A Detrimental Effect of Acetonitrile on the Kinetics of Underpotentially Deposited Hydrogen and Hydrogen Evolution Reaction, Examined on Pt Electrode in H₂SO₄ and NaOH Solutions

Round 1

Reviewer 1 Report

The hydrogen evolution reaction is the main reaction in the water electrolysis and has been one of the most studied electrochemical reactions. Platinum displays the highest activity for the hydrogen evolution reaction. Based on this, the article may be of potential interest to researchers.But, unfortunately, I can not recommend this article for publication in the Catalysts for several reasons.
Firstly, the quality of the article is low. Secondly, the title of the article requires editing. The title of the article does not correspond to the content, in particular, there is no information how acetonitrile is influence to the electrochemical hydrogen evolution reaction rate. Thirdly, the article provides a technical description of the experimental data without appropriate analysis.Fourth, it seems to me that other research methods should be used in the article to obtain more detailed information about the kinetics of the process. The effect of the concentration of acetonitrile and the concentration of electrolytes on the rate of hydrogen evolution should be investigated in detail. For this, it is can be used other electrochemical research methods (for example, chronoamperometry, Tafel plots, etc.)
Finally, it should be investigated how acetonitrile influence to the hydrogen adsorption on platinum. For this, it is can be obtained the values of the amount of adsorbed hydrogen on Pt in NaOH and H2SO4 at various potentials. This will allows to determine the limiting stage of the hydrogen evolution reaction.
I am sorry, but the article cannot be published in presented form.

Author Response

Reviewer # 1:

1. English language editions: In the revised manuscript, the language has been additionally checked and somewhat improved. However, when referring to stylistic/grammatical errors, the Reviewer is obliged to present at least several such examples within the manuscript. Otherwise, a value of such a comment is not very meaningful…….Moreover, as the Review #1 contains numerous and rather basic linguistic problems itself, one could wonder if such comments are indeed valuable (see e.g. para 3: “For this, it is can be obtained the values…..”; “this will allows….”; para 2: “For this, it is can be used…..”; para 2: “there is no information how acetonitrile is influence to……”).
2. Introduction: as per the Reviewer’s request, Introduction section of the revised manuscript has now been enriched with additional reference papers (see Refs. 1-6 there).
3. Research Design; Description of Research Methods; Results Presentation; Conclusions Presentation: In our opinion, general structure and content (including extended experimental descriptions) of all these manuscript sections have been prepared appropriately and with sufficient care. Also (again), the Reviewer did not point out at specific deficiencies within an original manuscript.
4. Firstly, the idea behind writing this paper was to present and discuss a detrimental impact that acetonitrile (a potentially important air contaminant) does induce on the processes of HER and UPD of H on the catalytic surface of polycrystalline Pt electrode, not to duplicate the well-known/described literature results on the HER (or the UPD of H). It has to be stated that our major goals have definitely been achieved. Secondly, the recorded here HER and UPD of H data have been compared to those obtained at one of the best (at that time) electrochemical laboratories in the world (see Refs. 22, 24-26 in the original manuscript). Then, it is very rare that the manuscript title strictly refers to the experimental conclusions, see e.g. the title of Ref. 26 (Conway, B.E.; Barber, J.; Morin, S.): Comparative evaluation of surface structure specificity of kinetics of UPD and OPD of H at single-crystal Pt electrodes, Acta 1998, 44(6-7), 1109-1125. Although in our opinion the title of this article strictly corresponds to the manuscript content, as per the Reviewer’s request we decided that the manuscript title be appropriately revised (see the new title above and in the revised manuscript).
5. Data analysis: It should clearly be stated that the recorded (in absence and presence of AcN) resistance and capacitance data (in-line with the CV results) have comparatively been (and similarly to other important works, see Refs. 22 and 23 of the original manuscript) evaluated/discussed, where appropriate conclusions have also been made (see section 2.1., para 1 and 2/pages 2 and 3; sections 2.2. and 2.3./pages 4-13 and Conclusions section).
6. We agree upon with the Reviewer: in the revised manuscript, we have now included Tafel polarization plots (along with their discussion), obtained comparatively in absence and presence of acetonitrile, independently for acidic and alkaline solutions (see Figs. 2c and 4c, and pages 5, 8, 11 and 13 of the revised manuscript).
7. In fact, we have originally studied the HER and UPD processes under the influence of AcN at two selected acetonitrile (1.85x10^-5 and 1.85x10^-3 M) concentrations (see Tables 1 and 2 there for details). Then, examination of the AcN effects at various concentrations of supporting electrolytes is important, but the latter should rather be presented in another experimental paper. However, it has to be stated that further expansion of current manuscript (already quite extensive) into examination of various concentrations of H₂SO₄ and NaOH solutions would only obscure the currently presented data and most importantly the paper’s goal!
8. It has to be stated that purely detrimental influence of acetonitrile on the Pt adsorbed (chemisorbed) hydrogen (UPD: underpotentially deposited H) has clearly been explained in the original manuscript [a primary surface AcN co-adsorption effect evidenced in rising of the R_H parameter has been unambiguously described (both electrode potential and anion: HSO₄^- and OH^- dependence), see pages 8, 9, 11 and 13, also Tables 1 and 2 there]. Moreover, further assessment of the corresponding potential dependent H surface coverages (q_H) in both supporting electrolytes at selected AcN concentrations (and their influence on the HER) could perhaps be done. However, the latter (carried-out with a 1-3% H monolayer precision) would require extremely high laboratory purity and precision, typically needed in Pt/Pt single-crystal hydrogen electrochemistry work. In addition, the above was definitely outside the scope of this work.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments 

Article having a tittle “Influence of acetonitrile on the kinetics of underpotentially deposited hydrogen and hydrogen 3 evolution reaction, examined on Pt electrode in H2SO4 and NaOH solutions” Before publication, following issues need to be addressed 

1. In 2.2. while, explaining electrochemical studies, “the electrochemical cell was disassembled and soaked in hot sulphuric acid for at least 3 hrs” please explain why you are using hot condition and mention temperature range and how you are maintaining up to 3hrs.
2. In 3.1 for cyclic voltammetry behavior in acidic and alkaline condition, please check for better understanding and also see catalytic improvements    try different M of 0.1 M (acid) and 0.5M (alkaline) respectively. 
3. In the table 1for 0.5M H2SO4 (UPD of H) as E/mV increases from 100 to 200 and the CpH values showing decreasing order but in the case of 0.5M H2SO4+ 1.85*10-5 M ACN (UPD of H) @ 150 mV CpH values increased and then decreased please explain why so? 
4. In the table 2 for 0.1M NaOH (UPD of H) as E/mV increases from 100 to 200 and the CpH values showing decreasing order but in the case of 0.1M NaOH + 1.85*10-5 M ACN (UPD of H) @ 200 mV CpH values increased while compare to 150 mV please explain why? 
5. Other than the aforesaid correction, please revise the manuscript for any typo as well as grammatical errors  

Author Response

Reviewer # 2:

1. Concentrated sulphuric acid has been used to clean the working cell from potential organic impurities adsorbed on the glassware. Additionally, the high temperature condition (above ca. 60-80 °C) was maintained for the period of 3 hours by means of laboratory magnetic hotplate stirrer, which was used to facilitate the kinetics of this process. Please note that the above is a standard procedure employed for cleaning glassware in all high quality electrochemistry laboratories.
2. In fact, we have originally studied the HER and UPD processes under the influence of AcN at two selected acetonitrile (1.85x10^-5 and 1.85x10^-3 M) concentrations (see Tables 1 and 2 there for details). Then, examination of the AcN effects at various concentrations of supporting electrolytes is important, but the latter should rather be presented in another experimental paper. However, it has to be stated that further expansion of current manuscript (already quite extensive) into studying of various concentrations of H₂SO₄ and NaOH solutions would only obscure the currently presented data and most importantly the paper’s goal!
3. A general consequence of rising electrode potential (for both 0.5 M H₂SO₄ and 0.1 M NaOH supporting solutions) along with the R_H resistance values is diminution of the C_pH pseudocapacitance parameter (characteristic UPD of H behaviour at Pt and other metals exhibiting this phenomenon). Understandably, the surface adsorption of AcN molecules results in a significant reduction of the C_pH parameter (see Tables 1 and 2 for details). Finally, increased single value of the C_pH recorded in Table 1 in the presence of 1.85x10^-5 M AcN at 150 mV is just an experimental result. One has to understand that not all recorded results always follow the scientifically expected trend/s……..
4. The quoted here by the Reviewer C_pH mismatch is just an analogous problem to that observed in H₂SO₄, but exhibited in NaOH solution (please see the comments given above for sulphuric acid conditions in Table 1).
5. As per the Reviewer’s request, in the revised manuscript additional English language amendment (where necessary) has been made.

Author Response File: Author Response.pdf

Reviewer 3 Report

Authors demonstrate with ac impedance and cyclic voltammetry that acetonitrile causes a substantial detrimental effects to the kinetics of both UPD of H and HER electrode processes compared to bare Pt electrode in acid and alkaline electrolyte. For the reviewer this work is not of high impact whereas it could be revised after major revision.    

The manuscript does not include any physico-chemical analysis of the working electrode before and after addition of acetonitrile. This could be helpful to understand any modification of platinum electrode.    

Eq.3, 4 and 5 appear as "copy and paste". Could you enhance the quality? Why do the authors report only the reactions in acidic environment?

Please, improve the quality of all the figures.

Tables are difficult to easily read and authors need a graph (example hystograms) for a comparison of Pt-based electrode  with or without addition of acetonitrile in solution.

Please increase the number of references, mainly in the introduction section.

Comments for author File: Comments.pdf

Author Response

Reviewer # 3:

1. As per the Reviewer’s request, in the revised manuscript additional English language revision (where necessary) has been made.
2. Research Design; Results Presentation: In our opinion, general structure and content (including extended experimental descriptions) of this manuscript have been prepared appropriately and with sufficient care. Also (unfortunately), the Reviewer did not point out at specific deficiencies within the original manuscript……
3. Indeed, no physico-chemical analysis of Pt catalyst has been carried-out. However, it must be pointed out that the structure and general mechanism of acetonitrile adsorption on the Pt surface was originally (and rather in detail) elaborated in previous studies by the B.E. Conway Electrochemistry Group (see Refs. 7-9 of the original manuscript). Also, one could expect that the final product of AcN reduction on the Pt surface (most likely with an active involvement of UPD and OPD H species) would be ethylamine (see Conclusions section); however, such detailed spectroscopy examinations (although interesting, but very difficult to perform during the worldwide expansion of the COVID-19 pandemic) were definitely beyond the scope of our work.
4. In the revised manuscript, equations 3-5 have all been remade. Also, additional, alkaline-based HER equations have been integrated with the manuscript (see equations 6-8 on page 2 of the revised manuscript).
5. In the revised manuscript, the quality of all Figures has been improved.
6. Indeed, both manuscript Tables include numerous results, but all information (including the examined processes, AcN concentrations, the recorded capacitance and resistance parameters, etc.) has been clearly presented (see also bold and italic fonts there). Now, introduction of new Figures (also containing numerous and likely to some extent unclear details) into the manuscript would not only change some of its structure, but it would definitely not be in-line with the Comments of other two Reviewers……
7. Introduction: as per the Reviewer’s request, Introduction section of the revised manuscript has now been enriched with additional reference papers (see Refs. 1-6 there).

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I carefully read the article. The article is well revised. The authors nicely integrated reviewer's comments into the manuscript. The article can be published after some correction: nevertheless, it is necessary to provide the data about how the concentration of acetonitrile influence to the rate of hydrogen evolution reaction (for example, at a potential of 0.05 V according to cyclic voltammetry in a solution NaOH and H2SO4, the rate of hydrogen evolution reaction is changes) and how the amount of adsorbed hydrogen on the surface of the platinum electrode is changes with increasing concentration of acetonitrile.

Author Response

In our opinion, we have managed to properly and fully answer all comments raised by this Reviewer (including those concerning the influence of acetonitrile concentration on the rate of hydrogen evolution reaction along with that of the process of UPD of H). The above was clearly & sufficiently presented in the a.c. impedance section of the manuscript (see both Tables, impedance Figures and the corresponding discussion of these results there, but also please refer to our recent “Comments” file: p. 4-8, pages 1 & 2).

 

Moreover, the authors of this work (especially when one of them: Boguslaw Pierozynski is a former Ph.D. student and research associate of Professor Brian Evans Conway) are fully aware of the fact that important details on how acetonitrile chemisorption influences/blocks adsorption of hydrogen atoms on the Pt surface (on poly- and some major single-crystal Pt planes) were originally presented in works published by the University of Ottawa Electrochemistry Group (see details on the potential dependent evaluation of acetonitrile coverages, adsorption transient experiments and anodic H desorption effect in Refs. 7 and 8 of the original manuscript).

 

Also (in reference for cyclic voltammetry Figures 1a and 1b), it has to be stated that the bulk process of the HER has been examined for potentials negative to the RHE (see Tables 1 and 2 there). The new sharp cathodic features observed in the presence of AcN near the reversible potential for hydrogen evolution in Figure 1 (especially in alkaline solution) could be due to the further process of surface CH₃CN reduction. Also, it is well-known (especially from numerous HER/UPD of H, Pt-based articles) that hydrogen evolution at modified surfaces or at surface-defects (e.g. induced via extended high-temperature annealing) might be initiated “sooner”…….. Nevertheless (again), the above was outside the scope of our work.

Reviewer 3 Report

Authors improved the overall manuscript. Thus, the reviewer accepts as it is.

Author Response

We wish to express our sincere appreciation for the Reviewer’s in-depth comments, suggestions and corrections, which have greatly improved our manuscript.