nano Lett. 2014, 14, 831-838. (32) Zhang, H.; Qiu, W.; Zhang, Y.; Han, Y.; Yu, M.; Wang, Z.; Lu, X.; Tong, Y., Surface Engineering of Carbon Fiber Paper for Efficient Capacitive Energy Storage. J. Mater. Chem. A 2016, 4, 18639-18645. (33)Suktha, P.; Chiochan, P.; Iamprasertkun, P.; Wutthiprom, J.; Phattharasupakun, N.; Suksomboon, M.; Kaewsongpol, T.; Sirisinudomkit, P.; Pettong, T.; Sawangphruk, M., 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

High-Performance Supercapacitor of Functionalized Carbon Fiber Paper with High Surface Ionic and Bulk Electronic Conductivity: Effect of Organic Functional Groups. Electrochim. Acta 2015, 176, 504-513. (34) Song, Y.; Feng, D. Y.; Liu, T. Y.; Li, Y.; Liu, X. X., Controlled Partial-Exfoliation of Graphite Foil and Integration with MnO2 Nanosheets for Electrochemical Capacitors. Nanoscale 2015, 7, 3581-3587. (35) Iamprasertkun, P.; Krittayavathananon, A.; Sawangphruk, M., N-Doped Reduced Graphene Oxide Aerogel Coated on Carboxyl-Modified Carbon Fiber Paper for High-Performance Ionic-Lliquid Supercapacitors. Carbon 2016, 102, 455-461. (36) Chen, H.; Zeng, S.; Chen, M.; Zhang, Y.; Li, Q., Fabrication and Functionalization of Carbon Nanotube Flms for High-Performance Flexible Supercapacitors. Carbon 2015, 92, 271-296. (37) Yuksel, R.; Sarioba, Z.; Cirpan, A.; Hiralal, P.; Unalan, H. E., Transparent and Flexible Supercapacitors with Single Walled Carbon Nanotube Thin Film Electrodes. ACS Appl. Mater. Interfaces 2014, 6, 15434-15439. (38) Chen, Y.; Du, L.; Yang, P.; Sun, P.; Yu, X.; Mai, W., Significantly Enhanced Robustness and Electrochemical Performance of Flexible Carbon Nanotube-Based Supercapacitors by Electrodepositing Polypyrrole. J. Power Sources 2015, 287, 68-74. (39) Shang, P.; Zhang, J.; Tang, W.; Xu, Q.; Guo, S., 2D Thin Nanoflakes Assembled on Mesoporous Carbon Nanorods for Enhancing Electrocatalysis and for Improving Asymmetric Supercapacitors. Adv. Funct. Mater. 2016, 26, 7766-7774. (40) Yang, P.; Ding, Y.; Lin, Z.; Chen, Z.; Li, Y.; Qiang, P.; Ebrahimi, M.; Mai, W.; Wong, C. P.; Wang, Z. L., Low-Cost High-Performance Solid-State Asymmetric Supercapacitors Based on MnO2 Nanowires and Fe2O3 Nanotubes. Nano Lett. 2014, 14, 731-736. (41) Ma, Z.; Shao, G.; Fan, Y.; Wang, G.; Song, J.; Shen, D., Construction of Hierarchical alpha-MnO2 Nanowires@Ultrathin delta-MnO2 Nanosheets Core-Shell Nanostructure with Excellent Cycling Stability for High-Power Asymmetric Supercapacitor Electrodes. ACS Appl. Mater. Interfaces 2016, 8, 9050-9058. 22


Page 22 of 25

Page 23 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(42) Wang, G.; Wang, H.; Lu, X.; Ling, Y.; Yu, M.; Zhai, T.; Tong, Y.; Li, Y., Solid-State Supercapacitor Based on Activated Carbon Cloths Exhibits Excellent Rate Capability. Adv. Mater. 2014, 26, 2676-2682. (43) Hsia, B.; Kim, M. S.; Carraro, C.; Maboudian, R., Cycling Characteristics of High Energy Density, Electrochemically Activated Porous-Carbon Supercapacitor Electrodes in Aqueous Electrolytes. J. Mater. Chem. A 2013, 1, 10518-10523. (44) Li, Y.; Lu, C.; Zhang, S.; Su, F.-Y.; Shen, W.; Zhou, P.; Ma, C., Nitrogen- and Oxygen-Enriched 3D Hierarchical Porous Carbon Fibers: Synthesis and Superior Supercapacity. J. Mater. Chem. A 2015, 3, 14817-14825. (45) Huang, Y.; Peng, L.; Liu, Y.; Zhao, G.; Chen, J. Y.; Yu, G., Biobased Nano Porous Active Carbon Fibers for High-Performance Supercapacitors. ACS Appl. Mater. Interfaces 2016, 8, 15205-15215. (46) Kaewsongpol, T.; Sawangphruk, M.; Chiochan, P.; Suksomboon, M.; Suktha, P.; Srimuk, P.; Krittayavathananon, A.; Luanwuthi, S.; Iamprasertkun, P.; Wutthiprom, J.; Phattharasupakun,

N.;

Sirisinudomkit,

P.;

Pettong,

T.;

Limtrakul,

J.,

High-Performance Supercapacitor of Electrodeposited Porous 3D Polyaniline Nanorods on Functionalized Carbon Fiber Paper: Effects of Hydrophobic and Hydrophilic Surfaces of Conductive Carbon Paper Substrates. Mater. Today Commun. 2015, 4, 176-185. (47) Xiong, Z.; Liao, C.; Han, W.; Wang, X., Mechanically Tough Large-Area Hierarchical Porous Graphene Films for High-Performance Flexible Supercapacitor Applications. Adv. Mater. 2015, 27, 4469-4475. (48) Zhuo, Q.; Gao, J.; Peng, M.; Bai, L.; Deng, J.; Xia, Y.; Ma, Y.; Zhong, J.; Sun, X., Large-Scale Synthesis of Graphene by the Reduction of Graphene Oxide at Room Temperature Using Metal Nanoparticles as Catalyst. Carbon 2013, 52, 559-564. (49) Stobinski, L.; Lesiak, B.; Malolepszy, A.; Mazurkiewicz, M.; Mierzwa, B.; Zemek, J.; Jiricek, P.; Bieloshapka, I., Graphene Oxide and Reduced Graphene Oxide Studied by the XRD, TEM and Electron Spectroscopy Methods. J. Electron Spectrosc. Relat. Phenom. 2014, 195, 145-154. (50) Frackowiak, E.; Beguin, F., Carbon Materials for the Electrochemical Storage of 23



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Energy in Capacitors. Carbon 2001, 39, 937-950. (51) Kim, Y.-T.; Ito, Y.; Tadai, K.; Mitani, T.; Kim, U.-S.; Kim, H.-S.; Cho, B.-W., Drastic Change of Electric Double Layer Capacitance by Surface Functionalization of Carbon Nanotubes. Appl. Phys. Lett. 2005, 87, 234106.

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Table of Contents Graphic 82x68mm (300 x 300 DPI)


Porous Functionalized Self-Standing Carbon Fiber Paper Electrodes

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