Reversible hydrogen storage in vapour deposited Mg-5 at.% Pd powder composites

• Mg–Pd bulk composites derived from Pd/Mg/Pd/Mg/Pd films reversibly store 3.5 wt.% H2.
• Hydrogenation and dehydrogenation occur under mild conditions.
• Hydrogenation and dehydrogenation temperatures increase in successive cycles.
• Formation of Mg6Pd and Mg5Pd2 above 450 K limits stability to 15 cycles.

Mg-5 at.% Pd powder composites derived from multilayered films of Mg and Pd deposited in Pd/Mg/Pd/Mg/Pd layer configuration by thermal evaporation reversibly store about 3.5 wt.% hydrogen up to 15 cycles under mild conditions of pressure and temperature. Hydrogenation takes place at 0.15 MPa hydrogen pressure while dehydrogenation occurs in a dynamic rotary vacuum. Each process is completed in about three hours. The temperature of a dehydrogenation or hydrogenation step is about 5–10 K higher than the preceding hydrogenation or dehydrogenation step. The hydrogenation temperature of the first cycle is 343 K whereas the dehydrogenation temperature of the 15th cycle is 423 K. The hydrogen storage capacity of composite is the manifestation of fine-grained microstructure of Mg and the catalytic properties of Pd. It declines beyond 423 K due to the exhaustion of metallic Pd as a result of the formation of Mg–Pd intermetallic compounds. This approach presents a simple and rapid method of preparing Mg–Pd composites for hydrogen storage applications.