On the Problem of “Super” Storage of Hydrogen in Graphite Nanofibers

Round 1

Reviewer 1 Report

In this manuscript the authors delve into the hot topic of hydrogen storage in GNFs, and they do so through a curious and unorthodox way, by “taking a skeleton out of the closet”.

In fact, they take experimental results (that have been considered controversial and not reproducible) from other authors and making use of theoretical tools and mathematical skills they focused on explaining that those results claiming a super hydrogen storage in GNFs must be trusted.

It is shown that the physics of accumulation of "reversible" high-density hydrogen intercalated in nanocavities between the base carbon layers in GNF relates to the manifestation of the spillover effect in terms of thermoelastic phase equilibrium.

The theoretical analysis is well explained and sufficiently structured, but it does not replace the desire repetition of experiments by other groups to prove the reproducibility of experimental results.

in fact, this is an aspect that the authors themselves recognize when they say that “further experimental and theoretical studies are needed”.

Anyway, since the authors have done an original, worthy, and well-founded work, it is fair to consider that their manuscript deserves to be published, if the following aspects are included by the authors:

1) The search for more recent experimental techniques that can be used to eventually reproduced the claimed results.

2) The inclusion of the recent MB-TDS technique in the Introduction section and in References: 

doi.org/10.3390/ma5020248 

 doi.org/10.1063/1.3385686

3) Detailed theoretical explanation of how spillover effect may be active in the nanocavities in order clarify the claimed high-density of hydrogen storage.

Author Response

Response to Reviewer 2 Comments

In this manuscript the authors delve into the hot topic of hydrogen storage in GNFs, and they do so through a curious and unorthodox way, by “taking a skeleton out of the closet”.

In fact, they take experimental results (that have been considered controversial and not reproducible) from other authors and making use of theoretical tools and mathematical skills they focused on explaining that those results claiming a super hydrogen storage in GNFs must be trusted.

It is shown that the physics of accumulation of "reversible" high-density hydrogen intercalated in nanocavities between the base carbon layers in GNF relates to the manifestation of the spillover effect in terms of thermoelastic phase equilibrium.

The theoretical analysis is well explained and sufficiently structured, but it does not replace the desire repetition of experiments by other groups to prove the reproducibility of experimental results.

in fact, this is an aspect that the authors themselves recognize when they say that “further experimental and theoretical studies are needed”.

Anyway, since the authors have done an original, worthy, and well-founded work, it is fair to consider that their manuscript deserves to be published, if the following aspects are included by the authors:

 Point 1: The search for more recent experimental techniques that can be used to eventually reproduced the claimed results.

Response 1: Thank you for your thorough review. We have added the following sentence in the manuscript:

“In order to eventually reproduce the claimed results on hydrogen storage [5, 8, 10, 11], it is necessary to study, with using the recent theoretical and experimental techniques, the data [5] about the effect of cycle experiments on the GNF hydrogen absorption/desorption characteristics (Figs. 5, 6, 9 and 10 in [5]), the pore size distribution measurements (Fig. 11 in [5]), the effect of surface properties on the hydrogen adsorption on GNF (Figs. 13 and 14 in [5]) and some others.”

Point 2: The inclusion of the recent MB-TDS technique in the Introduction section and in References:

doi.org/10.3390/ma5020248

 doi.org/10.1063/1.3385686

Response 2: We have included the mention of MB-TDS technique and corresponding proposed references:

“One can expect that the conclusions arising from the results of the work will help to reproduce the effect of hydrogen “super” storage in the GNF, and modern thermal desorption techniques, such as “molecular beam thermal desorption spectrometry” (MB-TDS) [33, 34], will bring more accurate experimental results for further theoretical work.”

33. Lobo, R.F.M.; Santos, D.M.F.; Sequeira, C.A.C.; Ribeiro, J.H.F. Molecular Beam-Thermal Desorption Spectrometry (MB-TDS) Monitoring of Hydrogen Desorbed from Storage Fuel Cell Anodes. Materials 2012, 5, 248-257. https://doi.org/10.3390/ma5020248
34. Lobo, R.F.M.; Berardo, F.M.V.; Ribeiro, J.H.F. Molecular beam-thermal hydrogen desorption from palladium. of Sci. Instr. 2010, 81, 043103. https://doi.org/10.1063/1.3385686

Point 3: Detailed theoretical explanation of how spillover effect may be active in the nanocavities in order clarify the claimed high-density of hydrogen storage.

Response 3: We have added the following paragraph to the manuscript:

“Detailed consideration of how the spillover effect and the Kurdjumov phenomenon on the thermal elastic phase equilibrium may be active in the nanocavities in order clarify the claimed high-density of hydrogen storage is presented in work [24] and also in work [18], which has an open access on the internet. It can be also considered as a direct comparison between theoretical and experimental analyses of the results.”

Reviewer 2 Report

The manuscript by Nechaev et al. reports a novel investigation on the dynamics of hydrogen storage in graphite nanofibers. The analytical method reported by the authors seem to provide new insights on the physics of desorption processes by thermodynamic analysis of previously published experimental data. In the current status the manuscript seems an early stage work. The authors need to state the novelty of the work in a clearer manner.  It is not clear how the micrograph shown in Fig.4 is representing a direct proof of hydrogen adsorption. Can the authors provide additional TEM/HRTEM micrographs of experimental analyses that can agree with the work in ref.11? How the adsorption takes place? A direct comparison between theoretical and experimental analyses may enhance the quality of the manuscript.

Author Response

Response to Reviewer 3 Comments

The manuscript by Nechaev et al. reports a novel investigation on the dynamics of hydrogen storage in graphite nanofibers. The analytical method reported by the authors seem to provide new insights on the physics of desorption processes by thermodynamic analysis of previously published experimental data. In the current status the manuscript seems an early stage work.

Point 1: The authors need to state the novelty of the work in a clearer manner. 

Response 1: Thank you for the detailed review. We have added the following sentence in the manuscript:

“The novelty of this work lies in the combination of effective interdisciplinary methods and approaches of high originality and novelty, including detailed thermodynamic analysis, detailed analysis of thermal desorption data, and computer (numerical) simulation.”

Point 2: It is not clear how the micrograph shown in Fig.4 is representing a direct proof of hydrogen adsorption.

Response 2: We have added the following sentence in the manuscript:

“Detailed consideration of how the micrograph shown in Fig.4 is related to a direct proof of “super” hydrogen adsorption is presented in work [24] and also in work [18], which has an open access on the internet.“

Point 3: Can the authors provide additional TEM/HRTEM micrographs of experimental analyses that can agree with the work in ref.11?

Response 3: We have added the following sentence in the manuscript:

“The similar transmission electron micrographs of graphitic nanofibers were also obtained in the works [9, 10].”

Point 4: How the adsorption takes place?

Point 5: A direct comparison between theoretical and experimental analyses may enhance the quality of the manuscript.

Response to points 4, 5: The following paragraph has been added in the manuscript:

“Detailed consideration of how the spillover effect and the Kurdjumov phenomenon on the thermal elastic phase equilibrium may be active in the nanocavities in order clarify the claimed high-density of hydrogen storage is presented in work [24] and also in work [18], which has an open access on the internet. It can be also considered as a direct comparison between theoretical and experimental analyses of the results.”

Round 2

Reviewer 1 Report

Now I think that the manuscript has been
sufficiently improved to warrant publication in C.

Reviewer 2 Report

The authors have replied well to the questions raised by this reviewer, the manuscript can be accepted.