Improved the Methanol Electro-Oxidation and Carbon Monoxide Tolerance for Direct Methanol Fuel Cells Using Strontium Molybdate

Round 1

Reviewer 1 Report

The article presents a detailed and qualitative study the activity of new materials in the methanol oxidation reaction. The article can be published, however, there are some remarks:

1.    In Figure 8, there is some discrepancy in the values of the maximum current density of the samples. So, in figure «a» the sample Pt/C seems to be noticeably better than Pt/Sr_0.50Mo_0.50O_4-δ-C. Explain the reasons or make changes to the text.

2.    Are the authors sure of such accuracy of the measured ESA?

3.    You need to work on the figures. In Figure 4c, the inscriptions and axis labels are poorly readable. The lines on the Nyquist plots should be made in color, consistent with the other plots.

4.    It is necessary to add to the methodology a description of how equivalent schemes were determined.

Author Response

Reviewer 1

1. In Figure 8, there is some discrepancy in the values of the maximum current density of the samples. So, in figure «a» the sample Pt/C seems to be noticeably better than Pt/Sr₅₀Mo_0.50O_4-δ-C. Explain the reasons or make changes to the text.

Reply:

The better reasons for DMFCs performance of Pt/Sr_0.50Mo_0.50O_4-δ-C has made on page 12.

2. Are the authors sure of such accuracy of the measured ESA?

Reply:

The electrochemically active surface area (ECSA_H) was calculated and using the following equation: ECSA_H [m²/g] = Q_H / (0.21 [mC/m²] × m_Pt) [57], where Q_H [mC/cm²] is the average of the integrated hydrogen adsorption and desorption area [mA/cm²·V] eliminating the double layer region [58] such as Figures 5(b) and 6(b) obtained by Origin 8.5 software. The ECSA_CO was calculated using the following equation: ECSA_CO [m²/g] = Q_CO / (0.42 [mC/m²] × m_Pt) [60]. Q_CO [mC/cm²] in this equation is the charge under the CO oxidation peak such as Figures 5(b) and 6(b) obtained by Origin 8.5 software.

3. You need to work on the figures. In Figure 4c, the inscriptions and axis labels are poorly readable. The lines on the Nyquist plots should be made in color, consistent with the other plots.

Reply:

The inscription of the equivalent has been modified, as shown in Figure 5(c). As shown in Figures 5(c) and 6(c), all lines on the Nyquist pots have been made in color.

4. It is necessary to add to the methodology a description of how equivalent schemes were determined.

Reply:

The experimental impedance data fitted using EIS Spectrum Analyser software obtained the equivalent circuit model. The description has been added on page 14.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript entitled “Improved the Methanol Electrooxidation and Carbon Monoxide Tolerance for Direct Methanol Fuel Cells using Strontium Molybdate” by Chiang and Hsu; were used Pt/SrMoO₄@valcun carbon as an electrocatalyst for methanol electrooxidation (MOR) and carbon monoxide (CO) tolerance. The physical and chemical morphology studies of prepared electrocatalysts have been characterized by using various techniques such as XRD, SEM, TEM, XPS, etc. The present manuscript is fascinating. The author’s presentation and results in the discussion part are good. However, the authors should address the following major issues in their manuscript before publication in the “Catalyst” journal:

-       I recommend to adding a table to compare and discuss the electrocatalytic activity, onset potential, and electrochemically active surface area of the Pt/SrMoO₄@valcun carbon with other catalysts in the literature.

-       Was the effect of scan rate on methanol oxidation on the surface of the catalyst studied?

-       The conditions for calcination (e.g. Heating rate, atmosphere, etc.) should be mentioned in the experimental part.

-       What is your explanation for the decrease in conductivity after the calcination of SrMoO₄?

-       Was the electrocatalytic activity of SrMoO4 without platinum tested before and after calcination?

Author Response

1. I recommend to adding a table to compare and discuss the electrocatalytic activity, onset potential, and electrochemically active surface area of the Pt/SrMoO₄@valcun carbon with other catalysts in the literature.

Reply:

The onset potential and ECSA for MOR and COR of various electrocatalysts have been shown in Table 2 and Table 3. Moreover, their electrochemical performances have been discussed on pages 7-8.

2. Was the effect of scan rate on methanol oxidation on the surface of the catalyst studied?

Reply:

We apologize for this comment. We didn’t study different scan rates on methanol oxidation of the surface of Pt/Sr_0.5Mo_0.5O_4−δ-C.

3. The conditions for calcination (e.g. Heating rate, atmosphere, etc.) should be mentioned in the experimental part.

Reply:

The conditions for calcination have mentioned in section 3.1 of the experimental part.

4. What is your explanation for the decrease in conductivity after the calcination of SrMoO₄?

Reply:

In XPS results, the relative areas of integrated peak intensities of Mo⁵⁺ decreased, and in contrast to that of Mo⁶⁺ increased with calcination temperature increase, as shown in Table 1. The Mo⁶⁺ relative area increased, meaning more Sr_0.5Mo_0.5O_4−δ compound formation with increasing calcination temperature. However, the less amount of Mo⁵⁺ on Sr_0.5Mo_0.5O_4−δ compounds could attract fewer Pt²⁺ ions to form metallic Pt⁰ on the surface of Sr_0.5Mo_0.5O_4−δ, causing their conductivity to decrease.

5. Was the electrocatalytic activity of SrMoO4 without platinum tested before and after calcination?

Reply:

We apologize for this comment. We didn’t discuss the electrocatalytic activity of SrMoO₄ without platinum being tested before and after calcination. Due to 15%-Pt/uncalcined Sr_0.5Mo_0.5O₄-C electrocatalyst has a lower power density (0.84 mW/cm²). Therefore, without Pt of Sr_0.5Mo_0.5O₄ before and after calcination conjectured that MOR and COR could be lower.

Author Response File: Author Response.pdf