Novel Bifunctional Nitrogen Doped MoS2/COF-C4N Vertical Heterostructures for Electrocatalytic HER and OER
Round 1
Reviewer 1 Report
This Manuscript reports an experimental and theoretical exploration of N-MoS2/COF-C4N nanocomposites for HER and OER reaction. The results indicated that the N-MoS2 part in the composites is mainly contributed to HER activity and COF-C4N possess excellent OER activity. The structure of the manuscript is basically complete, but there are some points which could improve in revision, which are listed below.
- The authors emphasize the vertical structure between molybdenum disulfide and COF substrate, but XRD and SEM results do not support this view. I don't think the description of “vertical structure” is appropriate.
- The authors declared there are uniformly distributed pores on the surface of COF-C4N. But it is not obvious that there are pores in Fig. 3a.
- The complex N-MoS2/COF-C4N1:1 shows the best electrocatalytic activity. Is this ratio the feed ratio or the actual ratio?
There are too many formatting errors. For example, line 99, line 106-109, line 223, line 286, etc. The author should check the manuscript carefully.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
This manuscript reports the relatively impressive electrocatalytic activity for both HER and OER on a MoS2/CoF-C4N nanostructure. While the concept is exciting and thorough experimental/theoretical study was done, several concerning issues should be addressed before it can be considered for publication in Catalysts, detailed below.
1. The authors said that their synthetic method is simple and facile in the Abstract and Introduction. It is not convincing. Indeed, many benzene- and furan-based chemicals, usually toxic, are used for the synthesis. Not to mention a long time of more than seven days to get the final MoS2/CoF-C4N catalyst. I suggest removing the words “simple” and “facile.”
2. There are many unnecessary capitalized words such as Thiourea, Molybdenum… Please check
3. Any abbreviation should be defined at it first appears. For example, COF has never been defined in the whole manuscript.
4. Unit in the manuscript contains a large number of mistakes and typos. First, a space is required between a number and a unit, with except for %. Accurateness and consistency should be made.
For example:
- Line 99: 4 M not 4m
- Line 141-145 and Fig. 4c: mV s-1 not mV S-1
- Line 141: rpm not rmp
- Figure 2: Binding energy not Binding Energy or enery.
5. Please explain why ITO substrate is used instead of carbon cloth in EIS measurement.
6. The fitting and peak assignment are incorrect in S 2p spectra (Fig. 2g). First, for 2p orbital, there is only one 2p1/2 and one 2p3/2. The peak of 2p1/2 and one 2p3/2 should have the same FWHM. More importantly, considering the S 2p peak has closely spaced spin-orbit components (Δ=1.16eV, intensity ratio=0.5), I believe that there are only two components should be deconvoluted.
7. In the Nyquist plot, the scale length at x-axis should be equal to the length at y-axis. Otherwise, the plots will be deformed and the non-ideal capacitance behavior will be misinterpreted.
8. Morphology characterization and surface chemical structure after the electrolysis would be very interesting and add value to this manuscript. SEM (or TEM) and XPS of the sample after the reaction should be given.
9. Some figures were not explained at all, for example, Fig. 4c. More importantly, I noted that authors measured scan rate-dependent CV at potential of where J achieved -10 mA. It is a methodological mistake. Indeed, the capacitive-current plot can’t be linear (Fig. 4g, black line). One should be aware that double-layer capacitance only can be estimated accurately by the measurement and calculation of CVs with multiple scan rates in a non-Faradaic region where the measured capacitive currents are associated with the Cdl. Therefore, those figures must be re-measured.
10. Last, as the authors have demonstrated that MoS2/CoF-C4N can act as bifunctional electrocatalst for both HER and OER. An additional measurement using two-electrode set-up should be provied. Then authors are suggested to compare their cell voltage with the previously reported studies.Comments for author File: Comments.pdf
Author Response
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Author Response File: 
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Reviewer 3 Report
In this manuscript, the authors reported a simple, facile and effective strategy to fabricate a completely new nitrogen doped MoS2/COF-C4N vertical heterojunction (N-MoS2/COF-C4N) as precious-metal- free bifunctional electrocatalysts for both HER and OER. Compared with MoS2 and COF-C4N, the obtained vertical N-MoS2/COF-C4N catalyst showed enhanced HER with low overpotential of 106 mV at 10 mA cm-2, which is 6 times lower than MoS2. The superior acidic HER activity, molecular mechanism and charge transfer characteristic of this vertical N-MoS2/COF-C4N was investigated experimentally and theoretically in detail. And its basic OER activity almost equals to that of COF- C4N with overpotential of 349 mV at 10 mA cm-2, which showed that in-situ growing method maintains the exposure of the C active sites to the greatest extent. The research is meaningful, and I would like to recommend its publication after minor revisions.
(1) Did the size and shape of N-MoS2/COF-C4N affect the performance of electrocatalysts? And how?
(2) Figure 4c and 4f, the scanning speed should be provided in the captain.
(3) During electrocatalytic process, did the authors investigate any Mo leaking? And evidence?
(4) Some related references might be included in the revised manuscript: 10.1039/D1TA05892D; 10.1016/j.elecom.2021.107024; 10.1016/j.cej.2021.133730
(5) Reference 32, should be international
(6) TOC is required
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The authors have addressed all my comments appropriately, and accordingly have improved the manuscript. It is now publishable in Catalysts.
