Improved Oxidative Stability by Embedded Cerium into Graphene Oxide Nanosheets for Proton Exchange Membrane Fuel Cell Application

Round 1

Reviewer 1 Report

The manuscript should be reconsidered after the following comments are addressed adequately. 

Figure 1- One of the important aspects of this manuscript is the concentration x Nafion-GO/Ce-x (where x 0.5,1,2 and 5 wt%). Why all the concentrations have not been compared through XRD, FTIR, and XPS and only one? This experiment and the data is incomplete. Provide results and/or reasoning including in the text.

Figure 1- Caption is wrong. (a) is not XRD but FTIR and so on. Correct this.

FTIR comparison- There are multiple peaks of interest in a GO hybrid FTIR like this. Why only C=O and C-O have been seen. What about electron delocalization (C=C) in GO plane has been used as a comparison of CO extent for hybrid material? It is a pretty general practice.

XRD- Discussion on XRD in the text is confusing. The author must clarify where XRD is being discussed and where FTIR/XPS. Presently the discussion is very confusing and the text should be corrected for a better understanding

Discussion on the Elemental mapping of pristine and composite membrane is incomplete. No discussion on SEM, why elemental mapping is compared in figure 2, and what is the conclusion of this comparison? 

Reason for different degradation extent between 300-500C for TGA in figure 5- Could this be just the extent of polymer burning out and the inorganic stable materials including GO leaving behind? The text doesn't clarify this but mostly focuses on the stability of hybrid material at a slightly higher temperature than pristine.

Author Response

Reviewer 1

Comments and Suggestions for Authors

The manuscript should be reconsidered after the following comments are addressed adequately. 

Figure 1- One of the important aspects of this manuscript is the concentration x Nafion-GO/Ce-x (where x 0.5,1,2 and 5 wt%). Why all the concentrations have not been compared through XRD, FTIR, and XPS and only one? This experiment and the data is incomplete. Provide results and/or reasoning including in the text.

Ans. Thank you for this comment and we are much agree that the concentration variation study could put some highlight for future optimization studies. In addition to that the aim of the current research is more focused on the stability of the synthesized membrane for oxidative environment and a lot of research papers has already been published towards the optimization of the concentration of cerium with valuable characterizations. Moreover, cerium ion has featured tendency for radical scavenging but higher concentration could lead to decrease in the proton conductivity due to neutralization of functional groups responsible for ionic transportation. Thus, graphene oxide has been selected as host material to validate the maximum effect of cerium as radical scavenger without sacrificing the proton conductivity up to an extent. Additionally, the successful intercalation is supported by spectroscopical characterizations provided in the manuscript.

Figure 1- Caption is wrong. (a) is not XRD but FTIR and so on. Correct this.

Ans.  The respective captions are modified in the revised manuscript (Pag.5).

FTIR comparison- There are multiple peaks of interest in a GO hybrid FTIR like this. Why only C=O and C-O have been seen. What about electron delocalization (C=C) in GO plane has been used as a comparison of CO extent for hybrid material? It is a pretty general practice.

Ans.  Thank you for this valuable suggestion. The values bearing the corresponding IR values regarding electron delocalization (C=C) in GO plane has been added to the revised manuscript (Pag.4, Figure.1).

XRD- Discussion on XRD in the text is confusing. The author must clarify where XRD is being discussed and where FTIR/XPS. Presently the discussion is very confusing, and the text should be corrected for a better understanding.

Ans.  Thank you for this recommendation. The paragraph is rewritten again to clarify the FTIR, XRD studies in the revised manuscript (Pag.4, Figure.1).

Discussion on the Elemental mapping of pristine and composite membrane is incomplete. No discussion on SEM, why elemental mapping is compared in figure 2, and what is the conclusion of this comparison? 

Ans. As per following comment the content of Figure 2, has been modified. The images containing elemental mapping has been removed and with that the discussion about SEM has also been added in the revised manuscript. (Pag.5, Paragraph.2)

Reason for different degradation extent between 300-500C for TGA in figure 5- Could this be just the extent of polymer burning out and the inorganic stable materials including GO leaving behind? The text doesn't clarify this but mostly focuses on the stability of hybrid material at a slightly higher temperature than pristine.

Ans.  Thank you for the valuable suggestion. This sentence has been further clarified more and added to the manuscript to make it more understandable for the readers. Further, a dTg study has also been added to highlight the stepwise weight loss as a function of temperature. (Pag.8, Figure.5, Paragraph-1).

Author Response File: Author Response.docx

Reviewer 2 Report

In this paper a deep and interesting investigation of the collaborative effect of cerium particle embedded into graphene oxide to enhance the chemical stability of proton exchange membrane for fuel cell (PEMFC) has been carried out.

The durability of the membrane was investigated by measuring in weight loss of the membranes before and after Fenton’s test.

The obtained results are presented and discussed.

The conclusions are supported by the results presented.

Some recommendations:

1) Avoid lumped references; include a short critical comment or appreciation for each reference.

2) Highlight the novelty of this study at the end of the Introduction.

3) Include recent references to support the timeliness of this study and the advantages of the results obtained compared to other similar studies (references published in the last 5 years must be more than 50% of the total references).

Author Response

Reviewer II

Comments and Suggestions for Authors

In this paper a deep and interesting investigation of the collaborative effect of cerium particle embedded into graphene oxide to enhance the chemical stability of proton exchange membrane for fuel cell (PEMFC) has been carried out.

The durability of the membrane was investigated by measuring in weight loss of the membranes before and after Fenton’s test.

The obtained results are presented and discussed.

The conclusions are supported by the results presented.

Some recommendations:

1) Avoid lumped references; include a short critical comment or appreciation for each reference.

Ans.  The references have been edited following reviewer comment.

2) Highlight the novelty of this study at the end of the Introduction.

Ans.  Thank you for this comment. Given suggestion is added to the manuscript. (Pag. 2, Paragraph.2)

3) Include recent references to support the timeliness of this study and the advantages of the results obtained compared to other similar studies (references published in the last 5 years must be more than 50% of the total references).

Ans.  Thanks for the reviewer’s comment. The references which showed similar result was added in this manuscript. (Ref. 16, 25-30).

Author Response File: Author Response.docx

Reviewer 3 Report

the authors present a composite membrane obtained from Nafion 212, GO and Ce ions GO. I suggest to authors modify some parts of their work, as follow:

• Synthesis of Composite Membranes: the authors synthesized composites in a vacuum oven at 80°C for 24 h. It is my curiosity to know which was vacuum used and if they had any problem obtaining a uniform membrane. My doubt is that at 80°C under vacuum some solvents, such as alcohols,  can boil.
• Equation (1) and Equation (6): The authors forgot the unit of measurement for IEC and swelling ratio.
• Pag. 4: At the end of the page replace “Figure 1 (b)” with “Figure 1 (c)”
• Figure 5: The discussion of TGA graph is not easy to understand. I suggest adding a graph of the derivate of the weight as a function of temperature. The addition of such a graph helps the reader to easily identify the stages of weight loss.
• Conclusion: the authors need to improve the conclusions.
• I suggest to authors add some other references

Author Response

Reviewer III

Comments and Suggestions for Authors

the authors present a composite membrane obtained from Nafion ²¹², GO and Ce ions GO. I suggest to authors modify some parts of their work, as follow:

• Synthesis of Composite Membranes: the authors synthesized composites in a vacuum oven at 80°C for 24 h. It is my curiosity to know which was vacuum used and if they had any problem obtaining a uniform membrane. My doubt is that at 80°C under vacuum some solvents, such as alcohols, can boil.

Ans.  Thank you very much for the comment. The synthesis of membrane followed by two-step synthesis. In the first step, the casted membrane is placed inside the oven at 80⁰C for 24 hours and then in the second step, the temperature was raised to 120⁰C for an extra 1 hour under vacuum to remove the complete solvent present over the surface of the membrane. The sentence has been mentioned in the experimental part (Pag.2, Paragraph-5).

• Equation (1) and Equation (6): The authors forgot the unit of measurement for IEC and swelling ratio.

Ans.  The units for respective equations have been added to the manuscript (Pag.4).

• Pag. 4: At the end of the page replace “Figure 1 (b)” with “Figure 1 (c)”

Ans.  Thank you for the suggestion. It has been replaced as suggested by the reviewer (Pag.5, Figure.1).

• Figure 5: The discussion of the TGA graph is not easy to understand. I suggest adding a graph of the derivate of the weight as a function of temperature. The addition of such a graph helps the reader to easily identify the stages of weight loss.

Ans.  Thank you for this valuable recommendation. To identify the stages of a graph is added to the revised manuscript showing the derivative of weight loss as a function of temperature (Pag.8, Figure.5).

• Conclusion: the authors need to improve the conclusions.

Ans.  As per the given suggestion, the conclusion section is improved and added to the revised manuscript (Pag.9)

• I suggest to authors add some other references

• Extra references have been added to the revised manuscript showing the comparisons with the methods reported earlier (Pag.10-11).

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The changes to the manuscript have been read.

Reviewer 3 Report

I thank the authors for making the required changes