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

摘要

Nowadays, new processes of H_2 generation from water via Al corrosion are mainly limited by Al passivation. Here we report on the systematic assessment of H_2 production by corrosion of Al in seawater suspensions prepared with NaAlO_2. The reported results are encouraging, since it was observed that seawater suspensions tested can prevent Al passivation during H_2 evolution, reaching 100% yields at ca. 700 cm~3 H_2 min~(-1). XRD analysis revealed the formation of solid Al(OH)_3 (bayerite) in initial seawater suspensions. So, model suspensions were prepared using NaAlO_2 + 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 NaAlO_2 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 NaAlO_2 solution with 20 gdm~(-3) Al(OH)_3 was selected as candidate to generate H_2 at pH ca. 12 with high efficiency. Consecutive runs of the selected composition were performed obtaining ca. 90% yields in all of them.