Kinetics of Electrocatalytic Oxygen Reduction Reaction over an Activated Glassy Carbon Electrode in an Alkaline Medium
, Raed H. Althomali 3, Jehan Y. Al-Humaidi 4,*, Mohammed M. Rahman 5 and Mohammad A. Hasnat 1,*Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe promising results were obtained in the paper on the modification of glassy carbon to enhance its electrocatalytic activity in the oxygen reduction reaction. Meanwhile there are several remarks according to which the manuscript is recommended to be revised before acception.
1. Was the surface area of GC electrode and its roughness changed during the modification? Why the current but not the current density was used in the analysis of electrochemical data?
2. Line 137 "Oxygen saturated 0.1M NaOH solution...'", but Line 153 "...in air saturated O2 in 0.1M NaOH", and Lines 158-159 "...by activate GC electrode in air saturated 0.1 M NaOH solution, ...". What kind of saturation was used in fact?
3. Line 146. It is necessary to substantiate in more detail the determinative role of the C=O groups formation in the ORR process acceleration.
4. Line 232-233. "Hence, the oxygen reduction reaction on activated GC (activate up to +1.8V) is a two electron transfer mechanism, and the final product is hydrogen peroxide". Can the product be identified by independent method to confirm this conclusion?
5. Line 263-264. Can the period of the stable worj of the electrode be estimated (hours? days? weels or more?)
6. The presentation of the results should be improved. The scale of the graphs on Figures 2B (both axes), 3A (both axes), 3B (Y-axis), 4 (both axes), 5 (Y-axis), 6 (both axes) is made very poorly, with such inconvenient step for analysis it is very difficult to compare the values of the measured values. The potentials are not indicated on Fig. 6C. Why the voltammograms for non-activated GC electrode was not shown on Fig. 6 for comparison?
7. There are many typos through the text, including subscripts in some equations; Lines 175, 191: Why the equations (1) and (2) are referred to? It seams to be wrong; Figure 5: Current units are not specified. Line 192-193: "...a larger Tafel slope suggests more polarization ..." Why then "... the η and Tafel slope have an inverse relationship"? What do "the quantity of electron allocations" (Lines 204-205), "the concentration of ORR in bulk" (Lines 205-206) mean? Why was 96500 C used as the Faraday constant instead of 96485 C/mol? Line 239: "... Fig. 4 (A) ...". Maybe 6(A) ? It is recommended to correct the manscript carefully.
Author Response
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Reviewer 2 Report
Comments and Suggestions for AuthorsThere is a significant problem with the motivation of this study. In the literature review, the authors point out the importance of the oxygen reduction reaction and the need to create cheap catalysts for this reaction. However, glass graphite is a poor catalyst, and modifying it does not solve the problem. At the same time, the authors, based on the results of the work, conclude that the resulting modified glass graphite is an excellent catalyst for the production of hydrogen peroxide. In this case, in the lit review it is necessary to pay more attention to the importance of hydrogen peroxide, its production and use.
This work is rather of fundamental importance; the results do not allow us to hope for obtaining good catalysts for applied purposes.
Table 1 contains various literature data, however, since the authors studied the activity of materials in an alkaline environment, it is necessary to add more sources studying the activity of carbon-containing materials in an alkaline environment.
Author Response
Replies to reviewer:02
There is a significant problem with the motivation of this study. In the literature review, the authors point out the importance of the oxygen reduction reaction and the need to create cheap catalysts for this reaction. However, glass graphite is a poor catalyst, and modifying it does not solve the problem. At the same time, the authors, based on the results of the work, conclude that the resulting modified glass graphite is an excellent catalyst for the production of hydrogen peroxide. In this case, in the lit review it is necessary to pay more attention to the importance of hydrogen peroxide, its production and use.
This work is rather of fundamental importance; the results do not allow us to hope for obtaining good catalysts for applied purposes.
Table 1 contains various literature data, however, since the authors studied the activity of materials in an alkaline environment, it is necessary to add more sources studying the activity of carbon-containing materials in an alkaline environment.
Authors’ reply: Many thanks to this reviewer. The work is important from the point of elucidating the reason of activation in attaining different electrochemical reactions. Here, we investigated the how potential activation can enhance ORR in the alkaline medium. As per suggestion of the reviewer, we have updated the references in Table 1. Now, we expect that the reviewer will be happy to accept our work for publication in this reputed Journal.
Reviewer 3 Report
Comments and Suggestions for AuthorsIn this manuscript, the authors reported very interesting results on how the anodization treatment of a glassy carbon electrode (GCE) in acidic media would facilitate its oxygen reduction reaction (ORR) kinetics in alkaline electrolyte towards a two-electron pathway. This work can provide insights into the catalytic effect of anodized GCE in two-electron ORR for hydrogen peroxide production, an important issue that has long been overlooked. The results were generally well organized and the manuscript were presented in a concise manner. I would suggest publication pending revisions that address the below concerns.
1. Figure 1, this reviewer has some queries about the XPS data. How come the three peaks do not overlap in the spectra? Are the author already showing the deconvoluted peaks? How about the original XPS spectra? Also, the authors discussed the change of peak intensity with change of anodization potential. However, from the figures, it is not quantitative. In other words, it is not obvious to see the changes directly from the spectra. The authors might consider plotting the relationship between peak intensity (or peak ratio) and anodization potential.
2. To appeal to a broader readership, recent works on ORR can be referenced in the Introduction (e.g., Energy Fuels 2021, 35, 13585; Small Methods, 2018, 2, 1800071).
3. For the data presented in Table 1, the authors noted that “All measurements have been carried out using Ag/AgCl (sat. KCl) as the reference electrode”. However, they still need to double check the reference scale used in the original publications. Please check Ref. 39 and Ref. 40 because the potential is not in a similar range as that of other reported values. These might be potentials against the RHE reference.
4. From figure 6b, we can see that the electron transfer number for the oxygen reduction reaction on activated GC (activate up to +1.8V) is 2. How about the electron transfer number for the other control samples, like the pristine GC and the GC activated at 1.5 V?
5. The authors claimed that the exchange current density at 0.26V was determined from the intercept of K-L plots (0.26V) by using equation (4), which was found 9.5×10-3 cm s-1. Why did this exchange current density have a unit of cm s-1?
6. The authors claimed that the standard reduction potential was obtained 0.27V. How was this determined from Figure 6d? Is it “0.27 V” or “-0.27 V”?
7. Related to comment 5 and 6, if changes are made, please also make changes to the Abstract and other relevant parts of the manuscript.
8. Figure 7, on the current scale, no numbers were given.
Comments on the Quality of English LanguageMinor changes to the writing are needed. For instance, in the Abstract “to synthesis hydrogen” (line 16) needs to be revised into “to synthesize hydrogen”, and the sentence at line 68 in the Introduction needs to be checked for grammar.
Author Response
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Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have taken into account the majority of comments. There are questions left concerning the roughness factor determination and use. (i) In what potentials interval the pristine and activated GCEs were scanned in 0.1M NaOH solution at variable scan rates? Are the currents obtained in such a way and shown on Figure S2, correspond to EDL charging only? Why then the currents on this figure are not extrapolated to the origin? (ii) Why the current densities on Figure 6 were not corrected taking into account the roughness factor found for activated GC electrode? The Figure 6 seems to be not changed.
Author Response
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Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have made the necessary additions, although the motivation for the work in the literature review is not clearly defined. I would like to clearly define effective catalysts for what process the authors wanted to obtain - the reaction of oxygen reduction to water or the production of hydrogen peroxide.
Author Response
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