Reversible Hydrogenation Studies of NaBH 4 Milled with Ni - 2 Containing Additives

7 ABSTRACT: NaBH4 has long been identified as a viable hydrogen-storage 8 material due to a theoretical gravimetric H2 capacity of 10.6 wt %. Because of 9 the high enthalpy of decomposition of 108 ± 3 kJ mol−1, thermal 10 decomposition of the pristine material does not occur until at least 500 °C, 11 and thus NaBH4 has yet to be utilized in hydrogen-storage processes. In this 12 study, NaBH4 has been milled with a variety of Ni-containing additives to 13 investigate the effects on the temperatures required for thermal desorption 14 of H2 by temperature-programmed desorption measurements and the 15 products characterized by powder X-ray diffraction (PXD). Ni-containing 16 additives have been determined to significantly enhance the thermal 17 desorption of H2 by at least 60 °C (Ni (65 wt %)) on Si/Al2O3. PCT cycling 18 experiments have been conducted to ascertain their effects on the reversible 19 hydrogenation of the milled NaBH4. PXD analysis indicates that Ni reacts 20 with B evolved during thermal decomposition to form NixBy species 21 including Ni3B, Ni2B, and Ni3B4. A catalyst screening study of NaBH4 with a variety of nanoparticles, chlorides, borides, and 22 mesoporous materials has also been conducted, the most effective of which has been found to be Pd nanoparticles, which have a 23 desorption temperature of 420 °C, a decrease of at least 85 °C.