The Evolution of Hexagonal Cobalt Nanosheets for CO2 Electrochemical Reduction Reaction
Round 1
Reviewer 1 Report
In this work, in-situ Raman spectra, differential electrochemical mass spectrometry, in-situ electrochemical impedance spectroscopy, and TEM were implemented to identify the mechanisms of ferromagnetic hexagonal-close-packed (hcp) Co nanosheets (NSs) with a higher activity in CO2RR. However, this work contained all the necessary experimental work. Yet, it lacks of novelty. The abstract has to be revised in a professional way.
This article revealed the experimental results, including in-situ Raman, EIS, TEM, etc. The authors logically presented these results. There is no primary concern about the work.
The efforts to study CO2 reduction are the highest priority in the scientific community due to the carbon zero emission regulation. The authors used the electrochemical reaction to facilitate CO2 reduction, proving a positive and potential method to reduce carbon emissions.
This work covered all the necessary scientific experiments to prove the concept and achieve the topic objects.
No problem with the methodology
Author Response
Dear Reviewers,
Thanks for the important comments for our paper “The Evolution of Hexagonal Cobalt Nanosheets for CO2 electrochemical reduction reaction. Those positive and constructive comments are very helpful for us to further improve our work. Based on these comments and suggestions, we have revised the paper, and all changes made in the revised manuscript are shown in revisions mode. Our answers to Editor and Reviewers’ questions are given below:
To Reviewer 1:
General comments: In this work, in-situ Raman spectra, differential electrochemical mass spectrometry, in-situ electrochemical impedance spectroscopy, and TEM were implemented to identify the mechanisms of ferromagnetic hexagonal-close-packed (hcp) Co nanosheets (NSs) with a higher activity in CO2RR. However, this work contained all the necessary experimental work. Yet, it lacks of novelty. The abstract has to be revised in a professional way.
This article revealed the experimental results, including in-situ Raman, EIS, TEM, etc. The authors logically presented these results. There is no primary concern about the work.
The efforts to study CO2 reduction are the highest priority in the scientific community due to the carbon zero emission regulation. The authors used the electrochemical reaction to facilitate CO2 reduction, proving a positive and potential method to reduce carbon emissions.
This work covered all the necessary scientific experiments to prove the concept and achieve the topic objects.
No problem with the methodology
General response: Thank you for your positive comments and kind recommendation on this work. We have revised the paper based on your suggestions.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Review attached
Comments for author File: Comments.pdf
Author Response
Dear Reviewers,
Thanks for the important comments for our paper “The Evolution of Hexagonal Cobalt Nanosheets for CO2 electrochemical reduction reaction. Those positive and constructive comments are very helpful for us to further improve our work. Based on these comments and suggestions, we have revised the paper, and all changes made in the revised manuscript are shown in revisions mode. Our answers to Editor and Reviewers’ questions are given below:
To Reviewer 2:
General comments: In the submitted manuscript, the authors demonstrate an effort to answer the specific question on the origin of the activity of hcp Co NSs for CO2 reduction, as a continuation of their previous work on the same system. In general, the purpose of this work and the presented results are valuable scientific contributions. Below are some issues that need clarification.
General response: Thank you for your positive comments and kind recommendation on this work. We have revised the paper based on your suggestions. Your questions are answered below:
Q1. Line 69. “Based on previous work [reference(s) needed here]…”.
A1. Thanks for your suggestion. We have put the reference on the place you mentioned.
Q2. Line 89. “Based on the previous CO2RR electrochemical window [13], …“ – Mere citation is not sufficient, as it is important to immediately see the initial potential for CO2 reduction (including HER overlap), as well as the current densities for the applied potentials used for all in situ measurements. Therefore, provide the result(s) concerning the linear sweep voltammetry in the stated potential window (extended negative limit compared to the already published CV in ref.13).
A2. Thanks for your thoughtful question. We have added the CV and LSV at 2.1 the catalytic properties in the revised manuscript.
Q3. Fig 1a. -Although the potential window is 0.2 to -0.9 vs. (RHE), the arrow on the right side indicates (as also written in the Legend) that data were collected starting from OCV (?) to 1.5 V. If OCV is an open circuit voltage, then it should be emphasized and its value given. Besides, the term OCV should be changed to commonly used open circuit potential (OCP).
Elsewhere in the text - instead of applied voltage, use applied potential.
A3. Thanks the comment. We have revised the manuscript replacing OCP with OCV.
Q4. The concluding paragraph is needed at the end of the Results section to make a connection between in situ results obtained by different techniques. In doing so, the Conclusion section might be shorter, less specific and more general.
A4. Thank you for your suggestion. We have added the discussion part and rewritten the conclusion.
Author Response File: Author Response.pdf
Reviewer 3 Report
1. Abstract is not well written and lack of experimental detail and important results.
2. The introduction part must be strongly improved. It should include important information such as literature reviews, rationalization, and hypothesis and needed more citation to related works.
3. The authors should make a critical comparison between this method and other methods.
4. replace the second and third parts
5. to paraphrase such words - Based on previous work, we found that Co has a good activity…
6. seriously improve or rewrite part of the conclusion
Minor editing of English language required. to paraphrase such words - Based on previous work, we found that Co has a good activity…
Author Response
Dear Reviewers,
Thanks for the important comments for our paper “The Evolution of Hexagonal Cobalt Nanosheets for CO2 electrochemical reduction reaction. Those positive and constructive comments are very helpful for us to further improve our work. Based on these comments and suggestions, we have revised the paper, and all changes made in the revised manuscript are shown in revisions mode. Our answers to Editor and Reviewers’ questions are given below:
To Reviewer 3:
Q 1. Abstract is not well written and lack of experimental detail and important results.
- The introduction part must be strongly improved. It should include important information such as literature reviews, rationalization, and hypothesis and needed more citation to related works.
- The authors should make a critical comparison between this method and other methods.
- replace the second and third parts
- to paraphrase such words - Based on previous work, we found that Co has a good activity…
- seriously improve or rewrite part of the conclusion
A. We agree with you on this and has changed in the revised manuscript.
Author Response File: Author Response.pdf
Reviewer 4 Report
In this work, the authors use various (Quasi) in-situ/operando characterizations (Raman, DEMS, TEM) to investigate the CO2 reduction reaction pathway on ultra-thin Co nanosheet. Under bias the local high pH environment favors the proton-electron transfer step of adsorbed COCO* intermediate, while the EIS reveals that at -0.4V vs RHE has a lower interfacial charge transfer resistance for charge transfer reactions. Overall, it is an interesting and fundamental work on exploring the CO2 reduction mechanism. However, the author failed to present their result effectively.
The manuscript also suffers from numerous shortcomings and a major revision would be necessary in order for it to be considered for publication.
1. Overall, the readability of this work is not strong. Authors should polish their writing. Examples include electric reduction, low carbon compound, etc.
2. The authors claim that by fitting the Raman peak area ratio of HCO3- and CO32- they can get pH, but there is no subfigure showing the ratio changes and the fitting, and no statement showing how the pH changes quantitatively.
3. The authors should include some statement on how surface sensitive Raman is to the interface and how far (deep) bias-induced pH change would occur.
4. A zoom-in Raman spectrum between 1000cm-1 and 2000cm-1 would be necessary as the large-scale Raman stack is poor to show the peak shift (and any other small peaks that appear not clear in the large-scale Raman spectrum).
5. What are the species from 1300-1650cm-1 around OCV? Carbon black? Why do they decrease?
6. The author should include more information in the figure caption. For example, what are the relationships between subfigure a and d? When did the author feed 13CO2 to replace12CO2?
7. Why do the author mention ferromagnetic? Is there any application of measurement using magnetic properties?
8. The author should include some figures showing the catalytic properties, product distribution and current density.
Comments for author File: Comments.pdf
1. Overall, the readability of this work is not strong. Authors should polish their writing. Examples include electric reduction, low carbon compound, etc.
Author Response
Dear Reviewers,
Thanks for the important comments for our paper “The Evolution of Hexagonal Cobalt Nanosheets for CO2 electrochemical reduction reaction. Those positive and constructive comments are very helpful for us to further improve our work. Based on these comments and suggestions, we have revised the paper, and all changes made in the revised manuscript are shown in revisions mode. Our answers to Editor and Reviewers’ questions are given below:
To Reviewer 4:
General comments: In this work, the authors use various (Quasi) in-situ/operando characterizations (Raman, DEMS, TEM) to investigate the CO2 reduction reaction pathway on ultra-thin Co nanosheet. Under bias the local high pH environment favors the proton-electron transfer step of adsorbed COCO* intermediate, while the EIS reveals that at -0.4V vs RHE has a lower interfacial charge transfer resistance for charge transfer reactions. Overall, it is an interesting and fundamental work on exploring the CO2 reduction mechanism. However, the author failed to present their result effectively.
The manuscript also suffers from numerous shortcomings and a major revision would be necessary in order for it to be considered for publication.
General response: Thank you for your positive comments and kind recommendation on this work. We have revised the paper based on your suggestions. Your questions are answered below:
Q1. Overall, the readability of this work is not strong. Authors should polish their writing. Examples include electric reduction, low carbon compound, etc.
A1. Thank you for your suggestion. We have revised the manuscript and polished our writing.
Q2. The authors claim that by fitting the Raman peak area ratio of HCO3- and CO32- they can get pH, but there is no subfigure showing the ratio changes and the fitting, and no statement showing how the pH changes quantitatively.
A2. Thank you for your question. According to the reference , Raman spectra obtained in the standard solutions with different pH values. The standard solution contained KHCO3 and K2CO3. The concentration of KHCO3 and K2CO3 added up to 1 M Calibration curve for the surface pH calculation. The Raman spectra were collected in the flow cell, where standard solutions flowed over the GDE and Ar flowed at the back of the GDE. The solution flow rate was controlled at 1 mL/min with a peristaltic pump and gas flow rate was controlled at 20 sccm with a mass flow controller. The concrete pH value of standard solution was obtained with pH meter. The carbonates or bicarbonates from the reaction between OH- and CO2 could be detected by Raman spectroscopy in the electrolyte layer near the electrode providing pH information by measuring the Raman signals of CO32- and HCO3- (Ref: Zhao, Y.; Zu, X.; Chen, R.; Li, X.; Jiang, Y.; Wang, Z.; Wang, S.; Wu, Y.; Sun, Y.; Xie, Y. Industrial-Current-Density CO2-to-C2+ Electroreduction by Anti-swelling Anion-Exchange Ionomer-Modified Oxide-Derived Cu Nanosheets. Journal of the American Chemical Society 2022, 144, 10446-10454, doi:10.1021/jacs.2c02594).
Q3. The authors should include some statement on how surface sensitive Raman is to the interface and how far (deep) bias-induced pH change would occur.
A3. Thank you for your questions. Our Raman spectroscopy can detect the signals at the depth of several hundred nanometers to micrometers at the laser of 532nm.
Q4. A zoom-in Raman spectrum between 1000cm-1 and 2000cm-1 would be necessary as the large-scale Raman stack is poor to show the peak shift (and any other small peaks that appear not clear in the large-scale Raman spectrum).
A4. Thank you for your suggestions. We have changed the Figure 2.a under your suggestions.
Q5. What are the species from 1300-1650cm-1 around OCV? Carbon black? Why do they decrease?
A5. Thank you for your suggestion. It’s carbon black. The reason for their decrease is that there is gas formed during the reaction, which affects the refraction of the laser.
Round 2
Reviewer 2 Report
The authors added the required results and modified the manuscript according to the comments. It is now ready for publication in the Catalysts journal.
Author Response
To Reviewer 2:
General comments: The authors added the required results and modified the manuscript according to the comments. It is now ready for publication in the Catalysts journal.
General response: Thank you for your positive comments and kind recommendation on this work.
Author Response File: Author Response.pdf
Reviewer 3 Report
However, I recommend the inclusion of the following article in the references section to enhance the readers' understanding and further support the presented findings:
1. Almagul R.Kerimkulova, Seitkhan Azat, Leticia Velasco, Zulkhair A. Mansurov, Peter Lodewyckx, Marat I.Tulepov, Makpal R.Kerimkulova, Inna Berezovskaya , Аldan Imangazy. Granular rice husk-based sorbents for sorption of vapors of organic and inorganic matters. Journal of Chemical Technology and Metallurgy,54,3,2019,pp.578-584
Author Response
To Reviewer 3:
Q1: However, I recommend the inclusion of the following article in the references section to enhance the readers' understanding and further support the presented findings:
- Almagul R.Kerimkulova, Seitkhan Azat, Leticia Velasco, Zulkhair A. Mansurov, Peter Lodewyckx, Marat I.Tulepov, Makpal R.Kerimkulova, Inna Berezovskaya , Аldan Imangazy. Granular rice husk-based sorbents for sorption of vapors of organic and inorganic matters. Journal of Chemical Technology and Metallurgy,54,3,2019,pp.578-584
A1. Thanks for your suggestion. We have put the article in the reference.
Author Response File: Author Response.pdf
Reviewer 4 Report
Overall the quality of the manuscript improved a lot. Some further improvement on Raman is necessary before the manuscript being recommended to be accepted.
1. How did the authors extract some intermediates, such as OCHO at 1508cm-1 from the carbon black background? Shouldn't them be buried into background?
2. The authors should also report zoom-in spectrum of CO* intermediate.
3. Since the authors made some statements on local pH change, they should fit these CO32- and HCO3- peak and quantify the pH. How do these pH change compared to Raman results on other materials?
Author Response
To Reviewer 4:
General comments: Overall the quality of the manuscript improved a lot. Some further improvement on Raman is necessary before the manuscript being recommended to be accepted.
General response: Thank you for your positive comments and kind recommendation on this work. We have revised the paper based on your suggestions. Your questions are answered below:
Q1. How did the authors extract some intermediates, such as OCHO at 1508cm-1 from the carbon black background? Shouldn't them be buried into background?
A1. Thank you for your questions. The peaks of the intermediates are observed by comparing the spectra at different potentials so that we can extract them from background.
Q2. The authors should also report zoom-in spectrum of CO* intermediate.
A2. Thank you for your suggestion. We have changed the Figure 2.a under your suggestions.
Q3. Since the authors made some statements on local pH change, they should fit these CO32- and HCO3- peak and quantify the pH. How do these pH change compared to Raman results on other materials?
A3. Thank you for your questions. This method is also applicable to other materials, and the pH change caused by the specific material in the reaction can be obtained by the change of peaks.
Author Response File: Author Response.pdf
