Thermal Swing Reduction-Oxidation of Me(Ba, Ca, or Mg)SrCoCu Perovskites for Oxygen Separation from Air

Round 1

Reviewer 1 Report

Please find the below comments: 1. Discuss the Stability of lead-based and lead-free halide perovskites as stability is the main topic in the title. 2. Types of sensors are well-explained, but applications of all types should also be discussed. 3. Sensing mechanism should be explained in detail stepwise.  4. As different types of perovskites are discussed, so accordingly discuss the characteristic properties of all types required for sensors in each.

Author Response

Reviewer #1

Please find the below comments: 1. Discuss the Stability of lead-based and lead-free halide perovskites as stability is the main topic in the title. 2. Types of sensors are well-explained, but applications of all types should also be discussed. 3. Sensing mechanism should be explained in detail stepwise.  4. As different types of perovskites are discussed, so accordingly discuss the characteristic properties of all types required for sensors in each.

 

Reply: The Authors believe that the reviewer comments are NOT related to our paper. In our paper, we address perovskite ceramics which are a class of pure inorganic materials for oxygen separation from air. Reviewer #1 mentions halide perovskite which is a hybrid organic-inorganic class of material generally used for solar cells.

Reviewer 2 Report

This manuscript report perovskite compounds for oxygen separation from air. Ba based perovskites resulted in improved oxygen release. The manuscript may be publishable in Processes if authors address the following issues:

 

1.      Authors mention in the introduction that “Perovskites compounds containing metal oxides (i.e., Ba, La, Sr, Co, Fe, Cu, Ca, Zn, Zr, Y among others)] have been widely reported for oxygen separation from air”. Therefore they need to clearly clarify what is the novelty/originality of their work.

2.      XRD patterns shown in Figure 2 need to be indexed.

3.      Equation 1 needs to be referenced with a citation.

4.      How does the performance of the studied perovskites for oxygen separation from air compares with leading perovskites or other materials? A comparison table is needed.

5.      The novelty of the work needs to be clearly stated.

6.      Mechanistically, how the perovskite crystals are separating oxygen from air? Recently, the separation mechanisms  of gases over crystals have been reported: Science 2020,367 (6478), 624-625. I would suggest the authors to take a look at this paper, and refer to it in the manuscript. It is quite important for the general audience to understand these mechanisms.

Author Response

Reviewer #2

This manuscript report perovskite compounds for oxygen separation from air. Ba based perovskites resulted in improved oxygen release. The manuscript may be publishable in Processes if authors address the following issues:

 

Reply: we thank the Reviewer for this positive feedback.

 

1. Authors mention in the introduction that “Perovskites compounds containing metal oxides (i.e., Ba, La, Sr, Co, Fe, Cu, Ca, Zn, Zr, Y among others)] have been widely reported for oxygen separation from air”. Therefore, they need to clearly clarify what is the novelty/originality of their work.

 

Reply: In the penultimate paragraph of the introduction section, we discuss that the majority of the work reported in literatures has been carried out using tertiary perovskite compounds. In the last paragraph of the introduction section, we state that the novelty of our work is the effect of oxygen separation using quaternary perovskite compounds focusing on A-site substitution. The abstract, results and discussion section contains our major findings that in terms of engineering application, short redox cycles are preferable for yielding a high oxygen production from air separation. This is part of novel designs as acknowledged by Reviewer #3. To provide further clarity, we edited the abstract as follows:

 

These results strongly suggest the major advantages of short thermal cycles as novel designs for air separation.

 

We also stressed the novelty point by editing the conclusions as follows:

The combination of these important parameters has the potential to novel engineering systems that show that BaSCC adsorbent vessels can be relatively small with great capacity for oxygen separation from air.

 

2. XRD patterns shown in Figure 2 need to be indexed.

 

Reply: Thank you and we have edited our paper as follows:

 

Page 4:

Fig. 2 exhibits the XRD patterns of MeSCC samples. These patterns contain multiple peaks with the major diffractions at 2θ 18.52 [001], 28.44 [020], 32.52 [211], 36.62 [310], 42.61 [030], 43.79 [202], 46.58 [212], 55.61 [330], 61.79 [041], 68.23 [422], 74.12 [601] , 75.55 [050] and 78.01 [620] [(PDF #00-040-1018) for magnesium; 18.75 [110], 29.33 [115], 32.48 [300], 36.56 [121], 40.46 [223], 42.53 [208], 43.59 [217], 44.70 [225], 46.34 [218], 57.1 [318], 62.04 [423], 69.71 [427], 73.93 [115] and 77.94 [613] (PDF 00-060-0753) for calcium; 18.546 [110], 28.46 [113], 32.53 [300], 43.857 [006], 46.51 [125], 47.64 [116], 55.46 [306] , 57.99 [045], 62.39 [235], 68.11 [505] and 75.47 [336] (PDF #04-015-9915) for strontium; and 19.95 [110], 26.71 [101], 31.11 [110], 41.48 [002], 44.11 [102], 52.83 [112], 54.37 [211], 65.25 [212], 71.46 [302] and 73.83 [311] (PDF #04-016-5545) for barium containing materials. These patterns show the formation of perovskite compounds containing crystal phases. Further, minor additional peaks at 36.54 [111], 42.61 [200], 62.06 [220], 73.89 [311] and 77.66 [220] corresponding to CoO pattern (PDF #00-043-1004) were observed for the samples with magnesium and calcium. Therefore, all MeSCC samples confirm that the metal cation (Mg, Ca, Sr and Ba) used was fully substituted in the A-site.

 

3. Equation 1 needs to be referenced with a citation.

 

Reply: We deducted this equation from a simple engineering mass balance applicable to our work. In fact, this type of equation is generally deductable by undergraduate students doing basic courses of chemical engineering. Therefore, we believe that this basic and general mass balance equation developed in this work does not need to be referenced.

 

Nevertheless, we reviewed Eq. 1 to be focused on the Production of oxygen instead of mass of sorbent. We have also split this into three equations by adding the cycling time equation and the total cycles per year. Again, these are simple mass balance, very general and basic equations that we believe do not need to be referenced. We have edited our paper as follows:

 

Pages 7 and 8:

The calculation of the annual production of oxygen (P_ox) was carried out on the engineering basis of 1000 kg mass of sorbent MeSCC (m_sorb) for the percentage of O₂ mass sorbed/desorbed (m_ox%) and the number of redox cycles per year (C_n,y) as in Eq. 1:

          (1)

The number of redox cycles per year (C_n,y) can be determined using Eq. 2:

      (2)

and the time taken for each cycle t_c can be calculated as per Eq. 3 and normalized from cycles per min to the total number of cycles per year as t_n,y:

      (3)

where h is the heating rate (°C min^-1) and DT is the temperature range (°C) between sorption (i.e., oxidation) and desorption (i.e., reduction), and t_eq is the time (min) taken to equilibrate and switch the redox cycles.

 

4. How does the performance of the studied perovskites for oxygen separation from air compares with leading perovskites or other materials? A comparison table is needed.

 

Reply: We agree with the Reviewer. We checked publications in literature, and found that the majority of papers show the TGA curve for desorption only, or just provided results in wt% instead showing redox sorption results Therefore, we added two new figures and a discussion to address this question as follows:

 

Pages 9 and 10:

Fig. 8a shows the O₂ mass desorbed from perovskites reported in literature. The BaSrCoCu in this work performed well with the 7^th best out of ten results. However, this paper shows that short redox cycles are preferable giving the highest O₂ production instead of full cycles with the largest temperature changes. Not all the results in Fig. 8a are available showing TGA redox cycling. Therefore, Fig. 8b attempts to provide a fair comparison for results available in literature as the ratio of mass change over temperature change. Higher ratio is preferable, meaning that more mass of O₂ is produced per 1 °C of temperature change.  The best material in this work BaSrCoCu performed well against other perovskites second to an optimized BaCoFe* only. Therefore, BaSrCoCu can be further optimized by changing the compositions of the A and B sites in order to deliver even higher performance.

Figure 8. (a) Comparison of perovskite performance of O₂ production (wt%) as in this work BaSrCoCu, SrFe  [14], SrFe [14], SrMnFe [12], LaCaFeCo [57], LaSrCoFe [42],  BaSrCo and improved BaSrCo* [58], SrFeCo [59] and CaCoZn [60]; (b) comparison of perovskite performance as the ratio of O₂ production per temperature change (wt% C^-1) as in this work BaSrCoCu, BaSrCo and improved BaSrCo* based on optimized short redox cycles, and CaCoZn and SrFeCo based on desorption temperature information only as redox cycles were not given.

 

 

We have also added the following citations to the reference list:

[57] J. Dou, E. Krzystowczyk, X. Wang, A.R. Richard, T. Robbins, F. Li, Sr_1-xCa_xFe_1-yCo_yO_3-δ as facile and tunable oxygen sorbents for chemical looping air separation, J. Phys. Energy 2 (2020) 025007.

[58] N. Gokon, T. Yawata, S. Bellan, T. Kodama, H.-S. Cho, Thermochemical behavior of perovskite oxides based on La_xSr_1-x(Mn, Fe, Co)O_3-δ and Ba_ySr_1-yCoO_3-δ redox system for thermochemical energy storage at high temperatures, Energy 171 (2019) 971-980.

[59]F. Fujishiro, N. Oshima, T. Sakuragi, M. Oishi, Oxygen desorption properties of perovskite-type SrFe_1−xCo_xO_3−δ: B-site mixing effect on the reduction properties of Fe and Co ions, J. Solid State Chem. 312 (2022) 123254.

[60] Q. Zheng, M. Lail, S. Zhou, C.-C. Chung, Novel CaCo_xZr_1-xO_3-δ perovskites as oxygen-selective sorbents for air separation, ChemSusChem 12 (2019) 2598-2604.

 

5. The novelty of the work needs to be clearly stated.

 

Reply: This question is the same as question 1. Please see our reply to your question 1 above.

 

6. Mechanistically, how the perovskite crystals are separating oxygen from air? Recently, the separation mechanisms of gases over crystals have been reported: Science 2020,367 (6478), 624-625. I would suggest the authors to take a look at this paper, and refer to it in the manuscript. It is quite important for the general audience to understand these mechanisms.

 

Reply: We agree with the Reviewer’s point to help the general audience. In fact, oxygen redox transport mechanism is quite well known in perovskite materials and differs entirely from conventional molecular gas separation mechanisms. We have revised our paper as follows:

 

Page 6:

The results in Fig. 4 fundamentally reflect the mechanism of oxygen separation from air that is well known for perovskite materials described by Eq. 1 as follows:

where A and B are the two cation sites of the perovskite crystal materials and O is the oxygen molecule. At low temperature, oxygen ions are incorporated or sorbed into the crystal structure also known as oxidation. At high temperatures, oxygen irons are released or desorbed from the crystal structure and combine at the surface of the particle to form O₂ molecule, in a process called reduction. This redox process is modulated by oxygen ions and differs completely from molecular gas separation by size exclusion in membranes based on porous crystals [51] and amorphous silica [52], or molecular gas sorption/desorption in pressure swing adsorption (PSA) process using solid sorbents [53] or amine functionalised solid sorbents [54].

 

We have added the following references:

[51] M.A. Carreon, Porous crystals as membranes, Science 367, 6478 (2020) 624-625.

[52] B. Ballinger, J. Motuzas, S. Smart, J. C. Diniz da Costa, Palladium cobalt binary doping of molecular sieving silica membranes, J. Membr. Sci. 453 (2014) 185-191.

[53] A. Jayaraman, R.T. Yang, Stable oxygen-selective sorbents for air separation, Chem. Eng. Sci. 60 (2005) 625-634.

[54] W. Wang, J. Motuzas, X.S. Zhao, J.C. Diniz da Costa, 2D/3D Assemblies of Amine-Functionalized Graphene Silica (Templated) Aerogel for Enhanced CO₂ Sorption, ACS Appl. Mater. Interfac. 11 (2019) 30391-30400.

 

Reviewer 3 Report

The author provided a novel study using perovskite for oxygen separation from air. This novel design could in potential provide new approaches for air separation industry.  Very detailed characterizations have been included in the manuscript and provided the foundation of the design. However, some explanations and discussions on the process design could be improved/further clarified and this will provide a more clear picture of the design.

1. Page 5, last paragraph, could the author provide a definition of the oxygen uptake (Figure 3)?  Based on Figure 3, all oxygen uptake is positive value, which could be confusing because for oxygen adsorption and oxygen desorption, if one process is “positive oxygen uptake”, then the other process should be “negative oxygen uptake”
2. Figure 3: could the author clarify whether it’s pure oxygen or air used for the characterization? 
3. Figure 4, in both figures the left y axial (mass variation and heat flow) are missing labels (values). 
4. Page 6-8, the author used term different terms such as “oxygen uptake”, “mass variation”, “uptake rate”, “release rate”. Could the author align on these terms? 
5. Page 6, the author mentioned mass gain for CaSCC is much slower than MgSCC, BaSCC and SrSCC. However, based on Figure 4a, MgSCC and SrSCC have both “slow decrease phase” (beginning) and “fast decrease phase”, could the author clarify which phase were used for comparison with CaSCC, and why that phase were selected.
6. Page 7: in the adsorption design, is there any heat loss (not 100% heat conversion) considered between oxidation and redox cycles? If so, could the author comment on how to accommodate the heat loss and energy cost? 
7. To separate oxygen from air, could the author comment on whether CO2 and H2O will be co-adsorbed  in the process? Though CO2 and H2O has lower fraction in air, however, when having N2 and O2 as industry product, the purity of N2 and O2 should be very high and CO2/H2O needs to be removed.
8. Also, could the author clarify the fraction of O2 that can be removed from air? Will the adsorption efficiency be impacted as O2 concentration decreasing during the process?
9. Page 7:what is “b” in equation 1 refers to?
10. Page 8, the optimization of the short cycle is one of the most important results in this study, could the author add more details on how  wt% and delta T was calculated? Maybe the author would provide an calculation example in SI?
11. Page 8: cycling time is a critical parameter for temperature swing adsorption. Thus, could the author add more details on how 5C was selected as the heating rate that can optimize cycle change time? 
12. It seems SI (Figure A1) was not included in the original manuscript. Could the author add it?
13. Material cost is important for air separation process. Could the author add some discussions on the total material cost? If the material cost is too high, is there any potentials that could lower the cost in the future? 

Author Response

The replies are in the attached file.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Accept

Reviewer 2 Report

All my comments/suggestions were properly addressed

Reviewer 3 Report

I would like to thank the author addressed all the comments/questions, and made the paper even better.