Combinatorial screening for the identification of Mg-based destabilized hydrogen storage materials

October 16, 2006 - 12:00pm

Limited energy resources and increasing pollution associated with the use of fossil resources have stimulated the search for cleaner, cheaper and more efficient energy technologies. One promising technology involves hydrogen that can be used in fuel cells and is stored in metal hydrides. However, for replacing existing technologies, still a large number of problems have to be solved, demanding for extensive fundamental research in the field of material science. Our experimental strategy, aimed at finding of novel (complex) hydrides is to carry out systematic experiments for various light-weight metal-hydrides. In the standard approach followed so far, the exploratory search for new light-weight hydrogen storage materials is very time consuming as a bulk sample is needed for each composition. We developed Hydrogenography, a thin film composition-spread technique, to follow optically the metal-to-hydride phase transition and measure the hydride formation enthalpy of thousands of alloys simultaneously [1-3]. By co-sputtering from off-centered magnetron sources, we produce Mgy(TM)1-y (TM = Ti, V, Ni) thin films with large compositional gradients. By gradually increasing the pressure and measuring the associated change in optical transmission, the pressure-transmission isotherms and thus the equilibrium plateau pressures of the metal-to-hydride transition are determined for all compositions simultaneously. From measurements at various temperatures, the enthalpy of formation of each individual composition is then obtained. The Mg-Ti-H system is promising for application in batteries [4] and solar collectors [5]. This system is used to demonstrate the validity and power of our novel optical approach for the hydride stability determination. We show that the shape of the optical isotherms reflects the structural changes observed in MgyTi1-yHx films [6]. A comparison with the segregating Mg-V-H system confirms that Mg-Ti-(H) thin films are, at the contrary to bulk, (meta-)stable alloys, both in the metallic and the hydride state. We apply then Hydrogenography to the quaternary Mg-Ni-Ti-H system and identify hydrides that absorb hydrogen with enthalpies of formation between –40 and –37 kJ/(mol H2), thus strongly destabilized relatively both to MgH2 and to the Mg-Ni and Mg-Ti systems. 1. A. Borgschulte et al., Appl. Phys. Lett. 85, 4884 (2004) 2. R. Gremaud et al., Appl. Phys. A 84, 77 (2006) 3. R Gremaud et al., Submitted to Nature Materials (2006) 4. R. A. H. Niessen, P. H. L. Notten, Electrochem. Solid-State Lett. 8, A534 (2005). 5. D. M. Borsa et al, Appl. Phys. Lett. 88, 241910 (2006) 6. D. M. Borsa et al, Submitted to Phys. Rev. B (2006) For more information about this seminar, please contact: Venkat Srinivasanx2679

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