"The reaction between aluminum and gallium works because gallium removes the aluminum oxide coating that would otherwise form when the material comes in contact with water. When the researchers ran measurements on their experiments, they showed that the formation of aluminum nanoparticles during the reaction accounted for the very high rate of hydrogen production."
"[N]ot only does the gallium dissolve the aluminum oxide, it also separates the aluminum into nanoparticles. "The gallium separates the nanoparticles and keeps them from aggregating into larger particles.'"
"People have struggled to make aluminum nanoparticles, and here we are producing them under normal atmospheric pressure and room temperature conditions."
interestingengineering.com/method-hydrogen-from-aluminum