Carbon-Induced Generation of Hierarchical Structured Ni0.75Co0.25

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Carbon induced generation of hierarchical structured Ni0.75Co0.25(CO3)0.125(OH)2 for enhanced supercapacitor performance Feng Wen, Yue Zhang, Xingyue Qian, Jianli Zhang, Rudan Hu, Xuemin Hu, Xin Wang, and Junwu Zhu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b12490 • Publication Date (Web): 07 Dec 2017 Downloaded from http://pubs.acs.org on December 13, 2017

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ACS Applied Materials & Interfaces

Carbon

induced

generation

of

hierarchical

structured

Ni0.75Co0.25(CO3)0.125(OH)2 for enhanced supercapacitor performance Feng Wen, Yue Zhang, Xingyue Qian, Jianli Zhang, Rudan Hu, Xuemin Hu, Xin Wang, Junwu Zhu* Key Laboratory for Soft Chemistry and Functional Materials, Ministry of Education Nanjing University of Science and Technology, Nanjing 210094, China Email: [email protected] (J. Zhu) Abstract The hierarchical nanostructures with heteroatom-doping have been considered as an important factor in electrode materials for advanced supercapacitors. Herein, with the aid of carbon, N and S co-doped Ni0.75Co0.25(CO3)0.125(OH)2/C (NSH) with hierarchical structure was synthesized through a facile one-step hydrothermal method. Notably, it is the first report on carbon precursor as structure inducer for designing a three-dimensional (3D) carnation-like hierarchical structure. Thanks to the carbon induction effect, and the introduction of N/S dopants, the obtained NSH with 3D architecture exhibits superior performances as electrode materials for supercapacitors. For example, the NSH offers a high specific capacity of 277.3 mAh/g at 0.5 A/g. Moreover, the assembled NSH//reduced graphene oxide hydrogel based hybrid supercapacitor exhibits high energy density of 44.4 Wh/kg and 11.7 Wh/kg at power density of 460 W/kg and 9.8 kW/kg, respectively. This result opens up opportunities for the carbon induced methods to control the morphology and structure of other

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similar materials. Keywords: carbon induced; N and S co-doped; carnation-like hierarchical structure; one-step hydrothermal; supercapacitors 1. Introduction The ever-increasing environmental issues and current energy crisis demands call for not only the urgent development of alternative clean energy but also advanced energy storing systems and conversion devices.1,2 Supercapacitors (SCs) have been recognized as the most important next-generation energy-storage devices to maintain national economy while keeping pace with the as mentioned issues. Generally, it is a core subject to research on various electroactive materials to improve electrochemical performance of SCs.3,4 Todate, some meso, micro and nanostructure materials have been studied for their applications in SCs with desired properties.5-10 Especially, the nickel and cobalt (Ni-Co) compounds have drawn intensive attention in this field for their high theoretical capacity and cost effectiveness.11-16 Nevertheless, due to the gradual decay of electroactive species during cycling process, the cycling stability and conductivity of Ni-Co based compounds are greatly weaker compared to carbon materials. This is a major drawback of Ni-Co based materials for practical applications. At this point, the design of 3D hierarchical nanostructures with meso/macro structure should go far towards to solve this problem. Building a hierarchical structure can provide an efficient way to overcome the above challenges. Particularly, the atomically thick nanolayer materials, which feature both short ion diffusion paths and significantly enhanced electroactive

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sites with high percentage of exposed surface atoms, provide a promising possibility to tune the energy storage performances on an atomic level.17-20 Due to the hierarchical organization, the charge transfer and ion diffusion from the interior to interfacial surface can be favorably achieved.21-27 Unfortunately, the preparation of hierarchical-structure often involves series of complicated experimental processes.28,29 Furthermore, the hierarchical architectures with nonuniform pores may collapse at high electrochemical scan rates, leading to the poor rate capability and limited potential applications.30 Recent studies have demonstrated that the introduction of carbon materials can greatly improve both capacity and cycling capability of nickel and cobalt hydroxides, and oxides.31-33 Many articles have reported the effect of carbon loading on various electroactive materials. Usually, carbon materials with high specific surface area can offer continuous conductive pathway for electron transport and improve the mechanical flexibility of active ingredients.34-38 Some multifarious carbonaceous materials, such as carbon nanospheres, reduced graphene oxide, carbon dots and carbon nanofoam papers have been used as additives or supports to enhance the electric conductivity and dispersion of metal composites, as well as increase surface area and surface wettability.39-42 However, to the best of our knowledge, carbon used for inducing generation of hierarchical structure has not been reported. Herein, we found that carbon can induce the generation of 3D carnation-like hierarchical structure, and successfully designed a one-step hydrothermal strategy to synthesize the N, S co-doped Ni0.75Co0.25(CO3)0.125(OH)2/C (NSH). Importantly, it is

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the first report that carbon materials can be used as morphology inducer to acquire the desired carnation-like hierarchical structure. In which, the macropore structure allows the rapid transport of electrolyte ions, while mesoporous can offer abundant ion-adsorption sites, leading to excellent electrochemical performances. Meanwhile, the N and S dopants further improve the capacity of obtained carbon-rich samples. Moreover, the hybrid supercapacitor assembled by NSH//reduced graphene oxide hydrogel exhibits good cycling stability and high energy density. 2. Experimental Section 2.1. Synthesis of NSH: All chemical reagents were purchased and used without further purification. Typically, Ni(NO3)2·6H2O (6.8 mmol) and Co(NO3)2·6H2O (3.4 mmol) were dissolved into 70 ml distilled water/ethylene glycol (3:4 by volume) mixture to form grayish green clear solution. Then, 30 mmol urea, 13 mmol thiourea and 11 mmol glucose were added into the above solution, followed by vigorous stirring for 0.5 h. After that, the homogeneous solution was transferred into 100 ml Teflon-lined stainless steel autoclave and maintained at 120 °C for 5 h. Then the obtained grey-green product (denoted as NSH) was washed with distilled water and freeze-dried. For comparison, the samples without introducing C, S and N (denoted as NCH) were prepared by using the similar experimental procedures, but in the absence of thiourea and glucose. Moreover, for the sake of investigating the role of C and N/S in the formation of hierarchical structure, the NCH-1 (in the absence of glucose), and NCH-2 (in the absence of thiourea) were prepared under the similar experimental procedures. Moreover, in order to observe the relation between morphology and

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carbon content, the samples were also obtained with different glucose contents in the absence of thiourea. Furthermore, to explain the increments of BET surface area are mainly caused by the 3D architectures rather than carbon itself, the physical mixing sample of NCH and carbon materials (obtained by hydrothermal treatment of glucose at 120 °C for 5 h) with equal mass ratio (denoted as NCH-3) was obtained after the same experimental procedures. 2.2. Synthesis of 3D reduced graphene oxide hydrogel (rGH): For the negative electrodes, the graphene oxide was prepared using Hummers’ method.37 The obtained graphene oxide suspension (5 mg/g) was transformed into glass tube, which was transformed into a 100 mL Teflon-lined autoclave, and maintained at 150 oC for 12 h. After the autoclave was naturally cooled down to room temperature, the obtained 3D rGH was immersed in distilled water for dialysis and subsequent use. 2.3. Structure characterization: The crystal structures were examined via a X-ray diffractometer (XRD, Bruker D8 Advance) using Cu Kα radiation (λ = 1.5418 Å). Fourier transform infrared spectroscopy (FTIR) spectra of KBr powder pressed pellets were recorded on a FTIR-8400S spectrometer (SHIMADZU). Surface chemical properties were determined by energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS, PHI QUANTERA II). Thermal gravimetric analysis (TGA) curves were recorded on a DTG-60 (Shimazdu Corporation, Japan) in air atmosphere, and the samples were heated from 25 to 600 °C at a heating rate of 10 °C/min. The morphology was characterized by a scanning electron microscopy (SEM, Quanta 250F) and a transmission electron microscopy (TEM, JEOL JEM-2100;

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Tecnai G2 F30, FEI). The surface area and pore size distribution analyses were performed through measuring N2 adsorption-desorption isotherms (Micromeritics ASAP 2020 Plus, America). 2.4. Electrochemical measurements: The electrochemical measurements, including cyclic

voltammetry

(CV)

and

galvanostatic

charge/discharge

tests

(chronopotentionmetry, CP) were conducted on a CHI760D electrochemical workstation (Chenhua, Shanghai), while the electrochemical impedance spectroscopy (EIS) measurements were tested on a Versastat-3 potentiostat/galvanostat (Princeton Applied Research). Cycling life measurements were performed using a Land battery electrochemical test (LAND CT 2001A, Wuhan) at a current density of 3 A/g. In a three-electrode system containing 1 M KOH solution as the electrolyte, a platinum foil and a saturated calomel electrode (SCE) were used as the counter and reference electrodes, respectively. The working electrode was fabricated by 80 wt% samples, 15 wt% acetylene black and 5 wt% PTFE binders, which was mixed together and coated onto the nickel foam current collector (1 × 1 cm). The weight of the active materials is approximately 5 mg. Then, the working electrode was dried at 60 °C for 5 h. Before the electrochemical tests, the as-obtained working electrodes were impregnated within the electrolyte overnight. To fabricate the asymmetric hybrid supercapacitor device, the obtained NSH or NCH sample was taken as the positive electrodes and the rGH as the negative electrodes. The electrodes were pressed together, separated by a piece of cellulose paper separator (NKK TF4035) in CR 2032 type coin cells with 1 M KOH as

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electrolyte. The loading mass ratio of cathode to anode was decided according to the charge balance theory. Moreover, the specific capacity, energy density and power density were calculated based on the galvanostatic charge-discharge curves, and all calculation methods are shown in supporting information, Section 2. 3. Results and discussions 3.1. Structural analysis In this paper, the NSH was synthesized by a one-step hydrothermal procedure containing Ni(NO3)2, Co(NO3)2, urea, thiourea and glucose. During the reaction process, a large quantity of C originated from glucose may induce the formation of carnation-like hierarchical structure. Meanwhile, N and S dopants originated from thiourea can improve the low capacity of carbon-rich materials. Here, we mainly investigate the key function of carbon on the formation of 3D hierarchical structure of NSH.

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Figure 1. (a) XRD patterns, (b) FT-IR spectra, (c) TG curves, (d) N2 adsorption isotherms and the pore size distribution curves of NSH and NCH. Figure 1a and Figure S1 show the XRD patterns of as-prepared products, and all diffraction peaks can be indexed to hexagonal phase of Ni0.75Co0.25(CO3)0.125(OH)2 (JCPDS No. 40-0216).31 Obviously, NCH and NSH display the dominated broad peaks at around 10.41 and 10.87°, respectively. Remarkably, after introducing C, N and S, the pattern of NSH shows wide and weak diffraction peaks, suggesting the weak crystallinity, which might be favorable for ion permeation when used in supercapacitor electrodes.43 It’s worth noting that the lattice expansion of nanoparticles can be attributed to a number of possible phenomena, including confinement effects, grain surface relaxation,44 formation of point defects, and uncompensated Coulombic interactions.45 In addition, the diffraction intensity is

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related to grain sizes and surface state of grains. In general, the thinner materials have larger surface area, accompanying with the more serious defect of surface structure. The structural defects would result in the reduction of diffraction intensity and the wider diffraction peaks.31 Therefore, the carnation-like NSH consisted of ultrathin sheets of 5-6 nm shows relatively broad diffraction peaks in XRD pattern. To further confirm the composition of obtained products, FT-IR measurements were carried out (Figure 1b). The strong and broad peak at 3440 cm-1 can be assigned to the O-H stretching vibration, which is the feature of hydrogen-band groups and molecular water. In addition, the narrow band at 1636 cm-1 is the bending mode of water molecules. The bands centered at about 1383, 1049, and 631 cm−1 can be indexed to stretching vibrations of ν(OCO2), δ(CO3), and ρ(OCO), respectively. Obviously, with doping of N and S, extra modes at 2927, 2851 and 1493 cm−1 are observed in NSH, corresponding to N-H, C-S and C-N bond stretching, respectively. These results clearly supported the presence of N, S and C in the obtained product. 8 Ni0.75Co0.25(CO3)0.125(OH)2 → 6 NiO + 2 CoO

(1)

(calculated weight loss of 25.4 %) 8 N, S-doped Ni0.75Co0.25(CO3)0.125(OH)2/C → 6 NiO + 2 CoO

(2)

( >calculated weight loss of 25.4 %) TG curve (Figure 1c) shows two successive decomposing stages, corresponding to the decarboxylation and dehydration processes,31 respectively. Notably, the presence of crystalline water in the product could enhance its electrochemical performance.46 9



Compared with NCH, NSH exhibits higher weight loss. It indicates that NSH has more molecules and ions between layers to allow appreciable protonic conduction, which is corresponding to the XRD results. The N2 adsorption/desorption isotherm of NSH and NCH (the inset of Figure 1d) exhibits type IV with H3 hysteresis loop in the IUPAC classification. Obviously, the BET surface area of NSH is nearly 2 times larger than that of NCH (without C, N, S) (187.44 vs 96.86 m2/g). The Barrett-Joyner-Halenda (BJH) analysis (Figure 1d) result of NSH presents a pore size distribution (PSD) around 12.5 nm, which is also wider than that of NCH (11.5 nm). While the NCH-3 (the physical mixing sample of NCH and carbon materials) only offers a surface area of 133.58 m2/g and a PSD around 12.2 nm (Figure S8a). Considering a similar composition of both NSH and NCH-3, the increments of surface area can only be attributed to the 3D hierarchical structure of NSH rather than carbon itself.

Figure 2. (a) XPS spectra of NSH; high resolution XPS spectra of (b) C1s, (c) S 2p, (d) N1s, (e) Ni 2p and (f) Co 2p of NSH. 10


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Figure 3. (a) AFM image and (b) corresponding height profile of NSH; (c) dark-field TEM image, (d) elemental mapping images and (e) EDS of NSH.

Figure 4. (a, b) TEM images of NSH, and (c) HRTEM image of NSH correspond to the circled rectangle area in (b). In order to further analyze the components of NSH, the XPS and EDS measurements were also conducted. The results further confirm that NSH contains Co, Ni, N, S, C and O as the predominant elements (Figure 2a-f, Figure 3c-e), which matches well with the previous discussion. The high-resolution XPS spectrum (Figure 2b) of C1s reveals a main peak assigned to the carbon bond of C–C (284.35 eV), weakly adsorbed species of C–N/C–O (287.10 eV) and C=O (288.02 eV), respectively.

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In the case of S-species (Figure 2c), evidently, the former two dominated peaks can be assigned to the S2p3/2 (162.20 eV) and S2p1/2 (163.66 eV) peaks for the -C-S-Ccovalent bond, which proves that S interacts with the carbon and has been successfully doped into the sample. While some oxidized sulfur species (167.97 eV) may result from the reaction of surface sulfur with adjacent oxygen molecules. The high-resolution XPS spectra of N1s (Figure 2d) presents the existence of C-N, C=N, N-C=O and N-C=S (may attribute to the residue of urea or thiourea) in NSH composite 47, further suggesting that the N and S dopants interact with carbon rather than nickel and cobalt based compound. Meanwhile, the core-level XPS signal of O1s (Figure S6b) displays a broad peak of OH－ (530.5 eV), and other peaks of C-O (531.1 eV) and C=O (532.1 eV). By using Gaussian fitting, the Ni 2p spectrum (Figure 2e) can be well-fitted by two spin-orbit and two shakeup satellites (marked as “Sat.”), which can be assigned to Ni2+ and Ni3+ cations. According to the fitting data, the peaks at binding energy of 854.7 and 872.8 eV can be indexed to Ni2+, while the peaks at 853.8 and 871.4 eV can be ascribed to Ni3+;

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In high-resolution XPS

spectrum of Co 2p (Figure 2f), two kinds of Co species are also observed. The fitting peaks at 781.3 and 796.7 eV can be indexed to Co2+, while the other two fitting peaks at 779.1 and 794.3 eV belong to Co3+.

29, 48

These results are consistent with the

results of XRD and FTIR, and further confirm the coexistence of N, S, C and the formation of Ni0.75Co0.25(CO3)0.125(OH)2 in NSH composite. Meanwhile, the existence of Co3+/Co2+ and Ni3+/Ni2+ cations in NSH composite could provide abundant active sites. Furthermore, the TEM elemental mapping results (Figure 3d) reveal that the

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heteroatom species, including N, S and C are almost uniformly distributed on the surface of carnation-like NSH. From the HRTEM image of NSH (Figure 4c), the lattice fringe of 2.56 Å can be assigned to the (012) plane of NSH.17, 18 Based on the above

measurements,

it

can

be

confirmed

that

dual

N,

S

co-doped

Ni0.75Co0.25(CO3)0.125(OH)2/C are successfully obtained.

Figure 5. (a-c) SEM images of NSH; (d-e) TEM images of NSH; (f) TEM image of NCH; SEM images of (g) NCH; (h) NCH-1; (i) NCH-2.

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Figure 6. Schematic illustration of the possible formation mechanism of the obtained samples. To further verify the key effects of C on the formation process of 3D carnation-like structure, the morphology of obtained products were investigated by SEM and TEM (Figure 4, Figure 5). As showed in Figure 5a-e, with the introduction of C, N and S, the NSH with 3D carnation-like structure are formed. Actually, at the similar experimental procedures, the single nickel compound with thin layered nanosheets (Figure S3b, e) and network-like cobalt compound (Figure S3a, d) can be obtained. Figure 5b-e further reveal that NSH is actually composed of ultrathin interconnected nanosheets. More interestingly, plenty of meso/macropores (several hundred nanometers to several micrometers) assembled by the nanosheets can be observed, which is conducive to the diffusion and migration of electrolyte ions. Besides, the AFM result indicates the thickness of ultrathin in NSH sheets with about 5-6 nm (Figure 3a-b). As showed in Figure 5f-g, without introducing C, N and S, the formed NCH is 14


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composed of the aggregation of nanosheets. This indicates that there is a different crystals growth process with or without glucose and thiourea supports (Figure 6). Obviously, the stacked seriously NCH might extremely impede the full utilization of surface area and block the access of electrolyte ions. Moreover, to figure out the important role of C rather than N/S in the formation of 3D carnation-like structure, the NCH-1 (without introducing C) and NCH-2 (without introducing N, S) were prepared to compare with NSH. In Figure 5h and Figure S3c, it is observed that NCH-1 consists of seriously stacked layered structure in the absence of C, indicating that C is the most important factor for the formation of 3D hierarchical structure, and N/S just plays an insignificant effect. To confirm this, NCH-2 was characterized and showed in Figure 5i and Figure S3f. As expected, without N, S, the analogous carnation-like hierarchical structure was successfully obtained in the presence of C, further proved the vital induction effect of C rather than N/S in the formation of carnation-like architecture. Moreover, the glucose content has a great influence on morphology of obtained samples. As showed in Figure S4, with the increase of adding amount of glucose, the uniform carnation-like products were gradually formed. However, the carnation-like structure began to broken and disappeared with the further addition of glucose. Clearly, the existence of carbon can induce the formation of carnation-like structure only with a proper amount of carbon. Thus, it can be speculated that a proper content of carbon has a vital influence on the formation of 3D structure. Based on this observation, the possible formation mechanism of carnation-like NSH is proposed in Figure 6. The structures of NCH, NCH-1 and NSH both contain

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the nickel and cobalt based compounds, but NSH obtained with the aid of C could lead to a higher surface area, which can be attributed to the 3D carnation-like architecture with meso/macropores. This result is consistent with the BET test results. Generally, the presence of C can not only induce the formation of hierarchical structure, but also provide good conductive channels for electrode materials. Based on the above discussion, all the structure analyses indicate that carnation-like NSH is successfully fabricated by this simple hydrothermal method. Besides, with the aid of C, the obtained NSH exhibits 3D morphology consisted of nanosheets (5-6 nm) with open meso/macropores, which is beneficial to improve its electrochemical performance. To further verify the association between the structure and electrochemical performance, a series of electrochemical tests were conducted afterwards. 3.2. Electrochemical behavior

Figure 7. (a) CV curves of NSH at different scan rates; (b) CV curves of NSH, NCH,

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NCH-1 and NCH-2 at a scan rate of 20 mV/s; (c) galvanostatic charge-discharge curves of NSH at different current densities; (d) galvanostatic charge-discharge curves, (e) gravimetric capacity measured at various charge/discharge current densities and (f) Nyquist plot of NSH, NCH, NCH-1 and NCH-2; the inset of (f) represents an equivalent circuit. The electrochemical performance of obtained samples was studied in 1 M KOH aqueous solution using a three-electrode system (Figure 7a). From the CV curves, the well defined redox peaks are observed, which are mainly attributed to the faradic reaction of nickel and cobalt ions (Ni2+↔Ni3+, Co2+↔Co3+). The redox peaks can be attributed to the reactions presented below: 42 ,49, 50 Ni(OH)2 + OH-↔ NiOOH + H2O + e-

(3)

Co(OH)2 + OH- = CoOOH + H2O + e-

(4)

CoOOH + OH- = CoO2 + H2O + e-

(5)

As specific capacity (QS) is proportional to the average areas of CVs, it is suggested that the NSH delivers the optimized electrochemical behavior and substantially larger current density compared with the other samples (Figure 7a, b). The improved electrochemical performance of NSH can be ascribed to its unique carnation-like architecture, high surface area and excellent electronic conductivity (Figure 7f) induced by C. Moreover, the introducing C may prevent the aggregation of Ni-Co compound nanosheets.13,

17

This fact aids to generate appropriate layer spacing,

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enabling the effective redox reaction at the interface of Ni0.75Co0.25(CO3)0.125(OH)2 and electrolyte. Additionally, the galvanostatic charge/discharge analysis of NSH (Figure 7c) reveals the enhanced rate capability and higher specific capacity than the other samples (Figure 7d-e). It is impressive that the NSH can offer high QS of 277.3, 265.6, 254.5, 163.6 and 126.6 mAh/g at discharge current densities of 0.5, 1, 2, 5 and 10 A/g, respectively. Significantly, NSH retains higher capacity than other samples with the current density increased from 0.5 to 5 A/g (59.0 % for NSH vs 26.33 % for NCH). Meanwhile, the QS of obtained samples with introducing C (NSH, 277.3 mAh/g; NCH-2, 236.0 mAh/g) is far higher than the other samples without introducing C (NCH, 177.4 mAh/g; NCH-1, 137.7 mAh/g) (Figure 7d), indicating the important influence of carnation-like architecture induced by C on their electrochemical properties. Moreover, NCH-2 (without introducing N, S) offers lower electrochemical behavior than NSH (236.0 vs 277.3 mAh/g). Although they have similar carnation-like structure (Figure 5b, 5i), NSH exhibits enhanced conductivity (Figure 7f) and a more perfect morphology than NCH-2. It indicates that N and S co-doping strategy can further reduce the internal resistance and improve the low capacity of carbon-rich materials. However, N and S dopants may interact with the carbon rather than nickel and cobalt based compounds. For example, in the absence of C, NCH-1 (only with introducing N, S) exhibits a lower specific capacity than NCH (137.7 vs 177.4 mAh/g). Besides, the existences of -C-S-C-, C-N, C=N, N-C=O and N-C=S bonds proved in the FT-IR and XPS spectra (Figure 1b, Figure 2 and Figure S2)

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indicates that the N and S dopants act on carbon rather than nickel and cobalt compounds. Therefore, in the absence of carbon, N and S dopants might aggregate together on the surface of nickel and cobalt compounds, leading to the depressed specific capacity. EIS analysis was performed to examine the electron diffusion behavior. As can be seen from Figure 7f, all Nyquist plot were characterized by two distinct parts: an inconspicuous arc in the high-frequency region and a linear line in the low-frequency region, and the inset of Figure 7f represents an equivalent circuit. Obviously, compared with NSH, the diffusive lines of NCH, NCH-1 and NCH-2 in the lower frequency region come away from an ideally straight line, suggesting the increasing diffusion resistance (Warburg impedance) of ions and an increased intrinsic resistance of charge transfer due to faradic reactions.39 Meanwhile, the ultrathin nanosheets (5-6 nm) can overlap each other to improve the conductivity through plane contact. In addition, NSH has more meso/macropores (Figure 5a-c) and larger surface area than NCH, which facilitates the fast diffusion and migration of electrolyte ions, resulting in the improvement of electrochemical performance of NSH compared to other reports.12, 31, 37, 51

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Figure 8. (a) CV curves of rGH and NSH measured by a three-electrode system at a scan rate of 20 mV/s; (b) CV curves at different scan rates and (c) charge/discharge curves at various current densities of NSH//rGH asymmetric cell measured by a two-electrode system; (d) CV curves at different scan rates and (e) charge/discharge curves at various current densities of NCH//rGH asymmetric cell measured by a two-electrode system; (f) Charge-discharge curves at 0.5 A/g, (g) specific capacity of 20


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asymmetric cells, (h) the Ragone plots, (i) cycling performance, and (j) Nyquist plot of NSH//rGH, NCH//rGH asymmetric cell in two electrodes system; Two assembled NSH asymmetric cells connected in series drive (k) two parallel red LED, (l) parallel red and yellow LEDs. To further evaluate the real application of the obtained samples, the asymmetric cells were assembled by taking NSH or NCH as the positive electrodes, with rGH (Figure S7e, f) as the negative electrodes in 1 M KOH electrolyte. Before the two electrode tests, rGH was investigated using a three-electrode system, exhibiting specific capacitance (C－) of 236.4 F/g at 1 A/g (Figure S7a-d). Figure 8a illustrates the relationship between NSH positive electrodes and graphene hydrogels negative electrodes by comparing their CV curves at a scan rate of 20 mV/s with an optimized mass ratio (NSH: rGH= 1: 4.8) in a three-electrode system. The above mass ratio was calculated based on the capacity values and potential windows (supporting information, Section 2, Eqn (2)). It reveals that the electrode potential window of NSH//rGH asymmetric cell can be extended to 0-1.7 V (vs. SCE). Moreover, the as-fabricated NSH//rGH device can deliver Qs of 52.3, 46.9, 35.6, 28.3, 21.1 and 13.7 mAh/g at 0.5, 1, 2, 3, 5 and 10 A/g, respectively (Figure 8g). Furthermore, NSH//rGH asymmetric cell exhibits promising energy density of 44.4 Wh/kg at 460 W/kg (Figure 8h). At a remarkable high power density of 9.8 kW/kg, NSH devices are also able to deliver an energy density of 11.7 Wh/kg. In addition, to study the cycling stability of NSH, the charge-discharge curves were measured for 3000 cycles at a current density of 3 A/g (Figure 8i). For the first 1000 cycles, the capacity of NSH devices remain

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stable as 98.5 % with the assistance of activation process. However, the activation process would finish after 1000 cycles while the structure degradation of electrode materials still goes on (Figure S6a). After 3000 cycles, the seriously destroyed 3D carnation-like structure causes a worse conductivity as Figure S6 showed, resulting in obvious decrements of capacity.26, excellent

stability

than

other

28

Furthermore, NSH device exhibits more

nickel

based

electrode

materials

such

as

Ni(OH)2/graphene composite hydrogels (87.3 %, 1000 cycles),37 and the nickel hydroxide/graphene hydrogels (95.2 %, 1000 cycles).52 Compared with NSH devices, the NCH//rGH asymmetric cell exhibits smaller specific capacity (0.5 A/g, 25.7 mAh/g), the lower energy density (21.8 Wh/kg at 430 W/kg), and lower capacity retention (83.3 % after 1000 cycles), as well as the higher internal resistances and diffusive resistance (Figure 8d-j). The high electrochemical performances presented by NSH can be attributed to the great effect of the carnation-like structure induced by carbon. In addition, to demonstrate the practical application of NSH//rGH, two assembled NSH asymmetric cells were connected in series with two parallel light-emitting diodes (LEDs) series and successfully lighted it for a period of time (Figure 8k, l). This real circuit test is robust enough to confirm that NSH is competent to realize promising actual applications for supercapacitors. 4. Conclusion In summary, the Ni0.75Co0.25(CO3)0.125(OH)2/C with N, S co-doping was synthesized via a one-step hydrothermal method. It is first proposed that carbon could induce the growth of carnation-like hierarchical architecture, while N and S dopants can further

22


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modify the structure of carbon-rich materials. Moreover, the presence of carbon offers continuous conductive pathway for electron transport. In virtue of the carnation-like hierarchical structure, NSH exhibits excellent capability. Especially, the NSH//rGH based hybrid supercapacitor device can show high energy density and good cycling stability. Furthermore, the simple synthesis strategy might be easily extended to the shape-controlled growth of other similar 3D hierarchical architectured materials.

Supporting Information The supporting information is available free of charge on the ACS Publication website. The characterizations of XRD, XPS, SEM, TEM, and BET for contrasted samples; Electrochemical measurements including CV curves, galvanostatic charge-discharge curves and Nyquist plot of rGH and other samples; The calculation equations of two and three electrodes.

Acknowledgements This investigation was supported by the Natural Science Foundation of China (No. 51472122), the Fundamental Research Funds for the Central Universities (No. 30915011201), the Funds of Changzhou international technology cooperation (CZ20160002) and “333 project” of Jiangsu.

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References (1) Chen, G.Q.; Wu, X.F. Energy Overview for Globalized World Economy: Source, Supply Chain and Sink. Renew. Sustain. Energy Rev. 2017, 69, 735-749. (2) Little, J. C.; Hester, E. T.; Carey, C. C. Assessing and Enhancing Environmental Sustainability: A Conceptual Review. Environ. Sci. Technol. 2016, 50, 6830-6845. (3) Saha, S.; Jana, M.; Samanta, P.; Murmu, N. C.; Kuila, T. Efficient Access of Voltammetric Charge in Hybrid Supercapacitor Configured with Potassium Incorporated Nanographitic Structure Derived from Cotton (Gossypium arboreum) as Negative and Ni(OH)2/rGO Composite as Positive Electrode. Ind. Eng. Chem. Res. 2016, 55, 11074-11084. (4) Ji, J.; Zhang, L. L.; Ji, H.; Li, Y.; Zhao, X.; Bai, X.; Fan, X.; Zhang, F.; Ruoff, R. S. Nanoporous Ni(OH)2 Thin Film on 3D Ultrathin-Graphite Foam for Asymmetric Supercapacitor. ACS Nano 2013, 7, 6237-6243. (5) Shen, J.; Li, X.; Wan, L.; Liang, K.; Tay, B. K.; Kong, L.; Yan, X. An Asymmetric Supercapacitor with Both Ultra-High Gravimetric and Volumetric Energy Density Based on 3D Ni(OH)2/MnO2@Carbon Nanotube and Activated Polyaniline-Derived Carbon. ACS Appl. Mater. Interfaces 2016, 9, 668-676. (6) Zhang, N.; Ding, Y.; Zhang, J.; Fu, B.; Zhang, X.; Zheng, X.; Fang, Y. Construction

of

MnO2

Nanowires@Ni1-xCoxOy

Nanoflake

Core-shell

Heterostructure for High Performance Supercapacitor. J. Alloys Compd. 2017, 694, 1302-1308.

24


Page 25 of 32 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


(7) Wang, N.; Zhao, P.; Liang, K.; Yao, M.; Yang, Y.; Hu, W. CVD-grown Polypyrrole Nanofilms on Highly Mesoporous Structure MnO2 for High Performance Asymmetric Supercapacitors. Chem. Eng. J. 2017, 307, 105-112. (8) Li, X.; Ding, R.; Shi, W.; Xu, Q.; Wang, L.; Jiang, H.; Yang, Z.; Liu, E. Hierarchical Mesoporous Ni-P@MnO2 Composite for High Performance Supercapacitors. Mater. Lett. 2017, 187, 144-147. (9) Zhao, C.; Shao, X.; Zhang, Y.; Qian, X. Fe2O3/Reduced Graphene Oxide/Fe3O4 Composite in Situ Grown on Fe Foil for High-Performance Supercapacitors. ACS Appl. Mater. Interfaces 2016, 8, 30133-30142. (10) Zhang, J.; Zhang, G.; Luo, W.; Sun, Y.; Jin, C.; Zheng, W. Graphitic Carbon Coated CuO Hollow Nanospheres with Penetrated Mesochannels for High-Performance Asymmetric Supercapacitors. ACS Sustain. Chem. Eng. 2016, 5, 105-111. (11) Liao, J. Y.; Oh, S. M.; Manthiram, A. Core/Double-Shell Type Gradient Ni-Rich LiNi0.76Co0.10Mn0.14O2 with High Capacity and Long Cycle Life for Lithium-Ion Batteries. ACS Appl. Mater. Interfaces 2016, 8, 24543-24549. (12) Guan, B. Y.; Yu, L.; Wang, X.; Song, S.; Lou, X. W. Formation of Onion-Like NiCo2S4 Particles via Sequential Ion-Exchange for Hybrid Supercapacitors. Adv. Mater. 2017, 29, 1605051. (13) Dong, S.; Dao, A. Q.; Zheng, B.; Tan, Z.; Fu, C.; Liu, H.; Xiao, F. One-step Electrochemical Synthesis of Three-dimensional Graphene Foam Loaded

25



Page 26 of 32

Nickel-Cobalt Hydroxides Nanoflakes and Its Electrochemical Properties. Electrochim. Acta 2015, 152, 195-201. (14) Zhang, C.; Chen, Q.; Zhan, H. Supercapacitors Based on Reduced Graphene Oxide

Nanofibers

Electrochemical

Supported

Performance.

Ni(OH)2 ACS

Nanoplates

Appl.

Mater.

with

Interfaces

Enhanced 2016,

8,

22977-22987. (15) Jabeen, N.; Xia, Q.; Savilov, S. V.; Aldoshin, S. M.; Yu, Y.; Xia, H. Enhanced Pseudocapacitive Performance of α-MnO2 by Cation Preinsertion. ACS Appl. Mater. Interfaces 2016, 8, 33732-33740. (16) Chen, S.; Yang, G.; Zheng, H. Aligned Ni-Co-Mn Oxide Nanosheets Grown on Conductive

Substrates

as

Binder-free

Electrodes

for

High

Capacity

Electrochemical Energy Storage Devices. Electrochim. Acta 2016, 220, 296-303. (17) Ma, H. N.; He, J.; Xiong, D. B.; Wu, J. S.; Li, Q. Q.; Dravid, V.; Zhao, Y. F. Nickel Cobalt Hydroxide@Reduced Graphene Oxide Hybrid Nanolayers for High Performance Asymmetric Supercapacitors with Remarkable Cycling Stability. ACS Appl. Mater. Interfaces 2016, 8, 1992-2000. (18) Zhao, Y. F.; Ma, H. N.; Huang, S. F.; Zhang, X. J.; Xia, M. R.; Tang, Y. F.; Ma Z. F. Monolayer Nickel Cobalt Hydroxyl Carbonate for High Performance All-Solid-State Asymmetric Supercapacitors. ACS Appl. Mater. Interfaces 2016, 8, 22997-23005. (19) Wang, M.; Jin, F. D.; Zhang, X. J.; Wang, J.; Huang, S. F.; Zhang, X. Y.; Mu, S. C.; Zhao, Y. P.; Zhao, Y. F. Multihierarchical Structure of Hybridized Phosphates

26


Page 27 of 32 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


Anchored on Reduced Graphene Oxide for High Power Hybrid Energy Storage Devices. ACS Sustain. Chem. Eng. 2017, 5, 5679-5685. (20) Chen, Z. Y.; Xiong, D. B.; Zhang, X. J.; Ma, H. N.; Xia, M. R.; Zhao, Y. F. Construction of A Novel Hierarchical Structured NH4-Co-Ni Phosphate toward an Ultrastable Aqueous Hybrid Capacitor. Nanoscale 2016, 6, 6636-6645. (21) Wei, G.; Xu, X.; Liu, J.; Du, K.; Du, J.; Zhang, S.; An, C.; Zhang, J.; Wang, Z. Carbon Quantum Dots Decorated Hierarchical Ni(OH)2 with Lamellar Structure for Outstanding Supercapacitor. Mater. Lett. 2017, 186, 131-134. (22) Shao, Y.; Zhao, Y.; Li, H.; Xu, C. Three-Dimensional Hierarchical NixCo1−xO/NiyCo2−yP@C Hybrids on Nickel Foam for Excellent Supercapacitors. ACS Appl. Mater. Interfaces 2016, 8, 35368-35376. (23) Du, H.; Wang, Y.; Yuan, H.; Jiao, L. Facile Synthesis and High Capacitive Performance of 3D Hierarchical Ni(OH)2 Microspheres. Electrochim. Acta 2016, 196, 84-91. (24) Tavandashti, N. P.; Ghorbani, M.; Shojaei, A. Controlled Growth of Hollow Polyaniline Structures: From Nanotubes to Microspheres. Polymer 2013, 54, 5586-5594. (25) Tao, S.; Ding, Y.; Jiang, L.; Li, G. Preparation of Magnetic Hierarchically Porous Microspheres with Temperature-Controlled Wettability for Removal of Oils. J. Colloid Interface Sci. 2017, 492, 73-80. (26) Duay, J.; Sherrill, S. A.; Gui, Z.; Gillette, E.; Lee, S. B. Self-Limiting Electrodeposition

of

Hierarchical

MnO2

27


and

M(OH)2/MnO2


Page 28 of 32

Nanofibril/Nanowires: Mechanism and Supercapacitor Properties. ACS Nano 2013, 7, 1200-1214. (27) Zhang, J.; Zhang, X.; Zhou, Y.; Guo, S.; Wang, K.; Liang, Z.; Xu, Q. Nitrogen-Doped Hierarchical Porous Carbon Nanowhisker Ensembles on Carbon Nanofiber for High-Performance Supercapacitors. ACS Sustain. Chem. Eng. 2014, 2, 1525-1533. (28) Hou, S.; Zhang, G.; Zeng, W.; Zhu, J.; Gong, F.; Li, F.; Duan, H. Hierarchical Core-Shell Structure of ZnO Nanorod@NiO/MoO2 Composite Nanosheet Arrays for High-Performance Supercapacitors. ACS Appl. Mater. Interfaces 2014, 6, 13564-13570. (29) Long, C.; Zheng, M.; Xiao, Y.; Lei, B.; Dong, H.; Zhang, H.; Hu, H.; Liu, Y. Amorphous Ni-Co Binary Oxide with Hierarchical Porous Structure for Electrochemical Capacitors. ACS Appl. Mater. Interfaces 2015, 7, 24419-24429. (30) Zhou, Q.; Xing, J.; Gao, Y.; Lv, X.; He, Y.; Guo, Z.; Li, Y. Ordered Assembly of NiCo2O4

Multiple

Hierarchical

Structures

for

High-Performance

Pseudocapacitors. ACS Appl. Mater. Interfaces 2014, 6, 11394-11402. (31) Zhu, G.; Xi, C.; Shen, M.; Bao, C.; Zhu, J. Nanosheet-Based Hierarchical Ni2(CO3)(OH)2 Microspheres with Weak Crystallinity for High-Performance Supercapacitor. ACS Appl. Mater. Interfaces 2014, 6, 17208-17214. (32) Wei, J. S.; Ding, H.; Zhang, P.; Song, Y. F.; Chen, J.; Wang, Y. G.; Xiong, H. M. Carbon Dots/NiCo2O4 Nanocomposites with Various Morphologies for High Performance Supercapacitors. Small 2016, 12, (43), 5927-5934.

28


Page 29 of 32 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


(33) Zhang, L.; Ding, Q.; Huang, Y.; Gu, H.; Miao, Y.-E.; Liu, T. Flexible Hybrid Membranes with Ni(OH)2 Nanoplatelets Vertically Grown on Electrospun Carbon Nanofibers for High-Performance Supercapacitors. ACS Appl. Mater. Interfaces 2015, 7, 22669-22677. (34) Chen, S.; Zhu, J.; Wu, X.; Han, Q.; Wang, X. Graphene Oxide MnO2 Nanocomposites for Supercapacitors. ACS Nano 2010, 4, 2822-2830. (35) Zhang, L.; Yang, X.; Zhang, F.; Long, G.; Zhang, T.; Leng, K.; Zhang, Y.; Huang, Y.; Ma, Y.; Zhang, M. Controlling the Effective Surface Area and Pore Size Distribution of sp2 Carbon Materials and Their Impact on The Capacitance Performance of These Materials. J. Am. Chem. Soc. 2013, 135, 5921-5929. (36) Doherty, C. M.; Caruso, R. A.; Smarsly, B. M.; Adelhelm, P.; Drummond, C. J. Hierarchically Porous Monolithic LiFePO4/Carbon Composite Electrode Materials for High Power Lithium Ion Batteries. Chem. Mater. 2009, 21, 5300-5306. (37) Meng, X.; Zhu, J.; Bi, H.; Fu, Y.; Han, Q.; Wang, X. Three-dimensional Nickel Hydroxide/Graphene Composite Hydrogels and Their Transformation to NiO/Graphene Composites for Energy Storage. J. Mater. Chem. A 2015, 3, 21682-21689. (38) Chen, S.; Zhu, J.; Wang, X. From Graphene to Metal Oxide Nanolamellas: A Phenomenon of Morphology Transmission. ACS Nano 2010, 4, 6212-6218.

29



(39) Li, D. L.; Gong, Y. N.; Zhang, Y. P.; Luo, C. Z.; Li, W. P.; Fu, Q.; Pan, C. X. Facile Synthesis of Carbon Nanosphere/NiCo2O4 Core-shell Sub-microspheres for High Performance Supercapacitor. Sci. Rep. 2015, 5, 12903. (40) Li, Q.; Lu, C. X.; Chen, C. M.; Xie, L. J.; Liu, Y. D.; Li, Y.; Kong, Q. Q.; Wang, H. Layered NiCo2O4/reduced Graphene Oxide Composite as An Advanced Electrode for Supercapacitor. Energy Storage Mater. 2017, 8, 59-67. (41) Wei, J. S.; Ding, H.; Zhang, P.; Song, Y. F.; Chen, J.; Wang, Y. G.; Xiong H. M. Carbon Dots/NiCo2O4 Nanocomposites with Various Morphologies for High Performance Supercapacitors. Small 2016, 12, 5927-5934. (42) Nguyen, T.; Boudard, M.; Carmezim, M. J.; Montemor, M. F. NixCo1-x(OH)2 Nanosheets on Carbon Nanofoam Paper as High Areal Capacity Electrodes for Hybrid Supercapacitors. Energy 2017, 126, 208-216. (43) Liu, Z.; Ma, R.; Osada, M.; Takada, K.; Sasaki, T. Selective and Controlled Synthesis of Alpha- and Beta-Cobalt Hydroxides in Highly Developed Hexagonal Platelets. J. Am. Chem. Soc. 2005, 127, 13869-13874. (44) Tsunekawa, S.; Ito, S.; Kawazoe, Y. Surface Structures of Cerium Oxide Nanocrystalline Particles From the Size Dependence of the Lattice Parameters. Appl. Phys. Lett. 2004, 85 (17), 3845-3847. (45) Perebeinos, V.; Chan, S. W.; Zhang, F. Madelung Model Prediction for Dependence of Lattice Parameter on Nanocrystal Size. Solid State Commun. 2002, 123, 295-297.

30


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Page 31 of 32 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


(46) Long, J. W.; Swider, K. E.; Merzbacher, C. I.; Rolison, D. R. Voltammetric Characterization of Ruthenium Oxide-based Aerogels and Other RuO2 Solids: The Nature of Capacitance in Nanostructured Materials. Langmuir 1999, 15, 780-785. (47) Jian, X.; Liu, X.; Yang, H. M.; Li, J. G.; Song, X. L.; Dai, H. Y.; Liang, Z. H. Construction of Carbon Quantum Dots/Proton-Functionalized Graphitic carbon Nitride Nanocomposite via Electrostatic Self-assembly Strategyand Its Application. Appl. Surf. Sci. 2016, 370, 514-521. (48) He, X. Y.; Liu, Q.; Liu, J. Y.; Li, R. M.; Zhang, H. S.; Chen, R. R.; Wang, J. High-performance All-solid-state Asymmetrical Supercapacitors Based on Petal-like NiCo2S4/Polyaniline Nanosheets. Chem. Eng. J. 2017, 325, 134-143. (49) Yang, J. H.; Tan, J.; Ma, D. Nickel Phosphate Molecular Sieve as Electrochemical Capacitors Material. J. Power Sources. 2014, 260, 169-173. (50) Ghosh, D.; Mandal, M.; Das, C. K. Solid State Flexible Asymmetric Supercapacitor Based on Carbon Fiber Supported Hierarchical Co(OH)xCO3 and Ni(OH)2. Langmuir 2015, 31, 7835-7843. (51) Du, H.; Wang, Y.; Yuan, H.; Jiao, L. Facile Synthesis and High Capacitive Performance of 3D Hierarchical Ni(OH)2 Microspheres. Electrochim. Acta 2016, 196, 84-91. (52) Wang, R. H.; Jayakumar, A.; Xu, C. H.; Lee, J. M. Ni(OH)2 Nanoflowers/Graphene Hydrogels: A New Assembly for Supercapacitors. ACS Sustain. Chem. Eng. 2016, 4, 3736-3742.

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Table of contents (TOC) graphic Carbon

induced

generation

of

hierarchical

structured

Ni0.75Co0.25(CO3)0.125(OH)2 for enhanced supercapacitor performance Feng Wen, Yue Zhang, Xingyue Qian, Jianli Zhang, Rudan Hu, Xuemin Hu, Xin Wang, Junwu Zhu* Key Laboratory for Soft Chemistry and Functional Materials, Ministry of Education Nanjing University of Science and Technology, Nanjing 210094, China Email: [email protected] (J. Zhu)

TOC graphic

Significantly,

with

the

aid

of

carbon,

N

and

S

co-doped

Ni0.75Co0.25(CO3)0.125(OH)2/C (NSH) with hierarchical structure was synthesized through a facile one-step hydrothermal method. More interestingly, the obtained NSH exhibits three-dimensional carnation-like hierarchical structure and excellent capability and high energy density.

32


Carbon-Induced Generation of Hierarchical Structured Ni0.75Co0.25

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