Volumetrics of Hydrogen Storage by Physical Adsorption
Round 1
Reviewer 1 Report
The authors, P.Stadie and coauthors, review volumetrics of H2 storage by physical asdorption. They present not only summary of the studies to date but also some important suggestion and recommendation to correctly study volumetric H2 strage materials. The reviewer thinks that this review article is acceptable for publication in Inorganics as it is.
Author Response
We thank the Reviewer for their positive feedback.
Reviewer 2 Report
The manuscript by Samantaray, Putnam and Stadie entitled "Volumetrics of Hydrogen Storage by Physical Adsorption” is a review which describes, categorizes and compares the volumetric storage and delivery across numerous different porous materials including metal-organic frameworks, porous carbons, and zeolites.
The hydrogen storage is an important problem from fundamental and technological perspective. The proper comparison of various materials for this application requires reproducible and well-defined protocols for reporting the results. The good practice should include all steps involved - from the preparation of the samples to data analysis steps.
This manuscript starts with fundamental definitions and quantities typically reported for gas storage at various pressures. In the following parts, the authors not only compare the data available in the literature but also critcally analyze the original results. This reviewer is very satisfied with the topic and the construction of this review. All the comparisons are clear and illustrated with readable tables and graphs.
This crticial and tutorial review fills the gap in the field of volumetric hydrogen storage and should be use as a guide for researchers working in the field of gas storage.
Therefore, I recommned its publication in this journal in the present form.
Author Response
We thank the Reviewer for their positive feedback.
Reviewer 3 Report
In this critical review, Samantaray, Putnam, and Stadie categorize and compare the volumetric storage and delivery performance of different porous materials including benchmark MOFs, porous carbons, and zeolites. The report is extremely relevant to the field and it deserves to be published at a fast speed by Inorganics since it compiles a number of data, which is useful for well-established researchers as well as those that just started to venture into the field. The report is extremely well-written and presents data using high-quality graphs in both the main manuscript and supplementary file.
minor issues:
1) In equations 1 and 3 (in between lines 176/177 and 185/186, respectively), the term ?g is only explained after equation 7 (line 237): "?g is the fluid density of pure compressed hydrogen under the temperature and pressure conditions of adsorption". I kindly suggest to the authors explain it the first time it appears in the manuscript. The same comment is valid for the acronym rGO. It is used in line 430 and it is only explained in line 456.
2) Table 2 appears in the main manuscript without any reference in the text. Are the data of powders, densified materials? For example, it presents a BET surface area value (77K) for MOF-5 2763 m2 g-1. I believe it was a mistake since the area is usually higher for a non-interpenetrated phase-pure MOF-5 as shown in Table S2 (supplementary file): 3633 m2 g-1. Therefore I suggest to the authors double-check it since it appears to be the area of densified MOF-5.
Additionally, few typos/mistakes were detected and I kindly suggest the authors verify them:
line 129: "the method chosen used has no bearing on..."
line 579: "H2"
line 708: "delvery"
line 710: "archetypical MOF". Should it be MOF-5?
Author Response
We thank the Reviewer for the thorough reading of our work. We find that the Reviewer's comments serve to improve our manuscript and give the following responses:
1) We happily accept these suggested changes (see lines 176 and 430).
2) The density value provided in Table 2 for MOF-5 powder is the one reported by Purewal and coworkers in 2012 (https://doi.org/10.1021/jp305524f) - it is consistent with all other work by Siegel and coworkers for loose (nondensified) MOF-5. Yaghi and coworkers have reported a higher value (e.g., https://doi.org/10.1021/ja049408c) but whether this is a BET surface area or a Langmuir surface area is in question. The Langmuir model typically overestimates the surface area of microporous solids. It seems to be the case that real-world MOF-5 (including high quality BASF standard materials) is typically measured to have a lower surface area of <3000 m^2/g despite that, as the Reviewer correctly points out, computational surface areas for MOF-5 are significantly higher.
3) We thank the Reviewer for finding these typos and have changed all of them.
Reviewer 4 Report
The manuscript submitted to Inorganics entitled Volumetrics of Hydrogen Storage by Physical Adsorption" by Samantaray and co-workers presents a concise short review with an adequate number of references and information. The clear majority of relevant literature about this subject is referenced and properly discussed. Not only this is a relevant topic with an increasing significance having in consideration the new guidelines and politics on energy for the next few years. This manuscript is also carefully prepared, concise, and is a welcome addition to the literature. Therefore, this short revision has enough novelty/importance and should be considered for publication. However, the conclusion would benefit if a personal point of view could be included. For instance, having in mind the most recent advancements in hydrogen storage what are the possible future research directions?
Thank you
Author Response
We thank the Reviewer for their positive feedback. We appreciate the encouragement to provide a more substantive point of view at the end of the article. Though we feel that while it is important to state our opinion as to the state of the current literature in the area of volumetric hydrogen storage by adsorption (as already put forth in the concluding remarks on page 20), further speculation or commentary than what is already given is not appropriate for a scientific review. We reproduce our final summarizing comments as to the point of future research directions (iii-iv, vi, lines 836 on) below:
"iii. automated tapping (jolting) is a key strategy to increasing H2 PS delivery at any temperature
"iv. light mechanical compaction (e.g., as performed for SNU‐70) can result in very high volumetric capacity and delivery gains over a loose powder
"vi. novel adsorbents should be designed with large void volume, high gravimetric surface area, and a dense, well‐organized skeletal framework with a primary focus on improving H2 delivery at cryogenic conditions, where current system‐level energy densities clearly outperform commercial batteries."
We hope these perspectives satisfy the reviewer and can guide future work in this area.
