Anodic Performance of Ni–BCZY and Ni–BCZY–GDC Films on BCZY Electrolytes

Round 1

Reviewer 1 Report

Experimental Section 2.2.2: authors indicate fuel mixture used was "humidified 4% H2/N2". is that 4% H2 in N2 or 4% H2O in H2/N2 in which case what was the H2/N2? how was the fuel mixture humidified? bubbled through water reservoir?

For physical and electrochemical characterization: how long were cells reduced for?

Section 3.2:

1) is it posssible for the authors to  quantify/estimate the porosity of each prep from the sem images using image analysis software like imagej? 

2) Not sure of the physical processes underlying the suppression or facilitation of particle growth by porosity. please elaborate and offer a physical model by which porosity induces regulation of particle size. my understanding is that a positive (linear) correlation could and should exist between porosity and surface area; but this relationship is merely correlational (ie one does not cause the other but is a consequence of the other phenomena). if anything small particle size results in higher surface area and allows for increased porosity. 

3) pg 5: "....so Ni/GDC grain boundary contacts could act as the inhabitation of Ni grain growth." what do the authors mean by "inhabitation"?

4) "In the case of dense, the effect of adding GDC is remarkable." Dense what? remarkable how? please elaborate.

Section 3.3:

Curious why the authors chose to characterize the impedance at >700C. the point of BCZY PCFC is that they facilitate operation at lower temps down to ~550C (a point the authors acknowledged in the intro). 

can the authors provide the statistical analysis they did on the temperature dependence of the polarization resistance (what they call the "anode resistance") to corroborate whether the activation energies obtained are statistically different (particularly for the Ni-BCZY-GDC and Ni-BCZY)? 

pg 3: "The cermet powders and sintered pellets were identified with an X-ray diffractometry..." "characterized" is probably the better word choice

pg 4: "In the present study, porous anode films of Ni–BCZY and Ni–BCZY–GDC exhibited smaller Ni grain size after sintering at 1450°C than the dense Ni-cermets even without and without adding GDC."

pg 6: "the apparent resistivity of the ohmic components was around 41.7–58.3  cm, which is compatible with the values reported for BCZY in a wet H2 atmosphere" do you mean "comparable"?

please  check for other modest grammar problems.

Author Response

2023.8.18

Dear Dr. Reviewer

We highly Thank you for your spending your time for reviewing our manuscript. We revised our manuscript according to your suggestions. We would appreciate it if you could review our revised manuscript. We highly thank you for your kind support.

Sincerely,

Y. Itagaki

Corresponding author

> Experimental Section 2.2.2: authors indicate fuel mixture used was "humidified 4% H2/N2". is that 4% H2 in N2 or 4% H2O in H2/N2 in which case what was the H2/N2? how was the fuel mixture humidified? bubbled through water reservoir? 

The humidified gas is prepared by passing 4%H2/N2 gas through a water reservoir, therefore H2 concentration should be below 4% after the humidification. We changed the description into “4%H₂/N₂ after passing through a water reservoir at room temperature”. 

>For physical and electrochemical characterization: how long were cells reduced for? 

Thank you for the comment. We added the description in P4 L12 as “Prior to the impedance measurements, the anode was reduced under flowing the humidified fuel gas until the anodic impedance exhibited the minimum value, that is about 2h.” 

Section 3.2: 

>1) is it posssible for the authors to  quantify/estimate the porosity of each prep from the sem images using image analysis software like imagej?  

Thank you for a valuable comment. We are considering it very important point to evaluate quantitatively the relationship between porosity and Ni particle size. We tried to quantify the porosity using image-J but it was rather difficult to distinguish pore from particle, and we can observe only top surface. Now we are trying to evaluate posorsity and particle size using Ni-cermet disks and planning to report as a next paper.     

>2) Not sure of the physical processes underlying the suppression or facilitation of particle growth by porosity. please elaborate and offer a physical model by which porosity induces regulation of particle size. my understanding is that a positive (linear) correlation could and should exist between porosity and surface area; but this relationship is merely correlational (ie one does not cause the other but is a consequence of the other phenomena). if anything small particle size results in higher surface area and allows for increased porosity.  

     Thank you for your insightful comment on the porosity and surface area. We are considering that the suppression of Ni grain growth as seen in Ni-BCZY anode film is caused by the pinning force of pores which retards grain-boundary migration of a matrix phase. We described this point in the beginning of P6 together with the Zener’s equation. Unfortunately, we could not numerically evaluate porosity and surface area of the thin electrode films because of its small quantity. Dr. Liu et al., reported one paper “Grain growth inhibition by porosity” which provide a model of pore-controlled grain growth. We also cited their work in P6.

We strongly agree with your understanding that porosity has a positive correlation with surface area of the film. The anodic properties of porosity-controlled anodes for PCFC are actually not reported intensively; some of the reports were added in the introduction part. Small particle of Ni should contribute large surface area or increase in the number of reaction site. For this point we would like to clarify and obtain quantitative knowledge on particle size, surface area, anode property, in our next research work. 

>3) pg 5: "....so Ni/GDC grain boundary contacts could act as the inhabitation of Ni grain growth." what do the authors mean by "inhabitation"? 

We are sorry, and that is misspelling “inhabitation”. We changed it to “inhibitor”. 

>4) "In the case of dense, the effect of adding GDC is remarkable." Dense what? remarkable how? please elaborate. 

Thank you for the comment. To elaborate it, we change the sentence in P5 L5 from the bottom, to “The Ni-BCZY sintered disk apparently larger grain size than the porous film, suggesting that the small size of Ni grains in the Ni-BCZY anode film is affected by the existence of pores. On the other hand, Ni grain growth is highly suppressed in the case of Ni-BCZY-GDC and Ni-GDC. Therefore, the slurry coated films of Ni-BCZY-GDC and GDC are affected in their Ni grain sizes by pores and/or GDC phase.” 

Section 3.3: 

>Curious why the authors chose to characterize the impedance at >700C. the point of BCZY PCFC is that they facilitate operation at lower temps down to ~550C (a point the authors acknowledged in the intro).  

We should apologize, and that is our careless and serious mistake. The temperature notation in the Nyquist plot in Figure 4 was incorrect. That is not 700,750,800^oC but 500, 550, 600^oC. We also corrected notation about temperature of Figure 5 in P8 L1 to “in the range of 500^oC-700^oC”. The Arrhenius plots in Figure 5 had been made between 500-700^oC.

>Can the authors provide the statistical analysis they did on the temperature dependence of the polarization resistance (what they call the "anode resistance") to corroborate whether the activation energies obtained are statistically different (particularly for the Ni-BCZY-GDC and Ni-BCZY)?  

Thank you for a valuable comment. We are considering that the difference in activation energy of Ni-BCZY and Ni-BCZY-GDC is significantly large, because this difference corresponds to the difference of conduction in bulk and grain boundary. We added a comment in the bottom of P7, as “We tentatively consider that those two values are of significant difference. Baral reported proton conductivity of BCZY. The activation energy for total conductivity of BCZY was evaluated as 0.48 eV in temperature range of 250-320^oC and 0.30 eV in 400-600^oC. Proton conductivity in the former range is governed by the conduction in grain boundary, and the latter is in bulk. Volume fraction of BCZY in the cermets are 40 and 20% in Ni-BCZY and Ni-BCZY-GDC, respectively. The higher activation energy in Ni-BCZY-GDC is probably due to that proton conduction at the grain boundaries contributes to the total conductivity more than that in Ni-BCZY.”

Comments on the Quality of English Language 

pg 3: "The cermet powders and sintered pellets were identified with an X-ray diffractometry..." "characterized" is probably the better word choice 

pg 4: "In the present study, porous anode films of Ni–BCZY and Ni–BCZY–GDC exhibited smaller Ni grain size after sintering at 1450°C than the dense Ni-cermets even without and without adding GDC." 

pg 6: "the apparent resistivity of the ohmic components was around 41.7–58.3 W cm, which is compatible with the values reported for BCZY in a wet H2 atmosphere" do you mean "comparable"? 

Thank you for your pointing out the errors in English language. We made several misspelling and grammatical errors. According to your advice, we corrected them and again we carefully checked our manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

I recommend the manuscript for publishing after minor revision:

1. Please, add the procedure for reduction of NiO to Ni into the experimental section. The temperature is mentioned in the caption of Figure 1, but there is no data for time duration.

2. Did you use the same equipment for impedance measurements and resistivity vs. temperature? Please, add the necessary detailed information in the experimental section.

The language quality is good. There is a few misspelled words:

page 1:

fuel cells (PEMFCs) is required not required. Platinum is extremely scarce and expensive,

metallic parts such as Ni-alloys should be used, which increases a cost of cell module

conventional yttria-stabilized zirconia (YSZ) electrolyte-based SOFCs to operate stably at

page 2:

electrode properties were investigated for Ni-BCZY-GDC with wight ratio of 6:2:2 and

page 4:

cermets even without and without adding GDC. In such porous membranes, the grain

Author Response

Dear Dr. Reviewer

Thank you for your spending your time for reviewing our manuscript. We revised our manuscript according to your suggestions. We would appreciate it if you could review our revised manuscript. We highly thank you for your kind support.

Y.Itagaki, Corresponding author

Comments and Suggestions for Authors 

I recommend the manuscript for publishing after minor revision: 

>Please, add the procedure for reduction of NiO to Ni into the experimental section. The temperature is mentioned in the caption of Figure 1, but there is no data for time duration. 

Thank you for a valuable comment. NiO reduction was conducted prior to the impedance measurements or the XRD analysis.  We added the procedure in sections 2.2.1 (P4 L12 from the bottom) and 2.2.2 (P4 L19 from the bottom). Reduction time is 2h this is added in Figure 1 caption. 

> 2. Did you use the same equipment for impedance measurements and resistivity vs. temperature? Please, add the necessary detailed information in the experimental section. 

Yes, we evaluated the anode resistances from the Nyquist plots shown in Figure 4. We added information in P7 L1 as “Figure 5 shows the temperature dependences of the anode resistances evaluated from the total width of arcs in the Nyquist plots in the range of 500℃–700°C, along with the derived activation energies.”

Comments on the Quality of English Language 

The language quality is good. There is a few misspelled words: 

page 1: 

fuel cells (PEMFCs) is required not required. Platinum is extremely scarce and expensive, 

metallic parts such as Ni-alloys should be used, which increases a cost of cell module 

conventional yttria-stabilized zirconia (YSZ) electrolyte-based SOFCs to operate stably at 

page 2: 

electrode properties were investigated for Ni-BCZY-GDC with wight ratio of 6:2:2 and 

page 4: 

cermets even without and without adding GDC. In such porous membranes, the grain 

I am sorry we made several misspelling and grammatical errors. We corrected them and again we carefully checked our manuscript.

Reviewer 3 Report

Dear Authors,

The study “Anodic Performance of Ni–BCZY and Ni–BCZY–GDC Films on BCZY Electrolytes “presents valuable insights into the development of cermet films for proton ceramic fuel cells (PCFCs). The researchers investigated the effect of different compositions, including Ni, BCZY, and GDC, on the anodic properties of the films.

The draft follows the journal format.

However, several points need clarification and further elaboration to strengthen the study's conclusions.

The introduction could be improved by providing more context on the importance and challenges of proton ceramic fuel cells and the relevance of cermet films in addressing these challenges.

The methods section includes detailed information regarding the synthesis of the cermet films. Details on the preparation of the film components (Ni, BCZY, and GDC), their ratios, and the sintering process (temperature, duration) are essential for reproducibility and to understand the microstructure of the resulting films.

Figure 1 being too small and difficult to understand. Please ensure that Figure 1 is presented large enough to show important details clearly, such as the peaks, for easy readability.

The manuscript needs some language editing to improve clarity and readability. There are a few grammatical and typos that should be addressed.

Overall, with some revisions and improvements, this work has the potential to be a valuable contribution to the field of fuel cell research.

Author Response

To Dr. Reviewer

Thank you for your spending your time for reviewing our manuscript. We revised our manuscript according to your suggestions. We would appreciate it if you could review our revised manuscript. We highly thank you for your kind support.

Sincerely,

Y.Itagaki, Corresponding author

> The introduction could be improved by providing more context on the importance and challenges of proton ceramic fuel cells and the relevance of cermet films in addressing these challenges. 

Thank you for your suggestion. We have further described our research on PCFC anode structure control and have made the strengths of our present work clearer. In P2 L27-44, described as “Microstructure such as porosity is the factor that can determine the electrode properties [24-27]. So far, many studies have been made to derive an optimal structure for Ni-cermet anodes of PCFC. Several studies have investigated the polarization resistance of anodes porosity-controlled by adding a porogen such as starch. Nasani et al., [26] investigated the influenece of porosity of anode on polarization resistance of Ni-BZY anode. Taillades et al., [27] controlled porosity and microstructure of Ni-BCY anode using a gelled starch as a pore former. They revealed that the use of gelling starch gives rise to the homogeneous open pores and higher metallic conductivity. Ni grain size distribution is also a decisive factor for anode catalytic activity. Thus, proper porosity control is an essential factor for high anode activity. Besides, since Ni-cermets containing the proton conducting oxides mentioned above are generally sintered at high temperature, it is concerned that Ni grain growth after the sintering reduces the catalytic activity. Infiltration of Ni solution into a pre-sintered oxide scaffold has been elaborated. [28-30]. This technique allows to sinter the impregnated Ni or other catalyst precursor at low temperature to achieve homogeneous distribution of Ni nanoparticle and to suppress NiO diffusion into the oxide phase. Fine particles dispersed may exhibit high initial catalytic properties, but the concern of Ni agglomeration during long-term operation cannot be eliminated.”

>The methods section includes detailed information regarding the synthesis of the cermet films. Details on the preparation of the film components (Ni, BCZY, and GDC), their ratios, and the sintering process (temperature, duration) are essential for reproducibility and to understand the microstructure of the resulting films. 

Thank you for your suggestion. The experimental section was described more in detail, mixing ratio of NiO, BCZY and GDC, and their mixing condition in 2.1.2, and condition of NiO reduction in 2.2.1 and 2.2.2.

>Figure 1 being too small and difficult to understand. Please ensure that Figure 1 is presented large enough to show important details clearly, such as the peaks, for easy readability. 

Thank you for the comment. We changed the size of Figure 1 to make it more readable especially for the peak markers. 

>The manuscript needs some language editing to improve clarity and readability. There are a few grammatical and typos that should be addressed. 

Overall, with some revisions and improvements, this work has the potential to be a valuable contribution to the field of fuel cell research. 

Thank you very much for your recommending our manuscript after revising several points. There are several careless misspelling and grammatical errors. We checked our manuscript carefully and corrected errors on editing,   

Round 2

Reviewer 1 Report

I'd like to thank the authors for their consideration of my comments and suggestions.