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

Abstract

Summary Kinetics study on the generation of hydrogen from an Al/water system is performed. The reaction is affected by three major factors such as the concentration of hydroxyl ions (pH values), catalysts, and temperature. However, these factors are interacted and sometimes difficult to separate. This study demonstrates how these factors affect the generation of hydrogen in an Al/water system. Aluminum hydroxide, Al(OH)3 (bayerite phase), synthesized using a chemical solution method, is proved to be a very effective catalyst for the reaction of Al and water. Approximately 95% yield (1300 mL) of hydrogen is produced from 1 g Al in 10 mL water using 3 g Al(OH)3 catalyst at room temperature within 1 minute. The generation rate of hydrogen is accelerated due to the catalyst Al(OH)3 and the exothermic heat. In this report, a ball‐mixing process, the ratio of Al:Al(OH)3:H2O, and the reacting temperatures are investigated to clarify the effect of catalyst Al(OH)3. The synthesized Al(OH)3 catalyst is found to reduce the activation energy of Al/water reaction from 158 kJ/mol to 73.3~76.9 kJ/mol. The roles of hydroxyl ions (ie, pH values), temperature, and catalyst on this phenomenal reaction are explained using a kinetics study and the concept of Fick first law. The 3 factors all improve the flux of hydroxyl ions through the passive Al2O3 layer; therefore, the generation of hydrogen is enhanced.

Improved hydrogen generation from Al/water reaction using different synthesized Al( OH ) 3 catalyst crystalline phases

“…The twisting and bond stretching frequency for gibbsite phase hydroxyl groups are at 3617, 3525 and 3085 cm −1 . The absorption bands at 3085 cm −1 are differentiated perpendicular to the (001) planes and the bands at 3617 and 3525 cm −1 are polarized in this plane, which is the corresponding gibbsite phase bond 36‐40 . The bayerite (S. No.1) has four absorption bands at 3658, 3556, 3482 and 3414 cm −1 for O‐H bonding.…”

“…The absorption bands at 3085 cm −1 are differentiated perpendicular to the (001) planes and the bands at 3617 and 3525 cm −1 are polarized in this plane, which is the corresponding gibbsite phase bond. [36][37][38][39][40] The bayerite (S. No. 775 cm −1 , 624 cm −1 , 518 cm −1 , and 426 cm −1 (S.No.1), 673 cm −1 , 487 cm −1 and 426 cm −1 (S.No.4) belong to the AlO 6 vibration mode.…”

Investigation on the Al/low‐melting‐point metals/salt composites for hydrogen generation

“…[1][2][3][4][5] There are various hydrogen production technologies including catalytic reforming, water electrolysis, water photolysis, biomass, metals, metal hydride, and so on, with all of them having their advantages and disadvantages. [6][7][8][9][10][11][12][13][14][15] For example, production of hydrogen from the fossil fuels though has high production efficiency, cannot be used as a long-term strategy for hydrogen economy due to its un-sustainability and airpollution; consumption of large quantity of electricity has made water electrolysis unfavorable though it can yield high-purity hydrogen; hydrogen production from the biomass, though is difficult to control with very low efficiency [16][17][18] but it is a promising method for the future. Ability to solve the problem of hydrogen storage and transportation has led to increasing attention being paid to the in-situ hydrogen generation via the reaction of metals (Al, Mg, Li, etc.)…”

Tunable kinetics of nanoaluminum and microaluminum powders reacting with water to produce hydrogen

“…The reaction rates and yields were optimized using Al(OH) 3 synthesized from Al (NO) 3 , given the high surface area and sharp edge of the hexagonal Al (OH) 3 crystals . The activation energy of the Al/water reaction was reduced from 158 kJ/mol to about 75 kJ/mol with the Al (OH) 3 catalyst . It was suggested that the addition of Al (OH) 3 , γ‐Al 2 O 3 , or α‐Al 2 O 3 helps dissociate the water molecules on the surface of these oxides and promotes the hydration of the oxide film on aluminum particles .…”

“…25 The activation energy of the Al/water reaction was reduced from 158 kJ/mol to about 75 kJ/mol with the Al (OH) 3 catalyst. 26 It was suggested that the addition of Al (OH) 3 , γ-Al 2 O 3 , or α-Al 2 O 3 helps dissociate the water molecules on the surface of these oxides and promotes the hydration of the oxide film on aluminum particles. 27 On the other hand, adding Na 2 CO 3 reduces the activation energy of low-temperature Al/H 2 O reaction (60°C-80°C) from 74.49 kJ/mol (without additive) to 43.03 kJ/mol (with 5-wt% Na 2 CO 3 addition).…”