Fundamentals and Principles of Solid-State Electrochemical Sensors for High Temperature Gas Detection

Round 1

Reviewer 1 Report

Review

Fundamentals and principles of solid-state electrochemical sensors for high temperature gas detection.

In this paper, the authors focused on the basic principles of operation and configuration of potentiometric, amperometric, combined (amperometric-potentiometric) and mixed sensors. In addition, the results of previous studies on carbon  oxides, nitrogen oxides, hydrogen, oxygen, ammonia, and humidity electrochemical sensors are reported and discussed.

I think the proposed article is interesting and necessary. The approach and presentation of the content are original. On the other hand, the work needs to be improved. My comments are as follows:

1. Figures 2-8 should be enlarged for better visibility.
2. In all mathematical formulas, the font size should be equal. For example, in formulas 10 and 11, the font sizes are different.
3. Page 11 (line number 461). Formula 20 was obtained from formulas (2) and (18). Please check the correctness of the formula (20); ln(a/b) = - ln(b/a)
4. Page 16 (line number 645) - instead of “with the equation (7)”, should be “with the equation (6)”
5. In chemical reactions (32-34, 36), dots should be put in place of commas.
6. Page 19 (line number 738). The chemical reaction (34) is incorrectly written.
7. Page 20 (line number 785). Please explain to the reader the marks Dexp and delta D.
8. Page 24 (line number 916 and 936). Please check the correctness of the formulas (39-40) - check the sign of the expressions.
9. Page 24 (line number 917) - instead of “To obtain equation (40) from (39)”, should be “To obtain equation (39) from (38)”
10. Page 24 (line number 943) - please put part of the formula in the correct position.
11. Page 26 (line number 981) - The chemical reaction (43) is incorrectly written.

Author Response

REVIEWER 1

In this paper, the authors focused on the basic principles of operation and configuration of potentiometric, amperometric, combined (amperometric-potentiometric) and mixed sensors. In addition, the results of previous studies on carbon oxides, nitrogen oxides, hydrogen, oxygen, ammonia, and humidity electrochemical sensors are reported and discussed.

I think the proposed article is interesting and necessary. The approach and presentation of the content are original. On the other hand, the work needs to be improved. My comments are as follows:

1. Figures 2-8 should be enlarged for better visibility.

Although initially, the format of the figures was chosen according to our preference, their size and position is permanently determined by the editorial board after the completion of the revision process and before publishing. Therefore, it is of no benefit to make any further changes in this area at this point.

2. In all mathematical formulas, the font size should be equal. For example, in formulas 10 and 11, the font sizes are different.

The size of the mathematical formulas has been equalized according to your comment.

3. Page 11 (line number 461). Formula 20 was obtained from formulas (2) and (18). Please check the correctness of the formula (20); ln(a/b) = - ln(b/a)

Thank you for the correction. We have corrected formula 20 according to your comment.

4. Page 16 (line number 645) - instead of “with the equation (7)”, should be “with the equation (6)”

You are right. We have corrected the error.

5. In chemical reactions (32-34, 36), dots should be put in place of commas.

We have replaced commas with dots in the equations you highlighted. Thank you for the correction.

6. Page 19 (line number 738). The chemical reaction (34) is incorrectly written.

Thank you for pointing out the error. We have corrected equation (34).

7. Page 20 (line number 785). Please explain to the reader the marks Dexp and delta D.

We have corresponded the abbreviations to their meaning in the relevant table caption according to your suggestion.

8. Page 24 (line number 916 and 936). Please check the correctness of the formulas (39-40) - check the sign of the expressions.

The signs of equations (39) and (40) were wrong. The signs have been corrected.

9. Page 24 (line number 917) - instead of “To obtain equation (40) from (39)”, should be “To obtain equation (39) from (38)”

You are right. The error has been corrected according to your comment. 

10. Page 24 (line number 943) - please put part of the formula in the correct position.

Following your suggestion, we have put the equation in the correct position

11. Page 26 (line number 981) - The chemical reaction (43) is incorrectly written.

Thank you for your suggestion. The error has been corrected.

Author Response File: Author Response.docx

Reviewer 2 Report

Tsiakaras and coworkers have a review article on proton-conducting and oxygen ion electrolytes based sensors. This review is based on the principle of operation and the configuration of the types of solid oxide gas sensors. The author have presented a detailed discussion on the previous literature results. Overall, this is a good contribution and I recommend its publication.

Author Response

Reviewer 2

Tsiakaras and coworkers have a review article on proton-conducting and oxygen ion electrolytes based sensors. This review is based on the principle of operation and the configuration of the types of solid oxide gas sensors. The authors have presented a detailed discussion on the previous literature results. Overall, this is a good contribution and I recommend its publication.

We thank you for evaluating positively the quality of our work. Furthermore, we checked and corrected where necessary the text for spelling errors, as you pointed out.

Reviewer 3 Report

This review as reflected from its title gives a comprehensive review on the working principles of the solid-state electrochemical sensor. It can be of some help for the beginners to get an overall idea on the area. The main problems are the presentation and lack of the in-depth description. The some of the presentation problems can be found the following items. The lack of the in-depth description is that besides the working principles, other issues such as the error, sensitivity, coupling  and enhancing mechanics can also be important. The following is some suggestions.

1. The usages of article are inappropriate, for example, in Abstract, “the impact of ozone depletion”should be “the impact of the ozone depletion”; “gas-detecting devices” should be “the gas-detecting devices”; “electrochemical gas sensors” should be “the electrochemical gas sensors” and so on.
2. Logically, the authors talk about the impact of the ozone depletion at the very beginning in Abstract, and in the text, nothing has been mentioned on this issue or the sensing application on the ozone gas. Therefore, I have no idea why they mentioned this ozone issue at the first place.
3. Some figures such as Figs. 2-5 contain too many (sub)figures, which makes the readers very difficult to read clearly. The authors are advised to dismantle them into less subfigures in one figure to make things clearer.

Author Response

REVIEWER 3

This review as reflected from its title gives a comprehensive review on the working principles of the solid-state electrochemical sensor. It can be of some help for the beginners to get an overall idea on the area. The main problems are the presentation and lack of the in-depth description. The some of the presentation problems can be found the following items. The lack of the in-depth description is that besides the working principles, other issues such as the error, sensitivity, coupling and enhancing mechanics can also be important. The following is some suggestions.

The present literature review aims to provide the fundamental theory and working principle of the main electrochemical gas sensors to students and researchers beginning their involvement with this topic. Regarding the fundamental theory, all the corresponding theoretical equations are presented, and their origin is described in-depth. Concerning the working principles, we believe that we provide comprehensive content for understanding, as several representative works are presented and thoroughly discussed for each type of gas sensor. Therefore, in our opinion, we succeeded the aim we had set. Sensitivity, coupling, and mechanism enhancement are indeed important factors for the operation of electrochemical gas sensor. We had considered including them in our discussion. However, in this case, the manuscript would far exceed the typical range of a scientific journal paper, and we would deviate from the initial aim we had set. These properties could be discussed in a future literature review paper dealing with the state-of-the-art solid electrolytes for electrochemical gas sensors and the up-to-date achieved development.

1. The usages of article are inappropriate, for example, in Abstract, “the impact of ozone depletion” should be “the impact of the ozone depletion”; “gas-detecting devices” should be “the gas-detecting devices”; “electrochemical gas sensors” should be “the electrochemical gas sensors” and so on.

Thank you for your comment. Based on your comment, we have checked and corrected where necessary the manuscript for syntax errors, as you pointed out.

2. Logically, the authors talk about the impact of the ozone depletion at the very beginning in Abstract, and in the text, nothing has been mentioned on this issue or the sensing application on the ozone gas. Therefore, I have no idea why they mentioned this ozone issue at the first place.

You are right; mentioning the ozone depletion issue in the abstract may mislead the readers that electrochemical ozone sensors are discussed in the current work. Since we chose to focus on the most popular gas sensors (NO_x, CO_x, H₂, O₂, and NH₄) in order not to exceed the range of a research paper, we decided to exclude the ozone reference from the abstract and not add a subchapter on electrochemical ozone sensors.  

3. Some figures such as Figs. 2-5 contain too many (sub)figures, which makes the readers very difficult to read clearly. The authors are advised to dismantle them into less subfigures in one figure to make things clearer.

Your advice is rational. Designing figures containing many subfigures may have as a side effect the creation of confusion. However, on the other hand, summarizing subfigures corresponding to a specific topic in a single figure can help readers obtain a general view at first sight. Furthermore, it can be helpful for readers to check their understanding after reading the relative theory by returning and evaluating again and briefly the comprehensive content summarized in a single figure. Moreover, in this way, they could easily gain access to specific information that they may later need to run through their mind. Besides, this is a common strategy followed the recent years for illustrating figures for literature review papers. Conclusively, we believe that the advantages of using single figures with many subfigures far outweigh the disadvantages, and thus we decided not to decompose the figures.

Round 2

Reviewer 1 Report

The authors made all the corrections that I proposed.
The manuscript has been improved. I recommend publishing this review article.