Carbon-Conjugated Co Complexes as Model Electrocatalysts for Oxygen Reduction Reaction
, Yung-Kang Peng 2,* and Jun Gu 1,*Round 1
Reviewer 1 Report
The suggested points to be revised are as following.
1. From the abstract, the authors claim to have the Co-complexes with well-defined structures which are anchored on the edge of carbon by pyrazine moieties.
The explanation is inadequate to support this statement. Please provide the clear evidence.
2. From XPS of three CB-conjugated Co complexes, there should be more clarification on why N:Co atomic ratios are slightly lower or higher than 4? Why is the Cl-Co atomic ratio in CB-pda-Co much lower than 2, compared with the one in CB-phen-Co?
3. By comparing TOF, CB-salophen-Co showed the highest TOF, implying that the CoN2O2 local structure possesses superior intrinsic activity towards ORR.
Please give more details to support this statement and have it related to the structure of each complex.
4. From Figure 1, images are not clear enough to say that the aggregation of Co atoms is not observed.
5. In Scheme 1, the chemical name of No 1-10 should be written.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this work, the authors reported “Carbon-conjugated Co complexes as model electrocatalysts for oxygen reduction reaction”. Three different model catalyst with well defined Co-complex structure were prepared by organic synthesis methods. the author claimed the they could analyze the number of electrochemicall accessible Co sites, as well as the intrinsic electrocatalytic activity of one Co site. The topic related with investigating the intrinsic catalytic activity of single atom catalytic active site is of great interest in this area, and the proposed approaches that author claimed are somewhat interesting. However, the conclusion is not quite convincing based on the results provided, so reviewer does not recommend the publication of the current manuscript in Catalysts.
1. Determination of the number of active site is very crucial in this kind of work. That is why it has been so difficult to draw a sound conclusion from the experimental works. For the adequate estimation of catalytic active component, it is recommended to provide conversion yield of each chemical reaction in scheme 1, as well as the contents in the final products.
2. Regarding with the homogeneity of the catalytic active site, there are major concerns in the electrochemical characteristic peaks in Figure 5. Some of them showed quite sharp characteristics which can be considered that they are underwent quite uniform reaction pathway. however, CB-pda-Co as well as CB-salophen-Co have very broad redox characteristics, which is considered that the active site is not that quite uniform. Moreover, if this is right assumption, it is impossible to draw right conclusion from this data.
3. How did the author calculate the area of oxidation peak in figure 5? it is recommended to provide the calculation procedure in the experimental session.
4. It is assumed that different active sites have different reaction pathways and corresponding energies. It is recommended to provide supplementary DFT calculaions of each active site and to make a discussion comparing that with the experimental results and conclusion in the current manuscirpt.
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The authors seek catalysis in ORR, exploing the concept of single atom. The main construct is TM(Co)-Nx center. Ligands involve phenyl species, as discussed in the narrative.
Questions:
1. Why use phenyl-species?
2. XRD should be performed with the CB-phen-Co, but also by generating a series of ligand without TMs. The 2nd XRD will generate details of the low mass.
3. Cl- is not wanted; why it is involved?
4. Despite the system is single atom, the ORR current is only 5 mA/cm^2; this performance does not show a single atom configuration.
5. strong characterize, but STM is needed to determine single atom behavior.
6. Why the total site density are differ from the active site density?
7. The Koutecky-Levich plots involve CO2; why?
8. Overall, the manuscript is good, but the process does not show single atom behavior
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
From the author's response, the clarification is acceptable.
Author Response
We thank the comment from the reviewer and highly appreciate the professionalism of the reviewer.
Reviewer 2 Report
Reviewer think the authors well responded to the original questions and now the quality of manuscript is much more improved. However, there are few comments should be revised and answered before it can be published in ‘Catalysis’.
1. After a careful examination of the number of active site for CB-salophen-Co, the total number of electrochemical active site density has changed from 45.6 to 36. This is almost 20% changes and is huge. The reviewer think it is necessary to execute the same careful examinations for other two samples for more accurate information to future researchers.
2. The color of Figure s5 is confusing and need to be revised. Two samples and two different functional groups should be identified.
3. Regarding with the answer for the Figure S5, the authors explain that the characteristic peaks come from the redox reaction of nitrogen moieties at a distance from the Co sites. However, it is considered that coordinated single Co site should have a redox activity. Why the author excluded the possibility of Co site participating in redox reactions? Reviewer recommends that author provide any experimental or literature evidences for the reasons.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
In this 2nd version the authors have improved significantly the data, the discussion, and in particular a stronger discussion to explain why the system could be a single atom. This is a good paper
Author Response
We thank the comment from the reviewer and highly appreciate the professionalism of the reviewer.
