Scaling up Metal Hydrides for Real-Scale Applications: Achievements, Challenges and Outlook

Round 1

Reviewer 1 Report

The manuscript speaks about the transfer of the hydrogen storage in metal hydrides from the laboratory level to the industrial world. It is well written and organized with the expception of few missprints (lines 405-406).

The authors are very well known in the field. I recomment the manuscript to be accepted. 

Author Response

The manuscript speaks about the transfer of the hydrogen storage in metal hydrides from the laboratory level to the industrial world. It is well written and organized with the expception of few missprints (lines 405-406).

The authors are very well known in the field. I recomment the manuscript to be accepted.

Authors´ reply:

We appreciate this positive reception of our manuscript. We have made changes to the lines 405-406 highlighted by the reviewer, and have carefully read the text to find any other misprints to correct these as well to make the text easier to read.

Reviewer 2 Report

This paper is in a way interesting as it describes several beginners’ errors in making and characterizing metal hydrides, especially when scaling up sample sizes. The paper describes problems with sample and alloy inhomogeneities as well heat transfer problems. This has, however, been done already early in the development of metal hydride storage alloys and corresponding storage systems.  These metals alloys are, however, today produced in the scale of several thousand of tons for NiMH batteries and several hundreds of tons by Treibacher and GfE for hydrogen storage in submarines. Commercial actors have already left these  problems behind.

Author Response

This paper is in a way interesting as it describes several beginners’ errors in making and characterizing metal hydrides, especially when scaling up sample sizes. The paper describes problems with sample and alloy inhomogeneities as well heat transfer problems. This has, however, been done already early in the development of metal hydride storage alloys and corresponding storage systems.  These metals alloys are, however, today produced in the scale of several thousand of tons for NiMH batteries and several hundreds of tons by Treibacher and GfE for hydrogen storage in submarines. Commercial actors have already left these problems behind.

Authors´ reply:

Thank you for your comment. While we do agree that some metal hydrides are being produced on a large scale for NiMH batteries, we believe there are still many challenges to be considered in the case of scaling up metal hydrides for large-scale hydrogen storage applications. The interest in solving specific challenges is confirmed by some relatively new referenced articles in our review, tackling problems through e.g. new three dimensional heat transfer models, studies of internal stresses caused by tank geometry etc. We believe the proposed review will be of great use for researchers investigating the materials research aspects of scaling up materials and systems based on metal hydrides, and helping designing new research studies inspired by recent numerical modelling. Our proposed review could be also helpful in avoiding the repetition of past mistakes pointed out by the reviewer.

Reviewer 3 Report

This article reviews the scale up methods for metal hydrides and their potential effects on the metal hydrides performance. I like the idea of this review paper which is often less discussed/neglected.

Successful application of large scale metal hydrides either for hydrogen storage or as energy storage systems requires our ability to accurately control the composition and microstructure of the alloys to reproduce the lab scale properties.

The article is well organised and addresses the main aspects of the scale up systems. There is not much I can comment on the scientific side of the article as it just reviews other previously published works.

There are missing references throughout the article that should be corrected ( I am not sure these are just missing in my downloaded version or they are actually missing).

Page 11 line 364, change each to reach

Author Response

This article reviews the scale up methods for metal hydrides and their potential effects on the metal hydrides performance. I like the idea of this review paper which is often less discussed/neglected.

Successful application of large scale metal hydrides either for hydrogen storage or as energy storage systems requires our ability to accurately control the composition and microstructure of the alloys to reproduce the lab scale properties.

The article is well organised and addresses the main aspects of the scale up systems. There is not much I can comment on the scientific side of the article as it just reviews other previously published works.

There are missing references throughout the article that should be corrected ( I am not sure these are just missing in my downloaded version or they are actually missing).

Page 11 line 364, change each to reach

Authors´ reply:

We thank the reviewer for the positive feedback and comments provided. We have gone through all of the 83 references to see if any were missing or if any other problems are present, and have not been able to find any issues with references. We have also made the suggested word change, and have carefully gone through the article to locate and correct any other possible spelling errors.

Reviewer 4 Report

The review entitled “scaling up metal hydrides for real-scale applications: achievement, challenges and outlook” attempts to present and discuss the different aspects of scaling-up of metal hydrides.

The review included experimental and simulation studies on the topic. Inside the experimental part, authors treated two aspects: a) production, activation and b) thermal management. In reality the problem related to scaling up is much more complex: the tank geometry, the filling of the tank, the compactness and the heat transfer. I would like that the authors split the experimental part in different section as follow:

-Synthesis

-Geometry of the tank

-Filling of the tank

-Heat management by additives

-Heat management by another methods

If is possible do the same in the simulation part

Finally, the manuscript contains lot of errors, they hinder the correct reading. They should check the manuscript before submit it.

So I suggest they recheck it carefully before resubmission.

Author Response

The review entitled “scaling up metal hydrides for real-scale applications: achievement, challenges and outlook” attempts to present and discuss the different aspects of scaling-up of metal hydrides.

The review included experimental and simulation studies on the topic. Inside the experimental part, authors treated two aspects: a) production, activation and b) thermal management. In reality the problem related to scaling up is much more complex: the tank geometry, the filling of the tank, the compactness and the heat transfer. I would like that the authors split the experimental part in different section as follow:

-Synthesis

-Geometry of the tank

-Filling of the tank

-Heat management by additives

-Heat management by another methods

If is possible do the same in the simulation part

Finally, the manuscript contains lot of errors, they hinder the correct reading. They should check the manuscript before submit it.

So I suggest they recheck it carefully before resubmission.

Authors´ reply:

Thank you for the feedback and comments provided. We have made changes to chapter 2 (Experimental) dividing/rearranging the text under the following sections:

• Synthesis using ball-milling and induction melting
• Tank Geometry and Filling
• Thermal management using ENG
• Thermal management by other methods

We have also made changes to chapter 3 (Simulation) dividing/rearranging the text under the following sections:

• Porosity
• Tank Design
• Thermal Management

As sections of the original text have been moved to the corresponding section, slight changes have been made to the text to accommodate this change.

Furthermore, we have carefully rechecked the text for errors and add changes to make it more readable.

Round 2

Reviewer 2 Report

The improvement  of the manuscript has increased its readability.

Reviewer 4 Report

The revised version is ok for me, it can be published.