A Recent Review of Primary Hydrogen Carriers, Hydrogen Production Methods, and Applications

Round 1

Reviewer 1 Report

In this review article, the authors summarize the results of a series of scientific papers, focusing on the development status of hydrogen energy utilization. While the topic is interesting, I feel that the quality of this review article needs to be improved before it can be considered for publication.

 1. The abstract is not complete. In this abstract, the main results and conclusions are missing.

2. The quality of the figures needs to be improved. The resolution must be higher.

Author Response

In this review article, the authors summarize the results of a series of scientific papers, focusing on the development status of hydrogen energy utilization. While the topic is interesting, I feel that the quality of this review article needs to be improved before it can be considered for publication.

Ans.: We are thankful to the reviewer’s comments. According to the reviewer’s suggestions I have improved the quality of review following the comments of the reviewer.

1. The abstract is not complete. In this abstract, the main results and conclusions are missing.

Ans.: We added the part of main result and conclusion in the abstract in the revised version of the manuscript.

2. The quality of the figures needs to be improved. The resolution must be higher.

Ans.:  We agree with the reviewer that some figures are not in the proper resolution. It has to be mentioned that those figures are taken directly from the original references, hence, it is impossible to change the quality of the figure.

3. Future perspectives, at the end of the conclusions, are a summation of sentences. The authors should focus on a couple of key points based on what is missing from the reviewed articles.

Ans. Thank you for the comment. We revised the conclusion part as a conclusion and perspectives and suggested some future tasks to enhance the present technologies according to the reviewed papers.

4. The literary survey is mostly adequate, however there are articles from the last century. Authors should focus on recent articles that have not been reviewed in other review articles. Articles published in the last 5 years or maybe even more recent. In addition, some related articles published in Catalysts are suggested to be cited.

For example, Catalysts 2023, 13(1), 176, https://doi.org/10.3390/catal13010176; Catalysts 2023, 12(7), 747; https://doi.org/10.3390/catal12070747

Ans.: We are thankful to the reviewer for the additional references to improve this review. To introduce the primary knowledge in each research field, we referred some old articles in this review work. In the revised version, we added those references as Ref.50 and Ref.54.  

5. The writing is inadequate, and the English needs improvement. There are many words with no subscript, e.g. Al2O3.

Ans. We are sorry for the typographical error and corrected in the revised version of the manuscript. The language also improved and final manuscript was checked by English editing company with native speaker in this research field.

6. The manuscript is well organized, and it offers a suitable summary and outlook on the field. However, the authors should make an effort trying to highlight their main findings and contributions to this research field, remarking their own contributions. Only two references on formic acid from the corresponding author have been cited.

Ans. Thank you for your comments. We revised manuscript in Page 11, Paragraph 5, and further added references to highlight our main findings.

Reviewer 2 Report

Comments to the authors:

This review summarizes about primary hydrogen carriers, hydrogen production methods, and applications. However, the work is only a simple/common summary of the previous work, lacking of the own views and valuable ideas. Moreover, some detail issues in this review need further attention. Considering the current status of the submitted manuscript, it is suggested to be supplemented for its resubmission. Some questions and suggestions are given below:

1.    Detailed comparison of advantages and disadvantages of hydrogen carriers should be added.

2.    In the section of Water electrolysis: Three water electrolysis techniques can be employed based on the electrolyte used: alkaline electrolysis (AEL), proton exchange membrane electrolysis (PEMEL), and high-temperature solid oxide electrolysis (HTEL). (Obviously, these three technologies are not based on the use of electrolytes)

3.    In the section of Water electrolysis: Compared to PEMEL, AEL offers a wider choice of electrocatalysts. (Logical error: PEMEL is not discussed before AEL interpretation, how to compare?)

4.    In the section of Methane and Methanol, what exactly does POM stand for partial oxidation of methane or Partial oxidation of methanol? Moreover, the discussion on ATR is lacking.

5.    The discussion on ammonia is too simplistic and should be increased.

6.    In the section of Hydrogen carriers & Production methods, Reference 35 is inconsistent with the main text. (Maybe there are problems with other references, because I only read this one, and it's wrong)

7.    Serial numbers should be uniform in the manuscript ((1), (2), (3) or (i), (ii), (iii)).

8.    Some detail errors should be further corrected, such as the upper and lower index of unit or compound, and so on.

Author Response

This review summarizes about primary hydrogen carriers, hydrogen production methods, and applications. However, the work is only a simple/common summary of the previous work, lacking of the own views and valuable ideas. Moreover, some detail issues in this review need further attention. Considering the current status of the submitted manuscript, it is suggested to be supplemented for its resubmission. Some questions and suggestions are given below:

Ans: Thank you for your kind suggestion on the incorporation of biomass related technology related to this topic. We also included the recent focus on the use of biomass sources for hydrogen production, which would be suitable for sustainable energy even though the high cost.

1. Detailed comparison of advantages and disadvantages of hydrogen carriers should be added.

Ans. Thank you for the comment. We added these points in the conclusions and perspectives in Page 15, Paragraph 6 and 7.

2. In the section of Water electrolysis: Three water electrolysis techniques can be employed based on the electrolyte used: alkaline electrolysis (AES), proton exchange membrane electrolysis (PEMEL), and high-temperature solid oxide electrolysis (HTEL). (Obviously, these three technologies are not based on the use of electrolytes.)

Ans. Thank you for your helpful comment. Accordingly, we deleted the “based on the electrolyte used” and revised the sentence in Page 3, Paragraph 1.

3. In the section of Water electrolysis: compared to PEMEL, AEL offers a wider choice of electrocatalysts. (Logical error: PEMEL is not discussed before AEL interpretation, ho to compare?)

Ans. Thank you for the comment. We agree with the reviewer’s comment and the sentence, “compared PEMEL”, was deleted and the revised sentence is in Page 3, Paragraph 3.

4. In the section of methane and methanol, what exactly does POM stand for partial oxidation of methane or Partial oxidation of methanol? More over the discussion on ATR is lacking.

Ans. We are thankful to the reviewer for pointing out an important point. We clarified the destination of POM in Page 9, Paragraph 1 and we added the discussion on ATR in Page 9, Paragraph 3 and 4.

5. The discussion on ammonia is too simplistic and should be increased.

Ans. We agreed the comment and added more information about the ammonia in Page 10, Paragraph 5.

6. In the section of Hydrogen carriers & production method, reference 35 is inconsistent with the main text. (Maybe there are problems with other references because I only read this one and its wrong)

Ans. We are sorry for the error and corrected in the revised version of the manuscript.

7. Serial numbers should be uniform in the manuscript.

Ans. Thank you, we have revised the serial numbers to (1), (2), (3), ….

8. Some detail errors should be further corrected, such as upper and lower index of unit or compound and so on.

Ans. We are very sorry about the typo errors. We also check and corrected them and final version was checked by English editing company with English native speaker.

Reviewer 3 Report

The work of Risheng and Kawanami aims at looking at a very hot topic, i.e., hydrogen, under different points of view, that are its sources, its production methods and its use. The manuscript is well written and well structured. It provides a good number of references. In my opinion, it can be published after that the following points will be addressed.

·         The novelty of this review should be reported in the introduction

·         In paragraph 2.1.1, the reference on the percentage of H2 production by electrolysis should be updated to one more recent (see https://www.iea.org/reports/hydrogen)

·         In paragraph 2.2.2, with regards to methanol reforming, in the frame of recent advances, it is worthy citing the investigation of reforming of methanol in the liquid phase (see among the others 10.1016/j.ijhydene.2021.09.206, 10.1016/j.cattod.2020.04.024). In this context, aqueous phase reforming is a recent technology which is important to cite for its ability to produce renewable hydrogen

·         In the same paragraph, methanol fuel cell should be cited as well (see 10.1016/j.jmst.2021.10.031)

·         Due to the recent gained interest, the use of liquid organic hydrogen carriers (LOHC) should be reported somewhere in the work. Maybe a paragrah could be added which encloses some innovative new fields of investigation (e.g., biohydrogen etc.)

·         Finally, I suggest adding a perspective paragraph, with the aim of highlighting potential synergies among the cited technologies and bottlenecks that should be overcome, so that a wider overview can be provided to the reader (and thanks to which a higher level of novelty can be reached, in my opinion)

Author Response

The work of Risheng and Kawanami aims at looking at a very hot topic, i.e., hydrogen, under different points of view, that are its sources, its production methods, and its use. The manuscript is well written and well structured. It provides a good number of references. In my opinion, it can be published after that the following points will be addressed.

Ans: Thank you so much for positive comments. According to the reviewer’s comment we have modified the manuscript.

1. The novelty of this review should be reported in the introduction.

Ans. Thank you for your suggestive comment. In the revised manuscript, we added the following points to project the novelty of this review.

1) At the abstract, and in the introduction section (page 2, line 12), we added the following sentence as follows;

“In this review of conclusions and perspectives, we summarized the advantages and disadvantages of hydrogen carriers and hydrogen production techniques and suggested the challenging tasks for the future research.”

“Moreover, we summarized the advantages and disadvantages of hydrogen carriers and hydrogen production techniques and suggested the challenging tasks for the future research.”

2. In paragraph 2.1.1, the reference on the percentage of H2 production by electrolysis should be updated to one more recent (see https://www.iea.org/reports/hydrogen).

Ans. Thank you so much for your comment. We added the suggested report as follow and added the reference in No. 10 as follows.

"Until recent years, electrolyzer manufacturing capacity reaches nearly 8 GW per year; the completion of all projects under construction could result in 134-240 GW of installed electrolyzer capacity by 2030, double the expectations from 2021 [10]."

3. In paragraph 2.2.2, with regards to methanol reforming, in the frame of recent advances, it is worthy citing the investigation of reforming of methanol in the liquid phase (see among the others 10.1016/j.ijhydene.2021.09.206,10.1016/j.cattod.2020.04.024). In this context, aqueous phase reforming is a recent technology which is important to cite for its ability to produce renewable hydrogen.

   Ans.: Thank you for the suggestion. We added the references (Ref.70 and Ref.72).

4. In the same paragraph, methanol fuel cell should be cited as well (see 10.1016/j.jmst.2021.10.031)

Ans.: We are thankful to the reviewer for helpful suggesting. We added the reference in the appropriate section as reference No. 74.

5. Due to the recent gained interest, the use of liquid organic hydrogen carriers (LOHC) should be reported somewhere in the work. Maybe a paragraph could be added which encloses some innovative new fields of investigation (e.g., biohydrogen etc.).

Ans.: We added the new topics for the hydrogen sources from biomass in the 2.5 section.

6. Finally, I suggest adding a perspective paragraph, with the aim of highlighting potential synergies among the cited technologies and bottlenecks that should be overcome, so that a wider overview can be provided to the reader (and thanks to which a higher level of novelty can be reached, in my opinion)

Ans.: We added the perspective paragraph in the last section 4 as “conclusions and perspectives”.

Round 2

Reviewer 1 Report

It can be published now.

Reviewer 2 Report

The authors answered my question well. I agree to accept it.