Hydrogen generation by aluminum corrosion in aqueous alkaline solutions of inorganic promoters: the Alhidrox process

Abstract

The research of alternative processes to obtain clean fuels has become a main issue because of the concerns related to the current energy system, both from economical and environmental points of view. Hydrogen storage and production methods are being investigated for stationary and portable applications. Up to now, a significant part of H2 production on demand was thought to be fulfilled by using chemical hydrides, but recent studies have proved the limitations of this approach. Conversely, H2 production based in the corrosion of light metals in water solutions is an interesting alternative. Among all of them, Al is probably the most adequate metal for energetic purposes due to its high electron density and oxidation potential. But concerning H2 production from Al corrosion in water, a major issue remains unsolved: metal passivation due to the formation of Al(OH)3 inhibits H2 evolution. In this work we show the last results obtained for the generation of H2 from water using Al powder using diverse alkaline solutions. It is confirmed that corrosion is not affected solely by the solution pH but also by the nature of the ionic species found in the aqueous medium. Moreover, we describe the AlHidrox process, which minimizes Al passivation under mild conditions by the addition of different inorganic salts as corrosion promoters, allowing 100% yields and flow rates up to 2.9 L/min per gram of Al. The feasibility of the process has been regarded in terms of stability (by conducting several successive runs) and selfinitiation without an external heating.