Reversible Hydrogenation Studies of NaBH₄ Milled with Ni-Containing Additives

Abstract

NaBH 4 has long been identified as a viable hydrogen-storage material due to a theoretical gravimetric H 2 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 NaBH 4 has yet to be utilized in hydrogen-storage processes. In this study, NaBH 4 has been milled with a variety of Ni-containing additives to investigate the effects on the temperatures required for thermal desorption of H 2 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 H 2 by at least 60 °C (Ni (65 wt %) on Si/Al 2 O 3 ). PCT cycling experiments have been conducted to ascertain their effects on the reversible hydrogenation of the milled NaBH 4 . PXD analysis indicates that Ni reacts with B evolved during thermal decomposition to form Ni x B y species including Ni 3 B, Ni 2 B, and Ni 3 B 4 . A catalyst screening study of NaBH 4 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.