Hydrogen generation by aluminum corrosion in seawater promoted by suspensions of aluminum hydroxide

Abstract

Nowadays, new processes of H2 generation from water via Al corrosion are mainly limited by Al passivation. Here we report on the systematic assessment of H2 production by corrosion of Al in seawater suspensions prepared with NaAlO2. The reported results are encouraging, since it was observed that seawater suspensions tested can prevent Al passivation during H2 evolution, reaching 100% yields at ca. 700 cm3 H2 min-1. XRD analysis revealed the formation of solid Al(OH)3 (bayerite) in initial seawater suspensions. So, model suspensions were prepared using NaAlO2 + Al(OH)3 in distilled water, which even improved the results obtained in seawater. Suspended particles of Al(OH)3 act as nuclei in a mechanism of seeded crystallization, which prevents Al surface passivation. Moreover, a synergistic effect of Al(OH)3 suspensions in combination with NaAlO2 solutions was key in promoting Al corrosion. The effect of NaCl in aqueous suspensions was also studied, but it was insignificant compared to this synergistic effect. The composition of suspensions was optimized and a 0.01 M NaAlO2 solution with 20 g dm-3 Al(OH)3 was selected as candidate to generate H2 at pH ca. 12 with high efficiency. Consecutive runs of the selected composition were performed obtaining ca. 90% yields in all of them.