Global-Local CNTs Conductive Network Couple with Co-Based Polyhedral Promotes the Electrocatalytic Reduction of Oxygen
Round 1
Reviewer 1 Report
The authors prepared a hybrid material that a carbon nanotube conductive network is linking ZIF-derived Co-modified polyhedral carbon, which is used as an electrocatalyst for the oxygen reduction reaction, showing a half-wave potential of 0.86 V in alkaline conditions. The structure and performance of the final catalyst are interesting. However, the manuscript at present cannot be accepted at journal of Catalysts because there are some issues as follow:
1. Introduction of the manuscript is good, but Results and discussion is poor. As a research paper, logicality and correctness are of importance. The reviewer suggests that the authors should recheck the logicality and correctness especially in Results and discussion.
2. Abbreviation is considerably confused in the manuscript. Every abbreviation should be defined when it is mentioned at the first. Furthermore, is the finally targeted material defined as gl-CNTs/Co@N-C or C-Z8/67/M. Such this phenomenon seems to be general in the manuscript. The authors should carefully collect these issues.
3. Some descriptions are incorrect. For example, the authors claimed “The high-resolution XPS spectra of Co 2p (Figure. 3b) exhibits two eminent peaks at about 780.4 and 796.3 eV, which correspond to Co 2p3/2 and Co 2p1/2, respectively. The peaks at 777.9 eV and 793.4 eV are in keep with metallic cobalt (Co0). In addition, two relatively obvious peaks located at around 786.0 eV and 802.5 eV belong to satellite peaks.” This fitting and discussion can be incorrect. In fact, in this work Co0 and Co2+ co-exist in the final material because there are single-atom Co-N species and Co nanoparticles. The authors should get the fitting data on the basis of appropriate references such as Adv. Funct. Mater. 2021, 31, 2103360; Adv. Powder Mater. 2022, 1, 100023.
4. SEM image in Figure 2a is good. However, the quality of SEM images in Figures 1a-d is relatively poor. The reviewer suggests that the authors should re-characterize the SEM imaging and give the better SEM images.
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
The authors report the preparation of 3D Co-N catalysts with a global-local CNT network for ORR. The catalyst prepared in this work showed good ORR performance in terms of both activity and stability. The enhanced ORR activity was attributed to several combined effects of the CNT conductive network, Co-N, N-doping, and mesopores. After review, I recommend that this paper be published after major revision.
- From the SEM images (Figure 1), the MWCNT grown on carbon particles cannot be seen. The high-magnification SEM images are required to confirm the global CNT structure of the catalysts.
- The authors claim that the hollow carbon particles were obtained from the carbonization of ZIF-8. However, there is no solid evidence showing the hollow structure of such carbon particles.
- The authors reported the surface area of only the c-Z8/67/M sample. The surface area and pore distribution of other samples should be shown and discussed for comparison.
- The line style of CV curves in Figure 4a should be revised. The CV curves measured in O2 should be solid, while those in N2 should be dashed.
- According to the XPS measurement, the elemental composition of the catalysts should be calculated from the quantitative analysis and summarized in Table.
- The sample name and color presented in the Tafel plot (Figure 4c) should be consistent with the other results (Figures 4a, 4b, and 4d). What is the red line in Figure 4c?
- The authors used two names (i.e., C-Z8.67/M and gl-CNTs/Co@N-C) for the same sample. This may lead to confusion for the readers. To avoid any confusion, it should be the same name throughout the paper.
- The ring currents measured from the RRDE should be shown along with the disk current in Figure 4b.
- There needs to be detailed information on electrode preparation and electrochemical measurements in the experimental section. The authors should provide detailed information on ink preparation and catalyst loading on the glassy carbon electrode. The catalyst loading and ink mixture have some significant influences on the ORR activity. The disk and ring geometries of the RRDE should also be given.
- To gain more insight and valuable information, I recommend adding the catalysts loading, nitrogen doping, and surface area to Table 1 for comparison.
- What is the Pt loading for the Pt/C benchmark? Please provide.
- Please carefully check superscripts and subscripts throughout the paper.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The present manuscript consists of the study of the catalytic activity of Co-N-C-based carbon materials prepared from 2-methylimidazole and templated into two ZIFs. The work is well-structured and well-written, although the English need to be rechecked. The results are interesting but the manuscript needs to solve some problems that are listed below before publishing:
1. Scheme 1 needs to show with high resolution the compounds used during the synthesis. Moreover, it would be helpful to include the nomenclature in the scheme.
2. The nomenclature must be explained not only in the experimental section but also in the results. It would be easy to understand the text and the results.
3. How can the authors claim better structural stability of the materials on the basis of SEM experiments? SEM is a very useful visual tool, but not to characterize the stability of the materials.
4. The authors mentioned that Co in Z67 promotes the graphitization degree of the materials, as illustrated in the XRD experiments of the materials. However, the material that does not present Z67 also exhibits this peak. This invalids the hypothesis of the authors.
5. Raman spectra are shown in the manuscript, but the results are not discussed at all. What are the differences? Are there any? Same for N2-adsorption isotherms.
6. Please, recheck the N1s spectra. The assignation of the peaks is not well-done and it is not supported by the literature. Pyridinic N species appear at 398.3 eV, Co-N at 399.5 eV, Graphitic N at 401.2, N-O at 402.8 eV. Moreover, these materials are heat treated at 900ºC. This means that pyrroles cannot be observed in the materials since they are not stable at temperatures above 600ºC. Therefore, the peak at 400.2 eV can only be related to N-C-O species. Please, check and include the following literature: Carbon, 2003, 41, 1925–1932 ; ACS Applied Materials and Interfaces 12(49), pp. 54815-54823 ; Carbon, 1995, 33, 1641–1653 ; Carbon 119, pp. 62-71
7. The commercial Pt/C electrocatalysts must be included in the LSV for comparison purposes.
8. In the chronoamperometric analysis (Figure 5c), the authors must indicate the potential of these experiments.
9. One of the most important points in this work is the use of the template and the effect on the ORR catalytic activity. However, once the electrochemical performance is shown, the authors do not mention and compare this electrocatalytic activity with those of the recent literature. Please check, include and discuss the following references of the literature: Fuel 330,125516 ; ChemNanoMat 6(2), pp. 218-222; Journal of Electroanalytical Chemistry 921,116702.
Author Response
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Reviewer 4 Report
This manuscript reports a three-dimensional (3D) nanoreactor of global-local CNTs for the electrocatalytic ORR. This work is intriguing and may promote further experimental design of ORR catalysts based on the carbon-based materials, thus can be considered for publication in this journal after addressing the following minor issues.
1. where is the reactive center of ORR on the developed CNT-based catalysts? How to distinguish the active sites from the various N-doped sites? Pyridinic N, pyrrolic N or graphene N? or the Co sites? It is still obscure.
2. The authors should provide the illustrated diagram of the catalyst structures.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
This manuscript can be accepted for publication in Catalysts.