A Novel Method for Generating H₂ by Activation of the μAl-Water System Using Aluminum Nanoparticles

Round 1

Reviewer 1 Report

The authors described a method for activation of the reaction of water with micro-scale aluminum particles with XRD, TEM, and other supporting experimental approaches. The author group has a long history of working on aluminum nanomaterials, with 9 of their papers cited in this article. For Figure 5, it will be beneficial to add the ICDD info to the figure. I would recommend the acceptance of the article in the current format.

Author Response

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Reviewer 2 Report

The proposed article studies the process of aluminum hydrolysis in mixtures of aluminum microparticles and nanoparticles protected by an organic compound. With a view to using this type of mixture for the production of hydrogen, the authors consider that the mixtures guaranteeing the best efficiency and the best cost and safety compromises are mixtures containing 90% microparticles and 10% of nanoparticles. In terms of understanding the phenomena, they come to consider that the hydrolysis of the nanoparticles generates a rise in pH causing the dissolution of the protective alumina layer covering the microparticles. It is this phenomenon, which explains the hydrolysis of microparticles in the presence of nanoparticles.

The work is clearly presented, well argued with in particular in the appendix, a serious study on the predominance of chemical species in solution during activation. The conclusions drawn are also convincing.

A few suggestions, likely to increase the impact and clarity some items of the article, are made below.

• It is mentioned in several places in the article that in the presence of Al(OH)3 a catalytic process is set up responsible for the accelerated hydrolysis of the aluminum microparticles. At the end of the article, however, it seems that it is the variation in pH caused by the formation of Al(OH)3 which is the real reason for the hydrolysis observed for the microparticles. Shouldn't we simply speak of an acid-base reaction rather than a catalytic process?
• The phenomenon allowing the hydrolysis of the microparticles being mainly related to a high pH, would it not be possible to hydrolyze aluminum microparticles by directly etching them with a basic aqueous solution? In this case, it would no longer be necessary to use expensive and potentially problematic nanoparticles in terms of safety. Would it be possible to discuss this option in the paper?
• The hydrolysis of aluminum is of great interest to the production of hydrogen in portable devices. Beyond this technological application, it seems that the activation of aluminum microparticles also has an interest in the field of additive manufacturing by laser fusion (Veron et al. Additive Manufacturing, 50 (2022) 102550 ). The activated aluminum (or AlSi12 alloy) particles can indeed be fused in the metallic state or in the oxide state, depending on the laser exposure conditions and thus allow the original production of multi-material parts. The problem of the reactivity of powders in this case, is a little different, but it would seem interesting to make the link between the proposed work and the field of additive manufacturing. This would give new perspectives and potentially would increase the impact of the work presented.
• Are the authors sure that they did not form AlO(OH)? Did they do any IR spectrometry analysis to make sure?

 

 

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The paper by Kader et al. shows a novel method to generate H2 from water with micron scale aluminum particles, where the reaction can be activated by the addition of poly(epoxyhexane)-capped aluminum nanoparticles. The reaction proceeds via the generation of Al(OH)3 (due to reaction of aluminum nanoparticles with water), which is basic in nature; and therefore, the increase in pH helps getting rid of the nonreactive aluminum oxide layer from micron-sized aluminum particles facilitating the production of hydrogen. The authors have done a nice job in identifying different stages of the reaction process; and in quantifying the amount of Al-nanoparticles needed for optimal cost vs production efficiency.

I just have couple of questions/comments:

Since, the authors describe that increase in pH helps for efficient H2 production, can’t one just start the experiment with basic water solution (by adding bases like NaOH or even Al(OH)3 in water to begin with). In that case, will it still make sense to add Al-nanoparticles to achieve the same goal? Have the authors done such a control measurement? It would be nice to compare its effect on overall efficiency.

Does the production of H2 have a dependence on the size of the aluminum-nanoparticles? If yes, my guess is higher surface area of larger size Al-nanoparticles could offset the need of the mass% of the particles needed for similar efficiency, and thereby, lowering down the cost.

I understand, that the authors argue that exothermicity of Al(OH)3 generation is not sufficient for the change in H2 production rate. However, is it possible to increase the temperature of the reaction vessel (say, 20-50 degree or even more) and observe its effect on the reaction rate?

I would encourage authors to include these data if available, or at least comment on what they expect in case these changes are made. This would give a nice platform to investigate such a system further for betterment of efficiency.

Author Response

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Author Response File: Author Response.docx