Recent Progress in Two-Dimensional Materials for Electrocatalytic CO₂ Reduction

Round 1

Reviewer 1 Report

This review summarized the recent progress in the electrocatalytic CO₂ reduction (ECR) by using two-dimensional (2D) materials, which is a promising strategy to synthesize high-value added chemicals and fuels. This review outlines the key aspects in the design and synthesis of the 2D electrocatalysts and corresponding ECR pathways. In addition, the review also highlights reaction mechanisms through theoretical prediction and in-situ characterization techniques. In summary, the review discusses some important works ranging from laboratory synthesis to commercial applications, which will be of high interest to researchers in ECR fields. I recommend the publication of this review after minor revision.

 Q1. The review is emphasized on the statement of materials. Accordingly, the authors should further summarize the deep relationship between the designed principles of electrocatalysts and highly-selective ECR performance.

Q2. In the Conclusions and Perspectives section, it looks more like merely a brief summary of the references you listed. Could the author provide some profound understanding and new outlook for the ECR field?

 Q3. The ECR can be performed at industrially relevant product formation rates in a rational-designed electrolyser, such as gas diffusion electrodes (GDE) and membrane electrode assembly (MEA). The authors should add some discussion about cell configurations/electrolyzers in the end of this review to sublime the quality of review in the ECR field.

Q4. The field ECR develops very fast. Therefore, some latest work about ECR should be discussed, such as: 10.1002/aesr.202100169; 10.1002/advs.202105204; 10.1021/acs.nanolett.1c00390; 10.1007/s12598-021-01772-7; 10.1007/s12598-021-01736-x

Author Response

Referee 1

Comments to the Author

This review summarized the recent progress in the electrocatalytic CO₂ reduction (ECR) by using two-dimensional (2D) materials, which is a promising strategy to synthesize high-value added chemicals and fuels. This review outlines the key aspects in the design and synthesis of the 2D electrocatalysts and corresponding ECR pathways. In addition, the review also highlights reaction mechanisms through theoretical prediction and in-situ characterization techniques. In summary, the review discusses some important works ranging from laboratory synthesis to commercial applications, which will be of high interest to researchers in ECR fields. I recommend the publication of this review after minor revision.

Thanks for the positive evaluation of our work.

Q1. The review is emphasized on the statement of materials. Accordingly, the authors should further summarize the deep relationship between the designed principles of electrocatalysts and highly-selective ECR performance.

Answer: Thanks for the constructive comments. The relationship between the design principles of electrocatalysts and highly selective ECR performance is important for ECR catalyst development. In this work a wide class of 2D materials have been reviewed. Generally, the intrinsic activity can be modified by ways such as doping, nano-compositing, constructing special structures and morphologies, etc. Meanwhile, the choices of the type of 2D materials catalysts could produce different products. Nevertheless, as the 2D materials covered in this review are very different, it is challenging to summarize a general design principle. However, we have summarized the strategy for each class of 2D materials at the end of each section. The main text has been updated in page 16 lines 11-18, page 20 lines 11-16, page 22 lines 6-11, page 25 lines 15-18, page 29 lines 8-13, and page 36 lines 9-13.

Q2. In the Conclusions and Perspectives section, it looks more like merely a brief summary of the references you listed. Could the author provide some profound understanding and new outlook for the ECR field?

Answer: Thanks for the constructive suggestions. As we stated in the answer to your first question, there is a wide class of 2D materials and they are very different and not directly comparable. Generally, the intrinsic activity can be modified by ways such as doping, nano-compositing, constructing special structures and morphologies, etc. From what has been reported in literature, it seems SAC loaded 2D materials are the most promising. We have updated these in conclusion and perspective, as stated in page 38 lines 24-26, page 39 lines 5-8, lines 26-33, page 40 lines 1-2.

Otherwise, as they are very different materials and we therefore have given a general design description of the design principle and outlook in the conclusion and perspective section.

Q3. The ECR can be performed at industrially relevant product formation rates in a rational-designed electrolyser, such as gas diffusion electrodes (GDE) and membrane electrode assembly (MEA). The authors should add some discussion about cell configurations/electrolyzers in the end of this review to sublime the quality of review in the ECR field.

Answer: The design of the electrolyser is quite important for the commercialization of ECR. Currently, most ECR studies are based on H-cell because it can quickly evaluate the catalyst activity due to its easy operation and adaptability to different kinds of electrode materials and configurations. Whereas there are few reports on other electrolysers such as GDEs and MEA. It has been demonstrated that microfluidic reactor utilizing GDEs and MEA electrolysers for ECR shows great advantages. We have briefly reviewed these electrolysers according to your suggestions, as updated in page 37 lines 1-34, page 38 lines 1-9.

Q4. The field ECR develops very fast. Therefore, some latest work about ECR should be discussed, such as: 10.1002/aesr.202100169; 10.1002/advs.202105204; 10.1021/acs.nanolett.1c00390; 10.1007/s12598-021-01772-7; 10.1007/s12598-021-01736-x

Answer: we have included and discussed the above reference, as updated in page 5 lines 27-34, page 6 lines 1-6, page 15 lines 21-25.

Reviewer 2 Report

The reviewed manuscript by Lu et al has covered most of the latest development of CO2 reduction research on 2D materials. In this context, various 2D materials-converting CO2 have also been comprehensively discussed. Overall, the review is well-written and would be beneficial for those researchers who focus on CO2 electrochemical reduction. Therefore I suggest this manuscript be published in Catalyst. I have only minor concerns as follows :
1. Authors are also suggested including more papers published in 2021-2022.
2. I think it would be better if authors can list the advantage and disadvantages of each 2D material for the use of CO2 reduction. 

Author Response

Referee 2

Comments to the Author

The reviewed manuscript by Lu et al has covered most of the latest development of CO₂ reduction research on 2D materials. In this context, various 2D materials-converting CO₂ have also been comprehensively discussed. Overall, the review is well-written and would be beneficial for those researchers who focus on CO₂ electrochemical reduction. Therefore, I suggest this manuscript be published in Catalyst. I have only minor concerns as follows:

Thank you very much for your positive evaluations!

1.Authors are also suggested including more papers published in 2021-2022.

Answer: We have replaced some references and added new reference published in 2021-2022, as updated in page 5 lines 5 (reference 44), page 5 lines 7 (reference 45, 46, 48), page 5 lines 31 (reference 54), page 5 lines 33 (reference 55), page 6 lines 2 (reference 56), page 6 lines 6 (reference 57), page 15 lines 23 (reference 122).

2. I think it would be better if authors can list the advantage and disadvantages of each 2D material for the use of CO₂ reduction. 

Answer: Thanks for the constructive suggestions. There are a wide class of 2D materials and they are very different and not directly comparable. For each 2D material, we have discussed the intrinsic properties such as good conductivity and stability, high surface area, expose of the active sites, unique electronic structures, etc. These merits are very important in electrocatalytic reactions. The drawbacks such as limited reserved for precious metal, high cost, poor conductivity, instability and difficult to preparation, etc.  have also been discussed in relevant sections for each 2D material. From what has been reported in literature, it seems SAC loaded 2D materials are the most promising. We have emphasized this, as updated in page 36 lines 9-13. We have further summarized the strategy for each class of 2D materials at the end of each section. The main text has been updated in page 16 lines 11-18, page 20 lines 11-16, page 22 lines 6-11, page 25 lines 15-18, page 29 lines 8-13, and page 36 lines 9-13.. Please also refer to our answers to Refer 1, question 1 and 2.