Hierarchically Electrodeposited Nickel/Graphene Coatings for Improved Corrosion Resistance of Ni Foam Flow Field in PEMFC

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1.    Page 3 line 110-111: ‘The hierarchical structure was obtained by depositing under two current densities with each current deposited for 10 minutes.’

It would be helpful if the authors explain why they chose specific combinations of current densities (e.g., 5 and 10 mA/cm² for Ni/G5-10). Specifically, the rationale behind why two-step deposition with different currents leads to a hierarchical structure that offers improved performance should be discussed in more detail. This explanation could include how the microstructure impacts corrosion resistance (e.g., more compact layers or refined grains).

Additionally, Ni/G5-10 has demonstrated the best performance, suggesting that smaller deposition currents might further enhance the material properties. Clarification on whether lower current densities were tested, or why they were not, would make the optimization process clearer to the reader.

2.    Please correct typos in the paper i.e. change ‘0.6v’ into ‘0.6V’ in Page 135

3.    The choice of testing temperatures (50°C and 80°C) needs more context. The authors should clarify why these temperatures were chosen, perhaps by linking them to the typical operating temperatures of PEMFCs or the expected range of practical applications for these coatings. It’s also helpful to mention if these temperatures were selected to simulate particular extreme conditions in PEMFC operations.

4.    Section 3.2: It is straightforward that Ni/G5-10 displayed the lowest current density. While Ni/G5-10 demonstrated the lowest current density, presenting only the final values (at 120 minutes) limits the completeness of the comparison. Including error bars or standard deviations for the current density during the testing period would add more reliability to the data and make the results more comparable.

It would also be beneficial to provide the current increase rates within specific intervals, such as the last 10 minutes, to give insight into the initial reaction kinetics and how stability evolves over time for each coating.

5.    I would think SEM is the key part in this paper. The SEM images help to reveal the mechanism why the choice of Ni/G5-10 has the best corrosion resistance. However, there are some problems in the SEM analysis part:

a.    The caption for Figure 4 lacks descriptive information. Adding descriptions for each subfigure in the main text can help the reader understand what each image is intended to convey. The animated particles in colors seemly represent the particle size from each step of deposition. This could be confusing: are the size of those particles precisely line with the real size? It is better to make a table of particle size measurements for each step for each sample;

b.    The colored particles in the SEM images can be misleading if they do not accurately represent the actual sizes. Including a table with quantitative particle size measurements from each deposition step would eliminate any ambiguity.

c.    The SEM images should clearly illustrate the distinguishing features of Ni/G5-10 compared to other samples. If these distinctions are not visually clear, the author should use quantitative analysis or markers to highlight specific features like Ni nanoparticles through image segmentation in the images taken at back-scattered imaging mode or elemental characterization i.e. EDS mapping. Additionally, clarifying if the cracks in the SEM images (Figures b, c, d) are artifacts from gold deposition or indicative of the material's properties would be helpful.

d.    TEM images could provide a more detailed view of the Ni and graphene mixing at the nanoscale, which may further elucidate the reason for the superior performance of Ni/G5-10.

6.    The XRD and XPS results should be discussed in more detail, specifically comparing Ni/G5-10 to other samples. A deeper analysis that explains why Ni/G5-10 offers improved corrosion resistance based on phase composition, crystallinity, or chemical state would significantly strengthen the discussion.

7.    Simply mentioning that the ICR value meets the 2025 DOE standard does not provide a complete perspective. Comparing the results to other contemporary studies can help establish the novelty and relevance of the work. It would be helpful if the authors discuss how their ICR value and corrosion resistance performance compare to other state-of-the-art materials, and why their approach represents a meaningful advancement.

Author Response

Please see the attachment。

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript “Hierarchically electrodeposited nickel/Graphene coatings for improved corrosion resistance of Ni foam flow field in PEMFC” is new and original. The authors successfully fabricated Ni/G composite coatings with hierarchical structure on foam nickel by electrodeposition under different current density. Compared with the coatings obtained under steady and gradient current, the hierarchically electrodeposited coating performed better stability of metal foam. Although the grain size was larger than that of the coatings, the com-posite of NiO and graphene covered on the surface of metal foam and formed a uniform and dense protective film. The work fit the journal scope. There are sufficient details given to replicate the proposed experimental procedures and analysis. Also, there are sufficient outcome-neutral tests of the hypotheses, including positive controls and quality checks. The figures and tables are of good quality. The methodology used is correct and the author’s conclusions are justified given the data.

Author Response

Thanks a lot for your affirmation, it means a lot to us.

Reviewer 3 Report

Comments and Suggestions for Authors

This is an interesting research job about corrosion protection with an electrodeposition covering on a foam, it's revealed good performance in the studied media but must improve by the adding of AFM images before and after deposition for example. Even, EDS spectra can be added to include the chemical composition of the covering and mapping the chemical distribution too.

I considered adding these two items this paper can be published

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The revision is reasonable. Paper can be accepted.

Comments on the Quality of English Language

There is no major language issue in this manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

The new version provided by the authors is better than the first one, and all suggestions and corrections were addressed correctly.