Christian Bonatto Minella

Structural and kinetic investigation of the hydride composite Ca(BH4)2 + MgH2 system doped with NbF5 for solid-state hydrogen storage

Designing safe, compact and high capacity hydrogen storage systems is the key step towards introducing a pollutant free hydrogen technology into a broad field of applications. Due to the chemical bonds of hydrogen-metal atoms, metal hydrides provide high energy density in safe hydrogen storage media. Reactive hydride composites (RHCs) are a promising class of high capacity solid state hydrogen storage systems. Ca(BH4)2 + MgH2 with a hydrogen content of 8.4 wt% is one of the most promising members of the RHCs. However, its relatively high desorption temperature of ∼350 °C is a major drawback to meeting the requirements for practical application. In this work, by using NbF5 as an additive, the dehydrogenation temperature of this RHC was significantly decreased. To elucidate the role of NbF5 in enhancing the desorption properties of the Ca(BH4)2 + MgH2 (Ca-RHC), a comprehensive investigation was carried out via manometric measurements, mass spectrometry, Differential Scanning Calorimetry (DSC), in situ Synchrotron Radiation-Powder X-ray Diffraction (SR-PXD), X-ray Absorption Spectroscopy (XAS), Anomalous Small-Angle X-ray Scattering (ASAXS), Scanning and Transmission Electron Microscopy (SEM, TEM) and Nuclear Magnetic Resonance (NMR) techniques.

Synthesis of LiNH2 + LiH by reactive milling of Li3N

The hydrogen sorption properties of Li3N under reactive milling conditions have been investigated in- and ex-situ as a function of polytype structure (alpha vs. beta), focusing on the influence of the micro-structure and/or the crystal structure upon hydrogen uptake. LiNH2 and LiH were synthesized by reactive milling of Li3N at 20 bar hydrogen pressure for 4 h. Reactive milling represents a quick and effective technique to produce LiNH2 by hydrogenation of Li3N at low hydrogen pressure and without any need for heating. As to our knowledge, we present a full hydrogenation of Li3N under the aforementioned conditions for the first time. The (de)hydrogenation and rehydrogenation behaviour of milled amides was evaluated using a combination of powder X-ray diffraction, differential scanning calorimetry, thermogravimetry and in situ Raman spectroscopy. In situ Raman spectroscopy showed a shift in the lithium amide stretching modes upon hydrogenation supporting a non-stoichiometric storage mechanism consistent with the literature. The microstructure and polytype composition of the Li3N dehydrogenated materials had no effect on the hydrogenation products and only minor effects on the hydrogen uptake profile during milling.

Mechanically activated metathesis reaction in NaNH2–MgH2 powder mixtures

The present work addresses the kinetics of chemical transformations activated by the mechanical processing of powder by ball milling. In particular, attention focuses on the reaction between NaNH2 and MgH2, specific case studies suitably chosen to throw light on the kinetic features emerging in connection with the exchange of anionic ligands induced by mechanical activation. Experimental findings indicate that the mechanical treatment of NaNH2–MgH2 powder mixtures induces a simple metathetic reaction with formation of NaH and Mg(NH2)2 phases. Chemical conversion data obtained by X-ray diffraction analysis have been interpreted using a kinetic model incorporating the statistical character of the mechanical processing by ball milling. The apparent rate constant measuring the reaction rate is related to the volume of powder effectively processed during individual collisions, and tentatively connected with the transfer of mechanical energy across the network formed by the points of contact between the powder particles trapped during collisions.

Performance Improvement of V–Fe–Cr–Ti Solid State Hydrogen Storage Materials in Impure Hydrogen Gas

Two approaches of engineering surface structures of V-Ti-based solid solution hydrogen storage alloys are presented, which enable improved tolerance toward gaseous oxygen (O2) impurities in hydrogen (H2) gas. Surface modification is achieved through engineering lanthanum (La)- or nickel (Ni)-rich surface layers with enhanced cyclic stability in an H2/O2 mixture. The formation of a Ni-rich surface layer does not improve the cycling stability in H2/O2 mixtures. Mischmetal (Mm, a mixture of La and Ce) agglomerates are observed within the bulk and surface of the alloy when small amounts of this material are added during arc melting synthesis. These agglomerates provide hydrogen-transparent diffusion pathways into the bulk of the V-Ti-Cr-Fe hydrogen storage alloy when the remaining oxidized surface is already nontransparent for hydrogen. Thus, the cycling stability of the alloy is improved in an O2-containing hydrogen environment as compared to the same alloy without addition of Mm. The obtained surface-engineered storage material still absorbs hydrogen after 20 cycles in a hydrogen-oxygen mixture, while the original material is already deactivated after 4 cycles.

Characterization of hydrogen storage materials both at the laboratory level and at the scale for prototype tanks

Light weight metal or complex hydrides offer the potential for a safe and energy efficient hydrogen storage alternative for stationary as well as mobile applications. Highest energy efficiencies, however, are achievable only if both working temperature and the reaction enthalpy of the respective hydrogen sorption process can be attuned to the accompanying hydrogen consuming process in such a way that the required heat for hydrogen release of the hydride can be provided by the corresponding waste heat [1]. Since the kinetic optimisation of novel high capacity hydrides as well as the tailoring of reaction enthalpies is an important research task. One way to do this is to combine different hydrides which react during decomposition in an exothermal way with each other and thereby reduce the value of reaction enthalpy while maintaining the average of the hydrogen capacities of the single hydrides. In parallel to such materials development and optimization activities upscaling of novel high capacity materials has to be demonstrated and tank concepts based upon these have to be investigated and optimized. Reactive Hydride Composites like combinations of MgH2 with M(BH4)x (M being Li, Na or Ca) show significantly reduced values of reaction enthalpies as well as improved aband desorption kinetics compared to the pure borohydrides. Furthermore, due to their high reversible gravimetric storage capacities of up to 11 wt.% they are interesting candidates for future hydrogen storage applications. In this presentation, recent results concerning reaction mechanisms, thermodynamic properties and sorption behaviour, cycling stability of borohydrides and Reactive Hydride Composites are presented. The progress in the optimisation of reaction kinetics reached so far will be described. Function and suitability of additives as potential catalysts on hydrogen aband desorption will be discussed. MS13-O3 Investigating Repeated Gas adsorption in zeolites for solar cooling applications. Marco Milanesio, Luca Palin, Davide Viterbo, Wouter van Beek, Dmitry Chernyshov, Atsushi Urakawa, Rocco Caliandro Dipartimento di Scienze e Tecnologie Avanzate and NanoSistemi IC, Universita del Piemonte Orientale, Via Michel 11, Alessandria, 15121, Italy; Swiss-Norwegian Beamlines at ESRF, BP 220, Grenoble, 38043, France; Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans, 16, Tarragona, E-43007, Spain; Institute of Crystallography, CNR, via Amendola, 122/o, Bari, 70126, Italy E-mail: marco.milanesio@unipmn.it