Synthesis and Evaluation of PtNi Electrocatalysts for CO and Methanol Oxidation in Low Temperature Fuel Cells

Round 1

Reviewer 1 Report

In the present manuscript titled as “Synthesis and evaluation of PtNi electrocatalysts for CO and methanol oxidation in low temperature fuel cells” authors reported the synthesis and characterization of Pt(Ni)/C and PtRu(Ni)/C catalysts. Both these catalysts were then studied for CO oxidation and Pt(Ni)/C catalysts were also investigated for methanol oxidation. Bimetallic catalysts were shown to be higher active compared to the Pt/C. Although the results shown here are interesting, significant improvement is necessary for before its publication

Please find below the comments and suggestions that needs to be addressed in detail.  

1. The quality of the English language is poor. It is very difficult to understand some of the sentences and some of the sections. While the results are interesting, poor choice of language hinders its credibility. I suggest authors to check with a language editor prior to the next submission.
2. Did authors do an elemental analysis to determine the wt% of Pt and Ni in the catalysts? Although TEM-EDS is a powerful technique to do elemental analysis, it might give an information based on the local structure. It is worth to carry out an elemental analysis and compare the results obtained by TEM-EDS.
3. Authors should use one digit after decimal to describe the peak position in XRD pattern. Why Pt 111 peak shows a sift towards lower 2θ value i.e. expansion of Pt lattice. While I understood this observation could not be explained by alloy formation, I could not follow the author’s conclusion about it. Can authors clarify this more?
4. Can authors calculate average particle size and particle size distribution from TEM image and compare with crystallite size obtained from XRD. They should add a column regarding the TEM particle size in Table 1.
5. Most of the literature concerning Ni nanoparticles and bulk Ni show FCC crystallographic phase of the Ni which is the most stable one, however, this articles shows the presence of hexagonal Ni. Can authors provide a brief explanation in this regard?
6. I could not find TEM characterization of PtRu(Ni)/C catalysts. Can authors add the characterization detail for the same as that has been tested for CO oxidation?
7. Page 8, line 242-245 – authors concluded that two peaks in CO oxidation (as shown in Figure 4a) is due to the structure sensitivity. However, later part an explanation was provided based on Pt particles with different Ni domain. I understand Pt rich PtNi particles are different than Ni rich PtNi particles, consequently, show different activity. However, structure sensitivity may not be a correct expression to describe the same. It is more often appropriate to distinguish particles with different size. Is the size of the PtNi particles different with different composition?
8. Page 8, line 246 – “can b” should be replaced as “can be”
9. The higher activity of Pt(Ni)/C was attributed to the electronic properties of PtNi particles wherein facile charge transfer from Ni to Pt facilitates the CO oxidation. However, no experimental evidence was provided in this case. Authors should provide XPS of Pt and Ni and analyze the charge transfer between these to metallic component
10. I am wondering about the structure of PtNi(Ru)/C particles. Is it a tri-layer structure with Ni core followed by successive Pt and Ru shell. Or is it composed of Ni core with PtRu alloy as shell? Can authors provide more structural details
11. It is apparent that Ru has most significant effect for the CO oxidation. In such case, why authors didn’t test PtRu(Ni) catalysts for methanol oxidation?
12. Page 9, line 276-277 – Authors mentioned that all the curves are normalized to the CO stripping charge. But they should specify CO stripping charge of which sample. The same applies to the Figure 1 describing the H UPD region of Pt/C and Pt(Ni)/C
13. Can authors explain the ESCA trend in detail that are shown in Table 1? Why it is highest in case of Pt/C and decreases in case of 8:1 Pt(Ni) and increases again with 3:1.
14. Authors should report the mass activity and specific activity at a specific potential otherwise it is difficult to follow the trend. For example at Figure 5a & 5b, activity of theses catalysts changes differently as a function of potential and hence comparison needs to be made at a specific condition.
15. The discussion in the methanol oxidation mechanism is not very clear. Also, it seems authors invoked oxidation of Ni to Ni(OH)2 plays a major role by facilitating CO oxidation. However, in a previous section where of CO oxidation is described, authors mentioned that it is the charge transfer from Ni to Pt is the one which contributes significantly as opposed to the Ni oxidation. Can authors clarify this anomaly?
16. What is the physical significance of decrease in charge transfer co-efficient in the present reaction condition? Can authors provide more insight into this?
17. Can authors use “V vs Ag/AgCl” rather “V” in all the figure caption. It is easier for reader to follow the figure.

Author Response

Thanks for your revision.

Please, see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The structural analysis of core-shell of Pt-Ni is interesting. The authors see the impact of the percentage of Ni to Pt that give more negative onset potential as well as activities. The paper itself is not really focused on Pt-Ni system. Please clean up the paper, and submit it. The reviewer recommends "accepted with minor revision"

1.  I do not understand why you mentioned PtRu alloy system and showed the equation but in your experiments, there is no comparison of PtNi vs. PtRu. Please compare it. 

2. In Table 1, EDX composition is inaccurate way to determine the content's profile. Please provide ICP method to proof Ni contents.

3. In Table 1, measure particle size distribution and compare XRD size, TEM size, and ECSA size. you can calculate dispersion form ECSA.  

4. Remove PtRu/C Co stripping part. Your paper is not for PtRu/C explanation. This is not a review paper.

5. need to do some more experiments such as stability test (chronoampertrometry). 

6.  Make the conclusion with one paragraph. It's not a summary of each paragraph. 

Author Response

Thanks for your revision.

Please, see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

This work is dealing with Synthesis and evaluation of PtNi electrocatalysts for CO and methanol oxidation in low temperature fuel cells. The present paper is worth of being published in the journal Catalysts. However, before publishing the following revisions should be taken into consideration:

 

• ABSTRACT: the authors wrote: In this work, Pt(Ni)/C and PtRu(Ni)/C catalysts were synthesized by electroless deposition of Ni on a carbon dispersion followed by sequenced Pt deposition and spontaneous deposition of Ru species. Line 14. But in Line 151 Figure 1, the authors have done the Ciclic voltammetry only Pt and PtNi, Why in this mesurements the Ru is missing?
• Figure 2 line 188: Have been considered other angles to determinate de particle size? Why the Ptru is not present in the xrd? The standard JCPDS of PtNi may be needed.
• The authors wrote : The size of the nanoparticles agrees with the mean crystallite sizes estimated using XRD (see Table 1) line 208. The particle size may be included in the table 1.
• Figure 3 line 217 TEM. The authors have done the analysis with Ru?
• BET surface area may be needed.
• Figure 5 line 364, the authors have used other concentration of METOH? Why in linear sweep Ru is missing?

Author Response

Thanks for your revision.

Please, see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

Review: Synthesis and evaluation of PtNi electrocatalysts for CO and methanol oxidation in low temperature fuel cells

 

In this article, authors Griselda et al. reported their finding of PtNi/C catalysts for CO and methanol fuel cells. Fuel cells research has long been regarded as a promising solution to the energy crisis. With this regard, this article has its practical importance. The catalysts the authors reported had shown better catalytic performance compared with PtC. The introduction part is lengthy but otherwise, the data are well presented and the paper itself is not hard to follow. I would suggest Catalysts to accept this manuscript. I have a couple of questions:

1. The reported catalyst has a Ni core. Since Ni is not quite stable in either acidic or basic testing media, do the authors observe any loss of Ni or deformation of catalysts after testing, especially after long runs? If no changes, does it suggest that Ni core is completely covered by Pt or PtRu.
2. Could the authors provide more explanation of the role of Ni in this catalytic system. Are the authors suggesting that when they prepare the sample, the Ni2+ is not fully reduced but rather leaving Ni oxide species? Is there a way to identify or quantify the Ni oxide species?
3. Also, could the authors clarify why the trend of ECSA in table 1. Why does the 8:1 sample have the lowest ECSA.
4. In Line 378, should it be J_s0 instead of J_0s.

Author Response

Thanks for your revision.

Please, see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The answers provided are satisfactory and thus I recommend the manuscript for the publication

Reviewer 3 Report

I would like thanks the authors for the revisionated version, this paper can represents a great inspiration for scientific community.