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摘要
KAlH4 is the unique monoalkali alanate that absorbs hydrogen reversibly with reasonable kinetics at moderate pressures without doping, offering an exciting playground to understand the role of additives. KAlH4 was successfully synthesized by reactive ball milling (RBM) of a potassium hydride and aluminum, 1:1 powder mixture tinder a hydrogen pressure of 8.5 MPa and low temperature (<65 degrees C). The synthesis without additives entails two consecutive hydrogenation steps through the formation of K3AlH6 as intermediate. Among the different additives investigated (TiCl3, ScCl3, and LOCl3)), TiCl3 is the most effective by reducing the hydrogenation time by a factor of 2. Moreover, it promotes the simultaneotis formation of K3AlH6 and KAlH4 during medhanochemical, synthesis before all KH is consumed. X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analysis indicate that the additives do not modify the structural properties of the formed alanate. Independently of TiCl3 addition, KAlH4 is decomposed by three consecutive steps with K3AlH6 and KH as intermediates. Thus, the absorption and desorption reaction paths are asymmetric when TiCl3. is used as an additive. Moreover, the TiCl3 additive efficiently reduces desorption temperatures and activation energies for KAlH4 and K3AlH6 decompositions, with that for KH remaining unchanged. These results suggest that TiCl3 enhances the mobility of Al species during desorption, likely through the fop-nation of species at the interphase and grain boundaries as NMR measurements suggest. Reaction kinetics is limited by nudeatiohand growth during absorption and by diffusion processes during desorption.
- 出版日期2016-9-29
- 单位中国地震局
