A Solid-State Reaction Route to Anchoring Ni(OH) - American

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A Solid-State Reaction Route to Anchoring Ni(OH)2 Nanoparticles on Reduced Graphene Oxide Sheets for Supercapacitors Zhipeng Sun and Xianmao Lu* Department of Chemical & Biomolecular Engineering, National University of Singapore, Singapore 117576 S Supporting Information *

ABSTRACT: A mechanically assisted solid-state reaction method is employed to prepare graphene/Ni(OH)2 nanocomposites for supercapacitor electrode materials. Morphological analyses reveal that, at a loading 50 wt % Ni(OH)2, nanoparticles with an average size of ∼10 nm are formed and uniformly dispersed on the surface of reduced graphene oxide sheets functionalized with benzenesulfonate. Electrochemical measurements of the composite material show a high specific capacitance of 1568 F g−1 (based on nickel hydroxide) at a current density of 4 A g−1, significantly higher than that of bare Ni(OH)2 nanoparticles prepared without the use of graphene. This much improved electrochemical performance is enabled by both the well-dispersed Ni(OH)2 nanoparticles that offer large accessible surface area and the hydrophilic functional groups on graphene surface that facilitate electrolyte transport. The scalable solid-state synthesis developed in this work is promising for a green chemical approach to the preparation of supercapacitor electrode materials with high performance.

1. INTRODUCTION Supercapacitors as a class of electrical energy storage devices have attracted much attention in recent years mainly because of their ability to deliver high power (>103 W kg−1) and to maintain long cycle life (>100000 cycles).1−5 Currently, there are three types of supercapacitor electrode materials: (i) carbon-based materials such as activated carbon and carbon nanotubes;6,7 (ii) conducting polymers such as polyaniline;8 and (iii) metal oxides or hydroxides such as RuO2,9 MnO2,10 and Ni(OH)2.11,12 For carbon-based materials, their capacitance relies primarily on electrical double-layer mechanism without the involvement of Faradic process. Therefore, despite their high charge−discharge cycling stability and high power density, carbon materials have relatively low specific capacitance, which is generally in the range of 100 to 300 F g−1.6 Conducting polymers and metal oxides, on the other hand, can offer much higher theoretical specific capacitance (e.g., >3000 F g−1 for nickel hydroxide)13 due to redox reactions (i.e., pseudocapacitance). Among a wide variety of pseudocapacitive materials based on transition metal oxides or hydroxides that have been explored,9−11 Ni(OH)2 is of particular interest because it is a cheap material with high theoretical specific capacitance.13−16 As a primary electrode material in alkaline batteries,17 Ni(OH)2 has shown well-defined pseudocapacitive behavior and thus holds great promise as a supercapacitor electrode.16,18−25 Ni(OH)2 with different morphologies and crystal structures has been prepared with methods such as electrochemical deposition,13 chemical bath deposition,22 soft template method,18 and hydrothermal15 or solvothermal26 syntheses. More interestingly, a solid-state reaction approach which allows facile scale-up has been employed to form Ni(OH)2 nanoparticles under ambient temperature.27,28 For Ni(OH)2 nanoparticles obtained with different methods, specific capacitances in the range of 300−3000 F g−1 have been reported. This wide variation of specific capacitances is because the preparation © 2012 American Chemical Society

method of Ni(OH) 2 has significant influence on its morphology and electrochemical performance. Despite the encouraging progress, one major drawback for Ni(OH)2 as supercapacitor materials is its poor conductivity (∼10−17 S/cm).17 Therefore, additives are often required for Ni(OH)2 to form composites to improve the performance.29−33 Methods including chemical precipitation23,32,34 and hydrothermal synthesis24 have been developed to fabricate Ni(OH)2/ carbon (including carbon nanotubes, mesoporous carbon, and active carbon) composites. Recently, the use of reduced graphene oxide (rGO) to boost the performance of metal oxide supercapacitors has received great interest.26,35,36 This is because graphene as a unique two-dimensional carbon material has high surface area (2630 m2 g−1) and good electrical conductivity, and it is predicted to be an excellent electrode material for energy storage devices.37−42 The addition of rGO sheets is expected to provide large support surface areas for the metal oxide nanoparticles and to improve the conductivity of the resultant composite materials.43,44 However, since rGO sheets usually suffer from serious agglomeration and loss of surface area due to van der Waals interaction between neighboring sheets, only limited improvement has been achieved so far (14−264 F g−1).38,39 One approach to prevent agglomeration of rGO nanosheets is to graft functional groups on their surface. Tour and coworkers report a mechanical method in which aryl-diazonium salts were in situ generated and reacted with rGO surface to form exfoliated and functionalized rGO sheets (F-rGO).45 It is indicated that the resulting F-rGO not only avoids serious agglomeration, but also provides a high hydrophilic surface area Special Issue: APCChE 2012 Received: Revised: Accepted: Published: 9973

November 22, 2011 January 14, 2012 January 20, 2012 January 20, 2012 dx.doi.org/10.1021/ie202706h | Ind. Eng. Chem. Res. 2012, 51, 9973−9979

Industrial & Engineering Chemistry Research

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collected and centrifuged, where the GO powder was obtained as precipitate. The resulting GO powder was filtered and washed with 3 L of diluted HCl solution (37% HCl/H2O = 1:10 v/v) followed by centrifugation. The GO powder was further washed with DI water to remove the residual HCl and dried under vacuum. Reduced graphene oxide (rGO) sheets were obtained using a chemical exfoliation method with hydrazine as the reducing agent.43 Afterward, 0.03 g of the resulting rGO was ground with 1.12 g of 1-methy-3-noctylimidazoliym tetrafluoroborate ([omim]BF4) and 0.1088 g of 4-sulfobenzenediazonium tetrafluoroborate (4-SBD) for 10 min before 0.01 g KOH was added to facilitate the functionalization.45 After 20 min, the resulting mixture was filtered on a Teflon membrane (0.45 μm pore size) and washed with acetone, ethanol, and water subsequently until the filtrate became clear and transparent. The product of F-rGO was then stored under vacuum at 60 °C for 12 h. Synthesis of Ni(OH)2 Particles and Graphene/Ni(OH)2 Composites. Ni(OH)2 powder was prepared based on a solidstate reaction.28 Briefly, a mixture of KOH (0.03 g) and NiC2O4·H2O (0.0241 g) was ground for 30 min, followed by filtering with water and ethanol. The resulting green powder containing Ni(OH)2 was stored in vacuum oven at 60 °C for 12 h before characterization. Graphene/Ni(OH)2 composite powders were also obtained based on a solid-state reaction approach (Figure 1). In a typical synthesis of F-rGO/Ni(OH)2 composite containing 50 wt % of F-rGO and 50 wt % of Ni(OH)2 (denoted as FGN5), NiC2O4·H2O (0.0241 g) and F-rGO (0.012 g) were mixed and ground in an agate mortar. After 20 min, KOH (0.03 g) was added, and the mixture was ground for an additional 30 min. The resulting powder was then filtered with water and ethanol and dried in a vacuum oven at 60 °C for 12 h. The same procedure was followed for the preparation of F-rGO/ Ni(OH)2 composites containing 30 and 70 wt % of Ni(OH)2 (denoted with FGN3 and FGN7, respectively), but with a different amount of NiC2O4·H2O. For comparison, composites containing nonfunctionalized rGO and Ni(OH)2 (50:50 wt %, denoted as GN5) were also prepared following the same procedure where rGO instead of F-rGO was used. Characterization. Powder X-ray diffraction (XRD) analyses were performed with a Bruker D8 Advance diffractometer with Cu Kα radiation (λ ≈ 1.54 Å). Fourier transform infrared (FTIR) spectra were recorded on a Shimadzu 3600 spectrometer. Morphologies of the as-prepared products were studied using a field emission transmission electron microscope (FETEM, JEOL JEM-2010) and a field emission scanning electron microscope (FESEM, LEO-1550). X-ray photoelectron spectroscopy (XPS) was performed on a Kratos AXIS UItra HAS spectrometer equipped with a monochromatized Al Kα X-ray source. Electrochemical Measurement. The working electrodes were fabricated as follows: 80 wt % active material (rGO, FrGO, Ni(OH)2, FGN5 or GN5), 15 wt % acetylene carbon, and 5 wt % polytetrafluoroethylene binder were first mixed well in ethanol to form a slurry. A 6 mg portion of the slurry was then coated onto nickel foam (surface area 1 cm2), and dried at 80 °C for 12 h in a vacuum oven, followed by pressing at a pressure of 1.5 × 107 Pa. The resulting electrode was then soaked in a 1 M KOH solution for 2 h. All electrochemical measurements were performed using a Biologic VSP potentiostat equipped with a three-electrode cell setup composed of a working electrode, a platinum foil counter-

for the loading of guest materials. The mechanically assisted solid state reaction method employed in their work and in the above-mentioned synthesis of Ni(OH)2 nanoparticles27,28 would allow mild reaction conditions, facile scale-up, and capability for green chemical synthesis. Despite the increasing interest in graphene/Ni(OH)2 composites as energy storage materials,26,31,46 however, we found that the preparation of functionalized graphene/Ni(OH)2 composites based on a solidstate reaction method is rarely reported. In this work, we developed a new synthetic route to the preparation of functionalized graphene/Ni(OH)2 composites and investigated their application as supercapacitor electrodes (Figure 1). In our

Figure 1. Mechanical-assisted synthesis of F-rGO/Ni(OH)2 composite.

mechanically assisted solid-state reaction approach, rGO is first functionalized with the benezenesulfonate group.45 The functionalized rGO sheets (F-rGO) were then coated with Ni(OH)2 nanoparticles via a solid-state reaction between NiC2O4 and KOH.27,28 The F-rGO sheets provide a large hydrophilic surface area for the loading of Ni(OH)2 nanoparticles. The functional groups on the F-rGO surface also facilitate uniform dispersion of Ni(OH)2 nanoparticles. Our experimental results reveal that, under a mass load of 50% Ni(OH)2, the composite exhibits a high specific capacitance of 1568 F g−1 (820 F g−1 if both Ni(OH)2 and graphene are considered) and good cycling stability (capacitance retention >90% for the first 500 cycles and ∼75% for 1000 cycles) at a current density of 4 A g−1 in 1 M KOH solution, indicating that this composite material is promising for supercapacitor application.

2. EXPERIMENTAL SECTION Synthesis of Functionalized rGO (F-rGO). Graphite oxide (GO) was prepared via a modified Hummer’s method.47 Briefly, graphite (2 g) and KMnO4 (15.0 g) were added to 120 mL of H2SO4 (98%) under ice-bath cooling and stirred for 2 h. The solution was diluted in 250 mL of DI water, followed by the addition of 20 mL of H2O2 (30%) at room temperature. After precipitation for 5 days, the upper supernatant was 9974

dx.doi.org/10.1021/ie202706h | Ind. Eng. Chem. Res. 2012, 51, 9973−9979


Article

functional groups on the growth of Ni(OH)2 nanoparticles. Figure 2d displays the morphology of such a sample with 50 wt % of Ni(OH)2 (GN5). In this sample, Ni(OH)2 nanoparticles with an average diameter of 11 nm seriously agglomerated on the rGO surface. According to the above results, it is believed that the existence of sulfonic functional groups on graphene sheets plays a critical role to form fine and uniformly distributed Ni(OH)2 nanoparticles. 4-SBD has been used to functionalize graphene sheets in previous studies. It has been demonstrated that the aryl group in 4-SBD can adsorb on the rGO surface, leaving the sulfonic group as a linker to anchor other species or nanoparticles.45 When (4-SBD)-functionalized rGO nanosheets were mixed with NiC2O4·H2O and KOH under agitation, Ni(OH)2 started to form. The sulfonic groups on the graphene sheets can serve as the nucleation center for the growth of Ni(OH)2 nanoparticles. The reason is that, when NiC2O4·H2O reacts with KOH to form Ni(OH)2, the crystalline water in NiC2O4·H2O is liberated.27 In the presence of a trace amount of water, the −SO3H groups on graphene sheets dissociate to form negatively charged SO3−,48 which can attract positively charged Ni2+ hydrated ions via electrostatic attraction.48,49 These bonded Ni2+ ions will then nucleate and grow to form Ni(OH)2 nanoparticles. Therefore, the use of hydrophilic functional groups effectively prevents agglomeration of Ni(OH)2 nanoparticles on graphene sheets. In addition, due to the relative strong interaction between the particles and the graphene sheets, the structure of the composite can be well maintained during the charge−discharge process, allowing high specific capacitance and good cycling stability.31,50 The graphene/Ni(OH)2 composites were examined using FTIR. Figure 3a shows that the FTIR spectrum of rGO exhibits a strong vibration band at 1532 cm−1, due to the stretching mode of C−C bond which is restored upon hydrazine reduction.51 For F-rGO and FGN5, characteristic peaks of benezenesulfonate groups, including the bands at 1177, 1031, and 686 cm−1 from S−O vibration, were observed. Since the FrGO sample was washed with copious amounts of acetone and ethanol repeatedly to remove the residual functional groups, the appearance of the characteristic peaks of benezenesulfonate group indicates that rGO is successfully functionalized with 4SBD. For FGN5, the FTIR spectrum shows two bands at 831 and 3647 cm−1, which are associated with the Ni−OH and OH vibrations, respectively.28,52,53 This reveals the existence of Ni(OH)2 in the FGN5 composite. The presence of Ni(OH)2 in the FGN5 composite was also confirmed from XPS measurements (Supporting Information, Figure S1). For GN5, although the Ni−OH vibration band at 3628 cm−1 appears in its FTIR

electrode, and a standard calomel reference electrode (SCE). An aqueous solution of KOH (1 M) was used as the electrolyte. Cyclic voltammetry (CV) tests were recorded between −0.2 and 0.6 V (vs SCE) at different scan rates. Galvanostatic charge/discharge curves were measured in the potential range of −0.1 to 0.5 V (vs SCE).

3. RESULTS AND DISCUSSION The TEM image shows that the reduced graphene oxide sheets functionalized with 4-SBD (denoted as F-rGO) are transparent, with some visible wrinkles and ripples (Figure 2a). After mixing

Figure 2. TEM images of (a) F-rGO, (b) FGN5, (c) Ni(OH)2, and (d) GN5. The insets are the corresponding SEM images.

F-rGO with NiC2O4·H2O and KOH under agitation, Ni(OH)2 nanoparticles were grown on the graphene surface to form graphene/Ni(OH)2 composites via a solid-state reaction route.28 For a composite comprising 50 wt % of Ni(OH)2 (denoted as FGN5), the TEM image reveals that small Ni(OH)2 nanoparticles with an average diameter of 10 nm are uniformly dispersed on the surface of the graphene sheets (Figure 2b). Following the same solid-state reaction but without the addition of graphene sheets, bare Ni(OH)2 nanoparticles were also prepared (Figure 2c), although the morphology of the Ni(OH)2 particles is in stark contrast to that of FGN5. In this case, large and porous Ni(OH)2 particle aggregates with sizes of about 100 nm were obtained. Nonfunctionalized rGO sheets were also used to form graphene/Ni(OH)2 composites to elucidate the effect of the

Figure 3. (a) FT-IR and (b) XRD spectra of rGO, F-rGO, Ni(OH)2, GN5, and FGN5. The XRD peaks labeled with the asterisk (∗) are for Ni(OH)2. 9975



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Figure 4. (a) Cyclic voltammograms of rGO, F-rGO, Ni(OH)2, GN5, and FGN5 at 5 mV s−1; (b) galvanostatic charge/discharge curves of rGO, FrGO, Ni(OH)2, GN5, and FGN5 at a current density of 4 A g−1.

I(V) is the instantaneous current. At a scan rate of 5 mV s−1, the calculated specific capacitances of rGO, F-rGO, GN5, Ni(OH)2, and FGN5 are 104, 170, 501, 577, and 750 F g−1, respectively. It should be noted that for GN5 and FGN5, both graphene and Ni(OH)2 are included in the weight of active materials. For these two samples, the capacitance contributed from Ni(OH)2 can be estimated using

spectrum, the S−O peaks are not observed since the rGO sheets in this sample were not functionalized. Figure 3b shows the XRD patterns of the rGO nanosheets, Ni(OH)2 nanoparticles, and their composites. For rGO and FrGO, a broad (002) reflection peak (2θ = 26.3°) is observed. The calculated interlayer spacing of 3.40 Å is slightly larger than that of bulk graphite (3.34 Å) due to the existence of residual oxygen-containing groups on the graphene sheets.39,45 For bare Ni(OH)2 nanoparticles, six peaks at 2θ = 19.3, 33.1, 38.5, 52.1, 59.0, and 63.1 were found, corresponding to the (001), (100), (101), (102), (110), and (111) reflections of Ni(OH)2 (JCPDS No. 14-0117), respectively.32 These peaks, together with the peak of C(002), also appear in the GN5 and FGN5 samples. However, the diffraction peak of C(002) is much weaker compared to that of rGO and F-rGO, indicating that the layerto-layer stacking of graphene sheets is reduced because of the existence of Ni(OH)2 nanoparticles. The sizes of the Ni(OH)2 nanoparticles were estimated based on Scherrer formula. For samples Ni(OH)2, GN5, and FGN5, the average particle sizes are 6.8, 6.7, and 7.9 nm, respectively. This result, together with the TEM measurements, indicates that the use of graphene sheets as the support does not affect the particle size of Ni(OH)2, but mainly changes the dispersion of particles on the graphene surface. Supercapacitor electrodes were fabricated using the graphene/Ni(OH)2 composites and their capacitances were evaluated. The cyclic voltammogramms of rGO, F-rGO, Ni(OH)2, GN5, and FGN5 are compared in Figure 4a. For rGO and F-rGO, well-defined peaks centered at 0.25 and 0.37 V were observed. These redox peaks correspond to the reaction between the residual functional groups on the graphene sheets and OH− ions in the electrolyte, suggesting that the reduction of oxide on the graphene surface was incomplete. For F-rGO, due to the additional 4-SBD functional groups, a higher redox current was observed than that of rGO. In contrast to rGO and F-rGO, bare Ni(OH)2 nanoparticles and Ni(OH)2/graphene composites showed two stronger peaksan anodic peak at 0.48 V and a cathodic one at 0.08 V, respectively. These two redox peaks are due to the following faradic reaction:22 Ni(OH)2 + OH− ↔ NiOOH + H2O + e−

CNi(OH)2 =

1

C = I × Δt /(ΔV × m)

mv(Vf

i

i

(4)

where I is the constant discharge current, Δt is the discharge time, m is the mass of active materials, and ΔV is the potential drop during discharge. At a current density of 4 A g−1, the specific capacitances for rGO, F-rGO, GN5, Ni(OH)2, and FGN5 are 60, 72, 655, 784, and 820 F g−1, respectively. If the contribution of graphene is excluded following eq 3, the capacitances of Ni(OH)2 for samples GN5 and FGN5 are 1238 and 1568 F g−1, respectively. The much improved specific capacitance of Ni(OH)2 in FGN5 composite, as confirmed from both CV and galvanostatic charge/discharge scans, indicates higher electrochemical utilization of Ni(OH)2 nanoparticles in FGN5 than that of GN5 and bare Ni(OH)2. This is expected since for the samples of bare Ni(OH)2 and GN5 composite, Ni(OH)2 particles aggregated significantly. But for FGN5, due to the existence of the sulfonic functional groups, the dispersion of Ni(OH)2 nanoparticles on graphene sheets is much improved so the accessible surface area is much larger. In addition, the hydrophilic functional groups on the graphene surface may facilitate OH− ions to diffuse more efficiently to reach the Ni(OH)2 nanoparticle surface and hence allow improved pseudocapacitive performance.49 To understand the effect of the mass ratio between F-rGO and Ni(OH)2 on the electrochemical performance, we prepared F-rGO/Ni(OH)2 composites containing 30 and 70 wt % of Ni(OH)2, denoted as FGN3 and FGN7, respectively. The cyclic voltammograms of samples FGN3, FGN5, and FGN7 are shown

(1)

V

∫ f I (V ) d V − V) V

(3)

The resultant specific capacitances of Ni(OH)2 in GN5 and FGN5 composites are 832 and 1330 F g−1, respectively. Clearly, the capacitance of Ni(OH)2 in GN5 composite is comparable to that of bare Ni(OH)2 (577 F g−1); while for FGN5, it is nearly 2.3 times larger. The specific capacitances were also evaluated from the galvanostatic charge/discharge tests (Figure 4b). On the basis of the discharge curves, the capacitances of the samples were calculated as follows:31

On the basis of the CV measurements, the specific capacitances of the samples were calculated using the following equation:50 C=

C total × m total − CF ‐ rGo × mF ‐ rGo mNi(OH)2

(2)

where m is the mass of the active material, ν is the scan rate, Vi and Vf are the potential limits of the voltammetric curve, and 9976



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Figure 5. (a) Cyclic voltammograms of FGN3, FGN5, and FGN7 at 5 mV s−1; (b) galvanostatic charge/discharge curves of FGN3, FGN5, and FGN7 at a current density of 4 A g−1.

Figure 6. (a) Specific capacitances of FGN5 at current densities of 4, 5.6, 8, and 11.2 A g−1, respectively; (b) cycling stability of FGN5 and Ni(OH)2 at a current density of 4 A g−1.

existence of the linker molecules (4-SBD) on the rGO surface could affect the conductivity of the composite material, leading to lower power performance at a high scan rate. The FGN5 electrode was selected for further high-rate capability and cycling stability tests. At different charge− discharge current densities of 4, 5.6, 8.4, and 11.2 A g−1, the measured capacitances are 820, 707, 578, 420 F g−1, respectively (Figure 6a). About 51.2% of capacitance was retained when the current density increased from 4 to 11.2 A g−1, indicating that FGN5 has good high-rate discharge ability. Cycling stability is another important performance indicator for supercapacitors. One effective approach to improve the cycling life of pseudocapacitive materials is to incorporate with carbon materials.4 Since the graphene/Ni(OH)2 composites in our study contain both Ni(OH)2 and graphene, better cycling stability of FGN5 is expected than that of bare Ni(OH)2 nanoparticles. To examine the cycling stability of the FGN5 composite, constant current (4 A g−1) charge−discharge cycling tests were carried out using a voltage window of 0.6 V. As shown in Figure 6b, the capacitance of the FGN5 decreased to 90.5% during the first 500 charge−discharge cycles. After 1000 cycles, ∼ 75% of the original capacitance was retained. Compared to bare Ni(OH)2 particles, which shows a capacitance retention of ∼62% after 1000 cycles, FGN5 exhibits improved cycling stability. The enhanced cycling stability of FGN5 is attributed to the incorporation of F-rGO in the FGN5 composite, similar to the effect observed in other composites such as Co(OH)2/graphene,51 RuO2/graphene,50 and MnO2/ graphene.54

in Figure 5a. Similar to FGN5, the redox peaks were also clearly observed for FGN3 and FGN7 due to the cycling reactions between Ni(OH)2 and NiOOH. Both anodic and cathodic peak currents increased in the order of FGN3 < FGN7 < FGN5, indicating that the composite with 50 wt % of Ni(OH)2 shows the highest capacitance. This trend was also confirmed from the galvanostatic charge/discharge curves shown in Figure 5bthe specific capacitance of FGN5 (820 F g−1) is larger than that of both FGN3 (515 F g−1) and FGN7 (740 F g−1). As pointed out before, the improved capacitance of Ni(OH)2 in graphene/ Ni(OH)2 composites is attributed to the increased surface area and enhanced diffusion of the electrolyte during the charge/ discharge process.23 With the increase of mass loading of Ni(OH)2 from FGN3 to FGN5, separation among graphene sheets can be well maintained due to the insertion of more Ni(OH)2 nanoparticles (see Figure 2b and Supporting Information, Figure S3a), leading to more efficient electrolyte diffusion and higher utilization of Ni(OH)2.23,24,50 However, further increase in the mass loading of Ni(OH)2 from FGN5 (50%) to FGN7 (70%) caused a decrease of capacitance. This is because at higher loading, nanoparticles start to aggregate (Supporting Information, Figure S3b) and partially lose accessible surface area.51 Therefore, the mass ratio of Ni(OH)2 to graphene plays a critical role in optimizing the morphology and capacitive performance of the composites. The effect of scan rate on capacitance was also examined. Supporting Information, Figure S2 shows that the capacitances of all samples decreased with increasing scan rate. When the scan rate increased from 5 to 10 mV/s, the capacitances of FGN3, FGN5, and FGN7 decreased by 37%, 35%, and 44%, respectively. The rapid loss of capacitances can be attributed to the reduced accessible surface area at a high scan rate. This is because at a high scan rate, only part of the surface area of rGO and Ni(OH)2 nanoparticles can be utilized. In addition, the

4. CONCLUSION In summary, graphene/Ni(OH)2 composites have been prepared by a facile and scalable solid-state reaction method. The resulting composites with well-dispersed Ni(OH)2 nano9977



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(14) Jayashree, R. S.; Vishnu Kamath, P. Suppression of the α−β nickel hydroxide transformation in concentrated alkali: Role of dissolved cations. J. Appl. Electrochem. 2001, 31, 1315. (15) Jiang, H.; Zhao, T.; Li, C.; Ma, J. Hierarchical self-assembly of ultrathin nickel hydroxide nanoflakes for high-performance supercapacitors. J. Mater. Chem. 2011, 21, 3818. (16) Yuan, Y. F.; Xia, X. H.; Wu, J. B.; Yang, J. L.; Chen, Y. B.; Guo, S. Y. Nickel foam-supported porous Ni(OH)2/NiOOH composite film as advanced pseudocapacitor material. Electrochim. Acta 2011, 56, 2627. (17) Motori, A.; Sandrolini, F.; Davolio, G. Electrical properties of nickel hydroxide for alkaline cell systems. J. Power Sources 1994, 48, 361. (18) Li, B.; Ai, M.; Xu, Z. Mesoporous β-Ni(OH)2: Synthesis and enhanced electrochemical performance. Chem. Commun. 2010, 46, 6267. (19) Zhao, D.; Zhou, W.; Li, H. Effects of deposition potential and anneal temperature on the hexagonal nanoporous nickel hydroxide films. Chem. Mater. 2007, 19, 3882. (20) Yuan, C.; Zhang, X.; Su, L.; Gao, B.; Shen, L. Facile synthesis and self-assembly of hierarchical porous NiO nano-/micro-spherical superstructures for high performance supercapacitors. J. Mater. Chem. 2009, 19, 5772. (21) Liu, X.; Yu, L. Influence of nanosized Ni(OH)2 addition on the electrochemical performance of nickel hydroxide electrode. J. Power Sources 2004, 128, 326. (22) Patil, U. M.; Gurav, K. V.; Fulari, V. J.; Lokhande, C. D.; Joo, O. S. Characterization of honeycomb-like ″β-Ni(OH)2″ thin films synthesized by chemical bath deposition method and their supercapacitor application. J. Power Sources 2009, 188, 338. (23) Wang, Y. G.; Yu, L.; Xia, Y. Y. Electrochemical capacitance performance of hybrid supercapacitors based on Ni(OH)2 carbon nanotube composites and activated carbon. J. Electrochem. Soc. 2006, 153, A743. (24) Liu, C. G.; Lee, Y. S.; Kim, Y. J.; Song, I. C.; Kim, J. H. Electrochemical characteristics of hydrothermally deposited nickel hydroxide on multi-walled carbon nanotube for supercapacitor electrode. Synth. Met. 2009, 159, 2009. (25) Lang, J.-W.; Kong, L.-B.; Liu, M.; Luo, Y.-C.; Kang, L. Asymmetric supercapacitors based on stabilized α-Ni(OH)2 and activated carbon. J. Solid State Electrochem. 2010, 14, 1533. (26) Lee, J. W.; Ahn, T.; Soundararajan, D.; Ko, J. M.; Kim, J.-D. Non-aqueous approach to the preparation of reduced graphene oxide/ α-Ni(OH)2 hybrid composites and their high capacitance behavior. Chem. Commun. 2011, 47, 6305. (27) Ye, X. R.; Jia, D. Z.; Yu, J. Q.; Xin, X. Q.; Xue, Z. One-step solidstate reactions at ambient temperaturesA novel approach to nanocrystals synthesis. Adv. Mater. 1999, 11, 941. (28) Liu, X.; Yu, L. Synthesis of nanosized nickel hydroxide by solidstate reaction at room temperature. Mater. Lett. 2004, 58, 1327. (29) Park, J. H.; Park, O. O.; Shin, K. H.; Jin, C. S.; Kim, J. H. An electrochemical capacitor based on a Ni(OH)2/activated carbon composite electrode. Electrochem. Solid-State Lett. 2002, 5, H7. (30) Lu, B.; Bai, J.; Bo, X.; Zhu, L.; Guo, L. A simple hydrothermal synthesis of nickel hydroxide-ordered mesoporous carbons nanocomposites and its electrocatalytic application. Electrochim. Acta 2010, 55, 8724. (31) Wang, H.; Casalongue, H. S.; Liang, Y.; Dai, H. Ni(OH)2 nanoplates grown on graphene as advanced electrochemical pseudocapacitor materials. J. Am. Chem. Soc. 2010, 132, 7472. (32) Zhang, J.; Kong, L. B.; Cai, J. J.; Li, H.; Luo, Y. C.; Kang, L. Hierarchically porous nickel hydroxide/mesoporous carbon composite materials for electrochemical capacitors. Microporous Mesoporous Mater. 2010, 132, 154. (33) Zhang, K.; Zhang, L. L.; Zhao, X. S.; Wu, J. Graphene/ polyaniline nanofiber composites as supercapacitor electrodes. Chem. Mater. 2010, 22, 1392.

particles on a F-rGO surface functionalized with hydrophilic groups show high specific capacitance 1568 F g−1 (or 820 F g−1 if both Ni(OH)2 and graphene are included) and good cycling stability (>75% retention for 1000 cycles) at a current density of 4 A g−1 in 1 M KOH solution. The synthesis developed in this work offers a promising approach for facile preparation of supercapacitor electrode materials with high electrochemical performance.

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ASSOCIATED CONTENT

S Supporting Information *

XPS spectra of FGN5; specific capacitances of Ni(OH)2, FGN3, FGN5, FGN7, GN5, rGO, and F-rGO samples at different scan rates; TEM images of functionalized graphene/Ni(OH)2 composites with different mass loading of Ni(OH)2. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Ministry of Education, Singapore (under Grant R279-000-273-133).

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REFERENCES

(1) Conway, B. E. Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications; Springer: New York, 1999. (2) Miller, J. R.; Simon, P. Materials science: Electrochemical capacitors for energy management. Science 2008, 321, 651. (3) Simon, P.; Gogotsi, Y. Materials for electrochemical capacitors. Nat. Mater. 2008, 7, 845. (4) Kotz, R.; Carlen, M. Principles and applications of electrochemical capacitors. Electrochem. Acta 2000, 45, 2483. (5) Arico, A.; Bruce, P.; Scrosati, B.; Tarascon, J.; van Schalkwijk, W. Nanostructured materials for advanced energy conversion and storage devices. Nat. Mater. 2005, 4, 366. (6) Frackowiak, E. F, B. Carbon materials for the electrochemical storage of energy in capacitors. Carbon 2001, 39, 937. (7) Yang, S. Y.; Chang, K. H.; Tien, H. W.; Lee, Y. F.; Li, S. M.; Wang, Y. S.; Wang, J. Y.; Ma, C. C. M.; Hu, C. C. Design and tailoring of a hierarchical graphene-carbon nanotube architecture for supercapacitors. J. Mater. Chem. 2011, 21, 2374. (8) Rudge, A.; Raistrick, I.; Gottesfeld, S.; Ferraris, J. P. A study of the electrochemical properties of conducting polymers for application in electrochemical capacitors. Electrochim. Acta 1994, 39, 273. (9) Conway, B. E.; Birss, V.; Wojtowicz, J. The role and utilization of pseudocapacitance for energy storage by supercapacitors. J. Power Sources 1997, 66, 1. (10) Lee, H.; Manivannan, V.; Googenough, J. B. Electrochemical capacitors with KCl electrolyte. C. R. Acad. Sci., Ser. II 1999, 2, 565. (11) Hu, C.-C.; Cheng, C.-Y. Ideally pseudocapacitive behavior of amorphous hydrous cobalt−nickel oxide prepared by anodic deposition. Electrochem. Solid-State Lett. 2002, 5, A43. (12) Cao, L.; Kong, L. B.; Liang, Y. Y.; Li, H. L. Preparation of novel nano-composite Ni(OH)2/USY material and its application for electrochemical capacitance storage. Chem. Commun. 2004, 10, 1646. (13) Yang, G. W.; Xu, C. L.; Li, H. L. Electrodeposited nickel hydroxide on nickel foam with ultrahigh capacitance. Chem. Commun. 2008, 6537. 9978



Article

(34) Huang, Q.; Wang, X.; Li, J.; Dai, C.; Gamboa, S.; Sebastian, P. J. Nickel hydroxide/activated carbon composite electrodes for electrochemical capacitors. J. Power Sources 2007, 164, 425. (35) Fan, Z.; Yan, J.; Zhi, L.; Zhang, Q.; Wei, T.; Feng, J.; Zhang, M.; Qian, W.; Wei, F. A three-dimensional carbon nanotube/graphene sandwich and its application as electrode in supercapacitors. Adv. Mater. 2010, 22, 3723. (36) Sun, Y. Q.; Wu, Q.; Shi, G. Q. Graphene based new energy materials. Energy Environ. Sci. 2011, 1113. (37) Stoller, M. D.; Park, S.; Yanwu, Z.; An, J.; Ruoff, R. S. Graphenebased ultracapacitors. Nano Lett. 2008, 8, 3498. (38) Vivekchand, S. R. C.; Rout, C. S.; Subrahmanyam, K. S.; Govindaraj, A.; Rao, C. N. R. Graphene-based electrochemical supercapacitors. J. Chem. Sci. 2008, 120, 9. (39) Wang, Y.; Shi, Z.; Huang, Y.; Ma, Y.; Wang, C.; Chen, M.; Chen, Y. Supercapacitor devices based on graphene materials. J. Phys. Chem. C 2009, 113, 13103. (40) Chen, D.; Tang, L.; Li, J. Graphene-based materials in electrochemistry. Chem. Soc. Rev. 2010, 39, 3157. (41) Liu, C.; Yu, Z.; Neff, D.; Zhamu, A.; Jang, B. Z. Graphene-based supercapacitor with an ultrahigh energy density. Nano Lett. 2010, 10, 4863. (42) Yang, X.; Zhu, J.; Qiu, L.; Li, D. Bioinspired effective prevention of restacking in multilayered graphene films: Towards the next generation of high-performance supercapacitors. Adv. Mater. 2011, 23, 2833. (43) Li, D.; Muller, M. B.; Gilje, S.; Kaner, R. B.; Wallace, G. G. Processable aqueous dispersions of graphene nanosheets. Nat. Nanotechnol. 2008, 3, 101. (44) Bei, F.; Hou, X.; Chang, S. L.; Simon, G. P.; Li, D. Interfacing colloidal graphene oxide sheets with gold nanoparticles. Chem.Eur. J. 2011, 17, 5958. (45) Jin, Z.; Lomeda, J. R.; Price, B. K.; Lu, W.; Zhu, Y.; Tour, J. M. Mechanically assisted exfoliation and functionalization of thermally converted graphene sheets. Chem. Mater. 2009, 21, 3045. (46) Li, B. J.; C., H. Q.; Shao, J.; Zheng, H.; Lu, Y. X.; Yin, J. F.; Qu, M. Z. Improved performances of β-Ni(OH)2@reduced-grapheneoxide in Ni-MH and Li-ion batteries. Chem. Commun. 2011, 47, 3159. (47) Park, S.; An, J.; Piner, R. D.; Jung, I.; Yang, D.; Velamakanni, A.; Nguyen, S. T.; Ruoff, R. S. Aqueous suspension and characterization of chemically modified graphene sheets. Chem. Mater. 2008, 20, 6592. (48) Kawai, T.; Ohtsuki, C.; Kamitakahara, M.; Miyazaki, T.; Tanihara, M.; Sakaguchi, Y.; Konagaya, S. Coating of an apatite layer on polyamide films containing sulfonic groups by a biomimetic process. Biomaterials 2004, 25, 4529. (49) Gao, B.; Yuan, C.; Su, L.; Chen, S.; Zhang, X. High dispersion and electrochemical capacitive performance of NiO on benzenesulfonic functionalized carbon nanotubes. Electrochim. Acta 2009, 54, 3561. (50) Wu, Z.-S.; Wang, D.-W.; Ren, W.; Zhao, J.; Zhou, G.; Li, F.; Cheng, H.-M. Anchoring hydrous RuO2 on graphene sheets for highperformance electrochemical capacitors. Adv. Funct. Mater. 2010, 20, 3595. (51) Chen, S.; Zhu, J.; Wang, X. One-step synthesis of graphene− cobalt hydroxide nanocomposites and their electrochemical properties. J. Phys. Chem. C 2010, 114, 11829. (52) Sierczynska, A.; Lota, K.; Lota, G. Effects of the addition of different carbon materials on the electrochemical performance of nickel hydroxide electrode. J. Power Sources 2010, 195, 7511. (53) Jeevanandam, P.; Koltypin, Y.; Gedanken, A. Synthesis of nanosized α-nickel hydroxide by a sonochemical method. Nano Lett. 2001, 1, 263. (54) Yan, J.; Fan, Z.; Wei, T.; Qian, W.; Zhang, M.; Wei, F. Fast and reversible surface redox reaction of graphene−MnO2 composites as supercapacitor electrodes. Carbon 2010, 48, 3825.

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A Solid-State Reaction Route to Anchoring Ni(OH) - American

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