Gram-Scale Synthesis of Carbon-Supported Sub-5 nm PtNi Nanocrystals for Efficient Oxygen Reduction
Round 1
Reviewer 1 Report
- Page 2 line 74: Please avoid using RT for room temperature
- Page 2, Section 2.2: The first and 2nd paragraphs are pretty similar. Avoid repeatation.
- The authors are requested to put the cyclic voltammograms. PVP and other such capping agents introduces artifacts. CVs may help. In any case I think CV is the basic electrochemical characterization that should be performed.
- Page 4, Figure 2: The authors must calculate the lattice parameter at least for PtNi/C -200 and compare it against Pt. The authors should also check the phase diagram of Pt-Ni for intermetallics and comment accordingly.
- Page 4 line 55: The lattice spacing of 0.216 corresponds to what. Pt or some composition of Pt-Ni.
- In figure 5(a) as well as SI (S5,S7,S8,S13): The limiting current is much lower for commercial catalysts in both acid and base which is unexpected. The authors must comment on it and possibly repeat the experiments with lower loading of catalysts on the RDE electrode.
- Figure 5 (b) Were the Tafel plots corrected for mass transfer and capacitance?? The range of current seems to be very small, less than an order of magnitude change.
- Figure 5 (e) The authors must explain the reason of very high oxidation currents for commercial Pt/c. It is unexpected.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
This work reports on one-pot wet-chemical route for carbon-supported sub-5 nm PtNi nanocrystals with a ~3% Pt loading. The as-prepared low Pt catalysts show a high oxygen reduction activity of 0.66 A mgpt-1 and outstanding durability over 10000 potential cycles. The mass activity and specific activity are 3.89 times and 9.16 times to those of 5% commercial Pt/C. For sure, achievement of particle size in the 5nm range is very interesting.
However, some important aspects must be clarified, especially regarding “gram-scale synthesis” terminology. In 2.2. electrocatalyst section, all masses of used catalyst precursors are in the milligram-scale. Since term “gram-scale” is mentioned in the title and should play a relevant role in the manuscript, this contribution is not suitable for publication in that form. It seems that material from so-called "gram-scale" synthesis has not been tested regarding its ORR activity. If the authors are not able to clearly support this concept with convinced arguments/references, all information related to gram-scaling have to be removed from the manuscript.
Other important comments:
- PtNi synthesis using metal acetylacetonate precursors is not new (doi.org/10.1021/nl3032795). The authors have to clearly underline/highlight novelty of their synthesis route and mentioned/compared it with already published ones.
- Since usually Pt alloys like PtNi are commonly used in acidic PEMFC cathode, it is very surprising that its activity for ORR was evaluated in alkaline KOH solution where non-noble metals are preferred.
- Results on activity of as-prepared PtNi catalysts for ORR in alkaline solutions should be compared with other similar works from the literature.
- The figure 5e on measurement in methanol containing electrolyte as well as corresponding comment are not consistent with the rest of the work and result evaluation/interpretation is very questionable. Since Pt concentration in PtNi alloy is much lower than in pure material, lower MeOH oxidation rate is obviously expected. Therefore, for fair comparison current intensity should be normalized to Pt mass only. Also here, motivation for testing methanol tolerance is not clear since Direct Methanol Fuel Cell use to operate with proton exchange Nafion membrane (acidic).
- PtNi atomic/molar composition of the best performing alloy material should be mentioned in abstract and conclusion sections.
Some minor remarks:
- p.3, line 124: in ADT description, the scan rate is missing. what is the speed of potential sweep bet. 0.6-1.1 V during ADT?
- p.2, line 70-82: in sec. 2.2 the description is repeated twice.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
In Gram-Scale Synthesis of Carbon-Supported Sub-5 nm PtNi Nanocrystals for Efficient Oxygen Reduction manuscript, the authors present a one-pot wet-chemical strategy to controllably synthesize carbon-supported sub-5 nm PtNi nanocrystals with a ~3% Pt loading. The results are interesting and could be suitable for publication in this journal after the following major corrections are addressed
1. The authors should note in the Abstract part all techniques of physicochemical characterization of examined samples used in the manuscript ( XRD, TEM, EDS, XPS, and ICP-OES ). Also, add some ORR kinetics parameters (number of exchange electrons, Tafel slope, half-wave potential, or onset potential during ORR) of the examined samples. Please, revised the next sentence: "Alloying Pt with a transition metal can greatly improve the activity and durability for oxygen evolution reaction (ORR)."
2. Please add appropriate references in the next sentence: "The diffraction peak between 20° and 30° is consistent with the Vulcan XC-72 (Fig. S2)."
3. The authors should present and discuss all physicochemical characterization details (XRD, TEM, EDS, XPS, and ICP-OES) of PtNi/C-3:1, PtNi/C-2:1, PtNi/C-1:1, and PtNi/C-1:3 samples, also of PtNi/C-150 °C, PtNi/C-170 °C, and PtNi/C-190 °C samples in the 3.1. section.
4. In the manuscript is noted that: " The considerable difference in onset and half-wave potential between these catalysts indicates that ORR activity is also determined by the metal contents of alloy nanoparticles." Please, explain this behavior of PtNi electrocatalysts during ORR.
5. The authors noted: "The polarization curves indicate that the Vulcan XC-72 supported PtNi nanoparticles have the best oxygen reduction performance." Why?
6. Please add appropriate references in the next sentence: " The main reason is that the contraction of Pt lattice spacing is more conducive to weaking the binding between O/OH and Pt sites."
7. Please, present onset, half-wave potential, Tafel slope, and the number of transferred electrons during ORR for all tested PtNi electrocatalysts and compared these results with literature reports.
Comments for author File: Comments.pdf
Author Response
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Round 2
Reviewer 1 Report
The manuscript can be accepted.
Author Response
Thanks.
Reviewer 2 Report
Most of my comments have been considered in the submitted revised version. However the electrolyte aspect is very confusing.
"Acidic and alkaline electrochemical properties 117 were tested in 0.1M KOH and 0.1M HClO4 solutions, respectively." It is very curious that results of experiment in HClO4 didn´t appear in the main document and are shown just in SI file. There are also no comment about these experiments with exception of 4e- transfer. Furthermore there are no indication of electroyte used related to results on PtNi activity for ORR in abstract/conclusion section and to references mentioned in introduction section.
Since as-prepared catalysts have been test in both alkaline and acid electrolytes, clear distintion between the results/comments should be done. Results related to Pt/XC72 activity for ORR in HClO4 presented in S6 and S9 are also very curious. The authors should clearly underline applications, namely membrane alkaline/acidic fuel cells and mention related references in introduction section. Also funded scientific comments on experiments in both systems are required. If the main focus is alkaline system, measurements in acidic HClO4 should be completely removed from the manuscript to avoid any confusion.
Author Response
We greatly appreciate the reviewer for recognizing the significance of our manuscript and all the thoughtful comments which help us to further improve our manuscript. The as-prepared catalyst shows a superior oxygen reduction activity in alkaline solution. At the same time, the catalyst exhibited poor performance in acidic solution. To avoid confusion for readers, we have removed the relevant test data in acidic solution as your suggestion.
Reviewer 3 Report
The results are improved and would be suitable for publication in this journal.
Author Response
Thanks.
Round 3
Reviewer 2 Report
As already mentioned in my previous report, the authors have to clearly point out in the abstract and introduction section the nature of the electrolyte and the kind of cell setup used. Please add these very important information for clarification accordingly:
Line 15: The as-prepared PtNi/C-200 catalyst with a Pt/Ni atomic ratio of 2: 3, shows a high oxygen reduction activity of 0.66 A mgpt-1 and outstanding durability over 10000 potential cycles in 0.1 M KOH under half-cell conditions...
Line 57: Benefiting from the PtNi alloy structure, the obtained PtNi/C shows excellent ORR activity, with a mass activity of 0.66 A mgpt-1 and a specific activity of 2.13 mA cm-2 at the potential of 0.9 V vs. reversible hydrogen electrode (RHE) in 0,1 M KOH, ....
Author Response
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Author Response File: Author Response.pdf
Round 4
Reviewer 2 Report
Since all my comments/remarks have been considered, I recommend this contribution for publication.
