Effect of Si content on H2 production using Al–Si alloy powders

The effect of Si content in Al–Si alloy powder with NaOH on H2 production was investigated. The total amount of H2 produced decreased as Si content increased, which is inconsistent with the results predicted by the chemical reaction. Si caused a delay in the rate of H2 production. Energy dispersive spectrometry showed that a large amount of unreacted Si remained in the matrix, and the unreacted fraction increased as the Si content increased. As the evolution reaction of Al and Al–Si alloys is exothermic, the temperature of all the specimens increased. Si addition reduced the hydroxide removal rate, which decreased the average H2 production rate. The initiation time for H2 evolution depends on the elimination rate of the oxide film formed during production of the powder. On increasing the Si content, SiO2 was formed, which is harder to eliminate than Al2O3; this delayed the initiation.

► The effect of Si content in Al–Si alloy powder on H2 production was investigated.
► Unlikely in calculations the measured total amount of H2 decreased with increasing Si.
► The temperatures of all the specimens increased, as H2 evolution is exothermic.
► The initiation of H2 evolution was fastest in Al–12Si due to fine eutectic structure.
► With increasing Si content, amount of coarse Si increased, delaying the initiation.