I want to generate hydrogen to acquire known pressure inside of an object.
I have calculated required mole number for hydrogen using the ideal gas equation by giving wanted pressure, volume and temperature. I was thinking about using the reaction 2Al + 6HCl = 3H2 + 2AlCl3. But amount of produced hydrogen moles are not efficient in my case.
Is there a reaction which is more efficient and easy to do like with Al + HCl?
Aluminum has a disadvantage. It is covered by a thin, transparent and waterproof layer of aluminum oxide $\ce{Al2O3}$, also called alumina. When dipped into an acidic solution, a piece of aluminum does not react immediately, because this alumina layer has first to be destroyed by the acid, and it may take one minute or two $$\ce{Al2O3 + 6 HCl -> 2 AlCl3 + 3 H2O}$$Once this $\ce{Al2O3}$ layer is destroyed, the reaction Al + acid is efficient and produces plenty of Hydrogen.
If you do not want to wait, you may replace aluminium by another metal. The most efficient metal is Magnesium, which reacts strongly and quickly with dilute solutions of HCl : $$\ce{Mg + 2 HCl -> MgCl2 + H2}$$ You may also use Zinc, which reacts also strongly (specially if there is one drop of Cobalt chloride in the HCl solution) $$\ce{Zn + 2 HCl -> ZnCl2 + H2}$$
If, for some reason, you would prefer aluminum, you could replace HCl by sodium hydroxide NaOH. The reaction of NaOH on Aluminium is much more energetic than HCl on Aluminum, because the alumina layer is quickly destroyed:$$\ce{Al2O3 + 2 NaOH + 3 H2O -> 2 Na[Al{OH)_4]}}$$ and then follows the violent reaction:$$\ce{2 Al + 2 NaOH + 6 H2O -> 2 Na[Al(OH)4] + 3 H2}$$
