In situ reflection high energy electron diffraction study of dehydrogenation process of Pd coated Mg nanoblades

The near surface structural evolution in dehydrogenation process of air exposed Pd coated Mg nanoblades was characterized in situ from room temperature to 573 K using reflection high energy electron diffraction RHEED . The evolved normalized diffraction intensity and the full width at half maximum of diffraction peaks have been correlated with the growth of crystal and the change in crystal size, respectively. With RHEED, we are able to detect crystal sizes smaller than 2 nm. At room temperature the dominant structures near surface were Pd and MgH2. With the substrate heating MgH2 started to gradually decompose at 380 K. When the temperature increased to 480 K MgH2 was nearly depleted and Mg6Pd alloys started to form. In addition, at high temperatures pure Mg reappeared and MgO was enhanced significantly even in high vacuum condition. We have discussed the effect of Mg oxide on the dehydrogenation process and the alloy formation between Pd and Mg as well as the accompanying migration of Mg to the surface at high temperatures. Based on our experimental results the structures and compositions that limit the hydrogenation/dehydrogenation cycle of Pd coated Mg nanoblades are suggested. Our findings can help the design of future recyclable hydrogen storage materials. © 2008 American Institute of Physics. DOI: 10.1063/1.2967735