Recent Advances in In Situ/Operando Surface/Interface Characterization Techniques for the Study of Artificial Photosynthesis
Round 1
Reviewer 1 Report
A thorough revision of the state-of-the-art and recent breakthroughs on in situ/ in operando surface characterization techniques applied to the study of artificial photosynthesis occurring at the solid-liquid interface is presented in the manuscript by Liang et al. The author exhibits a remarkable dominion on the literature including some own relevant publications related to the topic. The subsequent qualitative and quantitative interpretation of the results reported herein is accurate and reliable. I do not have any serious criticisms regarding the summary of the key results, methodologies, conclusions, references, clarity, or context. The experimental procedures and short but precise discussions described in the article comprise a good showcase of the techniques when applied to artificial photosynthetic processes (water splitting and CO2 reduction reaction). The separation of the manuscript in the different sub-sections considered by the author is consistent, meaningful, and orientative. The paper is of enough interest and puts together valuable original works that merit its publication in Inorganics. Nevertheless, prior to be considered for its publication, some minor revisions of the current version of the manuscript should be addressed by the author. The latter can be summarized in the following bullet points:
· In the third paragraph of page 2, there seem to be some missing details to fully understand what the authors mean
· The need to use a electrophoretic paint coating on the STM tip in EC-STM measurement is another drawback to be considered for the last paragraph of page 5
· Although firmly related, the SKPFM section seems not to make straightforward reference to the characterization of the artificial photocatalytic processes object of the study
· It should be stated that PS-EC-AFM accounts for potential-sensing electrochemical atomic force microscopy in page 11
Author Response
Reviewer #1:
Comment 1. In the third paragraph of page 2, there seem to be some missing details to fully understand what the authors mean
Response: Thank you for the careful review. We regret that this paragraph does not provide enough information. To be more clearly and in accordance with the reviewer concerns, we have added a more detailed interpretation in page 4 in the manuscript as following.
“For instanceas illustrated in Ref [25], the authors loaded cobalt borate on the hematite surface, and investigated the changes of cobalt borate through in-situ XAS and ex-situ XPS methods. Among which, the Co4+ was detectcted under a real-time reaction condition by in-situ XAS, while the ex-situ XPS did not captured the presence of Co4+”.
Comment 2. The need to use an electrophoretic paint coating on the STM tip in EC-STM measurement is another drawback to be considered for the last paragraph of page 5
Response: Thank you to the reviewer for the constructive comments which made our article more accurate and comprehensive. We have supplemented the drawback regarding the usage of an electrophoretic paint coating on the STM tip in EC-STM measurement. So we added the following sentence:
“Besides，the STM tips in EC-STM measurement are prepared in complex methods to deposit an electrophoretic paint coating to minimize the faradaic current at the tip/electrolyte interface.” in page 13.
Comment 3. Although firmly related, the SKPFM section seems not to make straightforward reference to the characterization of the artificial photocatalytic processes object of the study.
Response: We agree with the comment and add the sentence in page 15 of the revised manuscript as the following:
“Although, splendid progress has been made in KPFM, it is unfortunate that most of the KPFM operations so far have been carried out under vacuum or ambient conditions, and few of KPFM experiments in aqueous solution have been reported. It is due to the fact the DC or AC bias will cause changes in the dynamics of the EDL [74], the electrochemical reactions and electrokinetic effects of both polar water molecules and electrolyte ions, resulted in difficulties of acquiring accurate and reliable measurements in aqueous solution [75–81]. Thus, in this section, we mainly focus on in-situ observations under vacuum or ambient conditions rather than operando observations.”
Comment 4. It should be stated that PS-EC-AFM accounts for potential-sensing electrochemical atomic force microscopy in page 11
Response: We apologize for overlooking this issue and grateful for the suggestion. As suggested by the reviewer, we’ve changed “PS-EC-AFM” to “potential-sensing electrochemical atomic force microscopy (PS-EC-AFM)” in page 23.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript titled “Recent advancements of in-situ/operando surface/interface characterization techniques in the study of artificial photosynthesis” by Liang, H.; et al is a review work where the authors provides extensive information of relevant examples in the use of many characterization techniques like scanning probe microscopy (SPM), mainly atomic force microscopy (AFM), kelvin probe force microscopy (KPFM) and scanning electrochemical microscopy (SECM) in combination with X-ray techniques (e.g. X-ray photoelectron spectroscopy (XPS) or X-ray absorption spectroscopy (XAS), among others) to address the electrochemical performance of engineered materials with artificial photocatalytic applications. The knowledge acquired in the present work could significantly aid in the fields of the development of photocatalytical surfaces being also extendable for energy storage systems. The shown data are well-discussed during the main body of the reported manuscript. The scientific paper is well written. In my opinion the present manuscript is innovative and the methodological approached used matches with the scope of Inorganics. Nevertheless, it exists a lack of comparative studies with redox biomolecules coming from natural sources. This point must be addressed. For the above described reasons, I will recommend the publication in Inorganics once the following remarks are fixed:
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ABSTRACT
The authors should summarize the current abstract section. The current abstract structure is fine but it exists some repetitions that could be preventing by rephrasing some statements.
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INTRODUCTION
Authors provides a narrative introduction depicting the current state-of the art which will aid to the potential readers to better understand the reasons to conduct the present scientific study. Some remarks must be addressed in the different showcased sections to improve the scientific quality of this manuscript.
I) “Recognition of the climate crisis (…) these targets attainable between 2050-2060”. (page 2). Even if I agree with the authors, they should add some further alternatives respect to artificial photosynthesis routes. In this context, circular economy strategies could devote a pivotal role [1].
[1] Salviulo, G.; et al. Enabling Circular Economy: The Overlooked Role of Inorganic Materials Chemistry. Chemistry 2021, 27, 6676-6695. https://doi.org/10.1002/chem.202002844.
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2. SCANNING PROBE MICROSCOPY
This section provides a complete overlook about the use of scanning probe microscopy to address the properties and performance of those materials that render artificial photosynthesis. It may be also opportune to point out some examples in the employment of the described techniques on natural redox mediators. Here, some relevant literature examples are provided to be taken into account.
2.1. Scanning tunneling microscopy (page 3). STM was successfully exploited to assess the electron transfer properties of cytochrome b protein molecules immobilized on gold surfaces [2]. This is the first study where the electron transfer is measured by controlling the protein orientation under pseudo-physiological conditions.
[2] Della Pia, E.A.; et al. Fast electron transfer through a single molecule natively structured redox protein. Nanoscale 2012, 4, 7106-7113. https://doi.org/10.1039/c2nr32131a.
2.2. Atomic force microscopy (page 6). AFM can be devoted to elucidate the transition states of redox proteins like ferredoxin NADP+ reductase towards its redox mediators, ferredoxin and flavodoxin [3] and also with the respective nicotin adenine dinucleaotide phosphate (NADP+) cofactor molecule [4]. These are the first studies where redox flavoenzymes are studied at the single molecule level.
[3] Marcuello, C.; et al. Mechanostability of the Single-Electron-Transfer Complexes of Anabaena Ferredoxin-NADP(+) Reductase. Chemphyschem. 2015, 16, 3161-3169. https://doi.org/10.1002/cphc.201500534.
[4] Pérez-Domínguez, S.; et al. Nanomechanical Study of Enzyme: Coenzyme Complexes: Bipartite Sites in Plastidic Ferredoxin-NADP+ Reductase for the Interaction with NADP. Antioxidants 2022, 11, 537. https://doi.org/10.3390/antiox11030537.
2.2.2. Scanning electrochemical microscopy (page 10). Electron transfer of glucose oxidase (GOx) protein molecules can be quantified by AFM-SECM [5]. The resolution of this technique is in order of femtoamperes (fA) which enables to visualize the current of individual molecules through ferrocene chemical mediators to gold tips.
[5] Paiva, T.O.; et al. Enzymatic activity of individual bioelectrocatalytic viral nanoparticles: dependence of catalysis on the viral scaffold and its length. Nanoscale 2022, 14, 875-889. https://doi.org/10.1039/d1nr07445h.
3. X-RAY CRYSTALLIZATION TECHNIQUES (page 15). Since this technique requires ultra-vacuum conditions and the lack of liquid media which mimics the intracellular conditions existing in living biological sources no relevant examples are found for redox transfer biomolecules. X-ray crystallography can be mainly employ to decipher the tridimensional structure of redox biomolecules [6].
[6] Eo, Y.; et al. Structural Comparison of hMDH2 Complexed with Natural Substrates and Cofactors: The Importance of Phosphate Binding for Active Conformation and Catalysis. Biomolecules 2022, 12, 1175. https://doi.org/10.3390/biom12091175.
Then, it may be appropriate to create a Table to highlight the main advantages and limitations shown by materials involved in artificial photosynthesis compared to redox biomolecules coming from natural sources.
Finally, Figure 13 (page 22) contains two green arrows. This information should be specified in the respective Figure caption in addition to the reactions taken place in numbers I, II, III, IV and V. These details will significantly aid the target audience to better understand the depicted data.
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CONCLUSION
Conclusion section is well structured. Please, the authors should modify the name of this section by “Conclusions”.
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REFERENCES
Bibliography citations are not in the proper format of Inorganics. The authors should take care of this point.
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OVERVIEW AND FINAL COMMENTS
The submitted work is presented and the furnished details are interesting in the field of the fabrication of photocatalytic devices. Moreover, the authors present high-throughput techniques with excellent resolution to characterize the performance of redox materials which could be of enormous interest to design inspired catalytic systems. For this reason, I will recommend the present scientific manuscript for further publication in Inorganics once all the aforementioned suggestions will be properly fixed.
Author Response
Reviewer #2:
Comment 1. The authors should summarize the current abstract section. The current abstract structure is fine but it exists some repetitions that could be preventing by rephrasing some statements.
Response: We thank the reviewer for this comment. We agree with the reviewer and delete some repetitive statements in the abstract.
Comment 2. Authors provides a narrative introduction depicting the current state-of the art which will aid to the potential readers to better understand the reasons to conduct the present scientific study. Some remarks must be addressed in the different showcased sections to improve the scientific quality of this manuscript.
- I) “Recognition of the climate crisis (…) these targets attainable between 2050-2060”. (page 2). Even if I agree with the authors, they should add some further alternatives respect to artificial photosynthesis routes. In this context, circular economy strategies could devote a pivotal role [1].
Response: The authors thank the reviewer for this suggestion. We realize that only artificial photosynthesis but no other strategies had been mentioned. We have supplemented sentences
“Both of energy transitions and circular economy strategies [11] are key for accelerating progress towards ‘net zero’ greenhouse gas emissions and increased resilience to climate change. Among many energy transitions technologies, artificial photosynthesis …” in the introduction section.
Comment 3. This section provides a complete overlook about the use of scanning probe microscopy to address the properties and performance of those materials that render artificial photosynthesis. It may be also opportune to point out some examples in the employment of the described techniques on natural redox mediators. Here, some relevant literature examples are provided to be taken into account.
Response: We deeply appreciate the reviewer's suggestion. According to the reviewer's comment, we have added biomolecular content to the corresponding section in this chapter, citing references carefully recommended by the reviewers.
In page 12, these sentences: “STM was successfully exploited to assess the electron transfer properties of cytochrome b protein molecules immobilized on gold surfaces [2]. This is the first study where the electron transfer is measured by controlling the protein orientation under pseudo-physiological conditions.” were added;
In page 14, these sentences: “AFM can be devoted to elucidate the transition states of redox proteins like ferredoxin NADP+ reductase towards its redox mediators, ferredoxin and flavodoxin [3] and also with the respective nicotin adenine dinucleaotide phosphate (NADP+) cofactor molecule [4]. These are the first studies where redox flavoenzymes are studied at the single molecule level.” were added;
In page 31, these sentences: “Scanning electrochemical microscopy (page 10). Electron transfer of glucose oxidase (GOx) protein molecules can be quantified by AFM-SECM [5]. The resolution of this technique is in order of femtoamperes (fA) which enables to visualize the current of individual molecules through ferrocene chemical mediators to gold tips.” were added.
Comment 4. X-RAY CRYSTALLIZATION TECHNIQUES (page 15). Since this technique requires ultra-vacuum conditions and the lack of liquid media which mimics the intracellular conditions existing in living biological sources no relevant examples are found for redox transfer biomolecules. X-ray crystallography can be mainly employ to decipher the tridimensional structure of redox biomolecules [6].
Response: Thanks to the reviewer's suggestion, we have included an elaboration on the application of X-ray crystallography for deciphering the tridimensional structure of redox biomolecules and cited relevant literature. we added the following sentence:
“In addition, X-ray crystallography can be mainly employed to decipher the tridimensional structure of redox biomolecules [108].” in page31.
Comment 5. Then, it may be appropriate to create a Table to highlight the main advantages and limitations shown by materials involved in artificial photosynthesis compared to redox biomolecules coming from natural sources.
Response: First of all, the authors agree with the reviewer that, some supplemental review of advanced in-situ/operando surface characterization techniques in the studies of redox biomolecules coming from natural sources are necessary. This can enrich the content of the article and further extend the scope of this review to those readers from different backgrounds.
It is noteworthy that, the main topics of this Special Issue mostly cover the recent advancements in photoelectrochemical energy conversion, as well as other related topics, such as electrocatalysts development, device engineering, and fundamental understanding of reaction mechanisms towards photoelectrochemical or electrocatalytic water splitting and CO, reduction.
When we introduce each characterization technique (KPFM, SECM, XPS, etc.), we can appropriately supplement some of its applications in the study of biomolecules. However, we do have concern that, if we make an explicit table to compare the materials involved in artificial photosynthesis to those of redox biomolecules coming from natural sources, it would seem a bit off the topic. Therefore, after extensive discussions with our colleagues, we decided not to add this comparison table. We do thank the reviewer for this suggestion and hope the reviewer can understand our concern.
Comment 6. Finally, Figure 13 (page 22) contains two green arrows. This information should be specified in the respective Figure caption in addition to the reactions taken place in numbers I, II, III, IV and V. These details will significantly aid the target audience to better understand the depicted data.
Response: Figure caption have been corrected according to the constructive comment. We explain the reaction process indicated by the arrow to aid readers better understand this picture. We add these sentences:
“I: the catalytic cycle is initiated by adsorption of H2O onto Co; II: dissociation into adsorbed OH* and H* on the Co and nearby N, respectively (the asterisk denotes the adsorption site); III–V: another proton from an adjacent H2O molecule will react with the first H* to generate H2. It is well known that in alkaline HER, the first sluggish Volmer step is catalytic dissociation of a water molecule with the generation of H* (H2O + e− = H* + OH−).” in the Figure 13 caption.
Comment 7. Conclusion section is well structured. Please, the authors should modify the name of this section by “Conclusions”.
Response: We apologize for overlooking this issue and grateful for the suggestion. As suggested by the reviewer, we’ve changed “Conclusion” to “Conclusions” in page 45.
Comment 8. Bibliography citations are not in the proper format of Inorganics. The authors should take care of this point.
Response: I must apologize for my ignorance concerning the format of bibliography citations. Thanks to the reviewer’s comment, we have made corrections based on your advice.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The authors have fully fulfilled my requests. The current manuscript version has greatly improved its scientific quality. For this reason, I warmly suggest its further publication in Inorganics journal.
