Pt Monolayers on Electrodeposited Nanoparticles of Different Compositions for Ammonia Electro-Oxidation
Round 1
Reviewer 1 Report
This paper demonstrated the Pt monolayer deposited Ru, Rh, Pd, Ir, and Au nanoparticles and investigated their electrocatalytic activity for ammonia oxidation reaction. As the authors mentioned in introduction, similar research was done by same author. [ref 18,32] However, in this paper, the various Pt monolayer deposited Ru, Rh, Pd, Ir, and Au nanoparticles were prepared and tested. The manuscript is well written, however, there are a few questions for the result and discussion of experimental datum before the publication.
Comments and questions to reinforce the manuscript:
The Cu layer was introduced as an adhesion layer for Pt layer. After the galvanic exchange, the remaining Cu amount was used for the calculation of substituted Pt amount as shown in Table 1. Then, the composite nanoparticles have three components; Pt, Cu, and (Ru, Rh, Pd, Ir, or Au). How does the remaining Cu affect the activity of composite nanoparticle?
In Experimental section, it will be good for author to explain the detail how the NP on the GCE was transferred to the TEM grid in Figure 5 (TEM image). In addition, is there any other image with high resolution to show the lattice (or mismatch) of Pt monolayer on NP?
In Figure 7, the Pt/Au NP composite show better current density. How is the value comparing it with other reference materials or previous works?
Author Response
Response to Reviewer 1 Comments
This paper demonstrated the Pt monolayer deposited Ru, Rh, Pd, Ir, and Au nanoparticles and investigated their electrocatalytic activity for ammonia oxidation reaction. As the authors mentioned in introduction, similar research was done by same author. [ref 18, 32] However, in this paper, the various Pt monolayer deposited Ru, Rh, Pd, Ir, and Au nanoparticles were prepared and tested. The manuscript is well written, however, there are a few questions for the result and discussion of experimental datum before the publication.
Comments and questions to reinforce the manuscript:
Point 1: The Cu layer was introduced as an adhesion layer for Pt layer. After the galvanic exchange, the remaining Cu amount was used for the calculation of substituted Pt amount as shown in Table 1. Then, the composite nanoparticles have three components; Pt, Cu, and (Ru, Rh, Pd, Ir, or Au). How does the remaining Cu affect the activity of composite nanoparticle?
Response 1: Thanks for the reviewer’s comment. The preparation of PtML-M (Ru, Rh, Pd, Ir, or Au) particles mainly involves the underpotential deposition of Cu monolayer on various supporting nanoparticles and the subsequent replacement of Cu monolayer with Pt2+ ions. In this process, it was kept for a relatively long time of 20 min to ensure the complete replacement of Cu monolayer by Pt2+ ions in manuscript, which has also been reported by previous literature [1]. Therefore, it can be considered that there is no residual Cu on the supporting catalyst surface. Previous work using the same preparation method also confirmed that Cu was completely replaced and no Cu is left on the supporting catalyst surface [1,2]. Besides, the CV curve of the underpotentially deposited Cu has been reported by previous literature and the redox peak of Cu occurs at about 0.5 V (vs. RHE) [2] in H2SO4 solution, while no peak is observed at around 0.5 V (vs. RHE) in CV curves of PtML-M (Ru, Rh, Pd, Ir, or Au) nanoparticles measured in H2SO4 solution in the present work. This can exclude the possibility that there is residual Cu on the supporting catalyst surface. Based on the above discussion, it is believed that the underpotentially deposited Cu does not remain on the supporting nanoparticles surface, and thus the effect of Cu on the activity of catalysts is not considered in the manuscript.
Point 2: In Experimental section, it will be good for author to explain the detail how the NP on the GCE was transferred to the TEM grid in Figure 5 (TEM image). In addition, is there any other image with high resolution to show the lattice (or mismatch) of Pt monolayer on NP?
Response 2: According to the reviewer’s comment, the details of the nanoparticles on the GCE transferred to the TEM grid were added in experimental section. For the TEM testing, the electrodeposited nanoparticles were gently scraped and dispersed in ethanol on surface of GCE, and then the nanoparticle dispersions were transferred onto a Cu grid, which was directly conducted on surface of GCE. The relevant statement has been provided in page 12 of manuscript.
In addition, it is a quite useful suggestion for the authors to provide high resolution TEM image. As a typical representative, the high resolution TEM (HRTEM) of as-prepared PtML/Au nanoparticles are provided in page 11 of manuscript since it exhibits highest specific activity among the obtained catalysts. The HRTEM image shows the clear lattice fringes indicating a high crystallinity of the PtML/Au nanoparticles, and it also reveals that the PtML/Au nanoparticles are composed of multiple crystalline domains, suggesting the polycrystalline structure. Both Pt and Au are FCC structure materials with slightly differing lattice parameters: a = 3.92 Å for Pt and 4.08 Å for Au, so that 4.08% lattice mismatch exists between the two [3]. Therefore, it is difficult to directly observe the tiny lattice mismatch from HRTEM images of PtML/Au nanoparticles in the present work. Based on density functional theory calculations, previous work [4] has reported that the lattice mismatch between the PtML and Au results in a tensile strain exerted on the PtML, which is in favor of promoting electro-oxidation of methanol and ethanol. It is found that the tensile strain exerted on the PtML also enhanced catalytic activity for electro-oxidation of ammonia in present work. The reviewer’s comment gives a good guidance for our work. In our future work, the spherical aberration correction electron microscope with high resolution on atomic level will be tried to continue the research on this issue on mismatches of Pt monolayer on nanoparticles. The relevant statement has been added in page 9 of manuscript.
Point 3: In Figure 7, the Pt/Au NP composite show better current density. How is the value comparing it with other reference materials or previous works?
Response 3: According to the reviewer’s comment, the SA of PtML/Au nanoparticles prepared in this work for ammonia electro-oxidation was compared with previous work, and the corresponding values of SA are provided in Table 2 of manuscript. It is seen that the obtained PtML/Au nanoparticles exhibit relatively high SA for electro-oxidation ammonia among the various catalysts. The relevant statement has been added in page 9.
References
1. Zhang, J.; Mo, Y.; Vukmirovic, M.B.; Klie, R.; Sasaki, K.; Adzic, R.R. Platinum Monolayer Electrocatalysts for O2 Reduction: Pt Monolayer on Pd(111) and on Carbon-Supported Pd Nanoparticles. J. Phys. Chem. B 2004, 108, 10955-10964.
2. Adzic, R.R.; Zhang, J.; Sasaki, K.; Vukmirovic, M.B.; Shao, M.; Wang, J.X.; Nilekar, A.U.; Mavrikakis, M.; Valerio, J.A.; Uribe, F. Platinum Monolayer Fuel Cell Electrocatalysts. Top. Catal. 2007, 46, 249-262.
3. Mathur, A.; Erlebacher, J. Effects of substrate shape, curvature and roughness on thin heteroepitaxial films of Pt on Au(111). Surf. Sci. 2008, 602, 2863-2875.
4. Li, M.; Liu, P.; Adzic, R.R. Platinum Monolayer Electrocatalysts for Anodic Oxidation of Alcohols. J. Phys. Chem. Lett. 2012, 3, 3480-3485.
Reviewer 2 Report
Dear Authors, there are three minor corrections has to be performed
1. (optional) Lines 179-181: when we deal with an agglomeration of NPs it is beneficial to compare an average size of NPs by SEM/TEM and XRD (via Scherrer's equation); i.e., if possible, do perform powder XRD measurements and submit a comparison of these two parameters.
2. (strongly recommended) Lines 183-184: the narrow particle size distribution has been mentioned - please, insert the graphs where distributions will be shown. Ideally, a size distribution graph should accompany every picture with TEM.
3. (recommended) Despite a good introduction and a good review with correct references and exact citations, it will be quite useful for readers to find (in the text) more comparisons with known similar results from other groups. If possible, do mention in the discussions this sort of values, e.g., the surface area of Pt.
I hope these remarks are easy to be used to improve the manuscript. Best wishes!
Author Response
Response to Reviewer 2 Comments
Dear Authors, there are three minor corrections has to be performed
Point 1: (optional) Lines 179-181: when we deal with an agglomeration of NPs it is beneficial to compare an average size of NPs by SEM/TEM and XRD (via Scherrer's equation); i.e., if possible, do perform powder XRD measurements and submit a comparison of these two parameters.
Response 1: Thanks for the reviewer’s comment. As the reviewer mentioned, XRD can be used to estimate the size of nanoparticles. The accurate size of nanoparticles calculated by XRD is usually limited by many factors, such as the instrument and the curve fitting of XRD data. In addition, in the present work, the electrodeposited samples have little loading amount reaching the microgram level, which has also been reported in previous work [1-3]. There is no enough amount of electrodeposited sample for XRD measurements. Therefore, for comparison of the nanoparticle size, 100 nanoparticles were randomly selected and counted in SEM and TEM images, respectively. The size distribution histograms of nanoparticles were provided along with SEM and TEM images, which is convenient for intuitive comparison, and the relevant statements have been added in page 3 and 7 of manuscript, respectively.
Point 2: (strongly recommended) Lines 183-184: the narrow particle size distribution has been mentioned - please, insert the graphs where distributions will be shown. Ideally, a size distribution graph should accompany every picture with TEM.
Response 2: According to the reviewer’s comment, the particle size distribution histograms are provided in the inset of TEM image and the relevant statement has been added in page 7 of manuscript.
Point 3: (recommended) Despite a good introduction and a good review with correct references and exact citations, it will be quite useful for readers to find (in the text) more comparisons with known similar results from other groups. If possible, do mention in the discussions this sort of values, e.g., the surface area of Pt.
Response 3: According to the reviewer’s comment, the surface area of the obtained Pt-based catalysts was compared with that of Pt-based catalysts reported by other groups, and the corresponding values were listed in Table 2 of manuscript. Besides, as an important performance indicator, the comparison of the specific activity (SA) of PtML/Au nanoparticles prepared in present work with previous work was also provided in Table 2 of manuscript. It is quite useful for readers to compare with known similar results from other groups. The relevant statements have been added in page 9 of manuscript.
References
1. Liu, J.; Chen, B.; Ni, Z.; Deng, Y.; Han, X.; Hu, W.; Zhong, C. Improving the Electrocatalytic Activity of Pt Monolayer Catalysts for Electro‐oxidation of Methanol, Ethanol and Ammonia by Tailoring the Surface Morphology of the Supporting Core. ChemElectroChem 2016, 3, 537-551.
2. Liu, J.; Chen, B.; Kou, Y.; Liu, Z.; Chen, X.; Li, Y.B.; Deng, Y.D.; Han, X.P.; Hu, W.B.; Zhong, C. Pt-Decorated highly porous flower-like Ni particles with high mass activity for ammonia electro-oxidation. J. Mater. Chem. A 2016, 4, 11060-11068.
3. Liu, J.; Zhong, C.; Yang, Y.; Wu, Y.T.; Jiang, A.K.; Deng, Y.D.; Zhang, Z.; Hu, W.B. Electrochemical Preparation and Characterization of Pt Particles on ITO Substrate: Morphological Effect on Ammonia Oxidation. Int. J. Hydrogen Energy 2012, 37, 8981-8987.
