Ex-Situ Electrochemical Characterization of IrO2 Synthesized by a Modified Adams Fusion Method for the Oxygen Evolution Reaction
, Bernard J. Bladergroen 1, Vladimir Linkov 1, Bruno G. Pollet 1,2 and Sivakumar Pasupathi 1Round 1
Reviewer 1 Report
The manuscript deals with the IrO2 synthesis by the modified Adams route. This preparation process is well known in the literature. The effect of the calcination temperature has been also widely studied.
The results do not show any relevant novelty but could be useful for a refinement of the preparation process.
Regarding the durability studies, in my opinion, these have been carried out under mild conditions and thus they do not provide any relevant information. Cycling up to 1.4 V does not cause any stress to these type of catalysts. In addition, potential holding tests made just for a few hours can not be informative.
Recent reports in the literature, dealing with the durability of IrO2 and IrRuOx catalsyts, show durability tests of 1000 h or more. These appear necessary to derive proper conclusion about the degradation rate and relative mechanisms. Thus, it is recommended that similar durability tests are carried out at practical operating current densities or potentials and the results compared to the literature reports.
Author Response
Dear Reviewer
Thank you for taking the time to review our manuscript. Please find attached responses to your comments.
Yours sincerely,
Dr. Cecil Felix
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This manuscript by Felix et al. reports the effects of the NaNO3 amount and synthesis temperatures during the preparation of nano IrO2 catalysts by the modified Adams fusion reaction. Detailed electrochemical and physiochemical characterizations were conducted. The results reported in this work are convincing, but they should be rationalized in a better way. It can be published in Catalysts after addressing the following comments.
1. The authors claimed that the addition of excess NaNO3 is not a requirement, while it is clear that the amount of NaNO3 does lead to quite different CV curves and characteristic features. The author should interpret the reason and why these features did not actually contribute/change the OER activity/stability. More experiments or discussions should be conducted to explain what was reported in this work.
2. Can the authors measure the ECSA that might be a key factor for the OER performance?
3. In Table 2, why was the anodic charge density of IH_IrO2_350_1:10 much lower than other two samples at 350C?
4. Figure 2e,f: the commercial IrO2 looks like rod-shape. What did its size mean? Length? Diameter?
5. For some reason, I could not find the conclusion section of this manuscript.
6. Line 279: “Figure 5” should be “Figure 6”.
Author Response
Dear Reviewer
Thank you for taking the time to review our manuscript. Please find attached responses to your comments.
Yours sincerely,
Dr. Cecil Felix
Author Response File: Author Response.pdf
Reviewer 3 Report
In this work, Cecil et al reported the synthesis and electrocatalytic application of IrO2 particles through a solid-state reaction approach. The morphology, particle sizes, and electrocatalytic activity/stability of as-developed IrO2 particles are then studied and compared with commercial IrO2 particles. The conclusion seemed to point to the key effects of the smaller particle size that can be also controlled by the synthetic temperature.
The review believes that at its current form, this manuscript does not bring any new insights into neither IrOx electrocatalysts nor solid state chemistry. There are big inconsistences in the manuscript, along with lots of missed information. Therefore, a re-submission after a careful revision is suggested.
1) From the solid-state reaction equations, have the author considered the residual Cl- species from the precursors in the IrO2? Lots of studies showed that Cl species from the precursors are easily trapped in the as-synthesized materials, which, however, remains to be hard to remove. A recent study has confirmed that the residual Cl species are president in catalysts through a pyrolysis of CoCl2 and organic molecules (Advanced Materials 29 (47), 1703436-1703443). Therefore, the author should take XPS to check the existence of Cl species and oxidation state of Ir…This is important because it may influence the oxidation state at top surface of IrO2 catalysts. The author may want to conduct XPS measurement and discuss the role of residual Cl species accordingly.
2) In Figure 1, the author should import and show the standard IrO2 XRD patterns, instead of just labeling different peaks.
3) In Figure2, it is evidenced that low temperature give rise to small particles, as compared with high temperature synthesis. However, in the TEM images of catalysts from all the temperature, it can be clearly found that there was severe aggregation of particles. These lead to the large second particles… this is often observed in solid-state synthesis. How could the author claim a small particle size there?
4) For electrochemistry set-up, Pt counter electrode is not good for OER measurement since it may dissolve and deposit on catalysts. There are lots of concerns on the OER studies using Pt wire as counter electrode. Carbon rod would be better choice.
5) In the electrochemical measurement, lots of peaks evolved in the CV and disappeared in long-term cycling, the author should discuss them instead of ignoring them….there are several papers from Cornel University have discussed the origins of these CV peaks in IrO2-TiO2 thin films…their conclusion may not be correct, while the author should discuss the potential meanings of the CV peaks in Figure 3 and Figure 4.
6) In Figure 3, it is interesting to find that the on-set potentials for OER in IrO2 particles are super low, kind of closing to the thermodynamic value. This was made to be possible when just decreasing the particle size from optimization of experimental parameters in high-temperature solid-state synthesis? Why the small particles are both active and stable? The author should reconsider the electrochemistry measurement and the hypothesis.
Author Response
Dear Reviewer
Thank you for taking the time to review our manuscript. Please find attached responses to your comments.
Yours sincerely,
Dr. Cecil Felix
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Revisions are fine
Reviewer 2 Report
All my comments have been addressed, so it can be published now.
Reviewer 3 Report
Several major inconsistencies have been addressed by the authors after considering the review comments. However, the reviewer believe that this manuscript needs to be further improved through reconsidering the previous comments before it got published.
For comments 1#, the author should cite the reference and/or discuss the possible role of Cl- or Na+.
For comments 3#, the TEM-derived particle sizes must be re-considered. These references are not convincing at all.
For comments 4#, the author must at least conduct one of the experiments with carbon as counter electrode and compare with the CV/LSV results from Pt counter electrode.
For comments 5#, there are lots of unreliable assumption in the interpretation.
For comments 6#, it requires more careful discussions.
