Investigation of Photoelectrochemical Performance under the Piezoelectric Effect Based on Different Zinc Oxide Morphologies

Round 1

Reviewer 1 Report

This work is about “Investigation of Photoelectrochemical Performance under Piezoelectric Effect Based on Different Zinc Oxide Morphologies”. The paper mainly discuss about the photoelectrochemical performance on different Zinc oxide nanostructures under piezoelectric Effect. Needs major revision.

1. Novelty of the work and the rationale of arriving at the problem is not mentioned clearly in the introduction part.

2. In the Introduction section, define nanorods, nanosheets, and nanospheres briefly to distinguish their characteristics from each other.

3. The XRD of three ZnO nanostructures is suspicious. The author shows two different diffraction pattern for the same material. The XRD analysis of the ZnO nanorods shows a dominant (002) orientation, while this orientation is absent in ZnO nanosheets and nanospheres. The absence of (002) peak in ZnO nanosheets and nanospheres must be explained. 

4. What is the physical justification for the different band gap values obtained from the Tauc plot?  If all materials are the same phase without impurities, then the same band gap value should be obtained or the origin of the variations in the bandgap energies explained.

5. There is a lack of deep consideration for the relationship between the photoelectrochemical property and the material structure in the manuscript. There is very little discussion of the reasons for the observed performance of the photoelectrodes.

6. The author should check the captions in all the figure.

7. How about the stability of the different ZnO nanostructures photoelectrodes for longer time?

8. What is the overall implication or impact of the findings of this work?

9. Spelling and grammatical mistakes and other errors in the manuscript should be carefully checked.

Author Response

Reviewer #1: This work is about “Investigation of Photoelectrochemical Performance under Piezoelectric Effect Based on Different Zinc Oxide Morphologies”. The paper mainly discuss about the photoelectrochemical performance on different Zinc oxide nanostructures under piezoelectric Effect. Needs major revision:

1. Novelty of the work and the rationale of arriving at the problem is not mentioned clearly in the introduction part.

Answers to question 1: Thanks for your valuable suggestion. We have modified the expression of the sentences to clearly mention the novelty of the work and the rationale of arriving at the problem in the introduction part.

The revision located at page 3, between line 10 and line 17.

2. In the Introduction section, define nanorods, nanosheets, and nanospheres briefly to distinguish their characteristics from each other.

Answers to question 2: Thanks for your valuable suggestion. We have briefly defined these three morphologies in the Introduction section.

The revision located at page 3, between line 1 and line 3.

3. The XRD of three ZnO nanostructures is suspicious. The author shows two different diffraction pattern for the same material. The XRD analysis of the ZnO nanorods shows a dominant (002) orientation, while this orientation is absent in ZnO nanosheets and nanospheres. The absence of (002) peak in ZnO nanosheets and nanospheres must be explained.

Answers to question 3: Thanks for your suggestion. The (002) diffraction peaks of the nanosheets and nanospheres do not disappear. Due to the preferential orientation of the nanorods and the anisotropic growth of the nanosheets and nanospheres, the intensity of the (002) diffraction peak of the nanorods is extremely high. In order to distinguish the XRD patterns of the three samples in the graph, we have shifted the XRD patterns of the nanosheets and nanorods upwards, which results in the (002) diffraction peaks of the nanosheets and nanorods appearing to disappear in the figure. Moreover, we have zoomed in vertically on the 30° to 38° part of the XRD to compare the two patterns describing preferential orientation and anisotropic growth effects. The modified figures are as follows:

XRD patterns of three ZnO samples

In the third figure, it can be seen that the (002) diffraction peak does not disappear. Finally, we apologize for any misunderstanding you may have had duo to our graphical errors.

The first revision located at page 7, between line 10 to line 12.

The second revision located at page 21, line 1. The modified picture is Fig. 3a and b.

4. What is the physical justification for the different band gap values obtained from the Tauc plot? If all materials are the same phase without impurities, then the same band gap value should be obtained or the origin of the variations in the bandgap energies explained.

Answers to question 4: Thank you very much for the question pointed out by the expert.

• The physical justification for the different band gap values obtained from the Tauc plot. Most of the valence band electrons and conduction band electrons of semiconductors are distributed nearby the bandgap, so when the photon energy is satisfied by the bandgap, a large number of electrons can be excited by absorbing photon energy. Meanwhile, the absorption coefficient will increase with the number of photons. For semiconductor materials, Tacu et al. found the following relationship between the optical band gap and the absorption coefficient:

                                                    (Ahv)ⁿ = K (hv - E_g)                             (1)

If the value of (Ahv)ⁿ is set as the y-axis and the value of hv is set as the x-axis for the graph, the equation (1) can be seen as a linear equation, and E_g in a geometric sense represents the intercept of the line on the x-axis. Therefore, the linear part of the line is fitted linearly to obtain a linear equation that intersects the x-axis, and the x-value of the intersection point is the size of the sought bandgap.

• The issues of the different bandgap. After reviewing the relevant literature, we found that the Burstein-Moss shift occurs in samples with high carrier concentrations leading to a larger optical band gap of the sample (see for instance Anomalous optical absorption limit in InSb. Physical Review, 1954, 93: 632; Determination of optical constants and thicknesses of In₂O₃:Sn films from transmittance data. Thin Solid Films, 2007, 515: 7387-7392). In our synthesis of the three different morphologies of ZnO, the nanorods and nanospheres were synthesized at low carrier concentrations, whereas nanosheets were synthesized at high carrier concentrations (electrochemical deposition). Therefore, nanosheets have a large band gap and nanorods and nanospheres have a similar smaller band gap. We have added this discussion to the manuscript.

The revision located at page 8, between line 27 to line 28.

5. There is a lack of deep consideration for the relationship between the photoelectrochemical property and the material structure in the manuscript. There is very little discussion of the reasons for the observed performance of the photoelectrodes.

Answers to question 5: Thank you for expertly pointing out the problems with the manuscript. The relationship between the observed enhancement in photoelectrochemical property and material structure has been discussed in depth in our manuscript.

The revision located at page 9, between line 20 to line 24.

6. The author should check the captions in all the figure.

Answers to question 6: Thanks for your valuable suggestion. We have checked the captions in all figures carefully. The modified figure is as follows:

EIS of three ZnO samples without ultrasonic vibrations (Ultra) and with ultrasonic vibrations under illumination

The revision located at page 22, line 5. The modified picture is Fig. 8.

7. How about the stability of the different ZnO nanostructures photoelectrodes for longer time?

Answers to question 7: Thank you very much for the question pointed out by the expert. We have done a two-hour stability test on the samples. The results show that the photocurrent density of the three samples will stabilize after a long period of light exposure. The figure is as follows:

Stability measured under 1.23 V vs. RHE of three samples

8. What is the overall implication or impact of the findings of this work?

Answers to question 8: Thanks for your professional question. Our research has a potential implication for developing novel photoelectrodes for piezo-photoelectrochemical water splitting to produce H₂ and O₂.

9. Spelling and grammatical mistakes and other errors in the manuscript should be carefully checked.

Answers to question 9: Thank you for your valuable suggestions. We have carefully checked and revised spelling and grammatical mistakes and other errors in the manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript contains interesting results on the photoelectrochemical performance under piezoelectric effect based on different zinc oxide morphologies. The authors investigated the structure and properties of different types of zinc oxides by means of thorough analyses. The referee’s opinion is that this manuscript for publication in inorganics is required a minor revision as follows.

 

 

1. Abstract: the descriptions throughout the abstract are lengthy. The author should condense the contents suitable for abstract.

 

2. Use of the English language needs slightly improvement of the manuscript. Checking the text thoroughly or consulting a native speaker is recommended.

 

Author Response

Reviewer #2: This manuscript contains interesting results on the photoelectrochemical performance under piezoelectric effect based on different zinc oxide morphologies. The authors investigated the structure and properties of different types of zinc oxides by means of thorough analyses. The referee’s opinion is that this manuscript for publication in inorganics is required a minor revision as follows.

1. Abstract: the descriptions throughout the abstract are lengthy. The author should condense the contents suitable for abstract.

Answers to question 1: Thank you for your valuable suggestions. We have condensed parts of the abstract to make it more concise.

The revision located at page 1, between line 14 and line 19.

2. Use of the English language needs slightly improvement of the manuscript. Checking the text thoroughly or consulting a native speaker is recommended.

Answers to question 2: Thank you for your valuable suggestions. We have carefully checked and revised spelling and grammatical mistakes and other errors in the manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

 The topic (photoelectrocatalysis in the presence of piezoelectric effect) is interesting but the manuscript requires some major revisions, as descrived in the following:

 

1. An extensive English revision is needed to correct a multitude of grammar/typing mistales and improve the text both from a linguistic and scientific viewpoint. This is mandatory.

2. XRD results. I guess XRD patterns have been collected in a Bragg-Brentano configuration, typically used for powder materials. In order to complement such data, authors are encouraged to analyze the same samples even in a glancing incidence geometry and compare the two set of patterns describing preferential orientation and anisotropic growth effects. The XRD patterns of ZnO NSs ands NPs in Fig. 3 should be vertically enlarged.

3. XPS results. Fig. 5 should be graphically improved. On the x-axis, BE values should increase right to left, as commonly reported within the XPS community. The discussion about the O1s peak is not fully convincing (the low BE component is typically attributed to lattice oxygen, and the high BE one to –OH surface groups – see for instance Chem. Vap. Deposition 2007, 13, 618–625; ChemPhysChem 2010, 11, 2337–2340; Sensors and Actuators B 2010, 149, 1–7). The deconvolution of the O1s peak for ZnO NSs is questionable (it is more likely that two components contribute also to this peak).

Author Response

Reviewer #3: The topic (photoelectrocatalysis in the presence of piezoelectric effect) is interesting but the manuscript requires some major revisions, as descrived in the following:

1. An extensive English revision is needed to correct a multitude of grammar/typing mistales and improve the text both from a linguistic and scientific viewpoint. This is mandatory.

Answers to question 1: Thank you for your valuable suggestions. We have carefully checked and revised spelling and grammatical mistakes and other errors in the manuscript.

2. XRD results. I guess XRD patterns have been collected in a Bragg-Brentano configuration, typically used for powder materials. In order to complement such data, authors are encouraged to analyze the same samples even in a glancing incidence geometry and compare the two set of patterns describing preferential orientation and anisotropic growth effects. The XRD patterns of ZnO NSs and NPs in Fig. 3 should be vertically enlarged.

Answers to question 2: Thank you expert for pointing out the comment. We have vertically enlarged the XRD patterns of ZnO NSs and NPs to compare the two set of patterns describing preferential orientation and anisotropic growth effects. The modified figures are as follows:

XRD patterns of three ZnO samples

The first revision located at page 7, between line 10 to line 12.

The second revision located at page 21, line 1. The modified picture is Fig. 3a and b.

3. XPS results. Fig. 5 should be graphically improved. On the x-axis, BE values should increase right to left, as commonly reported within the XPS community. The discussion about the O1s peak is not fully convincing (the low BE component is typically attributed to lattice oxygen, and the high BE one to –OH surface groups – see for instance Chem. Vap. Deposition 2007, 13, 618–625; ChemPhysChem 2010, 11, 2337–2340; Sensors and Actuators B 2010, 149, 1–7). The deconvolution of the O1s peak for ZnO NSs is questionable (it is more likely that two components contribute also to this peak).

Answers to question 3: Thank you very much for the question raised by the reviewer.

• The issues of the improvement of figures. We have revised Figure 5 in accordance with your comments, and the modified figures are as follows:

XPS survey scan spectrum of three ZnO samples

The revision located at page 22, line 1. The modified figures are Fig. 5a to d.

• The issues of the discussion about the O1s peak. We have revised our discussion of the O 1s peak in response to your comments in order to get a better and more convincing conclusion.

The revision located at page 8, between line 8 to line 12.

• The issues of the deconvolution of the O1s peak for ZnO NSs. We refitted the O1s peak for the nanosheets, and the final fit is shown below:

XPS survey scan spectrum for O 1s of three ZnO samples

The revision located at page 22, line 1. The modified figure is Fig. 5d.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have answered all my questions and made significant changes in the revised version. The manuscript can be accepted for publication in its present form.