Peer review of: Single-site pyrrolic-nitrogen-doped sp2-hybridized carbon materials and their pseudocapacitance (2020)

RR2
Reviewers' Comments:
 Reviewer #1:
 Remarks to the Author:
 The authors have addressed all my concerns. Therefore, I would like to recommend its publication in
 Nature Communications.
 Reviewer #2:
 Remarks to the Author:
 Unfortunately the revision is not satisfactory in terms of the following points:
 (1)XPS analysis
 I have mentioned in my previous review that the authors should show the width of XPS peak used for
 fitting. The revision is not enough. This is an important point because, for example, general reader can
 easily doubt the deconvolution analysis in Fig. 3 if the different width is used for the fitting analysis. In
 fact, it seems not fair in the current version because Figs. b-n are fitted with multiple peaks while Figs.
 d-p were fitted by single peak (there is no clear explanation about this delicate point). That is, Figs. d-
 p can be probably fitted with multiple peaks! If so, the conclusion is totally different!
 Moreover, in the reply letter to the third reviewer, authors described as
 “In Ref. 21 (Page 361, Science 351, 361-365 (2016)), the authors described as follows: “To determine
 the active site conclusively, we develop four types of model catalysts with well-defined p-conjugation
 based on highly oriented pyrolytic graphite (HOPG): (i) pyridinic N-dominated HOPG (pyri-HOPG); (ii)
 graphitic N-dominated HOPG (grap-HOPG), and for comparison, (iii) edges patterned on the surface
 without N (edge-HOPG); and (iv) clean-HOPG (see supplementary methods and fig. S1).” Pyridinic N-
 dominated HOPG (pyri-HOPG) and graphitic N-dominated HOPG (grap-HOPG) mentioned by the
 authors don’t refer to pure pyridinic N or graphitic N doped HOPG. As shown in the inset of Fig. 1F in
 Ref. 21, the percentage of graphitic N in graphitic N-dominated HOPG is about 82.2 % (0.60/0.73)
 and the percentage of pyridinic N in pyridinic N-dominated HOPG is about 95 % (0.57/0.60).”
 But the indicated figure extracted from (Science 351, 361-365 (2016)) in the reply letter by the
 authors show higher quality compared to the result by the authors in terms of selectivity of the peak
 component in the material. The derived percentage (pointed out by the authors) is just a result due to
 the fitting accuracy (I doubt poor fitting analysis by the authors now because there is no clear
 description about this important analysis). In any case, the general reader cannot convince that the
 XPS results in Figs. 3d-p are composed by a single component.
 Moreover, there are other reports showing single component nitrogen doping (for example, J. Mate.
 Chem., 2011, 21, 8038).
 I thus suggest that authors should revise the manuscript as originally the third referee pointed out.
 (2) Pyridonic nitrogen and hydrogenated pyridinic nitrogen
 Authors added the description about pyridonic nitrogen to support the assignment for the pyrrolic
 nitrogen. The discussion is good. It is however not strong evidence but possible interpretation. The
 strong experimental evidences to support the assignment is still required, strictly to say.
 Moreover, authors did not revise the manuscript for the hydrogenated pyridinic nitrogen though some
 descriptions are there in the reply letter.
 (3) “Significant figures” and instrumental calibration
 In the revision, authors describe as “Therefore, interplanar spacing of the (002) plane of small
 microcrystalline graphite of SPNCMs (F, 1/1) was calculated to be 0.3645 nm, far larger than 0.3354
 nm, interplanar spacing of the (002) plane of ideal graphite.”
 
But there is no description about the accuracy about the value 0.3645 nm. In the previous version of
 the manuscript, the value was very rough. The authors should clearly describe the reliable “Significant
 figures”. Also, authors should clearly describe how to calibrate the instrumental deviation of the
 measured distances from XRD, TEM and STEM from the exact value.
 Reviewer #3:
 Remarks to the Author:
 Although the authors have added much data in the revised manuscript, the Reviewer still insists that
 the quality of the article is the most important criterion for the publication in prestigious journals, like
 Nature Commutation. Thus, the reviewer rejects acceptance of the revised manuscript for publication.
 Specific comments:
 1. Many of the results are improperly interpreted. First of all, the authors demonstrated the defects in
 the porous carbon mainly by Raman, for example: the author stated that “The Raman spectrum of
 NCMs (F, 1/1) has been added in Fig. 2a, and the corresponding ratio of intensity of D/G bands was
 determined to be 0.99, slightly lower than that of SPNCMs (F, 1/1) (1.03), possibly because alkaline
 activation induces more defective sites when nitrogen-containing functionals are completely converted
 to single pyrrolic nitrogen configuration. As shown in Figure 2a and Supplementary Figure 9, Raman
 spectra of SPNCMs (F, 1/1), SPNCMs (F, 1/3), SPNCMs (F, 1/7), and CMs (FPF) show similar feature of
 sp2-hybridized carbon materials with the disorder-induced D-band and a first-order graphite-like G-
 band. ID/IG values of these four carbon materials were determined to be 1.03, 0.96, 0.99, 1.02.” and
 “Similar to the Raman spectrum of NCMs (F, 1/1), that of SPNCMs (F, 1/1) (Fig. 2a) shows typical
 feature of sp2-hybridized carbon materials with abundant defects induced mainly by nitrogen doping,
 as inferred by the high intensity ratio of about 1.03 between the disorder-induced D-band at 1353 cm-
 1 and a first-order graphite-like G-band at 1593 cm-1 (ID/IG) of SPNCMs (F, 1/1)51.”
 However, Raman D band does not in any sense whatsoever represent disorder carbons, though many
 people have published so. The authors should cite proper Raman papers on special Raman
 spectroscopy of graphene or carbon materials, not materials papers with often wrong interpretations
 of fundamental Raman results. Check work by Andrea Ferrari, Denis Basko, Mildred Dresselhaus, Ado
 Jorio, Riichiro Saito, Kentaro Sato, or any other systematic work on Raman of graphene, defective
 graphene, amorphous carbon, defects and impurities in graphene-like materials.
 The above interpretation is only acceptable for well-ordered graphene. In fact, it is the opposite for
 highly defective graphitic carbon. The Tunistra-Koenig (T-K) relation breaks down, and the explanation
 of high D/G peak corresponding to high defect is not often correct. In addition, assigning D/G ratio
 without a systematic fitting can be meaningless. A comprehensive and appropriate Raman analysis
 should be carried out to substantiate structural claims. What’s more, it’s better to present a statistical
 analysis of the Raman D/G peak ratios.
 In this study, the D peak of the typical sample is too wide, and the diffraction peaks of (002) and
 (100) are broad, this kind of carbon just like amorphous carbon, rather than sp2-conjugated carbon!
 At least, the 2D band (the value should be labeled) in the Raman spectra and SAED should be
 provided for demonstrating the so-called sp2-conjugated structure!
 The authors stated that “The ratio of intensity of D/G bands of NCMs (F, 1/1) was determined to be
 0.99, slightly lower than that of SPNCMs (F, 1/1) (1.03), possibly because alkaline activation induces
 more defective sites,” However, they also described that Raman spectra of SPNCMs (F, 1/1), SPNCMs
 (F, 1/3), SPNCMs (F, 1/7), and CMs (FPF) with the ID/IG values of 1.03, 0.96, 0.99, 1.02 show similar
 feature of sp2-hybridized carbon materials with the disorder-induced D-band and a first-order
 graphite-like G-band. It is inappropriate to interpret the data according to their subjective needs!
 2. Page 6, Line 19. “Additionally, EDS analysis shows uniform doping of nitrogen species into the
 
turbostratic carbon framework for SPNCMs (F, 1/1) (Supplementary Fig. 1f, g).” Firstly. Because the
 elements of N and C are two neighbor light elements, it’s very hard to distinguish them from each
 other by this kind of element mapping, authors should reconsider it. Also, the shapes of the images in
 Supplementary Fig.s 1e, f, g are different!
 3. The reviewer doesn’t think the structures of NCMs and SPNCMs shown in Figure 1 are appropriate,
 as the O contents of the samples are not low!
 4. In the Reviewer’s opinion, the typical sample in this study is N and O co-dopd carbon, however, the
 authors didn’t take the effect of O on the dopant N into account at all!
 5. The authors stated that “thermal treatment below about 600 oC always yields lowly graphitized
 nitrogen-doped carbon materials with poor electrical conductivity...” What are the specific values of
 conductivity of the samples in this study, how about these values compared with commercial
 conductive carbon?
 6. The topic of this work is “sp2-conjugated Carbon Materials”, why the authors cited 16 of Ref.s on
 sp3 and sp carbon in the introduction section in the revised version? So much Ref.s (1/4 of the total)
 make the reviewer a little confused!
 7. For HR-XPS spectra, the basic rules of the deconvolution should be obeyed. At least, the half-width
 of each peak for one element should be consistent! There are still some problems of the deconvolution
 in Figure 3f, Supplementary Figure 6c, and Supplementary Figure 12c in the revised version!