Hydrogen Production by Hydrolysis of Bulk Porous Aluminum

The hydrolysis of bulk porous aluminum (Al) allows the production of hydrogen. However, in water, the yield and kinetics of the hydrolysis reaction are very low. In this study, in order to overcome these problems, the hydrolysis was carried out in a NaOH solution to eliminate the passivation phenomenon. Al materials were fabricated using uniaxial hot pressing that allows control of the relative density of the fabricated materials. The role of the porosity rate on the kinetics of the reaction was investigated. The results showed that the relative density rate significantly influenced the rate of hydrolysis; lower relative densities led to a faster reaction speed. Complete hydrolysis (i.e., 1245 mL/g of Al) is reached after 50 min for the 50% relative density sample, whereas it takes more than 300 min for the one with 90% relative density. A correlation between the microstructure and hydrolysis behavior exists. Two models were applied to highlight the reaction mechanisms. Hydrolysis at various temperatures allowed the determination of the activation energy of the reaction, which was found to be almost constant, whatever the relative density rate (i.e., Ea = 50–55 kJ/mol). The reactions were found to be primarily controlled by the surface.