Elucidating Mass Transport within Nanoporous Au for CO2 Electroreduction
Round 1
Reviewer 1 Report
This manuscript by Yang and co-workers demonstrates a study on the role of mass transport within nanoporous gold for CO2 electroreduction. The selectivity of the reaction is reported to be manipulated by the kinetic transport of proton and HCO3 ion within the nanoporous structure. The electrode with different thicknesses has been studied. I think this work has provided some potentially interesting insights into the field. Some minor issues are recommended to be addressed before publication.
1. Gold is very expensive. The use of only Au as an electrocatalyst is not cost-effective.
2. Please define any abbreviations that you use the first time they appear.
3. What is the pore size of the electrode?
Language polishing is needed.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript titled “Elucidating mass transport within nanoporous Au for CO2 electroreduction” presents a study on the CO2 electroreduction into CO using synthesized nanoporous Au shells. This is a novel and important contribution to the field, and the reported values are both promising and relevant to the scope of the Journal. However, the paper suffers from several issues that need to be addressed before it can be published in Catalysts. Specifically, the writing style needs improvement, as the manuscript is not well-organized and difficult to follow in places. Additionally, the conclusions drawn from the experimental results are not always well-supported, and in some cases appear to be speculative rather than based on concrete data. Therefore, there are still some improvements needed before publication in Catalysts.
1. Could you please provide a schematic diagram detailing the synthesis procedure of the nanoporous Au shells? This would help to clarify the process for readers.
2. In subsection 2.2, it would be helpful to include information on the volumes that were deposited. Please revise the manuscript to include this information. Additionally, could you please provide details on the loading of NAAs over the electrode surface? This would provide further insight into the experimental procedure.
3. Is Nafion 212 an anion exchange membrane?
4. The objective and novelty of this work require further clarification. It would be beneficial for the authors to clearly state the research problem they aim to address and outline the specific goals and objectives of the study. Additionally, highlighting the unique contributions of this research in comparison to previous studies in the field would help establish its novelty.
5. The manuscript structure needs improvement to better convey the research presented.
6. It would greatly enhance the reader's understanding if the authors could provide more detailed information regarding the other reduction products that were detected in the output stream at the cathode compartment. Additionally, the rationale for choosing carbon monoxide as the target product should also be elaborated upon. The authors may wish to discuss the advantages of carbon monoxide production compared to other reduction products and how it relates to the overall goals of the research
7. To provide a more comprehensive analysis of the experimental results, it would be valuable if the authors could conduct characterization both before and after the experiments.
8. In addition to the aforementioned characterization techniques, high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) would also be valuable tools for further characterization.
9. It would be beneficial to include both the Faradaic efficiency towards carbon monoxide and hydrogen in a single figure for greater clarity and ease of comparison.
10. The discussion of the results could be enhanced by providing more detailed analysis and interpretation.
11. It is important for the authors to provide an explanation for their choice of using 0.1M KHCO3 as the electrolyte, particularly in comparison to other commonly used aqueous electrolytes with Nafion membranes. This could include a discussion of the specific properties of KHCO3 that make it well-suited for the experiment, as well as any advantages or disadvantages it may have compared to other options. Additionally, the authors could consider discussing how their choice of electrolyte may impact the results and conclusions of the study.
12. The introduction needs to be revised to better explain the requirements for working under industrial conditions and the stability of the electrocatalysts used. Furthermore, the manuscript would benefit from an increased number of relevant and interesting references to support the research presented.
13. The authors are suggested to identify the uniqueness of this manuscript as compared to other works and revise their claim accordingly.
14. It would be beneficial to revise the abstract to more clearly convey the main objective and highlights of the manuscript.
The language used in the manuscript requires improvement in terms of its English expression.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Article – “Elucidating mass transport within nanoporous Au for CO2 electroreduction”
Authors – Wenpeng Yang, Lihua Qian, Rui Zheng, Dapeng Yang, Xiyuan Lu
Summary – The authors demonstrate the selective reduction of CO2 and suppression of HER by performing electrocatalytic reduction on nanoporous Au shells. The authors also show dependence of shell thickness on the selectivity of CO2 reduction. The authors mention increase of local pH inside the shells and mass transport to contribute to the observations.
Overall, the work presented deals with an important ongoing problem of selective CO2 reduction from the competitive HER that occur at higher negative potentials in electrocatalysis. This manuscript needs revisions before acceptance.
Major Comments –
1. Could the authors please include error bars on data presented in plots? Please also mention how many replicates were performed for each study. Minimum 3 replicates should be a norm for scientific data.
2. Please include the method used to calculate FA for CO and H2 formations from voltammograms. Could the authors also comment on the accuracy of determined FAs?
Other Comments –
1. In the Introduction section, could the authors add a few recent studies on selective CO2 reduction on electrocatalyst. Also, could the authors include if NAS has any advantages over other electrocatalyst studied for the same reaction?
2. In the Results section, could the authors include voltammograms recorded for electrocatalysis in this study?
3. Line 108. The authors mention HCO3- ions within microchannels are prompt enough”. Could the authors please explain what the sentence means? And how would HCO3- ions have higher transport than H+, if the authors mean that? Would there be a charge created inside the shells that would be responsible for this observation?
4. Could the authors comment on any other factors that could possibly play a role in selective reduction? Is there any information available on the crystal faces of Au on these NAGs?
5. A suggestion to the authors is to use numerical simulations to model mass transport on the NAS during electrocatalysis.
There are a couple grammar errors which can be easily corrected using grammar correcting apps or Word. Easy to understand the writing overall.
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
W. Yang and co-workers have prepared nanoporous Au shells (NASs), subsequently deposited as films with different thickness in order to study the influence of the presence of channels and pores on the selectivity and activity of CO2 electroreduction reaction. This reviewer believes that this work can be accepted after a general revision of the quality of the English language and after addressing the following minor revisions:
1) This reviewer believes that reporting the chemical reactions involved in the CO2ER in the introduction or in the discussion paragraph, can be of help in better understanding and in describing the complex nature of this scientific problem. In particular, this can better underling the role of the HCO3- ion discussed in the text.
2) In paragraph 2. Results (Page 2, line 69), the authors report the Au and Ag concentration in the NASs materials without indicating the type of characterization technique employed to obtain these results. This reviewer suggests to add this information.
3) In Figure 2 a and b, this reviewer suggests to restrict the interval of the FECO (cutting near 20%) and FEH2 (cutting up to 70 %) in order to better appreciate the difference in FE between the NAS-06 and the other materials tested.
4) In the paragraph 4. Materials and Methods, the authors must add a Characterization part explaining the methods used to acquire the TEM images of Figure 1 and the concentration of Ag and Au described in the Results paragraph.
5) There are some minor typos in this paper: in line 83 and 84, FECO must be corrected to FECO and in line 126 Re and Rct must be corrected in Re and Rct.
Comments for author File: Comments.pdf
This reviewer believes that the quality of the English language must be generally improved to better underling the outcome of this scientific work.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The revised version of the manuscript addresses all of the questions thoroughly, except for one concern: the choice of Nafion as a proton exchange membrane. Could you please provide a reference confirming that the Nafion 212 you used is indeed an anion exchange membrane?
The quality of English Language should be improved.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Authors did a good job at revisions.
The authors mentioned that the FE currently obtained with NAS are mediocre. Could the authors propose and add any ideas to either improve or deal with the FE values for selective CO2 reduction with NAS?
Author Response
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Author Response File: 
Author Response.docx
