N, S, P-Codoped Graphene-Supported Ag-MnFe2O4 Heterojunction Nanoparticles as Bifunctional Oxygen Electrocatalyst with High Efficiency
and Lifeng Dong 1,3,*Round 1
Reviewer 1 Report
Raman analysis is suggested to be included.
A table with analogous examples of electrocatalysts should be added from the literature, in order for the reader to assess the results of the present work with others.
Author Response
Thank you for your comments. Please find our response to comments from the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors have carefully considered all the comments and the manuscript is much improved. However, some new issues have arisen from the changes and some remain from the old version that need to be addressed for the manuscript to be publishable in Catalysts.
- The authors have conducted ICP-AES for determining the bulk elemental composition as suggested but present no experimental details and the loading is again given only as “around 20 wt.%”. Please present experimental details of sample digestion and analysis as well as actual numbers of metal content.
- Surface elemental contents are still missing. XPS data is already presented (do the spectra really remain unchanged with the new materials?), so the authors have already conducted the experiments. Please present the surface elemental contents as well.
- The authors have conducted new LSV and CV experiments as well as RDE ORR measurements (presumably with new materials where the metal content is “around 20 wt.%”). The peak currents in the CVs are increased by a factor of 2, while the ORR activity is reduced. What could be the reason for this?
- New OER experiments with the new materials should also be conducted. Currently, the authors present data from different catalysts that have the same name in the manuscript.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
It may be accepted in the current form.
Reviewer 2 Report
The authors have carefully considered all of my comments. The manuscript is now suitable for publication.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
The authors should explain the amorphous character of doped graphenes (XRD data). In the XRD data of hybrids, the carbon contribution should be given, so the scale will start from 15 degrees or so. The TEM images do not show clearly the presence of graphenes. The authors shouls include a couple images with less magnification to show the carbon nanostructures. Raman analysis is suggested to be included. Similar work has been shown by the authors (ref 30). There should be some short discussion about the comparison of electrocatalytic properties of such similar samples (the combination of heteroatom dopant changes only...). Finally a table with analogous examples of electrocatalysts should be added, in order for the reader to assess the results of the present work with others.
Reviewer 2 Report
This manuscript deals with the ORR and OER activity of Ag-MnFe2O4 particles supported on N, S and P-codoped graphene. While the topic is definitely of interest to the readers of Catalysts and what experimental work is presented seems solid, there remains a lot of work to be done on the manuscript before it could be publishable.
Specific issues:
1) The authors discuss the effect of the HSAB interactions on the mass transfer in electrocatalysts (page 2). However, the article they cite (reference 21 in the original manuscript), contains no such discussion, neither am I aware of the applicability of the HSAB theory towards mass transfer in electrocatalysis. This should be further explained or removed.
2) Recent topical publications should be referred: Santori, P. G.; Speck, F. D.; Cherevko, S.; Firouzjaie, H. A.; Peng, X.; Mustain, W. E.; Jaouen, F., J. Electrochem. Soc. 2020, 167 (13), 134505; Ratso, S.; Zitolo, A.; Käärik, M.; Merisalu, M.; Kikas, A.; Kisand, V.; Rähn, M.; Paiste, P.; Leis, J.; Sammelselg, V.; Holdcroft, S.; Jaouen, F.; Tammeveski, K. Renew. Energy 2021, 167, 800–810; Ratso, S.; Walke, P. R.; Mikli, V.; Ločs, J.; Šmits, K.; Vītola, V.; Šutka, A.; Kruusenberg, I., Green Chem. 2021, 23 (12), 4435–4445; Kaare, K.; Yu, E.; Käämbre, T.; Volperts, A.; Dobele, G.; Zhurinsh, A.; Niaura, G.; TamasauskaiteTamasiunaite, L.; Norkus, E.; Kruusenberg, I., ChemNanoMat 2021, 7 (3), 307–313.
3) The size of the STEM images used for the EDS mapping (Figure 1c) should be increased. As-is, it is very hard to see anything on the figure. The quality of the TEM images (Figure 2) should also be increased, as graphene is currently not visible due to low quality.
4) The experimental details of the synthesis of the materials are incomplete. The experimental section should allow for other researchers to repeat the experiments conducted by the authors. However, in this case, the details of the synthesis are referred from another article, where a lot of the experimental details are missing as well (for example, the real amount of MnFe2O4 or Ag is never reported, it is only said that a “certain amount” was added).
5) The authors claim that the metal particles have a smaller particle size on NSPG than NPG or SPG. This should be backed up with statistical evidence (from the TEM images).
6) There are many places in the manuscript where the wording is questionable, for example: “The superior properties of doped graphene itself not only make Ag-MnFe2O4 nanoparticles better supported on it, but also make the nanoparticles more stable when they participate in reactions by doping defects.” How are they “better supported” and how do defects make a material more stable? The idea can in some cased be derived, but the manuscript should most definitely be read and corrected by a native speaker.
7) The XPS signals are discussed to have a “slight negative shift”. These shifts should be quantified in each case.
8) What is the exact nature of the metals/metal oxides after the synthesis process? Is the Ag-MnFe2O4 present as different particles of Ag and MnFe2O4 or is there an alloy created?
9) What are the elemental compositions on the surface of the catalysts as determined by XPS? Bulk elemental composition by ICP-MS or other similar techniques should also be provided. Without knowing the metal loading, it makes no sense to compare the electrocatalytic activities.
10) What is the nature of the reduction peak at ~1.1 V vs RHE for the Ag-MnFe2O/NSPG catalyst (Figure 4a) that is not present in other materials?
11) Why is there a reduction peak present at ~0.8 V vs RHE at lower rotation rates on the Ag-MnFe2O/NSPG catalyst (Figure 4c)?
In conclusion, the manuscript could be publishable in Catalysts, but requires a major revision with a lot of added experimental work.
Comments for author File: 
Comments.docx
Reviewer 3 Report
Authors have reported that co-doped (N, S, and P) graphene supported Ag-MnFe2O4 catalysts for enhanced activity towards both oxygen reduction reaction and oxygen evolution reaction. However, I could not still understand a contribution of co-doped elements to electrocatalytic reactions. I would recommend to provide more detail including the reaction mechanism using surface analysis such as HR- STEM and -TEM measurements. In the current version of manuscript, I think that readers cannot follow the supporting effects by addition of some elements. The minor comments are bellow.
(1) In Figure 4B, what is the peak observed at ca. 0.78 V in AgMnFe2O4/SPG.
(2) Why AgMnFe2O4/NSPG shows a higher number of electron transferred, even though the observed limiting current is slightly low compared to other catalysts.
(3) I think metallic Ag, Mu, and Fe is dissolved in electrolyte solution at a higher potential region such as OER. Characterization after electrochemical test are necessary.
