Recent Advances in the Development of Nanocarbon-Based Electrocatalytic/Electrode Materials for Proton Exchange Membrane Fuel Cells: A Review

Round 1

Reviewer 1 Report

In this manuscript, the authors summarized recent advances in nanocarbon-based materials for PEM fuel cells. Multiple nanocarbon materials were mentioned and discussed in the draft, including graphene nanosheets, GO, rGO, CNT, vertical CNT, graphene with dopants, and carbon spheres. Overall, the paper is well organized, and many aspects of carbon for PEM were considered in the draft. Therefore, it is recommended that the paper be accepted with minor revisions.

1. That would be good if the authors could summarize the pros and cons of each nanocarbon for PEM in a table.

2. In Figure 6, the mechanism is for OER reaction. Though reversely, the mechanism will be the possible ORR route. However, it might not be very appropriate to have this as the figure for the session, which is also different from the main text "One of the possible mechanisms of ORR in sulphur-doped carbon 469 nanotubes is shown in Figure 6". Meanwhile, the referenced paper was published in 2016, which cannot be considered a recent advance. I suggest the authors find some N-doped carbon or others as examples in recent years, which are more prevalent for ORR reactions. 

Author Response

Dear Reviewer,

Thank you very much for your comments! Your opinion is very helpful to improve the quality of our paper. We have revised the manuscript according to your comments point by point. Please, find our detailed responses in the uploaded file.

With best regards,

Authors

Author Response File: Author Response.docx

Reviewer 2 Report

This paper discussed using structured nanocarbon-based materials primarily as supports for noble metals as electrode materials for PEM fuel cells. The review requires comprehensive revisions to enhance its overall quality before acceptance.

1. What is the novelty of this manuscript?

2. It is of utmost importance that the manuscript, especially the abstract, undergoes a thorough language check by a native speaker to rectify grammatical errors, significantly enhance the manuscript's readability, and maintain its professional tone.

3. All abbreviations must be defined at first mention.

4. The manuscript delves into the recent advances in nanocarbon-based electrocatalytic and electrode materials for PEM fuel cells. However, it would be beneficial to provide a clearer connection between the chosen examples and the “recent development” they represent, aiding the reviewers in understanding the manuscript’s context.

5. The manuscript also needs some organization before it can be accepted. For example, chapters 2 (Graphene Nanosheets) and 3 (Graphene oxides and reduced graphene oxides) should be combined into one singular chapter (Graphene and its derivatives) and discussed. Likewise, chapters 4 (Carbon nanotubes) and 5 (Vertically aligned CNTs).

6. The manuscript poorly describes Figure 2. The EDS images (Fig. 2d-g) are adequately discussed, but the SEM and TEM images are not. Either remove those images or discuss their relevance in the manuscript. A similar issue is observed in Figures 4 and 7.

7.  The aerogel synthesis is poorly described in the manuscript. Generally, (carbon) aerogel synthesis follows the same route irrespective of the precursor. They are (i) gelation, which involves (a) sol-gel polymerization, where a gel-like substance is formed, sometimes with the aid of a catalyst, and (b) aging, where the gel is strengthened; (ii) drying when the liquid in the hydrogel is removed without causing structural damage (an organic aerogel is formed here), and finally (iii) carbonization, where the aerogel is carbonized in an inert atmosphere (N₂ or Ar) to obtain the carbon aerogel. Sol-gel is just one of the steps in carbon aerogel synthesis and is not a synthesis technique/method to produce aerogels. Neither is supercritical drying, which is just one of many drying methods used to remove the liquid from the hydrogel to form the organic aerogel without destroying the aerogel structure. Also, to the best of my knowledge, CVD is generally used in synthesizing carbon nanotubes and carbon molecular sieves but never in aerogel synthesis. The entire section will need an extensive rewrite.

8. The carbon sources or precursors used to synthesize the discussed nanocarbon structures should be addressed or briefly mentioned.

9. Many different nanocarbon structures are discussed. What are their benefits and drawbacks (if any) when used as electrode materials for PEMFCs?

10. It is suggested that one or more tables be created to summarize all the results, which would be simpler and clearer.

11. Some recent work can be cited or discussed. For example, https://doi.org/10.1016/j.jiec.2024.01.044; https://doi.org/10.1039/D2CS00681B

12. The conclusion is written like a more detailed abstract. It is too short and offers almost no outlook. It is suggested that more perspectives be added.

Miscellaneous

P5, L197: After atomisation of the catalytic ink? Please check if the right word was used.

P5, L198: “The porous structure was maintained while the pore diameter decreased.” Determining pore diameter from an SEM image is rife with inaccuracy. Please check this.

P7, L246: Adsorb, not absorb. Reactants, not reagents.

P8, L350: “toCO₂” should be “to CO₂”.

Comments for author File: Comments.pdf

The paper presently has many grammatical errors and a native speaker should read through and correct them.

Author Response

Dear Reviewer,

Thank you very much for your comments! Your opinion is very helpful to improve the quality of our paper. We have revised the manuscript according to your comments point by point. Please, find our detailed responses in the uploaded file.

With best regards,

Authors

Author Response File: Author Response.docx