Rapid Hydrogen Generation from Aluminum-Water System Using Synthesized Aluminum Hydroxide Catalyst

Abstract

Abstract-Catalytic effect of Al(OH) 3 on the hydrogen generation from Al/water system is evaluated. The Al(OH) 3 powders are synthesized from various molar ratios of Al(NO 3 ) 3 : NaOH = 1:3 ~ 1:5. It was found that the Al(OH) 3 catalyst derived from the ratio Al(NO 3 ) 3 : NaOH = 1:3.5~1:4 in an ice bath exhibits the best catalytic effect and exerts the highest hydrogen generation rate. Over 95% yield of hydrogen from a 3 g Al/50 ml water system (with 15 g Al(OH) 3 and pH=12) can be generated within 100 s. That is, by using specially synthesized Al(OH) 3 catalyst at a Al:Al(OH) 3 :H 2 O=3:15:50 weight ratio, very rapid hydrogen generation rate (~667 ml/gAlmin), without using any alloying elements or extreme corrosive condition, can be realized.Index Terms-Aluminum hydroxide, aluminum nitrate, hydrogen generation.

Kinetics study on the generation of hydrogen from an aluminum/water system using synthesized aluminum hydroxides

“…As shown in Figure A,B, the first run of reaction took 50 seconds for incubation, and only 87% yield of hydrogen (~3500 ml) was produced in approximately 150 seconds. Compare to those approximately 100% yield of our previous studies, the first run shows a much less yield of hydrogen, and so do the following second and third runs. This is considered to be due to an incomplete reaction resulted from a small amount of unreacted Al powders sticking on the bottom of the flask, being covered by an increasingly thick layer of by‐product Al(OH) 3 .…”

“…Sufficient quantity of catalyst plays an important role in this reaction. It is considered that the numerous active sites of the hexagonal crystal structure of bayerite for hydroxyl ions dissociation from water molecules are the key criteria for a rapid generation of hydrogen, as depicted in our previous report . Sufficient quantity of Al(OH) 3 is required for an efficient catalysis process.…”

“…water, causing a more rapid reaction than those of pH ≤ 10. The activation energy, in this case, is as low as 33.25 kJ/mol, 26 which could be partially contributed from the residual hydroxyl ions. Lower activation energy resulted from a higher rate constants k at high pH values was not discussed in the literature.…”

“…The surface area of these Al(OH) 3 powders is 37.65 m 2 /g, which is higher than those of our previous studies. 13,[24][25][26] When these synthesized Al(OH) 3 powders were ball-mixed with Al metallic powders, numerous tiny Al(OH) 3 particles were stuck on the surface of Al powders, as shown in Figure 3B. We will discuss the effect of ball-mixing in Section 3.3.…”

“…It is considered that the numerous active sites of the hexagonal crystal structure of bayerite for hydroxyl ions dissociation from water molecules are the key criteria for a rapid generation of hydrogen, as depicted in our previous report. 26 Sufficient quantity of Al(OH) 3 is required for an efficient catalysis process. Ball-mixing of Al and Al(OH) 3 forced both powders to an intimate contact and shortened the distance for the diffusion of hydroxyl ions, therefore facilitated the hydrogen generation.…”