Microstructure of Al-Li alloy and its hydrolysis as portable hydrogen source for proton-exchange membrane fuel cells

Activated aluminum alloys are able to release hydrogen in neutral aqueous solutions at 298 K, but at lower theoretical hydrogen generation values than pure aluminum. This is because the additives in these alloys cannot react with water to produce H₂. In this paper, a new process to obtain hydrogen from milled Al-Li alloy in water is discussed. The optimized alloy is able to produce hydrogen yields >1245 ml hydrogen/g alloy with higher than 90% conversion efficiency and a controllable hydrogen generation rate at 298 K and 1 atm. The improved hydrolysis properties mostly come from the increased lithium content, which helps decrease grain size, accompanied by the phase evolution of Al-Li to Al₂Li₃ to Al₄Li₉. Further analysis of the Li/Al mole ratio of the hydrolysis byproduct LiAl ₂(OH)₇ shows that excess LiOH accelerates aluminum hydrolysis in water. Other effects, such as milling time, annealing temperature, and additives, are also reported and discussed.