Comparison of the Electrochemical Performances of Solid Oxide Fuel Cells with Sputtered Thin Barrier Layers Fueled by Hydrogen or Ammonia
, Bertrand Morel 2, Giovanni Carapella 3, Dario Montinaro 4, Alice Galdi 1, Hafiz Sami Ur Rehman 5, Pierpaolo Polverino 5, Cesare Pianese 5, Julie Mougin 2 and Luigi Maritato 1,*
Round 1
Reviewer 1 Report
The manuscript is focused on the study of the effects of the hydrogen fuel dilution and the fuel change, from pure hydrogen to pure ammonia, on the electrochemical behavior of SOFCs with a diffusion barrier layer made of Gd-doped ceria (GDC). The use of ammonia as a fuel can be a key solution in a faster transition to clean energy, which makes the substitution of hydrogen for ammonia in SOFCs a promising direction and the results reported by the authors appealing for researchers in the field of SOFCs.
In my opinion, the manuscript could be accepted for publication after some minor revisions.
1. The authors use commercial anode/electrolyte half-cells, modify the electrolyte surface by RF sputtered GDC layer and then deposite a cathode by screen-printing. The compositions of the anode, the electrolyte and the cathode, and the thickness and microstructure of all the layers should be described. It would be nice to provide a micrograph of the fuel cell cross-section.
2. How the equation in line 154 was obtained?
3. In Table 1, it is better to remove the first column.
4. Subfigures in Figures 4–9 should be labeled as a, b…
5. In Figure 8, the name of y-axis is to be added.
Author Response
Please find detailed responses in the attached file
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Review on the manuscript entitled “Exploring fuel flexibility of sputtered thin barrier layers SOFC cells: the effect of direct ammonia feeding on the performances”.
The paper is devoted to testing of SOFC cells in different H2-NH3 feeding gas mixtures in order to analyze SOFC performance. Similar experimental data can be interesting for the SOFC developers and researchers. Unfortunately, there are many problems in description and discussion of the experiment, and the manuscript could not be recommended for the publication in the current form.
The title is confusing: the phrase “Exploring fuel flexibility of sputtered thin barrier layers”. I don’t understand, what does “fuel flexibility of barrier layers” mean. Please, revise.
In the whole manuscript I have not found detailed information about the composition, layers thicknesses of all the layers, including anode support, anode functional layer, electrolyte, barrier layer, cathode layers. It is absolutely impossible to estimate the obtained data without this very important information.
Introduction
If you are feeding the SOFC with NH3, you will get NOx as a product. It is not green. At least this should be mentioned and discussed in the motivation part of the manuscript. How to deal with this point with regards to the “greenity” of such fuel.
Materials and methods
Please, describe your fuel cell structure in the proper way. It would be very useful to supply SEM of cross-sectioned SOFC.
Please, supply conditions used for RF magnetron sputtering. Which parameter(s) was optimized?
Results and discussion
I expected in this work to see data of the SOFC without barrier layer as a reference. If you have such data, please, supply.
Why do you calculate the “efficiency” in the current form? For low H2 flow rates it is obviously, that there is a concentration polarization of the anode (a lack of hydrogen in the reaction zone).
I disagree with explanation “at 650°C the polarization resistance shows a remarkable increase especially in correspondence of 6 Nml∙min-1cm-2, probably due to a combination of multiple effects such as the reduced ionic transport in the electrolyte at low operating temperatures”.
I don’t understand the basis of the following conclusion: “Due to the improved electrochemical performances gained in the case of cells with sputtered GDC thin buffer layers, these power and current density output values are always comparable or even higher than those obtained in industrial SoA SOFC cells with screen printed GDC layers “
You just claim and don’t explain your conclusions.
What does the barrier layer have to do with this data?
Author Response
Please find attached detailed responses in the attached file.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The article has been substantially revised in accordance with the comments of the reviewers. The new version needs formatting. I would still recommend the authors to add an SEM image of a cross-section or a cleavage of the cell.
Author Response
We thank again Reviewer 2 for helping improve our manuscript. For what concerns the first comment, we reviewed the format throughout the whole manuscript.
Regarding the second comment, we point out that SEM images (surface and cross-section) can be found in reference [26] of the manuscript: we underline that SEM here was performed on the GDC deposited on the anode/electrolyte substrate, while no SEM image of the complete cell can be published because of industrial confidentiality.
