Expediting Corrosion Engineering for Sulfur-Doped, Self-Supporting Ni-Fe Layered Dihydroxide in Efficient Aqueous Oxygen Evolution
, Hangning Liu 2, Lin Wang 2, Changhui Sun 2, Liangyu Gong 2, Xiaogang Zhang 1,* and Jiefang Zhu 3,*Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsComments for author File: 
Comments.pdf
NA
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsManuscript Title: Expediting Corrosion Engineering for Sulphur-Doped, Self-Supporting Ni-Fe Layered Dihydroxide in Efficient Aqueous Oxygen Evolution
Ms. Ref. No.: catalysts-2896622
In this manuscript, the authors employed a rapid room temperature corrosion engineering technique to generate various sulfur-doped NiFe LDH catalysts by precisely adjusting the quantities of Ni2+ and the reaction duration. The resulting S-NiFe LDH catalyst exhibited outstanding OER activity, with an overpotential of 120.0 mV at a current density of 10 mA cm-2. Furthermore, the catalyst demonstrated favorable reaction kinetics, evident from a Tafel slope of 39.5 mV dec-1 and a double-layer capacitance (Cdl) value of 31.3 mF cm-2. Following thorough evaluation, several concerns have emerged, casting doubt on the manuscript's originality and suitability for publication in the Catalysts journal. The primary issues are elaborated below for your review:
1. I regret to note several scientific inaccuracies in the current manuscript, particularly regarding the OER section:
(a) The authors' decision to utilize a wide potential window for cyclic voltammetry curves (0-2.0V) requires further elucidation.
(b) The observation that the sample with higher sulfur content, S-NiFe LDH-5 (5.0%), exhibits a higher overpotential than S-NiFe LDH-2 (3.7%) and S-NiFe LDH-10 (3.9%) demands an explanation.
(c) The Tafel slope depicted in Fig. 5d is scientifically questionable. S-NiFe LDH-2 (178.7 mV dec-1) displayed a lower potential value, while S-NiFe LDH-5 (39.8 mV dec-1) showed a higher potential value, contradicting expectations.
(d) Although the CV curves clearly exhibit reduction peaks from 1.0 to 1.2V at a scan rate of 50 mV s-1, these reduction peaks are not reflected in the Cdl measurement. Despite scanning from 10 to 200 mV s-1 in the potential window of 1.0~1.1V, no reduction peaks were observed in Fig. 5e and Figs. S5-7.
(e) In Fig. 5f, the overpotential value of S-NiFe LDH-20 (170 mV) exceeds that of S-NiFe LDH-2 (130 mV) and S-NiFe LDH-5 (150 mV). However, the Cdl value is higher for S-NiFe LDH-20 (17.7 mF cm-2) than S-NiFe LDH-2 (13.0 mF cm-2) and S-NiFe LDH-5 (6.9 mF cm-2), conflicting with expectations based on the electrochemical surface area. Clarification of this inconsistency is necessary.
2. In Table S1, the authors reported a total weight percentage of Ni, Fe, S, and O as 100.01%, which is scientifically inaccurate.
3. The manuscript should include an EDX spectrum.
4. In Fig. 2f, there appears to be a discrepancy between the SEM image and its corresponding elemental mapping. Clarification is needed.
5. In lines 163-164, the authors stated that the specific atomic percentages of sulfur in the NiFe LDH catalysts ranged from 3.7% to 5.0%. However, the observed OER activity is unexpectedly low for the S-NiFe LDH-2 and S-NiFe LDH-20 samples. An explanation for this inconsistency is required.
6. Despite the higher sulfur content observed in the S-NiFe LDH-5 samples according to XPS results, the S-NiFe LDH-10 sample exhibited greater electrochemical OER activity than S-NiFe LDH-5. Further clarification of this discrepancy is necessary.
7. Additional deconvolution of XPS spectra of Ni2+ is needed in Fig. 4b.
Comments on the Quality of English LanguageMinor editing of English language required
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors1. The complete manuscript emphasizes the goal of corrosion engineering, yet the Methodology section lacks mention of this term. What specific corrosion engineering procedures were employed in preparing the materials?
2. Provide the balanced chemical reaction for the synthesis of S-doped Ni.
3. From the synthesis reaction, it can be found that wet-chemical synthesis approach has been utilized by simple mixture of 10 mmol of NiCl2 6H2O (for Ni) and 0.3 mmol of Na2S2O3 (for S). In this case, the prepared materials may be NiS rather than S-doped Ni. Also, for the control of reaction, no other reactive or capping agents have been used in the manuscript. Justify.
4. What is the source for LDH in the prepared materials?
5. Provide the vendor and grade details for the RuO2 and KOH used in the manuscript.
6. How do the authors confirm that the prepared materials are double hydroxide rather than hydroxide?
7. The resolution of observed SEM images is poor, provide high-quality images.
8. In Pg 4, Line 141, for the concentration of Ni2+ to 2 mmol, the author suggested that the corrosion product has been formed over the IF substrate, but there is no such evidence in the Figure 3a. What do authors try to address about the corrosion in the prepared materials. If it is observed only in 2mmol of Ni, then how about the other concentration of the materials?
9. Page 5, Line 186, do the authors carried out any characterization for analyzing the electronic structure of the S-doped NiFe LDH?
10. The authors have carried out electrochemical characterization of commercial RuO2 for comparative purposes, however, the fabrication details of the RuO2 are missing in the materials characterization. Whether the RuO2 is coated in a similar IF substrate or some other electrodes. Provide the details.
11. What is the amount of catalysts (active) deposited or coated on each IF substrate?
12. It would be better for the comparative purpose to provide the electrochemical characterization of the bare IF as well.
13. Provide the EIS for all the carried-out samples with their equivalent circuit.
14. Kindly cross check the LSV and Tafel results again, it seems be to controversy with the obtained results.
15. How about the post-characterization results for the electrochemically characterized samples, in order to confirm its stability and reliability towards real-time applications?
16. Provide the comparative table for the OER activity of the synthesized samples with the existing literatures.
17. Page 7, line 230, conclusion, there are several reports existing on ultra-thin lamellar structured microspheres, so I would like to suggest the authors to remove ‘unique’ from the sentence.
18. Aforementioned in Comment 1, there is no corrosion strategy involved in the synthesis reaction, in conclusion, what does the rapid room temperature corrosion strategy signify?
19. References 1-3 cited is irrelevant to the provided context. Kindly check and update with the recent references.
20. Likewise, References 4 and 5, do not refer to PEM fuel cells, kindly check.
21. Kindly remove reference 14 as the provided statement has been originally referred to Ref 13.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsIn my opinion the paper presents an interesting top-down method to synthesize electrodes for use in electrocatalysis. The manuscript seems to have already undergone revision, and it is commendable that the authors have included additional structural characterization. Naturally, some mistakes have appeared with the revisions, and I have done my best to point out inconsistencies. I believe that after some minor corrections and revisions the paper can be accepted for publication.
Abstract: “featuring a minimal overpotential of 120.0 mV to deliver a current density of 10 mV cm-2” should be 10 mA cm-2.
Introduction: “water gas process” is more commonly referred to as steam reforming in my opinion.
Please check the introduction for missing words or incomplete phrases. E.g. line 49-50 “commonly recognized to be commercially (used?) in …”; line 55 “the combine (combination?) of Fe with …”.
2. Results and Discussion would benefit from subchapters, e.g. 2.1. Structural characterization, 2.2. OER activity, etc.
In the TEM discussion it is said that “lattice fringes corresponded a lattice spacing of 0.26 nm between two adjacent fringes, corresponding to the (0 1 2) crystal plane of the S-NiFe LDH material”. The (0 1 2) plane belongs to Ni. It would therefore be more correct to say that.
Table S2 is mentioned before Table S1. As far as I can tell Table S1 is not referenced in the text at all.
P6 lines 191 – 192. “The surface chemical composition of the four samples was analyzed by XPS (Figure 4a)”. This seems to be repeating what was said earlier. Please rephrase.
P7 lines 217 – 218. “Notably, the peak current density of S-NiFe LDH was significantly higher than that of the other three catalysts.” Please specify the exact sample. Do you mean the reductive peak for S-NiFe-LDH-10 at ~ 1.0 V? Also, please be more specific than “Rich electrochemical interface”. According to your discussion, you could claim that more Ni3+ was reduced to 2+.
P7 lines 221 – 222 “S-NiFe LDH-10 has much superior OER activity compared to S-NiFe LDH-2, S-NiFe LDH-5, S-NiFe LDH-20”. From Fig. 5b S-NiFe LDH-10 and 20 are identical in activity.
P7 lines 230-231 “According to the Tafel slop values, the S-NiFe LDH-10 correspond to the Tafel process, the S-NiFe LDH-2, S-NiFe LDH-5 and S-NiFe LDH-20 follow a Volmer process.” Please clarify what you mean by Tafel and Volmer processes. Also, this claim should be substantiated with a reference. I would also avoid claiming different mechanisms from a relatively small difference in Tafel slope. Mixed kinetics are a common occurrence.
4.1. Materials and agents. It is claimed that the thickness of iron foam is 0.1 mm. Is that correct?
In the text, materials and methods, and the supporting info, please fix where needed that the CV measurements for double layer capacitance were carried out at 0.5 – 0.6 V and not 1.0 – 1.1 V.
It should be at least mentioned in the materials and methods section that EIS spectra were interpreted by fitting to equivalent circuits.
Lastly – how was the surface area of the foam measured? For future research, when working with 3D structured electrodes like metallic foams you should keep in mind that the surface area is vastly different from the geometric surface area. That is to say, a 1 cm x 1 cm piece of metallic foam will have a surface area of not 1 cm2 (or 2 cm2 if we assume the other side is not electrically isolated), but much more. This is also why your measured double layer capacitances are so high. You could mention in materials and methods that e.g. “the results were normalized to surface area, which was assumed to be 2 x 2 cm = 4 cm2”. As far as I know there are no universal answers to this problem, so it is up to each researcher to interpret the data.
Comments on the Quality of English LanguageMinor revisions throughout the text could be carried out to make the paper easier to read. I would also advise to try and be more specific when interpreting data.
Author Response
We would like to thank the reviewer for the valuable comments and suggestions based on which we have revised the manuscript carefully to make it stronger, more complete and compelling. All changes have been highlighted in the revised manuscript by formatting the text in blue. Detailed revisions and our corresponding point-to-point responses to the reviewers’ comments are listed in the attachment.
Author Response File: Author Response.pdf
Reviewer 5 Report
Comments and Suggestions for AuthorsAccelerating corrosion engineering of sulfur doped self-supporting Ni-Fe layered dihydroxide for efficient aqueous oxygen evolution
Comments:
This paper presents an interesting method to fabricate a sulfur doped NiFe LDH catalyst using iron foam as the substrate. The catalyst, obtained by this corrosion strategy, exhibits a distinctive morphology (ultrathin lamellar microscopy) which is beneficial for improvement of its electrocatalytic performance.
The paper is interesting for reader because provides relevant information about using the corrosion strategy to the fabrication of anion-doped catalysts and their electrocatalytic applications.
The authors provide data regarding the morphology and composition of the S-NiFe LDH catalyst, including SEM, XRD, XPS, and Raman Spectroscopy measurements.
Evaluation of the electrochemical performance of the new electrocatalyst points out that the S-NiFe LDH catalyst has good catalytic activity towards OER attributed to its distinctive three-dimensional structure and sulfur dopants, as well as a better catalytic activity with RuO2 catalyst for OER.
The manuscript is clear, relevant for the field and presented in a well-structured manner. The presentation of the results is detailed, supplemented with micrographs and graphs as well as extensive descriptions of the results obtained.
Upon a closer examination of the paper, I noticed certain omissions by the authors which must be corrected before publication.
- Abstract: pg. 1, line 22 current density of 10 mV cm-2; correct is mA cm-2.
- Results and Discussion: pg. 7, line 212 and 216. The statement “As shown in Figure 5a, the S-NiFe LDH-2, S-NiFe 212 LDH-5, S-NiFe LDH-10 and S-NiFe LDH-20 showed distinct redox peaks, in which the oxidation peak at approximately 0.30 V corresponds to the valence transition of Fe(II)/Fe(III). Peaks at around 1.0-1.5 V are attributed to the valence transition process of Ni(II)/Ni(III)” must be backed up by references.
Author Response
We would like to thank the reviewer for the valuable comments and suggestions based on which we have revised the manuscript carefully to make it stronger, more complete and compelling. All changes have been highlighted in the revised manuscript by formatting the text in blue. Detailed revisions and our corresponding point-to-point responses to the reviewers’ comments are listed in the attachment.
Author Response File: Author Response.pdf
Reviewer 6 Report
Comments and Suggestions for AuthorsMinor revisions required;
1-Explain the potential of different materials for improving OER such as, MnO2/ZnO, CeCoO3, ZnS/PANI, WO3-PANI and Mn-doped iron selenide.
2-Explain the novelty of the present work in the introduction.
3-Add a comparison table with the literature.
4- Rewrite the conclusions
Author Response
1-Explain the potential of different materials for improving OER such as, MnO2/ZnO, CeCoO3, ZnS/PANI, WO3-PANI and Mn-doped iron selenide.
Reply: Our work has no direct relationship to the above materials. Instead, I have supplented three related references according to reviewer 4 and 5.
2-Explain the novelty of the present work in the introduction.
Reply: We have mentioned the novelty of the present work in the third paragraph of the revised manuscript.
3-Add a comparison table with the literature.
Reply: A comparison table with the literature can be seen from the supplementary information.
4- Rewrite the conclusions The conclusions have re-written the conclusion in the first round revisions according to the 10th queries of reviewer 1.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsAuthors have made efforts to enhance the manuscript; however, there are still gaps that need addressing before publication.
-
The activity of the synthesized catalyst appears exceptionally higher than the benchmark catalyst in terms of onset potential. This is surprising given the nature of such materials; even IrO2 doesn't perform as well.
- Fig5g shows the chronoamperometric stability where the S-NiFe LDH shows enhancement in OER performance after 250 ks (68hrs). This implies that the catalyst is still getting activated and active sites are refreshing. So, ideally the catalyst could be operated for longer stability test. Why didn't authors continue the stability beyond 86 hours?
-
Authors are encouraged to provide evidence of structural stability after stability testing, such as XPS and TEM analysis, to better understand the structural integrity of the catalyst and its ability to withstand a 68-hour stability test.
-
The high frequency resistance appears to be quite high, which raises doubts about such exceptional OER activity. Authors should elaborate on how impedance analysis relates to OER activity.
NA
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors1. The title clearly indicates that the prepared sample is sulfur-doped self-supporting Ni-Fe layered dihydroxide. However, the authors did not determine the sulfur content of the prepared samples, which is a controversy in this current study. I cannot accept your responses 1b and 5 without a proper explanation. XPS is the authentic method to determine the surface chemical composition.
2. The best samples should be consistently referred to as S-NiFe LDH-10 and S-NiFe LDH-6 h throughout the manuscript and in the figures.
3. The authors studied the concentration effect of metal salt by conducting the reaction with Ni2+ concentrations of 2 mmol, 5 mmol, 10 mmol, and 20 mmol, resulting in catalysts denoted as S-NiFe LDH-2, S-NiFe LDH-5, S-NiFe LDH-10, and S-NiFe LDH-20, respectively. However, the authors did not provide the surface chemical composition of the synthesized samples. The atomic or weight ratio of Ni to Fe, which is essential for this study, was not provided.
4. To verify the effect of metal concentration on the composition and crystal structure of the prepared samples, XPS and XRD analyses should be conducted for all the samples.
5. In Table S2, the authors reported a total weight percentage of Ni, Fe, S, and O as 75.0%, which is scientifically inaccurate. Please provide the accurate elemental composition totaling 100%. Last time, they quoted 100.01%, which is also inaccurate.
6. The Cdl values given in the main text for the samples S-NiFe LDH-2, S-NiFe LDH-5, S-NiFe LDH-10, and S-NiFe LDH-20 were 13.0, 6.9, 31.3, and 17.7 mF cm2, respectively (old values). However, in Fig. 5e, the Cdl values of S-NiFe LDH-2, S-NiFe LDH-5, S-NiFe LDH-10, and S-NiFe LDH-20 were 12.6, 14.9, 32.4, and 23.3 mF cm2, respectively (New values).
7. The authors need to learn how to fit the Tafel plot accurately. The Tafel plot in Fig. 5d is scientifically inaccurate. The sample with the lower potential value, S-NiFe LDH-20, has a higher Tafel slope of 83.4 mV dec-1. This discrepancy needs clarification.
8. The authors reported that the sample with a higher Cdl value (23.3 mF cm2) has a higher Tafel value (83.4 mV dec-1), which is scientifically inaccurate. Please clarify this issue.
9. The authors also reported that the sample with a higher Cdl value (14.9 mF cm2) has a higher overpotential (150 mV), which is also scientifically inaccurate. Please clarify this issue.
10. Table S3 shows mismatched Rct values according to the overpotential and Tafel values. An explanation is needed for this discrepancy.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have addressed all the concerns related to the manuscript and therefore I recommend the manuscript to the editors for possible consideration in the journal in its present form.
All the best
Author Response
Reviewer#3
The authors have addressed all the concerns related to the manuscript and therefore I recommend the manuscript to the editors for possible consideration in the journal in its present form.
Reply: We thank the reviewer for the approval and support of our work.
Round 3
Reviewer 1 Report
Comments and Suggestions for AuthorsN/A
Author Response
We thank the reviewer for the approval and support of our work.
