Effect of Temperature on the interaction rules between grain size and reaction rate of Al-Ga-based alloys for hydrogen generation

Abstract

Controllable hydrogen generation rate of Al-Ga-based on-site hydrogen supply materials significantly impacts their practical application. In many scenarios, the hydrolysis reaction occurs at elevated temperatures, which is a factor often overlooked in its effect on reaction kinetics. This study investigates the relationship between grain size and reaction rate in Al-Ga-based alloys for hydrogen generation, specifically examining temperature influences. We synthesized a series of Al-Ga-based alloys with antimony (Sb) as a refining agent, systematically varying the Sb content to modulate grain size. The hydrogen production rates were measured across various temperatures. Our results indicate that Sb effectively refines Al alloys, significantly affecting the Al-H₂O reaction rate by altering selective growth orientation and grain size. The most pronounced refinement is at 0.1 wt.% Sb, yielding the smallest grain size and highest hydrogen production rate, making it suitable for substantial hydrogen generation applications. Further investigations reveal a non-linear relationship between Sb's effect on grain size and the reaction rate. At elevated temperatures, the fragmentation of the Al alloy intensifies, amplifying the impact of grain size on the hydrogen generation rate. In contrast, this regulatory mechanism is diminished at lower temperatures. We also validated this relationship with previously reported Al-Ga-based hydrogen-producing alloys. These findings offer valuable insights, suggesting that strategic grain size modifications can effectively enhance hydrogen generation rates at elevated temperatures.