Large-Scale and Simple Synthesis of NiFe(OH)_x Electrode Derived from Raney Ni Precursor for Efficient Alkaline Water Electrolyzer

Round 1

Reviewer 1 Report

The research introduces a methodology aimed at tackling the challenge of upscaling the synthesis of highly efficient oxygen evolution reaction (OER) catalysts, essential for industrial applications in water electrolysis amidst the growing demand for green hydrogen. This study emphasizes the necessity for electrode materials capable of efficient performance on a larger scale. Specifically, it delves into the production of a self-supported NiFe(OH)x@Raney Ni anode, surpassing 300 mm in dimension, leveraging a commercially available Raney Ni-coated Ni mesh as a precursor material. Employing a straightforward immersion technique, the electrode showcases outstanding electrocatalytic OER activity, requiring only an overpotential of 240 mV to achieve 10 mA·cm². Additionally, the manufactured electrode demonstrates notable durability, sustaining stable operation for more than 100 hours under a current density of 500 mA·cm². Hence, the manuscript can be better fit another journal and here are some other comments:

1.      Did the authors investigate quantitative analysis of hydrogen/oxygen evolution over time?

2.      When calculating the potential to the reversible hydrogen electrode, the potential of reference electrode is missing. The correct Nerst equation should be: E RHE = E SCE + (reference electrode potential; theoretical for calomel electrode +0.244 V) + pHx0.059 (doi: 10.1021/acscatal.7b03949 10.1021/acsami.7b17257)

3.      Important details are missing, such as the excitation voltage and XPS lamp current, as well as the composition of the anode material.

4.      SEM images (Figure 1) posses different scales. Please, change the images so that the scale is the same, which makes it easier to analyze the images.

5.      EDS analysis quality is poor - there is no obvious “crack” in the middle, which should be reflected in the elemental analysis. I believe that conclusions should not be drawn based on this analysis. Based on this images there is a lot of Al in sample, not just residue.

6.      How would authors explain why the Al signal in EDS analysis is co intense, but XRD shows no signal from Al.

7.      Figure 2a - Authors should include the zoom to 2θ ~ 30º so that it is clearly visible whether the signal belongs to Ni or Al.

8.      After deconvolution of Fe 2p core level spectra clearly one signal around BE=713eV is missing.

9.      In “3.4. Electrochemical Measurements” part Authors describe the EIS analysis, however the EIS results are missing.

10.  Authors should consider including Tafel plot analysis to the manuscript.

11.  For comparison the authors should   include LSV measurements for pristine Raney Ni or Raney Ni-coated Ni mesh.

12.  How would the author explain the peaks in LSV in 1.2-1.4V region? Thy the curve is below 0 in initial phase?

13.  Can authors provide the LSV curves to the full extent including the loop? For example, like in this article: https://doi.org/10.3390/surfaces1010013

14.  Stability test in longer time should be investigated.

15.  How the authors chose the area for research in such a specific place (Figure 4a)? What is the surface of the mesh that is involved in the reaction in this electrolyzer?

The sentence structure here could be improved for better clarity and coherence. Consider breaking down complex sentences into shorter ones to enhance readability.

Author Response

Please see the attachment for the Reply to the Review Report.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this work, the authors fabricated a self-supported NiFe(OH)x@Raney Ni with scalable dimension exceeding 0.3 m via a facile immersion method, which exhibits remarkable performance and stability. The quality of this manuscript is good and can be published after well addressing the following comments.

1.     To highlight the importance of green hydrogen and improve the readability of the introduction, the authors are suggested to combine some data about global hydrogen requirement and economics in the background, which can refer to this work 10.1039/D3EE02695G.

2.     The references for PDF cards should be provided and some superscript and subscript mistakes should be corrected through the manuscript.

3.     To prove the rationality of O 1s XPS analysis, necessary references should be added.

4.     To briefly demonstrate the activity improvement of NiFe(OH)x@Raney Ni, the authors are suggested to discuss the synergistic effects between Ni and Fe, which can refer to this work 10.1002/cey2.465 for this point.

Author Response

Reply to the Reviewer

In this work, the authors fabricated a self-supported NiFe(OH)_x@Raney Ni with scalable dimension exceeding 0.3 m via a facile immersion method, which exhibits remarkable performance and stability. The quality of this manuscript is good and can be published after well addressing the following comments.

Response: We are grateful for the time and effort the reviewer had spent on our manuscript, and deeply appreciate the valuable review and positive comments of our manuscript, which have helped improve the manuscript quality.

Comment 1: To highlight the importance of green hydrogen and improve the readability of the introduction, the authors are suggested to combine some data about global hydrogen requirement and economics in the background, which can refer to this work 10.1039/D3EE02695G.

Response: Thank you for your suggestion. To further illustrate the demand for hydrogen energy, we refer to 10.1039/D3EE02695G and added relevant descriptions.

We inserted in the first paragraph of the introduction: Based on the analysis of the International Energy Agency (IEA) on the total global final energy consumption, the proportion of hydrogen energy in the total final energy consumption should increase to ~2% by 2030 and ~10% by 2050.

Comment 2: The references for PDF cards should be provided and some superscript and subscript mistakes should be corrected through the manuscript.

Response: Thank you for this suggestion. We have added citations for two standard cards, Al (PDF#04-0787) and Ni (PDF#04-0850) respectively. Additionally, we carefully revised the superscript and subscript issues throughout the manuscript.

Comment 3: To prove the rationality of O 1s XPS analysis, necessary references should be added.

Response: Thank you for this valuable suggestion. We cited reference 10.1016/j.cej.2023.141413 in the XPS analysis of O 1s to demonstrate the rationality of the analysis results.

Comment 4: To briefly demonstrate the activity improvement of NiFe(OH)_x@Raney Ni, the authors are suggested to discuss the synergistic effects between Ni and Fe, which can refer to this work 10.1002/cey2.465 for this point.

Response: Thank you for your suggestion. We have added a discussion on the synergistic effect of Ni and Fe, citing reference 10.1002/cey2.465.

We inserted in the line 181 page 5: Similar to previous reports, the high activity of the prepared catalyst is associated with the synergistic effect between Ni and Fe, and the strong Ni/Fe-O covalency facilitates electron transfer.

Round 2

Reviewer 1 Report

The authors have effectively addressed all inquiries raised, demonstrating a satisfactory level of responsiveness. Moreover, they have introduced additional tests that significantly enhance the quality of the research, further substantiating the suitability of the chosen materials. Considering these developments, I recommend accepting the publication.

I noticed a few errors that do not affect the understanding of the article