Versatile Bifunctional and Supported IrNi Oxide Catalyst for Photoelectrochemical Water Splitting

Round 1

Reviewer 1 Report (New Reviewer)

Manuscript “Versatile Bifunctional and Supported IrNi Alloy Catalyst for Photoelectrochemical Water Splitting” studied the photoelectrochemical properties of IrNi alloy supported on activated carbon. The influence on the properties of the material was investigated by changing the proportion of the alloy and the pH of the electrolyte. The results show that sample 4Ir1Ni@AC has the best catalytic performance. The manuscript can be published in “Catalysts” after a major revision. The concerns which should be considered by the authors are as follows:

1.     The images used in the manuscript are of low resolution.

2.     The performance of samples with Ni ratio less than 20% should also be explored.

3.     The scale of picture 3d should be adjusted. The peak of active carbon should also be marked, the standard peak patterns and the sample curves can be put together.

4.     In Figure 4a, it is necessary to indicate the existence position of the characteristic peak. And check the data selection and the calculation method of band gaps in Figure 4b.

5.     The display of Tafel slope in Figure S5 and S6 are not intuitive enough and needs to be modified by referring to other articles.

6.     The text explanation does not point to Figure 5c.

7.     In Chapter 4, the author mentioned "Tauc plots, and PL emission spectra affirmed the favorable d-band center and oxygen vacancies in 4Ir1Ni@AC catalyst", however, there are no other descriptions of oxygen vacancies in the article, and additional characterizations are needed to prove the existence of oxygen vacancies.

8.     There are some formatting irregularities in the manuscript, such as spaces and tenses. Authors are requested to check and revise carefully.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report (New Reviewer)

I have carefully read this paper entitled with “Versatile Bifunctional and Supported IrNi Alloy Catalyst for Photoelectrochemical Water Splitting ". As a result, I have only a few minor points that the authors should address before it is accepted for publication. Please, publish subject to the following revisions:

1-      There are a few grammatical mistakes. Please check the manuscript for grammar and English.

2-      Rewrite the novelty statement at the end of the introduction section.

3-      Authors should justify the importance of the current work of how this is different from earlier reports. So, it’s better to add comparison table material and its performance to show the importance of the manuscript.

4-      Please add EIS analysis to improve the charge transfer between the electrodes and the electrolyte.

5-      Please confirm the element after the prepared electrode by XPS or SEM elemental analysis

6-      Abstract and conclusion should be rewritten and showed more clear results and novelty of this study.

Author Response

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Reviewer 3 Report (New Reviewer)

The manuscript could be accepted after major revision. my comments are:

The quality of figures are very low. The high quality figures must be provided.
XPS analysis should be provided.

IrNi alloy or IrNi oxide alloy?

There is no obvious evidence for oxygen vacancies.

Author Response

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Round 2

Reviewer 1 Report (New Reviewer)

Reviewer 3 Report (New Reviewer)

Accept

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Versatile Bifunctional and Supported IrNi Alloy Catalyst for Photoelectrochemical Water Splitting is well-written and I recommended it for publication after major revisions. Here are the comments:

1. Please, note in the Abstract part that the SEM/EDX, XRD, and UV-visible technique of physicochemical characterization of examined samples was used.
2. Please add an explanation for the 3%Ni@AC and 3%Ir@AC abbreviation in the last paragraph of the Introduction part.
3. LSV curves of Ir and Ni metals and alloys on the activated carbon matrix for HER and OER look strange. Please, see ref. https://doi.org/10.1016/j.poly.2020.114871 and check all LSV HER and OER curves.
4. The authors should calculate the Tafel slope and onset potential of all six tested catalysts during HER and OER. Additionally, please these results compare with the literature reports.
5. Please add appropriate references for XRD and UV-visible analysis in the Results and discussion part.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The authors reported an interesting IrNi alloy catalyst with an Ir:Ni ratio of 4:1 that shows excellent hydrogen and oxygen evolution under 1 sunlight (100 mW cm^-2) irradiation at high rates in a wide pH range when assessed with NaOH, Na₂SO₄, and H₂SO₄. It was found that the cumulative effect of relatively high crystallinity, reduced charge recombination rate, and im-proved oxygen vacancies observed with the 4Ir1Ni@AC electrode is the reason for the superior activity obtained. A high level of durability for hydrogen and oxygen evolution under light illumination is seen in the chronoamperometric study over 15 h of operation. Before considering the acceptance of this manuscript, the authors should address the following issues:

1. Some grammar issues. For example, “… activity was tested in alkaline, neutral, and acidic media under 100 mW.cm^-2 light illumination (Fig. 1a-f) and without.” The authors should carefully check the whole manuscript to correct all typos and grammar issues.
2. In Figure 2d, the authors should provide the standard diffraction peaks of Ir and Ni for better comparison.
3. In Page 8, the authors claimed “Comparing the Mott–Schottky slopes, for 1Ir1Ni@AC these were slightly steeper than those of 4Ir1Ni@AC. This reduced Mott–Schottky slope was a result of the increased donor density in the material, which can be further ascribed to the oxygen vacancy [40,41].” This expression is incorrect. Actually, a lower Mott–Schottky slope means a higher donor density. The authors should double check the equation to calculate the donor density from Mott–Schottky slopes.
4. The authors used the Tauc plots in Figure 3b to show the bandgaps of 4Ir1Ni@AC and 1Ir1Ni@AC is not convincible, because the light absorption curves shown in Figure 3a cover all the visible light region. It is hard to see the difference in the light absorption range for all samples. In addition, there are three slopes in the Tauc plots for both samples. Why the authors choose those slopes to show the bandgap of the samples?
5. It is very interesting to see that the 4Ir1Ni@AC electrode shows so much high current densities under AM1.5 G illumination compared to that of in the dark. The authors should do more characterizations to understand the underlying mechanism.
6. Some related references are recommended to cite and discuss in the manuscript: J. Cent. South Univ., 2021, 28, 2345-2359; Tungsten, 2020, 2, 390-402; J. Mater. Chem. A, 2020, 8, 24307–24352.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript by Zavahir et al. presents photo-electrocatalytic water splitting on IrNi catalyst. Although authors have tried to characterized the material well, there are some points that must be improved/corrected before possible publication, as pointed below:

1)

Photoabsorption properties should be analyzed with diffuse reflectance spectroscopy. The figures 3a and 3b cannot be used for any valuable discussion.

2)

It is a pity that authors have not checked the amount (rate) of generated hydrogen and oxygen. I do recommend such experiments for valuable discussion (on the course of gas evolution – stability, etc.)

3)

The manuscript has been written carelessly, e.g.,

• inconsistency in writing (Electrolyte and electrolyte in Fig. 6 and 5, respectively; Time and time in Figure 6, etc.)
• The abstract should be more concrete, e.g., “high rates” means nothing.
• Keywords: “photoelectrocatalytic” is adjective not noun.
• Pronouns are not recommended in scientific writing (e.g., “we” in the first sentence of Conclusions).

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

1. Please revised all LSV HER and OER curves. Potential vs. RHE is wrong presented. HER LSVs should be presented from about 0 to about -0.8 V vs. RHE, and OER LSVs from 1.2 to about 1.8 V vs. RHE. Please check ref. 10.1039/d0dt04000b (Dalton Trans.,2021, 50,5473–5482).

2. Please revised HER and OER Tafel plots. Please check ref. 10.1039/d0dt04000b (Dalton Trans.,2021, 50,5473–5482).

Comments for author File: Comments.pdf

Author Response

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Reviewer 2 Report

The authors have addressed all comments from reviewers and the quality of the manuscript has been improved. Thus, the manuscript can be accepted at the current version.

Author Response

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Round 3

Reviewer 1 Report

·         Unfortunately, the potentials of LSV OER and HER curves in the manuscript were given vs. SCE, not vs. RHE. You need to use the next equation: E(RHE)=E(SCE)+0,242+0,059∙pH(solution).

·     Unfortunately, Tafel plots for HER are not correct. Check ref.  Q. Dang, et al. Applied Catalysis B: Environmental 257 (2019) 117905

Author Response

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