Generation of hydrogen upon immersion of Mg in Mn(Ac) 2 and the reaction mechanism

Abstract

Reactions between metals and H2O could provide high-purity hydrogen gas for portable fuel cell. However, the initial reaction is typically hindered due to the existence of a dense outer oxide film. Herein, rapid generation of hydrogen following immersion of Mg in a solution of Mn(Ac)2 is examined. The formation of an Mg/Mn galvanic cell results in the destruction of an oxide film, inducing a continuous reaction between Mg, Mn, and water. Moreover, Mn is then oxidized back to Mn2+, illustrating that the metal further participates in the generation of hydrogen. The detected reaction rate varies from 37.5 to 55 mL g−1 minute−1, and the hydrogen volume is ~1000 mL at 35°C. Furthermore, the in-situ potential changes with the generation of hydrogen, reflecting the fluctuation of the Mg2+ and OH− ions. Notably, the formation of flake-type Mn or Mn(OH)2 facilitates the permeation of water, OH− ions, and the overflow of hydrogen. Conversely, the accumulation of square-type Mg(OH)2 hinders permeation, lowering the hydrogen generation rate. The results of the present study provide new insights into the design of highly pure hydrogen generation systems by adjusting the solution composition.