Synthesis of a NiMoO4/3D-rGO Nanocomposite via Starch Medium Precipitation Method for Supercapacitor Performance
, Rasoul Sarraf Mamoory 1,*, Nicklas Blomquist 2, Manisha Phadatare 2 and Håkan Olin 2Round 1
Reviewer 1 Report
The authors reported a precipitation method to synthesize nickel molybdate and reduced graphene oxide nanocomposite as electrode material for energy storage devices. The electrochemical performance of the NiMoO4/3D-rGO electrode shows a capacitance of 900 F/g at a current density of 1A/g. However, the electrode material exhibits typical battery behavior (eg, large redox peaks separation, non-linear charge discharge profile, low coulombic efficiency etc. Ref. DOI: 10.1002/aenm.201902007). Thus, the authors should report data as per battery community appropriately, not supercapacitor. Besides, here are some more detailed questions:
Figure 1, peak positions of materials is obvious not at the indicated O-H bond position. Raman spectrum should be extended to 3000 cm-1 to see the presence of 2D peak for rGO. As the author claim, rGO can help improve the conductivity of NiMoO4, thus impedence data should be provided to compare the resistance. As we all know, supercapacitors have long cycle life (at least 10K cycles), here the capacitance retention is only 57% after 400 cycles, it is not reasonable. How is the morphology of NiMoO4/rGO after cycling?Author Response
Dear reviewer 1,
We thank you for your very helpful comments. Below you can find our response to the comments. Changes in the manuscript are presented below each comment and highlighted in the Revised manuscript with track changes.
Author Response File: 
Author Response.docx
Reviewer 2 Report
In this work, the authors synthesized the nanohybrid NiMoO4-rGO via starch medium precipitation, characterized the material and compared its energy storage performances with the bare NiMoO4.
The originally of this work consists in using starch to generate porosity and to reduce the GO during the heating process.
The work is clearly presented however there are some point to clarify before the paper could be accepted.
In the introduction the author discuss about the controversy Battery-like behavior versus pseudocapacitive. Although it is not a paper based on electrochemistry, the CV curves clearly show redox peaks as mentioned by the authors and the capacity value must be expressed in mAh/g or C/g. The reference 7 in the manuscript nicely explain why. The authors write that "all the diffraction peaks can be well indexed to the monoclinic ...." and then they show there is an impurity ......
This discrepancy should be corrected The attribution on the XRD pattern can mislead the readers, it looks like the intense peak around 30° is an impurity To my opinion, the IR data do not demonstrated the presence of rGO in the hybrid material whereas the Raman does.
The IR spectra of NiMoO4 and NiMoO4-3D-rGO are similar, there is no additional peak for the later to confirm the presence of rGO The intense peak on the IR spectrum of NiMoO4 around 1500-1700 cm-1 is not discussed, it is from the adsorbed nitrates? Why during the synthesis the molar ratio of Mo is 10 times higher than the one of Ni? Line 233 there is a mistake, it is figure 5a-b instead of 4a-b Why the capacity drops that much after 200 cycles? are there parasite reactions or the electrode is dissolved in the electrolyte? comparison of CV of the 1st and 400th cycle could help to answer Starch should generate porosity in the material however there is no porosity measurements. At least BET measurements should be performed. line 313 the authors say that NiMoO4/3D-rGO has a good cycling stability however the cycling measurements show the opposite.
400 cycles is very few for supercapacitors and such drop between the 1st and 400th cycle demonstrate that the cyclability is not goo
Author Response
Dear reviewer 2,
We thank you for your very helpful comments. Below you can find our response to the comments. Changes in the manuscript are presented below each comment and highlighted in the Revised manuscript with track changes.
Author Response File: Author Response.docx
Reviewer 3 Report
The manuscript reveals synthesis and application of NiMoO4/3D-rGO nanocomposite for supercapacitor performance. The manuscript is original and very interesting. Very interesting results obtained. Although some interpretations are not fully convincing and need to be improved prior to publishing.
Section 3.2: Symmetry in CV does not represent reversibility. Reversibility is related to a fast electron transfer. This interpretation should be corrected. Formation of NiOOH is under specific conditions. It might be possible when NiO is used, but it is more positive usually: Š. Trafela et al. Electrochim. Acta, 309, 2019, 346. Can the author discuss deeper this part of the manuscript. In the last paragraph of Results and discussions references are missing – some error occurred. 6 e and f need improvement: e) has 4 curves, but 5 lines are explained in the legend (on the diagram); it is unclear in f) which colour belongs to which electrode. In generally, please correct “Ag-1” to “A g-1” (with space), otherwise it looks like silver with oxidation state -1.
It is unclear how charge-discharge experiments were performed (experimental conditions). Conclusion states about fast electron transfer, however, electrochemical data, especially CV do not support this statement.
Author Response
Dear reviewer 3,
We thank you for your very helpful comments. Below you can find our response to the comments. Changes in the manuscript are presented below each comment and highlighted in the Revised manuscript with track changes.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors answered most of my questions, just more convincing response should be provided for the following questions.
1. The electrode material exhibits typical battery behavior (eg, large redox peaks separation, non-linear charge-discharge profile, low coloumbic efficiency, this is not the behavior of pseudocapacitance. check Nature Reviews Materials (2019): 1-15
2. As the author claim, rGO can help improve the conductivity of NiMoO4, thus impedance data should be provided to compare the resistance.
3. It is better to provide SEM images showing the morphology of NiMoO4/rGO after cycling.
Author Response
We thank you for your very helpful comments. Changes in the manuscript are presented below each comment and highlighted in the Revised manuscript with track changes.
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Thank you for the response,
I agree with most of them however I still do no agree with the unit for the capacity of your material (F/g versus C/g or mAh/g). I would advice you to read the paper from Brousse et al. Materials, 2019, 411, 1178 or Journal of Electrochemical Society, 2015, 162, A5185 concerning the capacity and capacitance.
The comparison with the literature could be done only if in all the reports the potential windows is always the same because a F (Farad) = C (Coulomb) /V (Volt). If V (potential windows used to determine the capacity) changes from one paper to another one, the comparison has no sense.
The capacitance of MnO2 in aqueous electrolyte can for instance be expressed in F.g-1 because the CV show a rectangular shape characterized by surface redox reactions. In the case of NiMoO4 the CV show well defined redox peak and the capacity of the material should be expressed in Coulomb per gram or mAh/g even in hybrid supercapacitors.
In the journal "Batteries" which is focused on the electrochemical energy storage, the unit of the capacity must be well attributed
Author Response
We thank you for your very helpful comments. Changes in the manuscript are presented below each comment and highlighted in the revised manuscript with track changes.
Please see the attachment.
Author Response File: Author Response.pdf
Round 3
Reviewer 1 Report
The revision has not been substantial but in most parts, it suffices. However, the problem associated with the impedance measurement still exists. EIS is a very very basic technique in the energy storage field, this paper will be more convincing if the author can provide the relevant data.
Overall, there are some interesting results, which might be of interest to other researchers. However, the manuscript should be better articulated to assist the readers in capturing the scientific significance of this research. Therefore, this manuscript can be recommended for publication after a minor revision.
Author Response
Thank you for your good comments. We have made a lot of changes in the article.
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
I would like to thank the author for changing the unit to Coulomb
I recommend to accept the manuscript in its present form
Author Response
Thank you for your good comments. We have made a lot of changes in the article.
Please see the attachment.
Author Response File: Author Response.pdf
