Synthesis of Bi2S3 thin films based on pulse-plating bismuth nanocrystallines and its photoelectrochemical properties

The solubility of Bi3+ in aqueous solution is an important factor that limits the fabrication of high-quality Bi2S3 thin films. In order to find a low-cost method to manufacture high-quality Bi2S3 thin films, we are reporting the preparation of the Bi2S3 thin films based on pulse-plating method in this paper for the first time. The nano-bismuth particles were obtained by electroplating on fluorine-doped SnO2 (FTO)-coated conducting glass substrates with saturated bismuth potassium citrate solution as the electroplating bath, and then it was put into a muffle furnace to oxidize. Finally, the thin films depositing on FTO glass substrates were put into the thioacetamide solution for vulcanization. In the end, the Bi2S3 thin films were successfully prepared on FTO glass substrates. Different characterization techniques were used to characterize the structure, morphology and photoelectrochemical properties of the prepared thin films. The test results revealed that we used this method to synthesize the high-quality Bi2S3 thin films, thus the Bi2S3 materials synthesized through this method are promising candidates in photoelectrochemical application.

1. For the synthesis method, the authors claimed that the Bi2S3 thin films were prepared based on pulse-plating method in this paper for the first time. So, what is the remarkable progress compared to the electroplating method for the preparation of Bi2S3 thin films (J Solid State Electrochem 2009, 13, 1339-1350.1007/s10008-008-0679-z)?
2. The Bi2S3 thin films on FTO surface were prepared primarily from the deposition of Bi films by using electroplating method, followed by thermal treatment for oxidation at different temperature and finally converted to Bi2S3 films. How can the bismuth oxides be guaranteed totally to be converted to Bi2S3 at 80 C for 10 min? From the evidence of PXRD patterns, the diffraction peaks of bismuth-metal films could be remarkably recorded being indexed to JCPDS: PDF number 44-1246. However, the characteristic peaks of Bi2S3 films as ascribed to JCPDS: PDF number 17-0320 were pretty weak, and they didn't provide other firm characterization for the chemical structure. How did the authors confirm the formation of Bi2S3 films deriving from the precursor oxides?
3. More experimental details should be provided. For examples, how were the UV-Vis adsorption spectra recorded? In transmission mode, reflection mode or other mode? What were the setup parameters for PXRD pattern performing? The testing conditions for photoelectrochemical measurements should be clearly described such as the purification of electrolyte solution by inert gas. The EIS tests should be clarified by providing the stable open-circuit potential value and frequency range. 4. The authors described that the reported method in the present work is able to deposit more uniform Bi2S3 thin films. However, from the SEM images, the roughness of Bi2S3 films seems very large. Could the authors compare the prepared Bi2S3 here to the previous works? Does the surface topography have the effect on the photoelectrochemical performance of Bi2S3 films? 5. This work showed the photoelectrochemical performance of as-synthesized Bi2S3 films. As demonstrated in literatures, the preferentially growing orientation of Bi2S3 nanorod along with [001] direction provides a rapid electron transport route for the photo-induced charge carriers (Dalton Trans., 2012, 41, 5581-5586;Crystengcomm. 2019Crystengcomm. , 21, 1474Crystengcomm. -1481. Do the authors could distinguish the orientation of Bi2S3 in the films? What do dominate the good photo-conversion efficiency of Bi2S3 films in the present work? How was the stability of Bi2S3 films, which is usually shown in the manuscript or electronic supplementary materials? How about the electronhole separation efficiency compared to Bi2S3-based composite films with other semiconductors? The comparison of photoelectrochemical performance of as-prepared Bi2S3 films to the previous ones should also be discussed.
6. For the Nyquist plot, why did the linear part corresponding to the diffusion process keep in perpendicular to Z' axle rather than the line with a slop of around 1? 7. The language used in the manuscript should be largely polished as any grammar mistakes were found. Such as, "Nanostructured Bi2S3 thin film with high surface area and low light reflectivity is one of the most promising solar cells."

Review form: Reviewer 2
Is the manuscript scientifically sound in its present form? No

Are the interpretations and conclusions justified by the results? Yes
Is the language acceptable? Yes

Do you have any ethical concerns with this paper? No
Have you any concerns about statistical analyses in this paper? No

Recommendation?
Major revision is needed (please make suggestions in comments)

Comments to the Author(s)
The authors report the synthesis and photoelectrochemical properties of Bi2S3 thin films samples for possible applications as photoelectrochemical devices. However, some suggestions and corrections are required for publication in Royal Society Open Science, which are as follows: 1 -In the XRD results, inform the crystal structure of Bi2S3, based on JCPDS data.
2 -To enrich the work, add a figure outlining the sample preparation process.
3 -Inform in the preparation methodology that sample 1, 2 and 3 refer to heat treatments at 300, 400 and 500oC. This information is only in the legend of the XRD. Decision letter (RSOS-200479.R0) We hope you are keeping well at this difficult and unusual time. We continue to value your support of the journal in these challenging circumstances. If Royal Society Open Science can assist you at all, please don't hesitate to let us know at the email address below.

Dear Dr Zhao:
Title: Synthesis of Bi2S3 thin films based on pulse-plating bismuth nanocrystallines and its photoelectrochemical properties Manuscript ID: RSOS-200479 Thank you for your submission to Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry.
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1. For the synthesis method, the authors claimed that the Bi2S3 thin films were prepared based on pulse-plating method in this paper for the first time. So, what is the remarkable progress compared to the electroplating method for the preparation of Bi2S3 thin films (J Solid State Electrochem 2009, 13, 1339-1350.1007/s10008-008-0679-z)?
2. The Bi2S3 thin films on FTO surface were prepared primarily from the deposition of Bi films by using electroplating method, followed by thermal treatment for oxidation at different temperature and finally converted to Bi2S3 films. How can the bismuth oxides be guaranteed totally to be converted to Bi2S3 at 80 C for 10 min? From the evidence of PXRD patterns, the diffraction peaks of bismuth-metal films could be remarkably recorded being indexed to JCPDS: PDF number 44-1246. However, the characteristic peaks of Bi2S3 films as ascribed to JCPDS: PDF number 17-0320 were pretty weak, and they didn't provide other firm characterization for the chemical structure. How did the authors confirm the formation of Bi2S3 films deriving from the precursor oxides?
3. More experimental details should be provided. For examples, how were the UV-Vis adsorption spectra recorded? In transmission mode, reflection mode or other mode? What were the setup parameters for PXRD pattern performing? The testing conditions for photoelectrochemical measurements should be clearly described such as the purification of electrolyte solution by inert gas. The EIS tests should be clarified by providing the stable open-circuit potential value and frequency range. 4. The authors described that the reported method in the present work is able to deposit more uniform Bi2S3 thin films. However, from the SEM images, the roughness of Bi2S3 films seems very large. Could the authors compare the prepared Bi2S3 here to the previous works? Does the surface topography have the effect on the photoelectrochemical performance of Bi2S3 films? 5. This work showed the photoelectrochemical performance of as-synthesized Bi2S3 films. As demonstrated in literatures, the preferentially growing orientation of Bi2S3 nanorod along with [001] direction provides a rapid electron transport route for the photo-induced charge carriers (Dalton Trans., 2012, 41, <a href="tel:5581-5586">5581-5586</a>; Crystengcomm. 2019, 21, 1474-1481). Do the authors could distinguish the orientation of Bi2S3 in the films? What do dominate the good photo-conversion efficiency of Bi2S3 films in the present work? How was the stability of Bi2S3 films, which is usually shown in the manuscript or electronic supplementary materials? How about the electron-hole separation efficiency compared to Bi2S3-based composite films with other semiconductors? The comparison of photoelectrochemical performance of as-prepared Bi2S3 films to the previous ones should also be discussed.
6. For the Nyquist plot, why did the linear part corresponding to the diffusion process keep in perpendicular to Z' axle rather than the line with a slop of around 1? 7. The language used in the manuscript should be largely polished as any grammar mistakes were found. Such as, "Nanostructured Bi2S3 thin film with high surface area and low light reflectivity is one of the most promising solar cells." Reviewer: 2 Comments to the Author(s) The authors report the synthesis and photoelectrochemical properties of Bi2S3 thin films samples for possible applications as photoelectrochemical devices. However, some suggestions and corrections are required for publication in Royal Society Open Science, which are as follows: 1 -In the XRD results, inform the crystal structure of Bi2S3, based on JCPDS data.
2 -To enrich the work, add a figure outlining the sample preparation process.
3 -Inform in the preparation methodology that sample 1, 2 and 3 refer to heat treatments at 300, 400 and 500oC. This information is only in the legend of the XRD.

Are the interpretations and conclusions justified by the results? Yes
Is the language acceptable? Yes

Recommendation? Accept as is
Comments to the Author(s) All concerns have been addressed. The manuscript is acceptable for publication in present form.

Review form: Reviewer 2
Is the manuscript scientifically sound in its present form? Yes

Comments to the Author(s)
The authors performed the reviews and the manuscript is recommended for publication in RSOS.

Decision letter (RSOS-200479.R1)
We hope you are keeping well at this difficult and unusual time. We continue to value your support of the journal in these challenging circumstances. If Royal Society Open Science can assist you at all, please don't hesitate to let us know at the email address below. Comments to the Author(s) The authors performed the reviews and the manuscript is recommended for publication in RSOS.

Reviewer: 1
Comments to the Author(s) All concerns have been addressed. The manuscript is acceptable for publication in present form.

Original Article Title: "Synthesis of Bi2S3 thin films based on pulse-plating bismuth nanocrystallines and its photoelectrochemical properties"
To: Royal Society Open Science -Chemistry Editor

Re: Response to reviewers
Dear Editor: Thank you for your letter and the reviewers' comments. Those comments are valuable and very helpful for revising and improving our paper. We have studied comments carefully and have made correction which we hope meet with approval. In the upload file, we edit the manuscript according (a) our point-by-point response to the comments (below) (response to reviewers) and (b) an updated manuscript with red highlighting indicating changes.

Appendix A
Reviewer#1, Concern#1: For the synthesis method, the authors claimed that the Bi2S3 thin films were prepared based on pulse-plating method in this paper for the first time. So, what is the remarkable progress compared to the electroplating method for the preparation of Bi2S3 thin films (J Solid State Electrochem 2009, 13, 1339-1350.1007/s10008-008-0679-z)?
Our revision and response: Thank you very much for pointing this out. The simple pulse-plating method provides an efficient strategy to prepare the Bi2S3 thin films with regular nanostructures and large superficial area. Compared to the electroplating method for the preparation of Bi2S3 thin films, we don't use the toxic non-aqueous dimethyl sulfoxide medium, the complexing agent and the surfactant. Our process was carried out in aqueous electrolyte which is expected safer and more friendly to the environment, as well as more cost-effective. We have added this comparison according to the paper (J Solid State Electrochem 2009, 13, 1339-1350.1007/s10008-008-0679-z). Revised portion are marked in red in the paper. Please see page 4, line 20-23. Moreover, we updated the manuscript by citing reference [26].

Reviewer#1, Concern#2:
The Bi2S3 thin films on FTO surface were prepared primarily from the deposition of Bi films by using electroplating method, followed by thermal treatment for oxidation at different temperature and finally converted to Bi2S3 films. How can the bismuth oxides be guaranteed totally to be converted to Bi2S3 at 80 °C for 10 min? From the evidence of PXRD patterns, the diffraction peaks of bismuth-metal films could be remarkably recorded being indexed to JCPDS: PDF number 44-1246. However, the characteristic peaks of Bi2S3 films as ascribed to JCPDS: PDF number 17-0320 were pretty weak, and they didn't provide other firm characterization for the chemical structure. How did the authors confirm the formation of Bi2S3 films deriving from the precursor oxides?
Our revision and response: Thanks for your comment. The time of vulcanization treatment was investigated. In the range of 10 min to 1 h, there was no obvious change could be witnessed on XRD patterns. 10 min is the optimized processing time. As shown in figure (a) below, among the samples, there are no diffraction peaks of bismuth oxide (JCPDS: PDF number 74-1374). Since the thickness of Bi2S3 film is only around 300 nm, the diffraction is weak. The X-rays can easily penetrate and reach the interface of FTO substrate.
In order to figure out the composition of film, EDS analysis was carried out, which demonstrated the existence of elements Bi and S (the atomic ratio is around 2:3), see figure (b). The other element peaks belong to the FTO substrate. Thus, it can be conclude that the bismuth oxides are mostly converted to Bi2S3. Revised portion are marked in red in the paper. Please see page 7, line 3-12.

Reviewer#1, Concern#4:
The authors described that the reported method in the present work is able to deposit more uniform Bi2S3 thin films. However, from the SEM images, the roughness of Bi2S3 films seems very large. Could the authors compare the prepared Bi2S3 here to the previous works? Does the surface topography have the effect on the photoelectrochemical performance of Bi2S3 films?
Our revision and response: Your suggestion is very reasonable. The increase of surface roughness will enhance the reflection effect of incident light on the interface and thus improve the photo-conversion efficiency. We have added the comparison according to the suggestion. Revised portion are marked in red in the paper. Please see (page 9, line 16-18) and (page 12, line 7-15).

Reviewer#1, Concern#5:
This work showed the photoelectrochemical performance of as-synthesized Bi2S3 films. As demonstrated in literatures, the preferentially growing orientation of Bi2S3 nanorod along with [001] direction provides a rapid electron transport route for the photo-induced charge carriers (Dalton Trans., 2012, 41, 5581-5586;Crystengcomm. 2019Crystengcomm. , 21, 1474Crystengcomm. -1481. Do the authors could distinguish the orientation of Bi2S3 in the films? What do dominate the good photo-conversion efficiency of Bi2S3 films in the present work? How was the stability of Bi2S3 films, which is usually shown in the manuscript or electronic supplementary materials? How about the electron-hole separation efficiency compared to Bi2S3-based composite films with other semiconductors? The comparison of photoelectrochemical performance of as-prepared Bi2S3 films to the previous ones should also be discussed. Our revision and response: Thank you very much for your suggestion. In our work, the as-synthesized Bi2S3 belongs to the orthorhombic system, space group Pbnm. Intensities of (211), (221), (301) are relatively high. The optimization of plating parameter to control growing orientation will be our future work. The increase of surface roughness will enhance the reflection effect of incident light on the interface and thus improve the photo-conversion efficiency. The Nyquist results shows that the materials of the prepared Bi2S3 thin films as photo-anodes can significantly promote the effective separation of photo-generated electrons and holes comparison to Bi2S3-based composite films with other semiconductors. Revised portion are marked in red in the paper. Please see page12, line 12-15.

Reviewer#1, Concern#6:
For the Nyquist plot, why did the linear part corresponding to the diffusion process keep in perpendicular to Z' axle rather than the line with a slop of around 1?
Our revision and response: Thanks. The slope coefficient of the straight line is relative to the ion transfer rate. Thus, the lower value of the charge transfer resistance and the more vertical straight line are beneficial for enhancing the ion transport, and thus improving the electrochemical performance. Revised portion are marked in red in the paper. Please see page 13, line 1-6.

Reviewer#1, Concern#7:
The language used in the manuscript should be largely polished as any grammar mistakes were found. Such as, "Nanostructured Bi2S3 thin film with high surface area and low light reflectivity is one of the most promising solar cells." Our revision and response: Thank you very much for your suggestion. We have revised the sentence to "Considering its high surface area and low light reflectivity, the prospect of nanostructured Bi2S3 thin film is promising for utilizing solar energy." Please see page 3, line 11-13. Moreover, we updated the manuscript by improving the level of English.

Reviewer#2, Concern#1:
In the XRD results, inform the crystal structure of Bi2S3, based on JCPDS data.
Our revision and response: Thank you very much for your suggestion. The structure of Bi2S3 belongs to the orthorhombic system, space group Pbnm. We have revised it according to the suggestion. Revised portion are marked in red in the paper. Please see page 6, line 35.

Reviewer#2, Concern#2:
To enrich the work, add a figure outlining the sample preparation process.
Our revision and response: Thank you very much for your suggestion. As shown in Figure 1, we have added a figure outlining the sample preparation process in the paper. Please see the Fig. 1.   Figure1. Schematic representation of the synthesis of Bi2S3 by pulse-plating method.
Reviewer#2, Concern#3: Inform in the preparation methodology that sample 1, 2 and 3 refer to heat treatments at 300, 400 and 500 ℃. This information is only in the legend of the XRD. Our revision and response: Thank you very much for your good suggestion. As shown in figure 4, we have added the SEM image and the EDS pattern of Bi2S3 thin film structures (sample 1 (300 °C)). Figure 4b indicated that only peaks of the elements Bi and S are present in the EDS spectrum, the other element peaks are belong to the FTO substrate. Revised portion are marked in red in the paper. Please see the Fig. 4 and page 9, line 1-3. Our revision and response: Thank you very much for your suggestion. We have revised it according to the suggestion. Revised portion are marked in red in the paper. Please see page 9, line 44-53.
Reviewer#2, Concern#6: In figure 4 (b) indicate which sample the measure refers to.
If possible, add the measurements of all analyzed samples.
Our revision and response: Thank you very much for your suggestion. We have revised it according to the suggestion. Please see the figure 6 (b). Reviewer#2, Concern#8: The figure legend can be further detailed with samples and measurement information. For example, the legend in figure 5 has no detailed information.

Reviewer#2
Our revision and response: Thank you very much for your suggestion. We have revised all of the figure legend and given detailed information according to the suggestion. We updated the manuscript.