Optically Transparent Gold Nanoparticles for DSSC Counter-Electrode: An Electrochemical Characterization

Round 1

Reviewer 1 Report

Review Report

Manuscript ID: molecules-1738847

Title: Optically transparent gold nanoclusters for DSSC counter-electrode: an electrochemical characterization

Journal: Molecules

The present study deals with the effect of sparger geometry on bubble formation dynamics  under oscillatory air supply. It was found that oscillatory air supply could significantly decrease bubble size when a hydrophilic plate was used. Also, it was found that under an oscillatory air state, bubble size and the number of coalesced trailing bubbles can be positively related to the chamber volume.

Reviewer’s suggestions

Line 30  Authors have to define the abbreviation PV technology.

Line 41 Replace the word “from” with “by” (a suggestion)

Line 57 Replace the word phrase “to exploit” with “exploiting” (a suggestion)

Line 60 The expressions “Dye sensitized solar cells” and “Quantum dot sensitized solar cells”, all words have to begin with a capital letter.

Line 71 The expressions “Dye sensitized solar cells” and “Quantum dot sensitized solar cells”, all words have to begin with a capital letter.

Line 98 and all below When authors mention the word “Figure” in the text it should be written with the first capital letter.

Line 129  “In (c) the insets are …” but there is just one insert.

Line 165. It will be effective if the authors present a value of the geometrical area. Additionally, it will be also very interesting if we can get from the authors the difference between these areas (let's say in %).

Line 168 Replace “figure 4b” with Figure 5b.

”On the contrary, gold films display a more reversible behavior ……” please provide some reasonable explanation.

 

Line 171 Authors have mentioned in the text “The linear scan voltammetry (figure 6) (1 mV/s) …” but the authors did not present the corresponding Figure. As I understand this figure should be numbered as Figure 7, and the existing Figure 7 should be numbered as Figure 8, etc. The authors have to present this figure.

 In Figures 5 a) and b): the y-axis is marked differently. Is there a particular reason why or just misstep? Please do correct it.

Line 190 Authors have to define the abbreviation “EIS”.

Line 194 The charge transfer resistance at the nanocluster electrodes was calculated from the Nyquist plot. Authors have to rephrase the entire paragraph. Additionally, the authors have to present a picture of the Equivalent Circuit used to calculate charge transfer resistance.

Line 210-212 Authors have to explain how they calculate the “fill factor” and explain more thoroughly how it is connected with higher serial resistance.

Line 222 Authors have to provide literature reference for equation 1.

Line 225 Authors claim “From the B term, obtained from the fitting …” but they again didn’t present the Equivalent Circuit which must be shown.

Line 248 Authors have to define the abbreviation HSA .

Figures 9 a) and b).  If authors used the abbreviation in figure captions then it should be used on figures too. Additionally, the authors claim that these are cyclic voltammograms, but I am not so convinced.

Authors need to go through the entire manuscript again and carefully detect parts where some of their observations are understandable. There are some parts of the manuscript that were very hard for me to understand.

Author Response

Referee 1

Manuscript ID: molecules-1738847

Title: Optically transparent gold nanoclusters for DSSC counter-electrode: an electrochemical characterization

Journal: Molecules

The present study deals with the effect of sparger geometry on bubble formation dynamics  under oscillatory air supply. It was found that oscillatory air supply could significantly decrease bubble size when a hydrophilic plate was used. Also, it was found that under an oscillatory air state, bubble size and the number of coalesced trailing bubbles can be positively related to the chamber volume.

This comment perhaps is not related to our article: our study does not deal with the effect of sparger geometry on bubble formation dynamics under oscillatory air supply. Probably this is a misunderstanding.

We are going to answer to the following suggestions since they are coherent to our article.

Reviewer’s suggestions

Line 30  Authors have to define the abbreviation PV technology.

We modified as suggested.

Line 41 Replace the word “from” with “by” (a suggestion)

We modified as suggested.

Line 57 Replace the word phrase “to exploit” with “exploiting” (a suggestion)

We modified as suggested.

Line 60 The expressions “Dye sensitized solar cells” and “Quantum dot sensitized solar cells”, all words have to begin with a capital letter.

We modified as suggested.

Line 71 The expressions “Dye sensitized solar cells” and “Quantum dot sensitized solar cells”, all words have to begin with a capital letter.

We modified as suggested.

Line 98 and all below When authors mention the word “Figure” in the text it should be written with the first capital letter.

We modified as suggested.

Line 129  “In (c) the insets are …” but there is just one insert.

We modified as suggested.

Line 165. It will be effective if the authors present a value of the geometrical area. Additionally, it will be also very interesting if we can get from the authors the difference between these areas (let's say in %).

The value of the geometrical area is 0.18 cm² which is similar to the value of the electroactive are 0.17 cm² (5.8 % is the difference between the areas). We added in the text the value of the geometrical area.

Line 168 Replace “figure 4b” with Figure 5b.

You are right: this was a misunderstanding. We modified.

”On the contrary, gold films display a more reversible behavior ……” please provide some reasonable explanation.

In the text, we already explained the observed lower reversibility in cyclic voltammetry with a higher charge transfer resistance observed by the EIS. It is known that a slowing down of the electron transfer kinetics causes a separation of the voltammetric waves, which progressively move away from the thermodynamic reversibility condition (about 60 mV for a monoelectronic process) therefore either the nanoclusters are less reactive, or, more likely, being less dense , compared to a reflective gold film, they offer a surface electrochemically, therefore suitable for lower electron exchange.

This is a sum of all discussion in 2.2.

 Line 171 Authors have mentioned in the text “The linear scan voltammetry (figure 6) (1 mV/s) …” but the authors did not present the corresponding Figure. As I understand this figure should be numbered as Figure 7, and the existing Figure 7 should be numbered as Figure 8, etc. The authors have to present this figure.

 This is a misunderstanding of us. We moved old figure 6 to figure 5c and we insert the new figure 6, the linear scan voltammetry.

 In Figures 5 a) and b): the y-axis is marked differently. Is there a particular reason why or just misstep? Please do correct it.

 We corrected.

Line 190 Authors have to define the abbreviation “EIS”.

We modified as suggested. Electrochemical Impedance Spectroscopy.

Line 194 The charge transfer resistance at the nanocluster electrodes was calculated from the Nyquist plot. Authors have to rephrase the entire paragraph. Additionally, the authors have to present a picture of the Equivalent Circuit used to calculate charge transfer resistance.

We rephrase the paragraph as suggested and we added the equivalent circuit as figure 7c.

Line 210-212 Authors have to explain how they calculate the “fill factor” and explain more thoroughly how it is connected with higher serial resistance.

The fill factor (FF) is usually calculated as the ratio among the maximum theoretical power and the real measured one for the cell ( ). For this reason, it represents an indicator of the quality of the cell. The serial resistance is correlated with the slope of the I-V curve at the V_OC point. This means that the higher the serial resistance, the smaller is the solar cell FF, with a slower increase of current with voltage. Usually, the serial resistance can be associated to the bulk resistance of the materials and the electrodes, the contact resistance at the interface between the various cell components and charge transfer resistance in the semiconductor material.

We reported the FF formula in the text. Reference 8 in the text.

Line 222 Authors have to provide literature reference for equation 1.

Equation 1 is now Equation 3 and we added a reference (number 38 A. Lasia, Electrochemical Impedance Spectroscopy and its Applications, Spring-er, 2014  ISBN 978-1-4614-8932-0 ISBN 978-1-4614-8933-7 (eBook) DOI 10.1007/978-1-4614-8933-7).

We added references for all equations and we insert to more equations for a better understanding.

Line 225 Authors claim “From the B term, obtained from the fitting …” but they again didn’t present the Equivalent Circuit which must be shown.

We insert the Equivalent Circuit as figure 8e.

Line 248 Authors have to define the abbreviation HSA.

We modified as suggested. High Stability Electrolyte (HSE)

Figures 9 a) and b).  If authors used the abbreviation in figure captions then it should be used on figures too. Additionally, the authors claim that these are cyclic voltammograms, but I am not so convinced.

We modified the captions. We recorded curves through cyclic voltammetry but for avoiding confusion with delete that sentence.

Authors need to go through the entire manuscript again and carefully detect parts where some of their observations are understandable. There are some parts of the manuscript that were very hard for me to understand.

We tried our best to re-write some difficult part and give to the manuscript a better fluency. We thank the reviewer for precious suggestions that helped in improving the quality of the paper.

 

Best Regards

Author Response File: Author Response.pdf

Reviewer 2 Report

 

The authors report electrochemical characterization of optically transparent gold nanoclusters for DSSC counter-electrode. There are several issues with this manuscript which need to be resolved and the major ones are outlined below.

 

1) What is the scientific novelty of the work? The authors are suggested to clarify this point in the abstract/introduction.

 

2) SEM images indicate the size of gold “clusters” to be ca. 40 nm. Is that appropriate to be defined as nanoclusters?

 

3) The inset of Fig. 4 is not clear.

 

4) Typo and language mistakes are required to be revised throughout the manuscript.

 

Author Response

Referee 2

 

The authors report electrochemical characterization of optically transparent gold nanoclusters for DSSC counter-electrode. There are several issues with this manuscript which need to be resolved and the major ones are outlined below.

 

1)            What is the scientific novelty of the work? The authors are suggested to clarify this point in the abstract/introduction.

In this paper, we fabricated and investigated for the first time, at our best knowledge, gold counter-electrodes made by gold nanoparticles prepared by a reduction of HAuCl₄ employing a new strategy never experimental used for DSSC.

In this way, we obtained a semitransparent counter-electrode and we avoid the presence of Chromium, which is necessary to ensure a good adhesion of gold layer to the FTO glass. Our results are very important because could be used in semitransparent Perovskite Solar cells as top electrode instead opaque gold or other cathodes.

We clarified this point in the abstract/introduction as requested.

In the introduction is reported the following:

In literature, one of the most common method to deposit a gold film is by thermal evaporation [20]. Recently, the laser ablation technique has been investigated to develop semi-transparent gold nanoparticles CE with excellent results in terms of PCE [30]. In this work, we aim to fabricate, for the first time at the best of our knowledge, a semi-transparent gold nanoparticles CE by chemical reduction: a new strategy, never used in DSSC. This process allows to reach the semi transparency of the deposited gold layer moreover it is a safer way for the human operator using less dangerous precursor than thermal decomposition indeed, we avoid the presence of Chromium, necessary to ensure a good adhesion of gold layer to the FTO glass in the thermal evaporation technique. Our research is worth of investigation since the chemical deposition process of a semitransparent gold nanoparticle layer may be used in semitransparent Perovskite Solar cells as top electrode instead of opaque gold or other metals.

 

3)            SEM images indicate the size of gold “clusters” to be ca. 40 nm. Is that appropriate to be defined as nanoclusters?

During the thermal decomposition process, relatively big clusters of gold nanoparticles are formed on the FTO surface. The reported average size of 40 nm is related to the nanoparticles in the clusters.

We acknowledge the reviewer for this comment: this is right indeed, it is better use the term of gold nanoparticles therefore we modified nanoclusters in nanoparticles.

 

3) The inset of Fig. 4 is not clear.

We modified the inset to make it clear.

 

4) Typo and language mistakes are required to be revised throughout the manuscript.

We modified some parts of the manuscript and re-write some difficult part to reach a better fluency. Moreover, we tried our best to correct English mistakes.

We thank the reviewer for precious suggestions and corrections that helped us in improving the quality of the manuscript.

Best regards

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I recommend to the Editorial office consider this manuscript for publication, in the present form. 

Reviewer 2 Report

The authors have sincerely revised this manuscript based on the reviewer's comments. Now that the reviewer can suggest the acceptance of this manuscript by Molecules.