Hydrogen storage properties of Mg-based multilayer films

Abstract

In this study, four multilayer film samples of polyimide/Mg, polyimide/Mg/Ti, polyimide/Mg/Pd, and polyimide/Mg/Ti/Pd were prepared by pulsed laser deposition and evaluated for hydrogen absorption-desorption properties. Polyimide/Mg and polyimide/Mg/Ti samples did not absorb hydrogen under conditions of 0.8 MPa and 200°C, while polyimide/Mg/Pd and polyimide/Mg/Ti/Pd samples absorbed hydrogen under the same conditions. The polyimide/Mg/Pd and polyimide/Mg/Ti/Pd samples desorbed hydrogen in the temperature ranges of 430-440°C and 140-200°C, respectively. The addition of Pd was necessary for the absorption of hydrogen because Pd promoted the dissociation of molecular hydrogen. The addition of Ti was necessary to decrease the temperature of dehydrogenation. The improved hydrogen absorption-desorption behavior could be caused by the structural change of MgH₂ from bct to fcc and the decreased thermal stability of fcc MgH₂ compared to that of bct MgH₂. The hydrogen storage amount of the polyimide/Mg/Ti/Pd film was determined with pressure-composition-temperature measurements. The sample absorbed 0.42 wt.% hydrogen at 200°C and 2.0 MPa and 0.49 wt.% at 200°C and 10 MPa; hydrogen desorption was incomplete under both conditions. While the hydrogen storage amount of the polyimide/Mg/Ti/Pd film is less than that of pure Mg, it may be increased by omitting the base material of polyimide film.