Kinetically Controllable Hydrogen Generation at Low Temperatures by the Alcoholysis of CaMg2 -Based Materials in Tailored Solutions.

Abstract

The alcoholysis of CaMg2 -based materials for hydrogen generation is reported. Compared to hydrolysis in water, hydrogen supply from alcoholysis shows an excellent potential for outdoor applications, which not only bypasses the formation of passivation layers deposited on the surface of particles but also breaks the temperature bottleneck in which hydrolysis occurs over 0 °C. To remove the troublesome freezing issue of the water solution system in low-temperature conditions, here, instead of pure methanol, methanol/water and methanol/ethanol solutions are applied to react with CaMg2 alloy (CM2 ) and its hydrides (H-CM2 ) for hydrogen generation. Compared with pure water and ethanol, the reaction of CaMg2 -based materials with methanol possesses much faster reaction kinetics and gives a considerable hydrogen yield. CM2 can generate 858 mL g-1 within only 3 min at room temperature as it reacts vigorously with methanol, as opposed to a low hydrogen yield with ethanol and water (395 and 224 mL g-1 within 180 min, respectively) under the same conditions. Even at -20 °C, there is still over 600 mL g-1 released at a conversion rate of 70.7 % within 100 min for methanolysis, which shows its prominent advantage for hydrogen production, especially in winter or subzero areas. Interestingly, the methanolysis byproducts can transform into metal hydroxides and methanol in the reaction with water, and the methanol may be separated and reused as an intermediate. Moreover, the hydrogen behavior of CaMg2 methanolysis can be well controlled by tailoring the components of the solutions to deliver a promising hydrogen supply system for the hydrogen economy.