Novel amorphous aluminum hydroxide catalysts for aluminum–water reactions to produce H2 on demand

Abstract

Production of aluminum (Al) through electrolysis is an energy intensive process. Al metal with its very high specific energy density of 28.8 MJ kg−1 can serve as an excellent energy storage vector. Al reacts with water (reaction (1)) at room temperature producing clean H2 thus providing an alternative to compressed gas storage.(1)2Al + 6H2O → 2Al(OH)3 + 3H2Reaction (1) does not proceed easily due to the presence of a 2–4 nm passive alumina surface layer. Aluminum hydroxide (Al(OH)3) catalyst disrupts this layer, sustaining reaction (1). The present work focuses on the catalysis aspects of reaction (1) by amorphous Al(OH)3 produced by urea hydrolysis of aluminum nitrate. H2 yields of up to 100% were obtained at 45 °C. Spent reaction product mixtures are autocatalytic with successive additions of Al micropowder (MP) yielding up to 133 ml H2/minute and reaction completion within 10 min at pH ≈ 10. There is an induction time initially due to the presence of dissolved ions, followed by production of H2. Reaction by-products are easily recyclable back to Al metal through subsequent calcining and electrolysis by the Al refining industry, which constitutes the energy storage part of the cycle.