Effect of air exposure on hydrogen storage properties of catalyzed magnesium hydride

Abstract

Air exposure of the magnesium hydride materials can lead to severe degradation on the hydrogen storage properties, and therefore is one of the key remaining challenges for its application. In this work, the effects of direct air exposure and solvent-protected air exposure for catalyzed MgH2 on the hydrogen storage properties are systematically investigated. Results show that the direct air exposure of catalyzed MgH2 leads to reduction of the hydrogen storage capacity, and moderate deterioration of the hydrogen absorption/desorption kinetics, but has limited impact on reversibility and cycle stability. A short-time air exposure (15 min) causes the decrease of hydrogen storage capacity of MgH2–5%VTiCr by 0.2 wt%, and long-time air exposure (2400 min) significantly deteriorates the hydrogen storage capacity by 1.95 wt%. During the direct exposure in ambient air, MgH2 reacts with oxygen and moisture, and the surface forms a layer consisting of Mg(OH)2 and MgO. Various solvents, hexane, acetone, and ethanol, are used to protect MgH2–5%TiMn2 material. The hydrogen storage properties of the solvent-protected materials after air exposure for 1500 min are evaluated, both the hydrogen storage capacity and kinetics are degraded after exposure. The acetone-protected MgH2–5%TiMn2 shows better kinetics and capacities compare to those protected by hexane and ethanol.