Three-Dimensional Ternary rGO/VS2/WS2 Composite Hydrogel for Supercapacitor Applications
Round 1
Reviewer 1 Report
In this paper, the authors prepared the three-dimensional ternary rGO/VS2/WS2 hybrid composite hydrogel for supercapacitor applications. The rGO/VS2/WS2 electrodes exhibit greater electrochemical performance and superior stability than rGO and rGO/VS2 composites. The manuscript is planned and organized well. Though, the following modifications need to be carried out before acceptance, I recommend minor revision for this manuscript.
1. Why did the authors choose two concepts to develop the ternary composite of rGO/VS2/WS2-1 and rGO/VS2/WS2-2? What mechanism implies to get the higher performance in rGO/VS2/WS2-1?
2. The title is not very impressive. Moreover, the high performance word is not needed in the title for this concept.
3. The experimental section is too wordy. Some information repeated in section 2.6 and 2.7. Merge this both the section
4. Figure 2b, in XRD, provides the detailed information for the crystal structure information.
5. Figure 8, The attained power density is high 3454 W kg-1 with high energy density of up to 21.11 Whkg-1. Why it occurred and explain the reason here.
Author Response
Reviewer 1
In this paper, the authors prepared the three-dimensional ternary rGO/VS2/WS2 hybrid composite hydrogel for supercapacitor applications. The rGO/VS2/WS2 electrodes exhibit greater electrochemical performance and superior stability than rGO and rGO/VS2 composites. The manuscript is planned and organized well. Though the following modifications need to be carried out before acceptance, I recommend minor revision for this manuscript.
We want to take this opportunity to thank our reviewer for his/her effort and expertise at the highest scientific level. We appreciate and are thankful for the reviewer's hard work. We express our appreciation to the reviewer for their insightful comments, which have helped us significantly improve our manuscript's quality. We have revised the manuscript according to the reviewer's suggestions. Our responses are given below in accordance with the comments/points raised by the reviewer.
Comment 1. Why did the authors choose two concepts to develop the ternary composite of rGO/VS2/WS2-1 and rGO/VS2/WS2-2? What mechanism implies to get the higher performance in rGO/VS2/WS2-1?
Answer: Thank you for your comments. To identify the resourceful composition in rGO/VS2/WS2 hydrogel for efficient supercapacitor performances, it is necessary to study the structural and morphological effects of VS2 and WS2 simultaneously and independently. With this connection, we created these two different concepts.
In rGO/VS2/WS2 composites, carbonaceous components like rGO are known to present a conductive channel and enhance interfacial contact between electrolyte and electrode. The electrochemical performance of the rGO/VS2/WS2-1 composite is improved by the short ion diffusion routes and short electron transport made available by VS2 and WS2.
Comment 2. The title is not very impressive. Moreover, the high performance word is not needed in the title for this concept.
Answer: Thank you so much for your valuable suggestion. We modified the title in the revised manuscript as follows “Three-dimensional ternary rGO/VS2/WS2 composite hydrogel for supercapacitor applications”
Comment 3. The experimental section is too wordy. Some information repeated in section 2.6 and 2.7. Merge this both the section
Answer: Thank you for your comments and advice. As per the reviewer's suggestion, we modified the experimental section.
2.5. Preparation of rG-V-W hydrogel
For preparing the ternary hydrogel, VS2/WS2 composite has been prepared in two ways. Firstly, ammonium metavanadate (0.47 g) was dissolved in a mixture of 30 mL of distilled water and 6 mL of ammonia. Afterwards, 0.3 g of Na2WO4.2H2O and 1.8 g of thioacetamide was added to the solution. The mixture was stirred vigorously for 30 min, forming a yellow–black solution, and then sealed in a 50 mL Teflon-lined stainless-steel autoclave. The autoclave was heated to 180 °C and maintained at the target temperature for 20 h. Then, the autoclave was allowed to cool to ambient temperature. The black product was washed with ethanol and deionized water several times. Finally, a VS2-WS2 product was dried in a vacuum at 60 °C for 10 h and named V-W-1. In another way, VS2 was prepared initially as mentioned in section 2.2. Then, the above similar procedure was followed to prepare the VS2-WS2 composite by using VS2 instead of ammonium meta-vanadate and named V-W-2. Figure 1 shows the synthesis of the rG-V-W-1 hydrogel. Typically, 0.01 g of as-prepared VS2/WS2 (VW-1) is included in 20 mL of graphene oxide solution and it has been effectively dispersed through sonication for 15 min. After sonication, 58 µL of ethylene diamine was added to the mixture and agitated for 10 minutes. This mixed solution was included in a 50 mL Teflon-lined autoclave. Then it was heated to 180 °C for 12 hours. The rGO/VW-1 hydrogel (abbreviated rG-V-W-1) was produced and cleaned by submerging it in deionized water multiple times after the autoclave had cooled to room temperature. Chemical reduction in 30 mL of hydrazine hydrate (50%) was used to alter the surface characteristics of the rG-V-W-1 hydrogel for 6 hours at 50 °C. The hydrogel will then be frozen and dried for 24 hours. The same procedure was used to prepare the rG-V-W-2 using V-W-2.
Comment 4. Figure 2b, in XRD, provides the detailed information for the crystal structure information.
Answer: Thank you for your comments and advice.
The peaks of VS2 in VS2-rGO agree with the hexagonal phase depicted in the JCPDS file no. 89-1640 [39]. Moreover, In XRD patterns of the rGO-VS2-WS2 composite hydrogel, the hexagonal crystal structure of WS2 (JCPDS NO. 01-087-2417) was obtained.
[49] J. Xu, Y. Zhu, B. Yu, C. Fang, J. Zhang, Metallic 1T-VS2 nanosheets featuring V 2+ self-doping and mesopores towards an efficient hydrogen evolution reaction, Inorganic Chemistry Frontiers, 6 (2019) 3510-3517.
[52]Sengupta, Shilpi, and Manab Kundu. "Carbon free nanostructured plate like WS2 with excellent lithium storage properties." ChemistrySelect 5.44 (2020): 14183-14189.
Comment 5. Figure 8, the attained power density is high 3454 W kg-1 with high energy density of up to 21.11 Whkg-1. Why it occurred and explain the reason here.
Answer: The EDLCs based electrode materials do not involve faradaic charge storage and only store charge through surface-controlled electrostatic processes. Generally, the capacitive charge-storage mechanism leads to increased power density. Accordingly, the carbonaceous structured materials possess sophisticated active surface properties to attain the higher capacitance properties with elevated structure. In this connection, the combination of rGO, VS2, and WS2 provides the considerable electric conductivity and large active sites because of arising the synergistic effect, which is the major reason to obtaining excellent specific capacitance. Thus, the ternary composition of rG-V-W attained high power density of 3454 W kg-1 with a high energy density of 21.11 Whkg-1.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript entitled "Three-dimensional ternary rGO/VS2/WS2 hybrid composite hydrogel for high-performance supercapacitor applications" reported a straightforward one-pot hydrothermal technique to construct a supercapacitor based on hydrogel 3D skeletal networks comprising rGO nanosheets with VS2/WS2 nanoparticles. The as-designed 3D framework with the excellent surface properties of rGO nanosheets with VS2 and WS2 nanoparticles as hydrogel, this electrode offers substantial intrinsic properties for attaining the high-performance supercapacitor. In general, it is an interesting and valuable topic to deserving a research article.
However, there are still many problems to be solved. So this reviewer would suggest a major revision before its acceptance.
1. Overall the draft is good but needs more careful editing.
2. Could the author explain why anhydrous ethylenediamine should be used as a cross-linking agent? The preparation of hydrogels has been relatively mature, and it is suggested to apply some of the latest literature.
3. In introduction section, some highly relevant review articles are suggested to be included: Design and fabrication of conductive polymer hydrogels and their applications in flexible supercapacitors; Nano Today 37, 101075, 2020; Journal of Materials Science 56, 173–200, 2021; etc.
4. The Figures should be in the same format. Regroup the Figures and replace some parts of the Figures that are not obvious.
5. Equations must be typeset using appropriate fonts and layout. Excel figures must not contain the superfluous outer frame. The same information must not be duplicated in Tables and Figures.
6. Error bars should be added to some of the results of multiple tests to conform to statistical science.
7. It is not beautiful to put too many pictures in Figures 5, should we add so many miscellaneous contents in the Figures? Please make corrections in the manuscript.
8. Many of the figures should be modified to have a better readability, especially the texts, scale bar, etc.
9. The relevant content of supercapacitor should be compared with the latest research. Here the reviewer provides the author with some literatures and suggests the author to cite them in the latest version of the manuscript: Chitin derived nitrogen-doped porous carbons with ultrahigh specific surface area and tailored hierarchical porosity for high performance supercapacitors; Nitrogen, sulfur co-doped hierarchical carbon encapsulated in graphene with “sphere-in-layer” interconnection for high-performance supercapacitor; ZnCl 2 regulated flax-based porous carbon fibers for supercapacitors with good cycling stability; Comparison of the heteroatoms-doped biomass-derived carbon prepared by one-step nitrogen-containing activator for high performance supercapacitor; Synthetic melanin facilitates MnO supercapacitors with high specific capacitance and wide operation potential window; Phosphorus-Doped Thick Carbon Electrode for High-Energy Density and Long-Life Supercapacitors; etc.
10. Please carefully check the whole manuscript. There are still some typos and grammar issues. In addition, please carefully check the references to ensure the full information is included.
Author Response
Reviewer 2
The manuscript entitled "Three-dimensional ternary rGO/VS2/WS2 hybrid composite hydrogel for high-performance supercapacitor applications" reported a straightforward one-pot hydrothermal technique to construct a supercapacitor based on hydrogel 3D skeletal networks comprising rGO nanosheets with VS2/WS2 nanoparticles. The as-designed 3D framework with the excellent surface properties of rGO nanosheets with VS2 and WS2 nanoparticles as hydrogel, this electrode offers substantial intrinsic properties for attaining the high-performance supercapacitor. In general, it is an interesting and valuable topic to deserving a research article.
However, there are still many problems to be solved. So this reviewer would suggest a major revision before its acceptance.
We want to take this opportunity to thank our reviewer for his/her effort and expertise at the highest scientific level. We appreciate and are thankful for the reviewer's hard work. We express our appreciation to the reviewer for their insightful comments, which have helped us significantly improve our manuscript's quality. We have revised the manuscript according to the reviewer’s suggestions. Our responses are given below in accordance with the comments/points raised by the reviewer.
Comment 1: Overall the draft is good but needs more careful editing.
Answer: Thank you so much for your valuable suggestion. As per the reviewer suggestion, we have carefully edited the manuscript and revised it accordingly.
Comment 2. Could the author explain why anhydrous ethylenediamine should be used as a cross-linking agent? The preparation of hydrogels has been relatively mature, and it is suggested to apply some of the latest literature.
Answer: Thank you for your comments and advice. The basic and weak reducing agent– ethylenediamine (EDA), was introduced into the GO colloidal solution to functionalize it and initiate sheet assembly into a three-dimensional network. We provided some of the reference studies, which are related to the preparation of hydrogels using anhydrous ethylenediamine as a cross-linker. EDA provides the crosslinking sites for the hydrogel and the partially reduced GO sheets. EDA initiates the ring-opening of epoxy groups present on the GO layers and the oxygen dangling bonds formed react with the rGO (including VS2 and WS2 nanoparticles) to form the hydrogel.
#Wu, Xiaozhong, et al. "Reduced Graphene Oxide Hydrogel for High Energy Density Symmetric Supercapacitor with High Operation Potential in Aqueous Electrolyte." ChemElectroChem 8.22 (2021): 4353-4359.
# Shang, Tongxin, et al. "3D macroscopic architectures from self‐assembled MXene hydrogels." Advanced Functional Materials 29.33 (2019): 1903960.
Comment 3. In the introduction section, some highly relevant review articles are suggested to be included: Design and fabrication of conductive polymer hydrogels and their applications in flexible supercapacitors; Nano Today 37, 101075, 2020; Journal of Materials Science 56, 173–200, 2021; etc.
Answer: Thank you so much for your valuable suggestion. We have added relevant references in the revised manuscript.
[11] Yang, Lei, Xutong Guo, Zhekai Jin, Wancai Guo, Gaigai Duan, Xianhu Liu, and Yiwen Li. "Emergence of melanin-inspired supercapacitors." Nano Today 37 (2021): 101075.
[12] Wang, Yifan, Lin Zhang, Haoqing Hou, Wenhui Xu, Gaigai Duan, Shuijian He, Kunming Liu, and Shaohua Jiang. "Recent progress in carbon-based materials for supercapacitor electrodes: a review." Journal of Materials Science 56, no. 1 (2021): 173-200.
[13] Duan, Gaigai, Luying Zhao, Chunmei Zhang, Lian Chen, Qian Zhang, Kunming Liu, and Feng Wang. "Pyrolysis of zinc salt-treated flax fiber: Hierarchically porous carbon electrode for supercapacitor." Diamond and Related Materials 129 (2022): 109339
[23] Han, Xinting, Guangchun Xiao, Yuchen Wang, Xiaona Chen, Gaigai Duan, Yongzhong Wu, Xiao Gong, and Hangxiang Wang. "Design and fabrication of conductive polymer hydrogels and their applications in flexible supercapacitors." Journal of Materials Chemistry A 8, no. 44 (2020): 23059-23095.
Comment 4.The Figures should be in the same format. Regroup the Figures and replace some parts of the Figures that are not obvious.
Answer: Thank you so much for your advice. Your suggestion will be more useful to improve the quality of the manuscript. We provided the same format and high-quality figures in the revised manuscript.
. Comment 5. Equations must be typeset using appropriate fonts and layouts. Excel figures must not contain a superfluous outer frame. The same information must not be duplicated in Tables and Figures.
Answer: We agree with the reviewer suggestion. We revised the manuscript based on the reviewer’s suggestion and the journals format
|
C = (IΔt)/(mΔV) |
(1) |
Comment 6. Error bars should be added to some of the results of multiple tests to conform to statistical science.
Answer: Thank you so much for your suggestion. We analyzed all the electrochemical results at least two times to check the reproducibility of our materials. We provided reproducible results in our manuscript.
Comment 7. It is not beautiful to put too many pictures in Figures 5, should we add so many miscellaneous contents in the Figures? Please make corrections in the manuscript.
Answer: Thank you so much for your advice. Your suggestion will be more useful to improve the quality of the manuscript. As per the reviewer's suggestion, we modified Figure 5. To avoid too many pictures in Figure 5, we split it into Figure 5 and Figure 6.
Comment 8. Many of the figures should be modified to have better readability, especially the texts, scale bar, etc.
Answer: Thank you so much for your suggestion. According to the reviewer’s suggestion, we provided the high-quality images in the revised manuscript for better readability, especially the texts and scale bar.
Comment 9. The relevant content of supercapacitors should be compared with the latest research. Here the reviewer provides the author with some literature and suggests the author cite them in the latest version of the manuscript:
- Chitin-derived nitrogen-doped porous carbons with ultrahigh specific surface area and tailored hierarchical porosity for high-performance supercapacitors;
- Comparison of the heteroatoms-doped biomass-derived carbon prepared by a one-step nitrogen-containing activator for high-performance supercapacitor
- Phosphorus-Doped Thick Carbon Electrode for High-Energy-Density and Long-Life Supercapacitors; etc
- ZnCl 2 regulated flax-based porous carbon fibers for supercapacitors with good cycling stability
- Nitrogen, sulfur co-doped hierarchical carbon encapsulated in graphene with “sphere-in-layer” interconnection for high-performance supercapacitor;
- Synthetic melanin facilitates MnO supercapacitors with high specific capacitance and wide operation potential window;
Answer: As per the reviewer suggestion, we explained and cited the above-mentioned references in our revised manuscript.
As an example, Zheng et al. used the mechanically induced sol-gel transition method prepared chitin-based activated carbon (ACNC-800) with a high nitrogen content (7.1%) for the supercapacitor electrodes. The electrochemical analysis was done using the three-electrode electrochemical system in NaOH medium. As a result, the achieved specific capacitance of (ACNC-800) was 245 F/g at 0.5 A/g. The increased surface area of the interconnected porous framework (ACNC-800) is the main reason for achieving high performance [17]. A simple, one-step co-pyrolysis method was used for preparing the N-doped hierarchical porous carbon (HPC) materials from biomass, and that prepared material was used as a supercapacitor electrode material. With urea-prepared HPC electrode obtains an excellent specific capacitance of 300 F /g at 1 A/g and an energy density of 14.3 Wh kg−1 [18]. Cao, et al. used phytic acid treatment for as-prepared P-doped and wood-derived carbon. The symmetrical supercapacitor device attained a high specific capacitance of 206.5 F g−1 at a current density of 1.0 mA cm−2 [19]. For supercapacitors, flax-based porous carbon was impregnated with ZnCl2 and activated at high temperatures. The electrode materials obtained the specific capacitance of 105 F/g at a 1 A/g current density. In another report, N-doped and S-doped pollen-derived graphene provide an interconnected "sphere-in-layer" structure of electrode materials [20]. N-doped and S-doped pollen-derived graphene electrodes display a specific capacitance of 420 F/g at 1 A/g. To avoid aggregation of the graphene sheet, the pollen-derived carbon sphere was represented as a porous spacer in the composite [21]. Guo, et al. used a direct one-pot polymerization technique to prepare the Mn-ion doped polylevodopa synthetic melanin nanoparticles and transformed them into tiny hybrid carbon nanoparticles. MnO-distributed MnO@CNPs electrode materials provide excellent specific capacitance of 545 F/g at 0.5 A/g in 6 M KOH electrolyte [22].
[17] S. Zheng, J. Zhang, H. Deng, Y. Du, X. Shi, Chitin derived nitrogen-doped porous carbons with ultrahigh specific surface area and tailored hierarchical porosity for high performance supercapacitors, Journal of Bioresources and Bioproducts, 6 (2021) 142-151.
[18] L. Cao, H. Li, Z. Xu, H. Zhang, L. Ding, S. Wang, G. Zhang, H. Hou, W. Xu, F. Yang, Comparison of the heteroatoms-doped biomass-derived carbon prepared by one-step nitrogen-containing activator for high performance supercapacitor, Diamond and Related Materials, 114 (2021) 108316.
[19] F. Wang, J.Y. Cheong, Q. He, G. Duan, S. He, L. Zhang, Y. Zhao, I.-D. Kim, S. Jiang, Phosphorus-doped thick carbon electrode for high-energy density and long-life supercapacitors, Chemical Engineering Journal, 414 (2021) 128767.
[20] G. Duan, L. Zhao, L. Chen, F. Wang, S. He, S. Jiang, Q. Zhang, ZnCl 2 regulated flax-based porous carbon fibers for supercapacitors with good cycling stability, New Journal of Chemistry, 45 (2021) 22602-22609.
[21] L. Cao, H. Li, X. Liu, S. Liu, L. Zhang, W. Xu, H. Yang, H. Hou, S. He, Y. Zhao, Nitrogen, sulfur co-doped hierarchical carbon encapsulated in graphene with “sphere-in-layer” interconnection for high-performance supercapacitor, Journal of Colloid and Interface Science, 599 (2021) 443-452.
[22] W. Guo, X. Guo, L. Yang, T. Wang, M. Zhang, G. Duan, X. Liu, Y. Li, Synthetic melanin facilitates MnO supercapacitors with high specific capacitance and wide operation potential window, Polymer, 235 (2021) 124276.
Comment 10. Please carefully check the whole manuscript. There are still some typos and grammar issues. In addition, please carefully check the references to ensure the full information is included.
Answer: Thank you so much for your advice. We carefully checked the revised manuscript. We avoided typos and grammar issues. We believe that the language of our revised manuscript is more suitable to get publication. Moreover, the MDPI offer us to improve the quality of the language (Production: Copy-editing, typesetting, XML and PDF conversion, and language editing (English editing is provided by native English speakers for all accepted papers). - https://www.mdpi.com/apc)
Reviewer 3 Report
This paper addresses the synthesis of composites based on hydrogel 3D skeletal networks comprising rGO nanosheets with VS2/WS2 nanoparticles. The composites with different V and W loading were investigated as electrode of supercapacitor using 3 mol L-1 KOH as the electrolyte. A specific capacitance of 220 F g-1 at 1 A g-1 current density and energy density of 30.55 Whkg-1 with a power density of 355 Wkg-1 is reported for rGO-VS2-WS2. Due to the need of highly performing storage systems, this work could be interesting. But the present manuscript is displaying lacks materials characterisation and discussion.
1. Poor English writing. There are many grammatical mistakes, typos, missing words, or wrong words in sentences. Some sentences are also not clear in meaning. Please go through the text of the whole manuscript and modify accordingly.
-Figures 6 and 7 mA/g should be change to A/g, am I right?
2. The size of the nanoparticles of vanadium and tungsten sulphide should be quantified in all composites. X-Ray diffractograms in Figure 2b not informative.
3. The main parameter that must be considered for any supercapacitor material is the specific surface area that controls the capacitance of electrode. Moreover, the authors repeatedly focus on the large specific area of graphene oxide hydrogel and composites. Please provide such values.
4. “Peak intensity for the 24.82° diffraction peak is 235 greater for rGO reduced by hydrazine than for rGO, indicating that hydrazine reduction 236 results in a more crystalline structure can be seen that the large diffraction peaks of the 237 pure rGO hydrogel indicate that all GO was converted into rGO with much-reduced func-238 tionality “. Probably it is not right to make decision about GO reduction degree on diffraction peak intensity. Raman spectroscopy would by more informative in this case.
5. Sulphur and carbon amount should be determined from CHN-S elemental analysis.
6. Figures 3 and 4 demonstrate morphology and composition study of synthesised materials. Micrographs with higher magnification should be provided. For demonstration of uniform decoration of GO by vanadium or tungsten sulfide TEM or STEM technic will be better.
7. Presentation of EDX mapping of elements (Fig. 3 and 4) is very poor. It is impossible to make a conclusion about the distribution of vanadium and tungsten on the surface of reduced graphene oxide.
Author Response
Reviewer 3.
This paper addresses the synthesis of composites based on hydrogel 3D skeletal networks comprising rGO nanosheets with VS2/WS2 nanoparticles. The composites with different V and W loading were investigated as electrode of supercapacitor using 3 mol L-1 KOH as the electrolyte. A specific capacitance of 220 F g-1 at 1 A g-1 current density and energy density of 30.55 Whkg-1 with a power density of 355 Wkg-1 is reported for rGO-VS2-WS2. Due to the need of highly performing storage systems, this work could be interesting. But the present manuscript is displaying lacks materials characterisation and discussion.
We want to take this opportunity to thank our reviewer for his/her effort and expertise at the highest scientific level. We appreciate and are thankful for the reviewer's hard work. We express our appreciation to the reviewer for their insightful comments, which have helped us significantly improve our manuscript's quality. We have revised the manuscript according to the reviewer’s suggestions. Our responses are given below in accordance with the comments/points raised by the reviewer.
Comment 1: Poor English writing. There are many grammatical mistakes, typos, missing words, or wrong words in sentences. Some sentences are also not clear in meaning. Please go through the text of the whole manuscript and modify accorditingly. Figures 6 and 7 mA/g should be change to A/g, am I right?
Answer: Thank you so much for your advice. We carefully checked the revised manuscript. As per the reviewer suggestion, we refined the language in the revised manuscript. We avoided typos and grammar issues. We believe that the language of our revised manuscript is more suitable to get publication. Moreover, the MDPI offer us to improve the quality of the language (Production: Copy-editing, typesetting, XML and PDF conversion, and language editing (English editing is provided by native English speakers for all accepted papers). - https://www.mdpi.com/apc). Thank you for your careful checking. We changed the mistakes in the unit in Figures 7 and 9
Comment 2: The size of the nanoparticles of vanadium and tungsten sulphide should be quantified in all composites. X-Ray diffractograms in Figure 2b not informative.
Answer: Thank you for your suggestion. In our present investigation, the optimized ratio between the rGO and VS2 source material is 90:10. In the binary and ternary composites, the concentration of rGO is significantly higher. Because of this reason, a high-intensity peak has been observed in the rGO. Moreover, the peak for rGO is wider. Due to this characteristic nature, the other compound peaks are minimized. However, we used XRD analysis to identify the presence of materials in the as-prepared composites. In the present study, we observed nearly 200 nm of vanadium and tungsten sulphide nanoparticles. As shown in the following Figure, it could be observed that the nanoparticles have effectively adhered to the surface and interlayers as seed grown from the inside.
Comment 3: The main parameter that must be considered for any supercapacitor material is the specific surface area that controls the capacitance of electrode. Moreover, the authors repeatedly focus on the large specific area of graphene oxide hydrogel and composites. Please provide such values.
Answer: Thank you so much for your advice. For our hydrogels, we attained a BET surface area of 135.24 m2 g-1. As the reviewer knows well that the interconnected 3D network materials usually possess a lesser specific surface area. Our major intention was to explain the higher electrochemical active surface area.
The double-layer capacitance (Cdl) of the rG-V-W-1 hydrogel electrode was calculated using cyclic voltammetry (CV) at various scan rates in order to calculate the electrochemical surface area (ESCA) of the electrode. CV was scanned at various scan rates of 5, 10, 15, 20, and 25 mV S-1 as shown in Figure S3a. The CV curves were plotted against the scan rate, and from that we obtain 2Cdl (Figure S3b.) The value of ECSA for the rG-V-W-1 hydrogel electrode is 0.11cm2 (for 1.8 mg hydrogel).
(a) Cyclic voltammetry analysis of rG-V-W-1 hydrogel electrode at different scan rates of 5, 10, 15, 20 and 25 mV/s. (b) 2cdl information of rG-V-W-1 hydrogel electrode.
Comment 4: “Peak intensity for the 24.82° diffraction peak is greater for rGO reduced by hydrazine than for rGO, indicating that hydrazine reduction results in a more crystalline structure can be seen that the large diffraction peaks of the pure rGO hydrogel indicate that all GO was converted into rGO with much-reduced functionality “. Probably it is not right to make decision about GO reduction degree on diffraction peak intensity. Raman spectroscopy would by more informative in this case.
Answer: Thank you for your suggestion. As per the reviewer’s suggestion, we have done Raman spectroscopy and the results are as follows.
The Raman spectra of graphene-based materials were used to further confirm the GO reduction. Figure S1. shows the Raman spectra of graphene oxide and rG-V-W-1 hydrogel. The GO displays two typical peaks at around 1351 cm−1 and 1607 cm−1, which well correspond to the D-band and G-band of carbon materials. In Figure S2, two characteristic peaks in Raman spectra of the rG-V-W-1 at 1355 cm-1 and 1599 cm-1 are assigned to D and G bands for carbon materials, respectively. The disorder-induced mode associated with structural defects was allocated to the D band, whereas E2g mode from the sp2 carbon domains is assigned to the G band. The proportion of the D and G bands in rG-V-W-1 hydrogel (ID/IG) value is 0.8.
The Raman spectra of the Graphene Oxide and rG-V-W-1 hydrogel.
Comment 5. Sulphur and carbon amount should be determined from CHN-S elemental analysis.
Answer: Thank you so much for your suggesting this point. We strongly apologize that we could not perform the CHN-S elemental analysis due to lack of facility. We keep this valuable suggestion from the reviewer for our ongoing and future research works.
Comment 6. Figures 3 and 4 demonstrate morphology and composition study of synthesised materials. Micrographs with higher magnification should be provided. For demonstration of uniform decoration of GO by vanadium or tungsten sulfide TEM or STEM technic will be better.
Answer: Thank you for your suggestion. For preparing sample grid of TEM, the synthesized rG-V-W-1 hydrogel was sonicated for 20 min in ethanol. After completing sonication, synthesized solution was dispersed on TEM grid. After dispersion, the grid was kept for drying for 10 min in air oven at 600C. Our hydrogel formed in 3D network structure. So, the surface property was changed slightly compared to SEM and TEM. Fig.S1 shows the TEM images of the rG-V-W-1 hydrogel, which confirms the VS2 and WS2 nanoparticles networks with rGO nanosheet and leads to unique nano network architecture GO sheets served as a new substrate for the nucleation and subsequent growth of VS2 and WS2 because they have extremely active edges and functional groups on their basal plane. Thus the tungsten and vanadium precursor is reduced to generate WS2 and VS2 on GO during the hydrothermal reaction in GO solution, and GO is then changed into rGO.
Comment 7. Presentation of EDX mapping of elements (Fig. 3 and 4) is very poor. It is impoto make a conclusion about the distribution of vanadium and tungsten on the surface of reduced graphene oxide.
Answer: Thank you so much for your suggesting this point. According to the reviewer’s suggestion, we analyzed for the ternary composite and provided the corresponding images in the revised version
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Accept in present form
Author Response
Reviewer: Accept in present form
Authors: It is our immense pleasure to say thanks to our reviewer for accepting our research work to get publish in inorganics.
Reviewer 3 Report
I am grateful to the authors for their work. The amendments made have significantly improved the presented material. However, several comments and questions were left without proper attention. In particular, the visual representation of the results of X-ray diffraction analysis and energy-dispersive X-ray spectroscopy (EDX) does not allow us to draw unambiguous conclusions about the structure and composition of the obtained materials.
1. The diffractograms of the obtained materials are not informative. The authors note the presence of peaks corresponding to the crystal structure of vanadium and tungsten sulfides. However, it is difficult to tell from the presented images about the presence of those. The intensity of the noted peaks of vanadium and tungsten sulfides is at the noise level. The presence of even 10% crystalline vanadium or tungsten sulfide would be identified by XRD. It may be worthwhile to increase some area to demonstrate the formation of the crystalline phase of sulfides. For comparison, you can also show the X-ray diffraction pattern of the sample with a higher loading of vanadium (rG-V-4). In addition, it would be advisable to add a diffraction pattern of the synthesized pure powders of vanadium and tungsten sulfides for comparison with diffractograms for composite materials.
2. The issue of providing EDX mapping results is still open. For rG-V-1 material, the distribution of elements (Figure 3f-h) is still uninformative. It is possible that a longer signal accumulation time is required in the selected area to form an image with a distribution of sulfide particles.
Author Response
Reviewer: I am grateful to the authors for their work. The amendments made have significantly improved the presented material. However, several comments and questions were left without proper attention. In particular, the visual representation of the results of X-ray diffraction analysis and energy-dispersive X-ray spectroscopy (EDX) does not allow us to draw unambiguous conclusions about the structure and composition of the obtained materials.
Authors: We want to take this opportunity to thank our reviewer for his/her effort and expertise at the highest scientific level. We appreciate and are thankful for the reviewer's hard work. We express our appreciation to the reviewer for their insightful comments, which have helped us significantly improve our manuscript's quality. We have revised the manuscript according to the reviewers''s suggestions. Our responses are given below in accordance with the comments/points raised by the reviewer
Comment 1. The diffractograms of the obtained materials are not informative. The authors note the presence of peaks corresponding to the crystal structure of vanadium and tungsten sulfides. However, it is difficult to tell from the presented images about the presence of those. The intensity of the noted peaks of vanadium and tungsten sulfides is at the noise level. The presence of even 10% crystalline vanadium or tungsten sulfide would be identified by XRD. It may be worthwhile to increase some area to demonstrate the formation of the crystalline phase of sulfides. For comparison, you can also show the X-ray diffraction pattern of the sample with a higher loading of vanadium (rG-V-4). In addition, it would be advisable to add a diffraction pattern of the synthesized pure powders of vanadium and tungsten sulfides for comparison with diffractograms for composite materials.
Answer: Thank you for your suggestion. As per the reviewer’s suggestion, we have done XRD for rG-V-4. Additionally, we developed the pure powders of vanadium sulfide and tungsten sulfide the results are as follows. The XRD patterns of as-prepared VS2, WS2, and rG-V-4 in are provided in the supporting information. The formation and presence of VS2 in the hydrogel has been evidently confirmed. As shown in the Figure S2, the typical VS2 diffraction peaks at 15.04, 35.7, 44.2, 57.2,62.11, 64.50, and 69.23° are clearly observed and correspond to the (001), (011), (012), (110), (111),(004), and (201) lattice planes, respectively. The crystal structure of pristine WS2 showed diffraction peaks at 2θ = 15.16, 28.63 and 43.96 which correspond to the (002), (004) and (006), planes of hexagonal 2H WS2 (PDF#08-0237). As shown in the as-prepared rG-V-4 peaks, the VS2 peaks are existed together with the rGO. We humbly informing our reviewer, that we used very smaller amount of TMDs source materials to develop TMDs in the hydrogel in our present investigation, where the rGO and linker amounts were more dominant in the hydrogel. Thus, we could not observe the most intense peaks for the TMDs.
Comment 2. The issue of providing EDX mapping results is still open. For rG-V-1 material, the distribution of elements (Figure 3f-h) is still uninformative. It is possible that a longer signal accumulation time is required in the selected area to form an image with a distribution of sulfide particles.
Answer: Thank you for your valuable suggestion. We agree with reviewer. As per the reviewer’s suggestion, we have done EDX mapping analysis for rG-V-1 material and we provide the results as follows in the revised manuscript.
Author Response File: Author Response.docx
Round 3
Reviewer 3 Report
After all accepted corrections, the article "Three-dimensional ternary rGO/VS2/WS2 composite hydrogel for supercapacitor applications" can be accepted after minor revision.
1. The SEM image of the area from which the element distribution maps were made should be added (Figure 3 and Figure 4).
Author Response
Reviewer: After all accepted corrections, the article "Three-dimensional ternary rGO/VS2/WS2 composite hydrogel for supercapacitor applications" can be accepted after minor revision.
Authors: This is the happiest news from our respected reviewer. We appreciate the time and effort that the reviewer has dedicated to deal our manuscript. We really appreciate and are thankful for the Reviewer's warm work
Comment 1. The SEM image of the area from which the element distribution maps were made should be added (Figure 3 and Figure 4).
Answer: Thank you so much for your valuable suggestion. According to the reviewer suggestion, we have added the corresponding image in Figure 3d in the revised manuscript. We already provided the corresponding image for Figure 4d in the manuscript.
