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NaBH4has long been identified as a viable hydrogen-storage material due to a theoretical gravimetric H2capacity 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 NaBH4has yet to be utilized in hydrogen-storage processes. In this study, NaBH4has been milled with a variety of Ni-containing additives to investigate the effects on the temperatures required for thermal desorption of H2by 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 H2by 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 NixByspecies including Ni3B, Ni2B, and Ni3B4. A catalyst screening study of NaBH4with 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.

This study elucidates the role of transition metal (TM) additives in enhancing hydrogen (H) reversibility and hydrogenation kinetics for the NaAlH4system. The isothermal hydrogen absorption kinetics of the planetary milled (PM) NaAlH4+ xTMCln(TM row 1 = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu; row 2 = Zn, Y, Zr, Nb, Mo, Ru, Rh Pd; row 3 = Pt; 2 < n< 5) and cryo-milled (CM) NaAlH4+ xTMCln(TM row 1 = Ti, V, Cr, Fe, Co, Ni, Cu; 2 < n< 3) systems have been measured at 140 °C and 150 bar system pressure. The variation in hydrogenation kinetics across the TM series for NaAlH4+ xTMClnis strongly dependent on the TM species and additive level, milling technique, and the type, structure, and morphological arrangement of nanoscopic Al1–xTMxphases that are embedded on the NaAlH4surface. In the most interesting case, the surface-embedded Al1–xTixphases in the TiCl3-enhanced NaAlH4system perform a dual catalytic function, where the outer Al1–xTixsurface performs dissociation/recombination of molecular H2and the inner Al1–xTixsurface allows the distortion of a minor number of Al–H bonds from AlH4–tetrahedra in the vicinity of the subsurface Al1–xTix/NaAlH4interface. The density of Ti atoms in the subsurface interface (which is Al:Ti composition- and H cycling temperature-dependent) shows the strongest effects on hydrogenation kinetics.

The substitution of the complex borohydride anion BH4−in calcium borohydride by the larger iodide anion I−is explored in order to tailor the hydrogen storage properties. Three new compounds are identified in the Ca(BH4)2−CaI2system and are structurally characterized using the Rietveld method and synchrotron radiation powder X-ray diffraction (SR-PXD) data. Calcium borohydride readily dissolves in the trigonal calcium iodide structure during ball milling, forming a solid solution Ca((BH4)1−xIx)2with a CaI2-type structure and an anisotropically contracted trigonal unit cell, a= 4.311(1) and c= 6.867(2) Å for x∼ 0.3 (T= 28 °C), space group P3̅m1. The trigonal tri-Ca((BH4)0.70I0.30)2transforms at ∼180 °C to an orthorhombic phase of similar composition, ort-Ca((BH4)0.64I0.36)2, with a CaCl2-type structure (a distorted β-Ca(BH4)2type structure) and cell parameters a= 7.271(2), b= 7.042(1), and c= 4.4601(7) Å (T= 322 °C), space group Pnnm. Further heating of the CaCl2-type compound to ∼330 °C leads to a transition to a tetragonal phase with cell parameters a= 4.1062(2) and c= 24.822(2) Å (T= 340 °C, x∼ 0.62), space group I4mm. This iodide-rich compound tet-Ca((BH4)0.38I0.62)2, has a new structure type. The tetragonal phase finally decomposes to CaHI and CaB6at T> 345 °C. All three novel compounds found in the Ca(BH4)2−CaI2system are stable at room temperature. The anion substitution ultimately changes the decomposition reaction pathway in which hydrogen is released from the tetragonal Ca((BH4)1−xIx)2via CaHI, but unfortunately the temperature of hydrogen release is still fairly high and similar to that for Ca(BH4)2.

The crystal structures of La2O2CO3II and Nd2O2CO3II have been shown by means of high-resolution powder neutron (PND) and synchrotron X-ray diffraction (SXRD) combined with selected area electron diffraction (SAED) studies to be far more complex than earlier anticipated, owing to ordering of carbonate groups between (Ln2O2+2)nlayers. In contrast to earlier descriptions, the carbonate groups appear to be rather regular. Relative to an average model, the SAED patterns show additional scattering in the form of closely distributed, but essentially discrete, spots along 〈13, 13, l〉*. Most of the observed scattering, H, can be described as H=G±mq1+nq2, where G is the Bragg reflections of the underlying average P63/mmclattice, q1=[13, 13, ±12]*, q2=[13, 13, ±23]*, and mand nare integers. The additional scattering reflects ordering of the carbonate groups into trigonal layers between the (Ln2O2+2)nlayers, but it remains open whether q1and q2represent two separate structures with different stacking sequences of such layers or whether they correspond to an even more complex stacking sequence. In any case, some disorder and rotational domain twinning are present. Two structure models, one for each modulation wave vector, were constructed. Rietveld-type refinements of PND data of La2O2CO3II were performed, approximating the complex, and at least partly disordered, stacking sequence as a two-phase mixture of the two modulated phases. Satisfactory convergence was achieved with Rp=6.4%, Rwp=8.3%, and χ2=3.32. The isothermal expansivities, αp, for La2O2CO3II and Nd2O2CO3II between 298 and 893 K were determined as 2.92×10−5and 2.70×10−5K−1, respectively.

The crystal structures of Nd4M3O10(M=Co, Ni) correspond to the n=3 members of the Ruddlesden–Popper series of An+1BnO3n+1. Rietveld-type analyses of high-resolution powder synchrotron X-ray and powder neutron diffraction (PND) data of Nd4Co3O10+δand Nd4Ni3O10−δreveal their crystal structures to be slightly monoclinically distorted. The symmetry lowering to space group P21/ais caused by tilting of the MO6octahedra within the (NdMO3)3layers. Long apical M–O distances are observed in the octahedra pointing toward the NdO layers. Magnetic susceptibility data for Nd4Co3O10.00indicate long-range antiferromagnetic ordering below 15 K. The ordered moment is too low to be detected by PND at 8 K. Above 60 K, two nearly Curie–Weiss paramagnetic regions are observed: 60–560 K and 650–920 K. Thermal analysis data for Nd4Co3O10+δin atmospheres of oxygen and nitrogen shows a complex behavior, with respect to both possible phase transitions and redox properties.

The performance of the new Powder Neutron Diffractometer PUS at the 2 MW JEEP II reactor shows the large potential for high resolution powder neutron diffraction even at a low flux reactor. The different components of the instrument are optimised with respect to flexibility and relationship between intensity and resolution. Wavelengths in the range 0.7–2.6 Å are available from a focussing composite Ge monochromator. The detector system consists of position sensitive proportional counters. The temperatures available for experiments range from 7 to about 1600 K. Nearly no malfunctions during the first 2 1/2 years of operation proves the robustness of the complete system. Several experiments show the potential for studies of rather complex crystallographic problems, even with small sample quantities (<200 mg), and timeresolved in-situ type experiments.