Review on Innovative Piezoelectric Materials for Mechanical Energy Harvesting

Round 1

Reviewer 1 Report

This paper needs extensive editing to trim off contents that are not strongly related to the topic of this paper. Besides above request, other suggested modifications are listed below: 

1. Under Table 1, please use a paragraph to explain in detail the some of the phrase used in the "features" and "bio compatibility". For example, "CMOS", do you mean "compatible with CMOS fabrication"? What is "medium biocompatibility"? Is it based on some standard? Also what do you mean by "direct deformation"?  Change "EH" to "energy harvesting (EH)"   2. Please add reliability performance for each material . Or longevity testing. Degradation issue. This is particularly important for readers to select materials for commercial applications.    3. For several materials, author mentioned "commercially available", please quote the brand or company website. It would also valuable to discuss in context.    4. Section 3 diverse the focus of this paper. I would suggest delete the whole section "3. Piezoelectric materials zoo."  Delete from lines 69 to 275. Instead, put one or two sentences in introduction. The focus of this paper is about piezo material used in energy harvesting. Listing all possible materials without details of property analysis and comparison is not useful.    5. The content of Section 2 can be found everywhere on the internet. I would suggest delete the whole section "2. Piezoelectric effect". Instead, put one or two sentences in introduction.    6. Please rewrite the lines 24-48, to be more concise. No need to spend large paragraph with materials which are not the target of this paper.    7. Where is Table 3? For table 1,  please add one column "fabrication methods" for all materials. If possible, do the same for Table 4.    In table 4, in the power column, "Spider Silk (Indian-native spider) – 4.56 μW/cm2", please address the area value in other materials to make the units consistent.    8. What is the reference criterial for Figure 7, in the context, you introduced 5 materials, but you selected 3 materials in Figure 7.    9. Please add reference to Figure 8 and put more explanation in the figure captions.    10. What is the definition of "green device" in line 501?    11. Line 528, "and the yield and tensile strength is 52.8 MPa and 81.8
MPa with respect to 67.5 MPa and 120.3 MPa", 52.8 MPa and 81.8 MPa are for the ZONCE and 67.5 MPa and 120.3 MPa for the EAPap?    12.Contents are out of focus of this paper should be deleted. For example, I would suggest delete line 591-620. 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript presents a comprehensive and thorough review on the piezoelectric materials for energy harvesting, the given references are up to date, the figures and tables are clear. and the manuscript has remarkable introductory and enlightening values for readers. The reviewer thinks the manuscript can be accepted to publish after two issues are addressed.

1. In equation(2), “σ_jk is the strain tensor”?

2. In line 452, “4.5.1.PVDF”, and Section 4.5 is L_iN_bO₃, does it mean that PVDF is a part of L_iN_bO₃?

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

In my opinion, the manuscript is suitable for publication in Energies journal but Authors must complete a major revision. Manuscript should be revised according to following comments:

1. Chapter “Introduction” must be improved:
a) the authors present the purpose of the article. However, authors should also present a scientific background. I suggest that the authors referred to other reviews , which were  concerned piezoelectric energy harvesting,
b) Table 1 should be transferred to the next chapter, as the Authors should explain exactly on what basis they determined the levels of biocompatibility, which are presented in the third column in Table 1.

2. Chapter “Piezoelectric materials zoo” must be improved:
a) it should be explained on what basis these five classes were selected,
b) it should be presented what material properties will be compared. These properties should be mathematically described in the previous chapter,
c) an analysis of all presented materials should be carried out by comparing selected material properties.

3. Chapters from 4 to 8 should be improved:
a) an analysis of all presented materials should be carried out by comparing selected material properties,
b) the legibility of the Figures 7, 8 and 10 should be significantly improved.

4. Chapter “Conclusions and future prospects” must be improved:
a) in my opinion, the conclusions consist of selected fragments of the content of some articles previously cited. Conclusions should result from the analyses of materials, which were presented in chapters 3-8,
b) some of the conclusions, especially on lines 1005-1026, do not follow from the rest of the article.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

1. Section 2 again is not highly focused on energy harvesting, I would again suggest delete the whole section 2. Table 1 is good enough. 

I enjoy reading the paragraph after section 3 (lead-free materials). The paper would look more concise and focused if section 2 is removed. 

2. "Unfortunately, these data are not available or known for all the listed materials." Understood, try list reliability data for materials that are known. Reliability is key in whether user choose to use one over the other. It is hard to avoid spend significant amount of paragraph to discuss the topic for review paper like this. Especially the paper claim to guide " selecting the best piezoelectric material for a specific mechanical energy harvesting application". 

3. Sorry, when I said "commercially available", I mean "mass adopted" into production line. For example, ST microelectronics has a production line for piezo MEMS. It is OK these info are not included in the paper but nice to have. 

4. Please reduce line 625- line 653 into 1-2 sentences. 

5. Line 654, "two material categories", please restate what are the two categories. 

6. Line 676-677, what is the "active material"? 

7. The letters in Figure 9 (a) (b) are blurred. Please overlap clearer texts. 

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

 I accept in present form.

Author Response

We would like to thank again the referee for his/her useful comments and the constructive criticism, which led to an improvement of the manuscript.

Round 3

Reviewer 1 Report

Glad to see the material zoo putting into appendix. 

One small thing:

Please use noun rather than adjective as the name of each topic. 
For example, 3. organic-> 3. organic materials     or 3. organic piezoelectric materials

5. 3D printed -> 3D printed materials

 6. Low dimensional-> Low dimensional materials.