2H Hybrid MoS2

Subscriber access provided by Kaohsiung Medical University

C: Energy Conversion and Storage; Energy and Charge Transport

Oxygen Incorporated and Polyaniline Intercalated 1T/2H Hybrid MoS2 Nanosheets Arrayed on Reduced Graphene Oxide for High Performance Supercapacitors Jie Chao, Lichun Yang, Jiangwen Liu, Renzong Hu, and Min Zhu J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b01473 • Publication Date (Web): 30 Mar 2018 Downloaded from http://pubs.acs.org on March 30, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30 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

The Journal of Physical Chemistry

Oxygen Incorporated and Polyaniline Intercalated 1T/2H Hybrid MoS2 Nanosheets Arrayed on Reduced Graphene Oxide for High Performance Supercapacitors

Jie Chaoa, Lichun Yanga, Jiangwen Liua, Renzong Hua and Min Zhua,* a

SUNWODA-SCUT Joint Laboratory for Advanced Energy Storage Technology，

South China University of Technology, Guangzhou, China, 510640 *Corresponding Author Email: [email protected]

1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 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

Abstract This work synthesizes the hybrid 1T/2H phase MoS2 nanosheets array on reduced graphene oxide for high performance supercapacitors under extreme environmental temperature via oxygen incorporation and polyaniline intercalation method. The oxygen incorporation, which leads to formation of MoS2 with hybrid phase of 1T and 2H structure, and polyaniline intercalation provide excellent conductivity and expand interlayer distance of MoS2. Meanwhile, the sandwiched oxygen-incorporated MoS2/polyaniline nanosheets array align on reduced graphene oxide creating sufficient hetero-interface among polyaniline, MoS2 and reduced graphene oxide, that constructs a conducting network which is beneficial for charge transfer and structure stability. The obtained oxygen-incorporated MoS2/polyaniline/reduced graphene oxide hierarchical nanosheets exhibit a capacitance of 752.0 F g-1 at 1 A g-1 in 1M H2SO4 in a three-electrode system, and have a capacitance retention of 80.4 % for initial cycle (282.3 F g-1) after 50,000 cycles when cycles at 50 A g-1. The material shows excellent performane in extreme wide range of temperature. The symmetric cell has the capacitance of 79.6 F g-1, 100.1 F g-1 and 122.0 F g-1 at 2 A g-1 at 0 oC, room temperature and 50 oC, and maintains about 89.9 %, 86.1 % and 73.9 % of initial capacitance, respectively after 30,000 cycles.

2


Page 2 of 30

Page 3 of 30 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


1. Introduction Supercapacitor is one of the most competitive energy storage devices to battle with the environmental and energy crises, because of its high power density, fast charge/discharge process and long cycle performance.1-3 However, the relative low energy capacity comparing with Li-ion battery limits its application. The development of electrode materials with high capacity quite as battery and maintaining the long cycle life simultaneously is of great importance as it plays the key role in supercapacitor. MoS2, as a typical transition metal sulfides with intimate relationship to graphite and composed of S-Mo-S layers under the weak van der Waals interaction, is considered as a promising electrode material for supercapacitor.4 Because it can not only contribute double-layer capacitance which is comparable to that of CNT array material,5 but also provide considerable pseudocapacitance, based on the fact that the large 2D permeable galleries benefit ion transport and intercalation. Furthermore, Mo central atom can exhibit a wide range of oxidation states from +2 to +6 like RuO2. 6 It means a potential vigorous charge storage capability. However, the capacity delivery of MoS2 is limited in practical application because of the poor intrinsic conductivity of MoS2 nanostructure, especially along two contiguous S-Mo-S layers.7 Fortunately, growth of monolayer MoS2 can thoroughly solve this problem. Due to the quantum confinement and surface effect, the monolayer MoS2 is metallic (1T) with direct band gaps, while the bulk MoS2 is semiconductors (2H) with indirect band gaps.8-10 Growth of monolayer MoS2 will significantly enhance the conductivity of MoS2 material and improve its accessible active surface, incidentally. Unfortunately, uniform growth of monolayer MoS2 with large area and low cost is still a considerable challenge.11 3



Page 4 of 30

Some recent researches indicates that the Mo atoms have selfsame atomic positions in 1T MoS2 and 2H MoS2.12 Engineering defects in MoS2 layers on purpose could readjust the electronic structure of MoS2, allowing the demonstration of 1T MoS2 behavior in 2H MoS2 to some extent.13 There have been plenty of attempts to make design of defects. Among which, doping of foreign ions, such as Li+, NH4+,

14, 15

and

controlling the formation of sulfur vacancy12 could effectively generate abundant defects and modulate the electronic structure of MoS2, prompting the triangle MoS2 (2H) topically transform to octahedral MoS2 (1T). Inspired by above results, we expect that doping of foreign ions may be an high-efficient strategy for combining the semiconductor featured 2H MoS2 with the metallic featured 1T MoS2. And integrating the doping method with nanostructure design may obtain high performance MoS2 based electrode materials. Herein, we design and synthesize hierarchical nanosheets of sandwiched O-MoS2/PANI nanosheets array vertically align on rGO nanosheets using organic/inorganic hybrid Mo3O10(C6H5NH3)2·4H2O/GO as precursor. PANI chains are intercalated into the adjacent O-MoS2 layers, improving the conductivity between the contiguous MoS2 layers and constructing sandwiched O-MoS2/PANI nanosheets. Meanwhile the sandwiched O-MoS2/PANI nanosheets array align on rGO creating intimate hetero-interface between O-MoS2, PANI and rGO. In addition, via oxygen incorporation, 2H MoS2 are partly transformed to 1T phase, which further improve the conductivity of O-MoS2/PANI/rGO HNSs. The synergistic effect of the sandwiched nanosheets array structure and the oxygen incorporation in MoS2 layers lead to high capacity and excellent cycle performance O-MoS2/PANI/rGO HNSs electrode material even at extreme condition. The combination of low-cost synthetic process and wide range temperature feasibility make the O-MoS2/PANI/rGO HNSs 4


Page 5 of 30 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


promising electrode material for supercapacitor. 2. Experimental Section Synthesis of O-MoS2/PANI/rGO HNSs: To synthesize O-MoS2/PANI/rGO HNSs, firstly, Mo3O10(C6H5NH3)2·4H2O/GO precursor is prepared based on previous report.16 300 mg GO which is prepared by a modified hummers’ method17 is dispersed in 100 mL deionized water and sonicated for approximately 5h to obtain a homogeneous suspension. Meanwhile, 1.65 g (NH4)6Mo7O24·4H2O and 1.75 g aniline are dissolved in 140 mL deionized water and then added into above GO suspension. Then, the pH value of the above suspension is pinpoint adjusted to 4.0 by 1M HCl under the monitor of pH-meter, following by stirring at 50 oC in an oil bath for 5 hours. The obtained Mo3O10(C6H5NH3)2·4H2O/GO are collected, washed and dried at 60

o

C. Second, Mo3O10(C6H5NH3)2·4H2O/GO precursor is transformed to

MoOx/PANI/GO. 1.35 g Mo3O10(C6H5NH3)2·4H2O/GO precursor is homogeneous dispersed in 100 mL deionized water, then adjusted the PH value to 1.7 by 1M HCl. Afterwards, 60 mL of HCl solution (pH 1.7) containing 2.4 g K2S2O8 is dropwise added into the suspension. After stirring for 6 hours at room temperature, the intermediate product of MoOx/PANI/GO is obtained. Last, the O-MoS2/PANI/rGO HNSs are synthesized by a simple hydrothermal method, in which 0.5 g MoOx/PANI/GO and 0.5 g thiourea are dispersed in 30 ml deionized water. After stirring for 30 min, the solution is transferred to a 50 ml Teflon-lined stainless-steel autoclave and kept in an oven at 160 for 48 h. The obtained black product are centrifuged, washed with deionized water and ethanol. Finally, the product are dried at 60 oC. The as-prepared product is called O-MoS2/PANI/rGO-160 HNSs. For comparison, the O-MoS2/PANI/rGO-140 HNSs, O-MoS2/PANI/rGO-180 HNSs and MoS2/PANI/rGO HNSs are synthesized with the hydrothermal temperature of 140, 5



Page 6 of 30

180 and 200oC, respectively. Characterizations: Morphology and structure of samples were analyzed by using field-emission scanning electron microscope (FESEM, Carl Zeiss, Supra 40), transmission electron microscope (TEM, JEOL-2100) at 200 kV, and X-ray diffractometer (XRD, Rigaku, MiniFlex 600) with Cu-Kα radiation. Infrared spectra analysis was made using Fourier transform infrared spectrometer (FT-IR, Nicolet iS50). The Raman analysis was conducted by a laser Raman spectrometer (Raman, Horiba) with an excitation wavelength of 632.8 nm. X-ray photoelectron spectroscopic (XPS) measurements were performed using an ESCALAB 250 spectrometer. Electrochemical

measurements:

To

fabricate

working

electrodes,

each

as-synthesized active materials, acetylene black and polyvinylidene fluoride (PVDF) with a ratio of 80:15:5 were mixed in ethyl alcohol to form slurry. The slurry was coated onto the graphite paper substrate (1cm×1cm) and dried at 60 oC in a vacuum oven for 12 h to remove the solvent. The weight of the active material in per working electrode is about 1 mg. A typical three-electrode system is made using the measured materials as working electrode, a Pt plate as counter electrode and a saturated Ag/AgCl electrode as reference electrode. In a typical two-electrode configuration, O-MoS2/PANI/rGO-160 were used as both cathode and anode. All the electrochemical measurements were conducted with 1M H2SO4 as electrolyte. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed on an electrochemical work station (Gamry Interface1000). EIS was carried out in a frequency range of 100 kHz to 10 mHz at charge cut-off potential with an perturbation potential of 5 mV. Galvanostatic charge/discharge measurements were performed on a supercapacitor test system (SCTS, Arbin). The electrochemical 6


Page 7 of 30 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


measurements conducted at 0 oC and 50 oC were operated in ice-water bath and thermostat water bath, respectively. 3. Result and discussion The synthesis process of O-MoS2/PANI/rGO HNSs is schematically displayed in Figure 1. The Mo3O10(C6H5NH3)2·4H2O/GO was used as precursor and self-template. The precursor possesses a uniform organic/inorganic hybrid structure at a molecular level. After the in-situ polymerization of aniline in the Mo3O10(C6H5NH3)2·4H2O which covered at GO (Figure S1), the obtained organic-inorganic hybrid MoOx/PANI/GO (Figure S2) was subsequently partially sulfurized and GO was reduced (Figure S3) in decreased temperature less than 200

o

C, resulting in

O-MoS2/PANI/rGO composite with remaining Mo-O bonds in MoS2 sheets inherited from MoOx.

Figure 1. Schematic illustration for preparation of O-MoS2/PANI/rGO HNSs

The influence of temperature on morphology of O-MoS2/PANI/rGO was evaluated by SEM and shown in Figure 2. After hydrothermal reaction for 48h at 140 o

C,

some

finely-discreted

nanosheets

appear

on

the

surface

of

O-MoS2/PANI/rGO-140 HNSs, which should be the O-MoS2/PANI sandwiched 7



Page 8 of 30

nanosheets obtained by insufficiently sulfuration under low hydrothermal temperature. With the temperature increasing from 160 oC (Fig. 2b) to 180 oC (Figure 2c) and up to 200 oC (Figure 2d), the sandwiched nanosheets become more and more distinct and dense, forming a regular nanosheets array vertically aligned on reduced oxide graphene, simultaneously.

Figure

2.

SEM

images

O-MoS2/PANI/rGO-160

HNSs,

of (c)

(a)

O-MoS2/PANI/rGO-140

O-MoS2/PANI/rGO-180

HNSs,

HNSs,

and

(b) (d)

MoS2/PANI/rGO HNSs.

The phase structure of O-MoS2/PANI/rGO HNSs are then investigated by XRD and shown in Figure 3a. The diffraction peaks of (002) planes of MoS2 show distinct variation with the change of hydrothermal temperature. In the high temperature of 200 o

C, the diffraction peak of (002) plane of MoS2 in MoS2/PANI/rGO HNSs shifts to

lower angle (12.7o) and corresponding to a slightly enlarged interlayer distance (7.0Å) compared with the pure MoS2 (6.1Å), which is caused by the intercalation of PANI into the MoS2 layers.16 It’s interesting that the peaks of (002) planes shift farther to 10.0o and become unconspicuous with decreasing the sulfurized temperature (160oC 8


Page 9 of 30 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


and 180oC), which corresponds to a further enlarged interlayer distance of 8.8 Å and a more disordered structure. It may result from the combined effect of the remaining Mo-O bonds and PANI intercalation. The enlarged interlayer distance and disorder stacking of S-Mo-S layers are ideal for H+ intercalation in supercapacitor configuration. Moreover, when the hydrothermal temperature reduced to 140 oC, the XRD pattern represents a typical amorphous feature except the broad and low-density peak of (002) plane of rGO located at 25.4o. In addition, no diffraction peaks attributed to molybdenum oxide was detected in the XRD patterns of O-MoS2/PANI/rGO. It suggests the successful oxygen incorporation into MoS2 layers rather than forms molybdenum oxide. Figure 3b shows the FT-IR spectra of O-MoS2/PANI/rGO-160 HNSs. The characteristic peaks at 1573 and 1496 cm-1 are attributed to the C=C stretching of the quinonoid and benzenoid rings.18-20 The peaks located at about 1300 and 1218 cm-1 are assigned to the C-N and C=N stretching of the aromatic amine.21, 22 The other peaks recorded at 1130 and 810 cm-1 represent the aromatic C-H in-plane bending and out-of-plane vibrations of aromatic rings, respectively.22, 23 The distinct FT-IR spectra of PANI confirms the existence of PANI in O-MoS2/PANI/rGO-160 HNSs. Figure 3c depicts the Raman spectra of O-MoS2/PANI/rGO-160 HNSs. The obvious presence of D band (disorderly defect structure) and G band (sp2-bonded carbon atoms) indicates the existence of rGO.3 Figure 3d shows the TEM image of O-MoS2/PANI/rGO-160 HNSs with similar structure as the SEM image shows even under 5 min ultrasonication in alcohol, which indicates a tight and strong contaction between O-MoS2/PANI and rGO. The HRTEM images reveal the low crystallinity of MoS2 (Figure 3e) and irregular stacking of S-Mo-S layers (Figure 3f), which is well consistent with the weak and broad diffraction peaks of the XRD pattern. What’s more, plentiful defects appear in the 9



Page 10 of 30

MoS2 nanosheets, which will be benefit for the ion diffusion.

Figure

3.

(a)

XRD

patterns

of

O-MoS2/PANI/rGO-140

HNSs,

O-MoS2/PANI/rGO-160 HNSs, O-MoS2/PANI/rGO-180 HNSs, and MoS2/PANI/rGO HNSs, (b) FT-IR spectrum, (c) Raman spectrum and (d-f) TEM images of O-MoS2/PANI/rGO-160 HNSs.

XPS has been used to better understand the phase and valence states of the O-MoS2/PANI/rGO

HNSs.

O-MoS2/PANI/rGO-140

The

spectrum

HNSs,

of

Mo

3d

of

O-MoS2/PANI/rGO-160

O-MoS2

in

HNSs,

O-MoS2/PANI/rGO-180 HNSs, and MoS2/PANI/rGO HNSs are shown in Figure 4. The Mo 3d could be decomposed into six main peaks. The peaks located at 229.3eV (Mo 3d5/2) and 232.2eV (Mo 3d3/2) indicate +4 oxidation state of 2H-MoS2,24, 25 and the peak at 231.5eV and 228.3 eV suggest the formation of 1T-MoS2.9 Besides, two other peaks can be noticed appearing at 232.9 eV and 235.8 eV, which can be

10


Page 11 of 30 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


ascribed to MoVI-O bonds.24, 25 It can be clearly seen that there are no peaks of 1T MoS2 appearing in the Mo 3d spectrum of O-MoS2/PANI/rGO-140 HNSs (Figure 4a), which may be due to the amorphous structure of MoS2 in O-MoS2/PANI/rGO-140 HNSs as the XRD pattern and SEM image show. With the temperature increasing, the peaks of MoVI-O is waning and the peaks of 1T MoS2 emerge in Figure 4c-d. When the temperature increase to 200 oC, the peaks for MoVI-O bonds still exists in the Mo 3d spectrum of the MoS2/PANI/rGO HNSs, but obviously weaker than they performs in that of the O-MoS2/PANI/rGO HNSs. It should be caused by the unavoidable surface oxidation in the air and will not contribute to the enlargement of the interlayer distance.24, 26, 27 The relative content of 1T phase, 2H phase and MoVI-O in O-MoS2 for

O-MoS2/PANI/rGO-140

HNSs,

O-MoS2/PANI/rGO-160

HNSs,

O-MoS2/PANI/rGO-180 HNSs, and MoS2/PANI/rGO HNSs are estimated according to their respective integral area of characteristic peaks and displayed in Table 1. According to Table 1, we can make an inference that the oxygen incorporation is successfully achieved in the O-MoS2/PANI/rGO HNSs, and is responsible for the transformation of 2H MoS2 to 1T MoS2. However, the 1T MoS2 would not appearing in the MoS2 with amorphous structure (140 oC), and the well crystallized structure (200 oC) would also be adverse to the introducing of 1T MoS2.

11



Page 12 of 30

Figure 4. XPS spectra of Mo 3d of (a) O-MoS2/PANI/rGO-140 HNSs, (b) O-MoS2/PANI/rGO-160 HNSs, (c) O-MoS2/PANI/rGO-180 HNSs, and (d) MoS2/PANI/rGO HNSs.

Table 1. Relative content (%) of 1T phase, 2H phase and Mo-O in O-MoS2 for O-MoS2/PANI/rGO-140 HNSs, O-MoS2/PANI/rGO-160 HNSs, O-MoS2/PANI/rGO-180 HNSs, and MoS2/PANI/rGO HNSs. 1T MoS2

2H MoS2

Mo-O

O-MoS2/PANI/rGO-140

0

40.2 (amorphous)

59.8

O-MoS2/PANI/rGO-160

25.2

33.3

41.5

O-MoS2/PANI/rGO-180

26

40.5

33.5

MoS2/PANI/rGO

12.3

65.4

22.3

The spectrum of S, O and C of S are displayed in Figure 5. As Figure 5a shows, 12


Page 13 of 30 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


the spectrum of S 2p can be divided into four peaks. The peaks at 161.5 eV (2p3/2) and 162.6eV (2p1/2) represent the 1T-MoS2, and the peaks at 162.8 eV (2p3/2) and 164 eV (2p1/2) are on behalf of 2H-MoS2.14, 28 It should be noted that S4+ peaks appears at 168.4 eV, most probably because of the partial oxidation of the MoS2 surface in the air.29, 30 The peak located at 530.8 eV in the O 1s spectrum (Figure 5b) could be attributed to the incorporation of oxygen into MoS2 layers31,

32

and should be

responsible for the enlarged interlayer distance of MoS2 layers, while the peak located at 532.0 eV should be attributed to the adsorbed water.25 The C 1s spectrum (Figure 5c) shows four main peaks which present C=C (284.5 eV), C-N (285.4 eV), C-O (286.5 eV) and C=O (288.2 eV).24 The relatively recorded weak peaks represented for C-O and C=O suggest that GO has been well reduced. All the analysis above confirm that the oxygen have been well incorporated into the MoS2 layers via the temperature controlled method, and the oxygen incorporation can enlarged the interlayer distance of MoS2 with the combined action of PANI intercalation, which means easier ion access for energy storage. Above all, the oxygen incorporation make the 2H MoS2 transform to 1T MoS2, partially.

Figure 5. XPS spectra of O-MoS2/PANI/rGO-160 HNSs: (a) S 2p, (b) O 1s, (c) C 1s.

To investigate the electrochemical performance, the three-electrode systems are adopted

for

O-MoS2/PANI/rGO-140

HNSs,

O-MoS2/PANI/rGO-160

13


HNSs,


Page 14 of 30

O-MoS2/PANI/rGO-180 HNSs, and MoS2/PANI/rGO HNSs. The CV curves (Figure 6a) reveal a noticeably increasing response current density of O-MoS2/PANI/rGO HNSs compared with MoS2/PANI/rGO HNSs, which could be attributed to the improvement of the intrinsic conductivity of MoS2 and further confirmed by EIS measurement (Figure S4). Two pair of redox peaks are also observed in the CV curves, which should be generated from the redox reaction of PANI.20,21,33,34 In addition, it is noteworthy that the area of the CV curve of O-MoS2/PANI/rGO-160 HNSs is larger than those of other O-MoS2/PANI/rGO HNSs and MoS2/PANI/rGO HNSs. This means that O-MoS2/PANI/rGO-160 HNSs have increscent capacitance when compared to O-MoS2/PANI/rGO-140 HNSs, O-MoS2/PANI/rGO-180 HNSs and MoS2/PANI/rGO HNSs. The charge/discharge test further confirms the inferences obtained from the CV curves. As shown in Figure 6b, the O-MoS2/PANI/rGO-160 HNSs has the longest discharge time compared with O-MoS2/PANI/rGO-140 HNSs, O-MoS2/PANI/rGO-180 HNSs and MoS2/PANI/rGO HNSs at the current density of 1 A g-1, which means a largest capacitance. In addition, the charge/discharge profiles of the O-MoS2/PANI/rGO-160 HNSs have good symmetry, as Figure 6c shows, which implies an excellent reversibility of charge/discharge reaction. According to the equation (1) which determine the appropriate specific capacitance from the discharge curves by integrating, i.e. finding the area under the discharge curve, the more adequate information can be obtained from the charge/discharge curves and is more suitable for the non-linearity charge/discharge curves35, 36 ೟ሺೆ

C=

ሻ

ଶூ ‫׬‬೟ሺೆ ೘೔೙ሻ ௎ሺ௧ሻௗ௧ ೘ೌೣ మ ௠௎೘ೌೣ

(1)

Where I is the discharge current (A), t is the discharge time (s), m is the weight of the active materials (g), and U is the potential (V), the specific capacitance of O-MoS2/PANI/rGO-140

HNSs,

O-MoS2/PANI/rGO-160 14


HNSs,

Page 15 of 30 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


O-MoS2/PANI/rGO-180 HNSs, and MoS2/PANI/rGO HNSs are calculated to be 631.5 F g-1, 752.0 F g-1, 558.6 F g-1, 515.1 F g-1. When the current density increase to 50 A g-1, the O-MoS2/PANI/rGO-160 HNSs still has superior capacitance of 282.3 F g-1 as Figure 6d shows. Then, the charge/discharge cycle was conducted at such high current density (50 A g-1) and show in Figure 6e. The O-MoS2/PANI/rGO-160 HNSs retain 80.4% of the initial capacitance after 50,000 cycles, which has obvious superiority comparing with O-MoS2/PANI/rGO-140 HNSs, O-MoS2/PANI/rGO-180 HNSs and MoS2/PANI/rGO HNSs, especially in comparison with MoS2/PANI/rGO HNSs. In addition, the coulombic efficiency closed to 100% as Figure 6d shows. These results demonstrate that O-MoS2/PANI/rGO-160 HNSs has superior electrochemical energy storage performance and exceptional structural stability (Figure S5) even compared with the reported advanced MoS2 based materials in the previous literature (see Table S1).

15



Page 16 of 30

Figure 6. (a) CV curves at 20 mV s-1 and (b) galvanostatic charge-discharge profiles at a current density of 1 A g-1 of the O-MoS2/PANI/rGO HNSs and MoS2/PANI/rGO HNSs (c) galvanostatic charge-discharge profiles of O-MoS2/PANI/rGO-160 HNSs at various current densities, (d) specific capacitance at various current density and (e) cycle performance at 50 A g-1 of O-MoS2/PANI/rGO HNSs and MoS2/PANI/rGO HNSs.

As the O-MoS2/PANI/rGO-160 HNSs show the best performance in three-electrode test, it was used to construct the symmetric cell both as cathode and anode to investigate its practical performance at various operating temperature. As Figure 7a shows, the CV curves of the symmetric supercapacitor at 0 oC, RT and 50 o

C show similar shape with no obvious oxidation-reduction peaks, which imply an

excellent capacitive behavior and good charge transmission in the electrode even at extreme high temperature of 50 oC. However, it doesn’t mean there has no redox reaction happened with the oxidation-reduction peaks disappearing as discussed in detail before.37 Because of the heightened sensitivity of the three-electrode configuration and insensitivity of the two-electrode configuration, the redox reaction peaks are usually distinct in the three-electrode configuration and disappearing in the two-electrode configuration. Meanwhile, with the temperature increasing, the responding current density increases, accordingly, and means a gradual enlarged capacitance. This phenomenon is caused by the normal characteristic that the faster ionic conductivity of the electrolyte at higher surrounding temperature.2,

38

The

charge/discharge profiles at the current density of 0.5 A g-1 in Figure 6b identify to the result obtained from the CV curves. The IR drops obtained from charge/discharge 16


Page 17 of 30 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


profiles is the product of the current and the resistance of the electrode materials as shown in the inset of Fig. 7b, reveal that the internal resistance within electrode is mildly decreased with the temperature increasing. According to the equation (1), taking m as the total mass of both the anode and cathode, the specific capacitance at 0 o

C, RT and 50 oC are calculated to be 142.7 F g-1, 161.7 F g-1 and 189.6 F g-1,

respectively. Increased the current density from 0.5 A g-1 to 5 A g-1, the specific capacitance decreased to 35.9 F g-1, 55.6 F g-1, 73.6 F g-1 (Figure 7c), with a capacitance retention of 24.9%, 34.4%, 38.8%, accordingly. Such a good rate capability indicates good charge storage property of O-MoS2/PANI/rGO-160 HNSs based symmetric supercapacitor. The charge/discharge cycle stability is also a crucial point to evaluate the performance of a supercapacitor. Figure 7d shows the cyclic performance for the O-MoS2/PANI/rGO-160 HNSs based symmetric supercapacitor at 2 A g-1 at different tempeature. The highest cyclic ability is obtained at 0 oC, and about 89.9% of initial capacitance (79.6 F g-1) maintained after 30,000 cycles. With the temperature increasing, it still remains very good cyclic ability although a down trending presents due to faster aging of the electrode material in higher temperature. At RT, the symmetric supercapacitor has an initial capacitance of 100.1 F g-1, and after 30,000 cycles the capacitance become approximately 86.1% of the initial cycle. When the temperature increase to as high as 50 oC, the capacitance retention still could be attained for 73.9% after 30,000 cycles comparing with the initial capacitance of 122.0 F g-1. These indicate, the O-MoS2/PANI/rGO-160 HNSs preserve an excellent structural stability in practical application even at extreme conditions as it performances in the three-electrode test system.

17



Figure 7. Electrochemical performance of the O-MoS2/PANI/rGO-160 HNSs tested with symmetric cell. (a) CV curves at the scan rate of 5 mV s-1 (b) galvanostatic charge-discharge profiles as well as the IR drop (the inset) at the current density of 0.5 A g-1, (c) Specific capacitance at different current densities and (d) cycle performance at 2 A g-1 at different temperature.

4. Conclusions The rGO supported hybrid 1T/2H phase MoS2 nannosheets array was successfully constructed via a simple oxygen incorporation and PANI intercalation method. The obtained O-MoS2/PANI/rGO HNSs present an enlarged interlayer distance of MoS2 nanosheets and make the 2H MoS2 partly transform to 1T MoS2 and thus increase the conductivity of the whole composite. Meanwhile, the sandwiched O-MoS2/PANI nanosheets array vertically aligned on rGO sheets avoids agglomeration of active materials and constructs a conducting network. This novel 18


Page 18 of 30

Page 19 of 30 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


hierarchical structure and the existence of 1T MoS2 not only facilitates the ion diffusion and electron transfer, but also enhances the structural stability with little capacitance degradation in the charge/discharge cycle, which leads to excellent electrochemical performance even at extreme conditions. In the three-electrode system, the O-MoS2/PANI/rGO-160 HNSs exhibits a specific capacitance of 752.0 F g-1 at 1 A g-1, and have a capacitance retention of 80.4% of the initial cycle (282.3 F g-1) after 50,000 cycles when conduct the charge/discharge cycles at a current density of 50 A g-1. In addition, the cyclic performance are also excellent in an extreme wide range of temperature. For a symmetric cell, about 89.9%, 86.1% and 73.9% of initial capacitance can be maintained, respectively, after 30,000 cycles at a current density of 2 A g-1 at 0 oC, RT, 50 oC, with the initial specific capacitance of 79.6 F g-1, 100.1 F g-1 and 122.0 F g-1. The excellent electrochemical performance suggests the promising application of the O-MoS2/PANI/rGO-160 HNSs in supercapacitors under extreme temperature. ASSOCIATED CONTENT Supporting

Information:

SEM

images

of

Mo3O10(C6H5NH3)2·4H2O/GO,

MoOx/PANI/GO and O-MoS2/PANI/rGO-160 HNSs after 50000 charge/discharge cycles; Nyquist plots tested in three-electrode configuration; XRD patterns of GO and rGO; Comparison with other’s work. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS 19



We acknowledge financial support from the National Natural Science Foundation of China for Innovative Research Groups (Grant No. NSFC51621001), National Natural Science Foundation of China (Grant No. 51402110, 51671089), Guangdong Natural Science Funds for Distinguished Young Scholar (Grant No.2017B030306004) and Natural Science Foundation of Guangdong Province (2016A030312011). References

(1) Miller, J. R.; Simon, P. Materials Science-Electrochemical Capacitors for Energy Management. Science 2008, 321, 651-652. (2) Vellacheri, R.; Al-Haddad, A.; Zhao, H.; Wang, W.; Wang, C.; Lei, Y. High Performance Supercapacitor for Efficient Energy Storage under Extreme Environmental Temperatures. Nano Energy 2014, 8, 231-237. (3) Xu, K. B.; Chao, J.; Li, W. Y.; Liu, Q.; Wang, Z. J.; Liu, X. J.; Zou, R. J.; Hu, J. Q. CoMoO4·0.9H2O Nanorods Grown on Reduced Graphene Oxide as Advanced Electrochemical Pseudocapacitor Materials. RSC Adv. 2014, 4, 34307-34314. (4) Ma, G. F.; Peng, H.; Mu, J. J.; Huang, H. H.; Zhou, X. Z.; Lei, Z. Q. In Situ Intercalative Polymerization of Pyrrole in Graphene Analogue of MoS2 as Advanced Electrode Material in Supercapacitor. J. Power Sources 2013, 229, 72-78. (5) Soon, J. M.; Loh, K. P. Electrochemical Double-layer Capacitance of MoS2 Nanowall Films. Electrochem. Solid ST. 2007, 10, A250-A254. (6) Khawula, T. N. Y.; Raju, K.; Franklyn, P. J.; Sigalas, I.; Ozoemena, K. I. Symmetric Pseudocapacitors Based on Molybdenum Disulfide (MoS2)-Modified Carbon Nanospheres: Correlating Physicochemistry and Synergistic Interaction on Energy Storage. J. Mater. Chem. A 2016, 4, 6411-6425. (7) Laursen, A. B.; Kegnaes, S.; Dahl, S.; Chorkendorff, I. Molybdenum Sulfides-Efficient and Viable Materials for Electro- and Photoelectrocatalytic Hydrogen Evolution. Energy Environ. Sci. 2012, 5, 5577-5591. (8) Acerce, M.; Voiry, D.; Chhowalla, M. Metallic 1T Phase MoS2 Nanosheets as Supercapacitor Electrode Materials. Nat. Nanotechnology 2015, 10, 313-318. (9) Tang, H.; Wang, J.; Yin, H.; Zhao, H.; Wang, D.; Tang, Z. Growth of Polypyrrole Ultrathin Films on MoS2 Monolayers as High-Performance Supercapacitor Electrodes. Adv. Mater. 2015, 27, 1117-1123. (10) Bang, G. S.; Nam, K. W.; Kim, J. Y.; Shin, J.; Choi, J. W.; Choi, S. Y. Effective Liquid-Phase Exfoliation and Sodium Ion Battery Application of MoS2 Nanosheets. ACS Appl. Mater. Interfaces 2014, 6, 7084-7089. (11) Lee, J.; Pak, S.; Giraud, P.; Lee, Y. W.; Cho, Y.; Hong, J.; Jang, A. R.; Chung, H. S.; Hong, W. K.; Jeong, H. Y.; et al . Thermodynamically Stable Synthesis of Large-Scale and Highly Crystalline Transition Metal Dichalcogenide Monolayers and Their Unipolar n-n Heterojunction Devices. Adv. Mater. 2017, 29, 1702206. (12) Cai, L.; He, J.; Liu, Q.; Yao, T.; Chen, L.; Yan, W.; Hu, F.; Jiang, Y.; Zhao, Y.; Hu, T.; et al. Vacancy-Induced Ferromagnetism of MoS2 Nanosheets. J. Am. Chem. Soc. 2015, 20


Page 20 of 30

Page 21 of 30 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


137, 2622-2627. (13) Ying, Q. Z.; Xue, H.; Wang, W. J.; Cao, H.; Yang, Q. H.; Fu, L. Opening Two-Dimensional Materials for Energy Conversion and Storage: A Concept. Adv. Energy Mater. 2017, 7, 1602684. (14) Wang, D.; Xiao, Y.; Luo, X.; Wu, Z.; Wang, Y. J.; Fang, B. Swollen Ammoniated MoS2 with 1T/2H Hybrid Phases for High-Rate Electrochemical Energy Storage. ACS Sustainable Chem. Eng. 2017, 5, 2509-2515. (15) Eda, G.; Fujita, T.; Yamaguchi, H.; Voiry, D.; Chen, M.; Chhowalla, M. Coherent Atomic and Electronic Heterostructures of Single-Layer MoS2. ACS Nano 2012, 6, 7311-7317. (16) Chao, J.; Deng, J. W.; Zhou, W. J.; Liu, J. W.; Hu, R. Z.; Yang, L. C.; Zhu, M.; Schmidt, O. G. Hierarchical Nanoflowers Assembled from MoS2/Polyaniline Sandwiched Nanosheets for High-Performance Supercapacitors. Electrochimica Acta 2017, 243, 98-104. (17) Jiang, L.; Zou, R.; Li, W.; Sun, J.; Hu, X.; Xue, Y.; He, G.; Hu, J. Ni(OH)2/CoO/Reduced Graphene Oxide Composites with Excellent Electrochemical Properties. J. Mater. Chem. A 2013, 1, 478-481. (18) Yang, L. C.; Wang, S. N.; Mao, J. J.; Deng, J. W.; Gao, Q. S.; Tang, Y.; Schmidt, O. G. Hierarchical MoS2/Polyaniline Nanowires with Excellent Electrochemical Performance for Lithium-Ion Batteries. Adv. Mater. 2013, 25, 1180-1184. (19) Zhang, J.; Wang, J.; Yang, J.; Wang, Y.; Chan-Park, M. B. Three-Dimensional Macroporous Graphene Foam Filled with Mesoporous Polyaniline Network for High Areal Capacitance. ACS Sustainable Chem. Eng. 2014, 2, 2291-2296. (20) Mi, H.; Zhang, X.; Yang, S.; Ye, X.; Luo, J. Polyaniline Nanofibers as The Electrode Material for Supercapacitors. Mater. Chem. Phys. 2008, 112, 127-131. (21) Wang, Y. G.; Li, H. Q.; Xia, Y. Y. Ordered Whiskerlike Polyaniline Grown on The Surface of Mesoporous Carbon and Its Electrochemical Capacitance Performance. Adv. Mater. 2006, 18, 2619-2623. (22) Xu, G.; Wang, N.; Wei, J.; Lv, L.; Zhang, J.; Chen, Z.; Xu, Q. Preparation of Graphene Oxide/Polyaniline Nanocomposite with Assistance of Supercritical Carbon Dioxide for Supercapacitor Electrodes. Ind. Eng. Chem. Res. 2012, 51, 14390-14398. (23) Ren, L. J.; Zhang, G. N.; Yan, Z.; Kang, L. P.; Xu, H.; Shi, F.; Lei, Z. B.; Liu, Z. H. Three-Dimensional Tubular MoS2/PANI Hybrid Electrode for High Rate Performance Supercapacitor. ACS Appl. Mater. Interfaces 2015, 7, 28294-28302. (24) Li, X.; Zhang, C.; Xin, S.; Yang, Z.; Li, Y.; Zhang, D.; Yao, P. Facile Synthesis of MoS2/Reduced Graphene Oxide@Polyaniline for High-Performance Supercapacitors. ACS Appl. Mater. Interfaces 2016, 8, 21373-21380. (25) Xie, J. F.; Zhang, J. J.; Li, S.; Grote, F.; Zhang, X. D.; Zhang, H.; Wang, R. X.; Lei, Y.; Pan, B. C.; Xie, Y. Controllable Disorder Engineering in Oxygen-Incorporated MoS2 Ultrathin Nanosheets for Efficient Hydrogen Evolution. J. Am. Chem. Soc. 2013, 135, 17881-17888. (26) Yang, X.; Fu, W.; Liu, W.; Hong, J.; Cai, Y.; Jin, C.; Xu, M.; Wang, H.; Yang, D.; Chen, H. Engineering Crystalline Structures of Two-dimensional MoS2 Sheets for High-Performance Organic Solar Cells. J. Mater. Chem. A 2014, 2, 7727-7733. 21



(27) Weng, Q.; Wang, X.; Wang, X.; Zhang, C.; Jiang, X.; Bando, Y.; Golberg, D. Supercapacitive Energy Storage Performance of Molybdenum Disulfide Nanosheets Wrapped with Microporous Carbons. J. Mater. Chem. A 2015, 3, 3097-3102. (28) Gigot, A.; Fontana, M.; Serrapede, M.; Castellino, M.; Bianco, S.; Armandi, M.; Bonelli, B.; Pirri, C. F.; Tresso, E.; Rivolo, P. Mixed 1T-2H Phase MoS2/Reduced Graphene Oxide as Active Electrode for Enhanced Supercapacitive Performance. ACS Appl. Mater. Interfaces 2016, 8, 32842-32852. (29) Fan, X.; Xu, P.; Zhou, D.; Sun, Y.; Li, Y. C.; Nguyen, M. A. T.; Terrones, M.; Mallouk, T. E. Fast and Efficient Preparation of Exfoliated 2H MoS2 Nanosheets by Sonication-Assisted Lithium Intercalation and Infrared Laser-Induced 1T to 2H Phase Reversion. Nano Letters 2015, 15, 5956-5960. (30) Yang, X.; Zhao, L.; Lian, J. Arrays of Hierarchical Nickel Sulfides/MoS2 Nanosheets Supported on Carbon Nanotubes Backbone as Advanced Anode Materials for Asymmetric Supercapacitor. J. Power Sources 2017, 343, 373-382. (31) Anwar, M.; Hogarth, C. A.; Bulpett, R. Effect of Substrate Temperature and Film Thickness on The Surface Structure of Some Thin Amorphous Films of MoO3 Studied by X-ray Photoelectron Spectroscopy (ESCA). J. Mater. Sci. 1989, 24, 3087-3090. (32) Liu, A.; Zhao, L.; Zhang, J.; Lin, L.; Wu, H. Solvent-Assisted Oxygen Incorporation of Vertically Aligned MoS2 Ultrathin Nanosheets Decorated on Reduced Graphene Oxide for Improved Electrocatalytic Hydrogen Evolution. ACS Appl. Mater. Interfaces 2016, 8, 25210-25218. (33) Kim, M.; Kim, Y. K.; Kim, J.; Cho, S.; Lee, G.; Jang, J. Fabrication of A Polyaniline/MoS2 Nanocomposite Using Self-Stabilized Dispersion Polymerization for Supercapacitors with High Energy Density. RSC Adv. 2016, 6, 27460-27465. (34) Luo, J. W.; Zhong, W. B.; Zou, Y. B.; Xiong, C. L.; Yang, W. T. Preparation of Morphology-Controllable Polyaniline and Polyaniline/Graphene Hydrogels for High Performance Binder-Free Supercapacitor Electrodes. J. Power Sources 2016, 319, 73-81. (35) Laheaeaer, A.; Przygocki, P.; Abbas, Q.; Beguin, F. Appropriate Methods for Evaluating The Efficiency and Capacitive Behavior of Different Types of Supercapacitors. Electrochem. Commun. 2015, 60, 21-25. (36) Yang, P.; Mai, W. Flexible Solid-State Electrochemical Supercapacitors. Nano Energy 2014, 8, 274-290. (37) Stoller, M. D.; Ruoff, R. S. Best Practice Methods for Determining An Electrode Material's Performance for Ultracapacitors. Energy Environ. Sci. 2010, 3, 1294-1301. (38) Chen, X. Y.; He, Y. Y.; Song, H.; Zhang, Z. J. Structure and Electrochemical Performance of Highly Nanoporous Carbons from Benzoate-Metal Complexes by A Template Carbonization Method for Supercapacitor Application. Carbon 2014, 72, 410-420.

22


Page 22 of 30

Page 23 of 30 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


TOC Graphic

23



Figure 1. Schematic illustration for preparation of O-MoS2/PANI/rGO HNSs 855x421mm (96 x 96 DPI)


Page 24 of 30

Page 25 of 30 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


Figure 2. SEM images of (a) O-MoS2/PANI/rGO-140 HNSs, (b) O-MoS2/PANI/rGO-160 HNSs, (c) OMoS2/PANI/rGO-180 HNSs, and (d) MoS2/PANI/rGO HNSs. 696x526mm (96 x 96 DPI)



Figure 3. (a) XRD patterns of O-MoS2/PANI/rGO-140 HNSs, O-MoS2/PANI/rGO-160 HNSs, OMoS2/PANI/rGO-180 HNSs, and MoS2/PANI/rGO HNSs, (b) FT-IR spectrum, (c) Raman spectrum and (d-f) TEM images of O-MoS2/PANI/rGO-160 HNSs. 999x554mm (96 x 96 DPI)


Page 26 of 30

Page 27 of 30 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


Figure 4. XPS spectra of Mo 3d of (a) O-MoS2/PANI/rGO-140 HNSs, (b) O-MoS2/PANI/rGO-160 HNSs, (c) OMoS2/PANI/rGO-180 HNSs, and (d) MoS2/PANI/rGO HNSs. 136x105mm (300 x 300 DPI)



Figure 5. XPS spectra of O-MoS2/PANI/rGO-160 HNSs: (a) S 2p, (b) O 1s, (c) C 1s. 207x55mm (300 x 300 DPI)


Page 28 of 30

Page 29 of 30 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


Figure 6. (a) CV curves at 20 mV s-1 and (b) galvanostatic charge-discharge profiles at a current density of 1 A g-1 of the O-MoS2/PANI/rGO HNSs and MoS2/PANI/rGO HNSs (c) galvanostatic charge-discharge profiles of O-MoS2/PANI/rGO-160 HNSs at various current densities, (d) specific capacitance at various current density and (e) cycle performance at 50 A g-1 of O-MoS2/PANI/rGO HNSs and MoS2/PANI/rGO HNSs. 517x577mm (96 x 96 DPI)



Figure 7. Electrochemical performance of the O-MoS2/PANI/rGO-160 HNSs tested with symmetric cell. (a) CV curves at the scan rate of 5 mV s-1 (b) galvanostatic charge-discharge profiles as well as the IR drop (the inset) at the current density of 0.5 A g-1, (c) Specific capacitance at different current densities and (d) cycle performance at 2 A g-1 at different temperature. 838x592mm (96 x 96 DPI)


Page 30 of 30

2H Hybrid MoS2

Recommend Documents