Nanostructured Iridium Oxide: State of the Art

Round 1

Reviewer 1 Report

Title: Nanostructured Iridium Oxide: State of the Art

Article Type: Review article

Manuscript Number: inorganics-1832301-v1

In this review, the authors have shown IrO₂ that were synthesized in the form of a wide variety of nanostructures ranging from nanopowder, nanosheets, nanotubes, nanorods, nanowires, and nanoporous thin films. This review describe the main employed synthetic methodologies that are followed to prepare selectively the various types of nanostructures, highlighting in each case the advantages brought by the nanostructuration illustrating their performances and applications.

My recommendation is that the authors carefully consider the below points, revise appropriately.

1. My suggestion is that the authors may consider more representative words for application in the keywords as significance as possible for this review article.

2. Page 2 line 24~25; ”Iridium Oxide ….a rutile crystalline structure …with a P42/mnm space group”, the authors may consider add a single crystal diffraction molecular structure diagram in this section in favor of the readers to recognize the geometry structure in single crystal.

3. My suggestion is that the authors may consider showing the applications for each case that were published in previous literature to enhance the cognition for reader.

4. Not only the reaction equation but also the SEM diagram in all figures in this article should be clarity. Some of image of crystal in the figures are not clear. My suggestion is that the authors should support the intelligibility figures to meet the requirements of this journal.

5. In this article some figure or table were modified from other literature that can be concerned with academic integrity. My suggestion is that the authors should carefully handle it properly. 

Author Response

 Reviewer 1

In this review, the authors have shown IrO₂ that were synthesized in the form of a wide variety of nanostructures ranging from nanopowder, nanosheets, nanotubes, nanorods, nanowires, and nanoporous thin films. This review describe the main employed synthetic methodologies that are followed to prepare selectively the various types of nanostructures, highlighting in each case the advantages brought by the nanostructuration illustrating their performances and applications.

My recommendation is that the authors carefully consider the below points, revise appropriately.

1. My suggestion is that the authors may consider more representative words for application in the keywordsas significance as possible for this review article.

Answer: Keywords have been adequately modified.

2. Page 2 line 24~25; ”Iridium Oxide ….a rutile crystalline structure …with a P42/mnm space group”, the authors may consider add a single crystal diffraction molecular structure diagram in this section in favor of the readers to recognize the geometry structure in single crystal.

Answer: Fig.1 has been added in the review which provides the PXRD indexed pattern of IrO₂ together with the Unit cell and the coordination mode of IrO₂.

3. My suggestion is that the authors may consider showing the applications for each case that were published in previous literature to enhance the cognition for reader.

Answer: Details on applications have been added throughout the main text. Furthermore, a table summarising the most important applications of IrO₂ together with their challenges has been also added.

4. Not only the reaction equation but also the SEM diagram in all figures in this article should be clarity. Some of image of crystal in the figures are not clear. My suggestion is that the authors should support the intelligibility figures to meet the requirements of this journal.

Answer: According to the reviewer, the reaction equation has been clarified. Further details have been added in the main text to better describe the reported images and several figures have been replaced by high definition images to enhance clarity. However, we may have also been limited in some cases by the low resolution of the source images.

5. In this article some figure or table were modified from other literature that can be concerned with academic integrity. My suggestion is that the authors should carefully handle it properly. 

Answer: Modified schemes or modified images have been replaced by original ones, all permissions to reproduced them for this review have been requested to the relative editorial offices.

We would like to thank Reviewer 1 for his/her suggestions and advices.

Author Response File: Author Response.docx

Reviewer 2 Report

I enjoyed reading this review as an inorganic chemist to gain a quick comprehension of the synthetic methods of IrO2 products and the state of art. I would like to see this review published and have a reference to go for the topic.

I have some suggestions to improve the review: In the abstract, you have mentioned the following applications and you even mentioned them in the bulk of the manuscript. However, with the exception of the electrochromic devices (change from transparent to blue/black), it would be difficult to understand the other applications.

1. Could you elaborate more on electrocatalysis, e sensors, fuel cell, and supercapacitors? We don't need too many details but more chemical insights. Please, include also the current challenges for each. Maybe you could summarize it in a Table.  Of course, you could limit the application search to the most recent examples.

2. Besides the macroscopic structure as nanotubes, could you also mention the typical coordinations found. expected for these materials?

3. Could you also include the redox potential if available and compare it with other tipical metal oxides.

Author Response

 Reviewer 2

I enjoyed reading this review as an inorganic chemist to gain a quick comprehension of the synthetic methods of IrO₂ products and the state of art. I would like to see this review published and have a reference to go for the topic.

I have some suggestions to improve the review: In the abstract, you have mentioned the following applications and you even mentioned them in the bulk of the manuscript. However, with the exception of the electrochromic devices (change from transparent to blue/black), it would be difficult to understand the other applications.

1. Could you elaborate more on electrocatalysis, e sensors, fuel cell, and supercapacitors? We don't need too many details but more chemical insights. Please, include also the current challenges for each. Maybe you could summarize it in a Table.  Of course, you could limit the application search to the most recent examples.

Answer: Details on applications have been added throughout the main text. Furthermore, a table summarising the most important applications of IrO₂ together with their challenges has been also added. We thank the reviewer for this excellent suggestion.

2. Besides the macroscopic structure as nanotubes, could you also mention the typical coordinations found. expected for these materials?

Answer: We hope to have fully understood the reviewer’s request. Fig.1 has been added in the review which provides the PXRD indexed pattern of IrO₂ together with the Unit cell and the coordination mode of IrO₂.

3. Could you also include the redox potential if available and compare it with other typical metal oxides.

Answer: Since IrO₂ displays metallic like conduction the only available data that could be given to answer reviewer 2 is the work function of IrO₂. Table 2 has been inserted in introduction which lists the main metal oxides, their work functions as well as their type of conductivity. In the case of semiconductors, the band gap was also added.

We would like to thank Reviewer 2 for his/her suggestions and positive feedback.

Author Response File: Author Response.docx

Reviewer 3 Report

The authors, in this review, have collected the state of the art on nanostructured iridium oxide. They have listed the various techniques required for the synthesis of this material and the applications in which it is used. Despite the high cost of iridium, this type of material still has interesting properties that overcome this problem. The review is well organized and clearly written. The subdivision of the topics follows the shape and morphology of the IrO2-based nanostructures. For each of them all the different preparation methods used are listed and a correlation is made between the different structures and the final chemical properties of the obtained material. I believe that the manuscript is easy to read, complete and useful for having a complete view on the topic of nanostructured IrO2.

For these reasons I think it can be accepted for publication.

Author Response

We would like to thank Reviewer 3 for his/her kind words, and we are delighted to know that he/she found our review complete and useful.

Round 2

Reviewer 2 Report

Thank you for addressing all suggestions. The summary table for application looks very clear.