Reversible hydrogenation studies of NaBH4 milled with Ni-containing additives

Abstract

NaBH4 has long been identified as a viable hydrogen-storage material due to a theoretical gravimetric H2 capacity of 10.6 wt %. Because of the high enthalpy of decomposition of 108 ± 3 kJ mol -1, thermal decomposition of the pristine material does not occur until at least 500 C, and thus NaBH4 has yet to be utilized in hydrogen-storage processes. In this study, NaBH4 has been milled with a variety of Ni-containing additives to investigate the effects on the temperatures required for thermal desorption of H2 by temperature-programmed desorption (TPD) measurements and the products characterized by powder X-ray diffraction (PXD). Ni-containing additives have been determined to significantly enhance the thermal desorption of H2 by at least 60 C (Ni (65 wt %) on Si/Al2O3). PCT cycling experiments have been conducted to ascertain their effects on the reversible hydrogenation of the milled NaBH4. PXD analysis indicates that Ni reacts with B evolved during thermal decomposition to form NixB y species including Ni3B, Ni2B, and Ni 3B4. A catalyst screening study of NaBH4 with a variety of nanoparticles, chlorides, borides, and mesoporous materials has also been conducted, the most effective of which has been found to be Pd nanoparticles, which have a desorption temperature of 420 C, a decrease of at least 85 C. © 2013 American Chemical Society.