Temperature Influence on the Synthesis of Pt/C Catalysts for Polymer Electrolyte Membrane Fuel Cells
, Gyungse Park 3, Ho-Jung Sun 4, In-Tae Kim 5, Sehkyu Park 2, Hyung-Ryul Rim 6, Hong-Ki Lee 6 and Joongpyo Shim 1,*Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn this manuscript, the authors presented a synthesis of different Pt particle sizes by varying the synthesis temperature and the effects of Pt size on the performance of PEMFC.
Major Comments:
- Show the images processed to obtain the particle size distribution (PSD). I do not think the TEM images shown in Figure 2 are used to get the PSD. These images can be added to Supplementary files. Further deviation in D50 should be reported.
- The Y-axis of Figure 4 (b) is crystallite size (discussion in Lines 133-143), not particle size. Please modify the discussion. The crystallite sizes obtained from XRD do not vary significantly. However, at high temperatures, the sizes vary significantly. Please explain the reason.
- For better representation, please index the XRD peaks in the graph.
- Authors should be careful when discussing particle and crystalline sizes. The confusion is clearly visible in the manuscript.
- It would be interesting to show the parity between crystallite and particle sizes. This also proves the efficacy and repeatability of the synthesis.
- Figure 6 does not show any trend. Probably by adding synthesis temperature as an additional axis, the data can be explainable with possible trends. The data for 0.7V is missing.
- Please include commercial catalyst data in Figure 7 (b) for better understanding.
- The stability aspects of the best catalyst are missing.
- Figure 4 (a) shows Pt formation at 70oC. However, the color change shown in Figure 8 is clearly visible from 100oC. What could be the reason? Does it have any product yield effects?
Minor Comment:
-Line 221: What is CB? CB is not defined.
Author Response
In this manuscript, the authors presented a synthesis of different Pt particle sizes by varying the synthesis temperature and the effects of Pt size on the performance of PEMFC.
Major Comments:
Comment 1: Show the images processed to obtain the particle size distribution (PSD). I do not think the TEM images shown in Figure 2 are used to get the PSD. These images can be added to Supplementary files. Further deviation in D50 should be reported.
Answer: PSD graphs in Figure 3 were drawn from Image analysis (software Image J) of TEM pictures. I added PSD graphs in supplementary information (Figure S1).
Comment 2: The Y-axis of Figure 4 (b) is crystallite size (discussion in Lines 133-143), not particle size. Please modify the discussion. The crystallite sizes obtained from XRD do not vary significantly. However, at high temperatures, the sizes vary significantly. Please explain the reason.
Answer: Yes. It is crystalline size calculated from XRD. We revised it from “particle” to “crystalline” in manuscript. Above 80oC, the Pt particles were clearly impregnated on carbon. However, crystalline size of Pt was slightly decreased from ~3.5nm to ~3.0nm. above 120oC. Actually, we clearly don’t know why it changed according to temperature. We are still working on it.
Comment 3: For better representation, please index the XRD peaks in the graph.
Answer: Each peak of XRD in Figure 4 were indexed.
Comment 4: Authors should be careful when discussing particle and crystalline sizes. The confusion is clearly visible in the manuscript.
Answer: It is defined them in manuscript. Particle size was visually measured from TEM and crystallin size was calculated from XRD.
Comment 5: It would be interesting to show the parity between crystallite and particle sizes. This also proves the efficacy and repeatability of the synthesis.
Answer: Yes, I agree with you. However, the measurement of particle size and crystalline size platinum in Figure 3 and 4 were used by different technique. So, it is very hard to get relationship between visual and optical analyses. We added simple comments for these in line 142~143.
Comment 6: Figure 6 does not show any trend. Probably by adding synthesis temperature as an additional axis, the data can be explainable with possible trends. The data for 0.7V is missing.
Answer: We understood your comments because it’s not clear. However, we want to say that current densities were changed by crystalline size of Pt which was induced from reaction temperature. The dependence for synthetic temperature was already shown in Figure 6(b).
We skipped the graph for 0.7V because of not much change.
Comment 7: Please include commercial catalyst data in Figure 7 (b) for better understanding.
Answer: The cell performance of commercial catalyst was added in Figure 7(b).
Comment 8: The stability aspects of the best catalyst are missing.
Answer: This work is focusing on only reaction temperature during Polyol process. We did not test these catalysts for durability test such as AST. I think durability is beyond of this work.
Comment 9: Figure 4 (a) shows Pt formation at 70oC. However, the color change shown in Figure 8 is clearly visible from 100oC. What could be the reason? Does it have any product yield effects?
Answer: That was another experiment to show the reduction of Pt ion visually. We waited 2-30 min to get samples from solution after reaching the desired temperature. However, normally we sustain 3 h for full reduction of Pt ion. Figure 2~4 show the deposition of Pt particles on carbon under 80oC. We believe 70-80oC is enough temperature to oxidize ethylene glycol. The color of 80oC sample in Figure 8 is mainly due to the duration time of reduction.
Minor Comment:
Comment 11: Line 221: What is CB? CB is not defined
Answer: It is carbon black. We revised it as “carbon black (CB)” in manuscript.
Reviewer 2 Report
Comments and Suggestions for AuthorsIn this manuscript, the authors present the comprehensive characterizations of Pt/C catalysts synthesized using polyol method at different conditions for the application of fuel cell. The results show that Pt/C synthesized at 100 ℃ showed the highest electrochemical activity, which is attributed to the crystallinity of the supported Pt particles. Also, the Pt/C synthesis was proved successful with decreased amount of ethylene glycol and lower synthesis temperature.
Overall the manuscript is in good shape but needs several minor changes, and I have the following comments and questions for the authors related to this manuscript:
1. In line 72 – 74, “Moreover, …, which exceeds 1,000 times for Pt ion.” This sentence needs a reference.
2. In Section 2, line 87, “At lower temperatures, there is relatively more reduction,…” Were the pH measurements conducted independently or in the same reaction mixture? And measured in the same time scale? Although the dehydration reaction of EG may be endothermic, the kinetics will decrease with temperature (which you mentioned later in the manuscript) and thus the conversion should be lower if measured at the same time. Could you give a reasoning or clarification on your statement about “more reduction”?
3. For Figure 4a, it will be better to show the 2θ values assigned to carbon and platinum in the figure (like adding dashed vertical lines). Also, please add in the figure caption what the numbers and “com” means, since they are not that straightforward. For Figure 4b, it will be great to add a brief discussion in the text on whether the results in Figure 4b align with that in Figure 3.
4. For the paragraph in line 164 – 170, It looks like you are missing sentence(s) here to discuss the content of Figure 6a and reference your figure. That way you clarify what do you mean by “The bar graph on the right”.
5. For Figure 6c and 6d, first of all, I would call this more like a V-shaped plot, since the current density does not increase monotonically with the crystalline size of Pt. Therefore, you cannot just draw an exponential trend line and ignore the lower points in the middle, and you need to modify your discussion for this figure too. Second, since in the text your statement is that the current density increases with crystalline size of Pt, you should switch the x and y axis to distinguish the independent and dependent parameters. Lastly, the word "crystalline" in the axis title is not spelled correctly. It misses a "l".
6. A general suggestion for formatting, try not to split the same figure to different pages (Figure 3 and 6), since it will make it harder to read. Same thing applies to figure caption (Figure 1).
Author Response
In this manuscript, the authors present the comprehensive characterizations of Pt/C catalysts synthesized using polyol method at different conditions for the application of fuel cell. The results show that Pt/C synthesized at 100 ℃ showed the highest electrochemical activity, which is attributed to the crystallinity of the supported Pt particles. Also, the Pt/C synthesis was proved successful with decreased amount of ethylene glycol and lower synthesis temperature.
Overall the manuscript is in good shape but needs several minor changes, and I have the following comments and questions for the authors related to this manuscript:
Comment 1. In line 72 – 74, “Moreover, …, which exceeds 1,000 times for Pt ion.” This sentence needs a reference.
Answer: Reference was added in line 74.
Comment 2. In Section 2, line 87, “At lower temperatures, there is relatively more reduction,…” Were the pH measurements conducted independently or in the same reaction mixture? And measured in the same time scale? Although the dehydration reaction of EG may be endothermic, the kinetics will decrease with temperature (which you mentioned later in the manuscript) and thus the conversion should be lower if measured at the same time. Could you give a reasoning or clarification on your statement about “more reduction”?
Answer: pH was measured at same time scale from different batch. It was measured after 3h (which already mentioned in experimental) when temperature reach to desire value. pH indirectly shows the amount of glycolic and oxalic acid as product for the oxidation of ethylene glycol. Low pH means more production of oxalic acid. Thus, we explained more reduction of platinum in manuscript. Honestly, we couldn’t find any relationship between pH of solution after reduction process and physical properties of platinum particles such as size, loading, etc. We are still working on it.
Comment 3. For Figure 4a, it will be better to show the 2θ values assigned to carbon and platinum in the figure (like adding dashed vertical lines). Also, please add in the figure caption what the numbers and “com” means, since they are not that straightforward. For Figure 4b, it will be great to add a brief discussion in the text on whether the results in Figure 4b align with that in Figure 3.
Answer: Index for platinum in Figure 4(a) was added to understand the peaks and the meaning of “Com” was added in caption. The explanation for Figure 4(b) was added for comparing with Figure 3 in detail, as “However, the size in Figure 4(b) are slightly different with that of Figure 3 because the difference may come from using other technique to analyze.”
Comment 4. For the paragraph in line 164 – 170, It looks like you are missing sentence(s) here to discuss the content of Figure 6a and reference your figure. That way you clarify what do you mean by “The bar graph on the right”.
Answer: Thank you for your comments. The explanation for Figure 6(a) was added in manuscript (line 163-165)
Comment 5. For Figure 6c and 6d, first of all, I would call this more like a V-shaped plot, since the current density does not increase monotonically with the crystalline size of Pt. Therefore, you cannot just draw an exponential trend line and ignore the lower points in the middle, and you need to modify your discussion for this figure too. Second, since in the text your statement is that the current density increases with crystalline size of Pt, you should switch the x and y axis to distinguish the independent and dependent parameters. Lastly, the word "crystalline" in the axis title is not spelled correctly. It misses a "l".
Answer: Yes, I agree with your comments. It is clear to show the dependence of Pt size on the cell performance when the x and y axis were switched. We changed Figure 6 (c) and (d).
The words in axis were correctly revised.
Comment 6. A general suggestion for formatting, try not to split the same figure to different pages (Figure 3 and 6), since it will make it harder to read. Same thing applies to figure caption (Figure 1).
Answer: Thank you for your comments. But formatting will be revised by journal.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsMost of the comments were satisfactorily addressed by the authors. A few minor issues need to be rectified for acceptance.
1. Error in D50 should be reported.
2. Figure 4: Peaks at 25o are not indexed.
3. Figure 7 (b): Adding commercial in Fig. 7(b) (instead of 6 (b)) would tell more about the best materials authors developed.
Author Response
Most of the comments were satisfactorily addressed by the authors. A few minor issues need to be rectified for acceptance.
1. Error in D50should be reported.
Answer: D50 was selected from particle size distribution of TEM. The particle in the TEM images was counted as size. Also, the cumulative distribution with particle size is shown in Figure S1 (Supplementary information). What is error in D50?
2. Figure 4: Peaks at 25oare not indexed.
Answer: The peak at 25o was indexed in Figure 4.
3. Figure 7 (b): Adding commercial in Fig. 7(b) (instead of 6 (b)) would tell more about the best materials authors developed.
Answer: Yes. I added the data for commercial catalysts in Figure 7(b).
