Making aluminum from aluminum oxide by electrolysis, than reacting it with water to make hydrogen must have a lower efficiency than making directly hydrogen from water by electrolysis.
Gallium is inert in this application, its role is to prevent the passivation of aluminum that happens normally when aluminum is exposed to air and water.
An amalgam of aluminum (i.e. an alloy of aluminum with mercury) would produce hydrogen in the same way. The advantage of gallium in this application, and also in other applications where gallium is used to replace mercury, is that gallium is not toxic (because being trivalent, it forms insoluble compounds, unlike mercury, which forms soluble ions).
This method of making hydrogen is useful only for portable hydrogen generators, intended to be used in places where you could not carry a hydrolysis generator or compressed hydrogen.
Interesting. Are there any situations where carrying water would be better than carrying compressed (or hydride) tanks? I would think there wouldn't be much, if any weight benefit, especially with the recent advances in lightweight design for aircraft tanks.
Gallium is inert in this application, its role is to prevent the passivation of aluminum that happens normally when aluminum is exposed to air and water.
An amalgam of aluminum (i.e. an alloy of aluminum with mercury) would produce hydrogen in the same way. The advantage of gallium in this application, and also in other applications where gallium is used to replace mercury, is that gallium is not toxic (because being trivalent, it forms insoluble compounds, unlike mercury, which forms soluble ions).
This method of making hydrogen is useful only for portable hydrogen generators, intended to be used in places where you could not carry a hydrolysis generator or compressed hydrogen.