Among the various hydrogen storage options (such as compressed gas, sorbents, metal-organic frameworks, chemical hydrides), solid-state storage in complex metal hydrides has attracted particular attention due to the very high storage densities and favorable thermodynamics that can be achieved in these systems. Unfortunately, adoption of complex hydrides for vehicular storage is hindered by the inability to extract and recharge hydrogen at sufficiently rapid rates. There have been a few notable successes in accelerating reaction kinetics (e.g., Ti-doped alanates), but generalization of these methods to other high-capacity complex hydrides has been difficult. We show that first-principles density-functional theory (DFT) calculations can be used to quantitatively predict the kinetics of solid-state mass transfer in complex hydrides. In particular, DFT calculations of defect free energies and solid-state diffusivities are used as input to a diffusion-reaction model of solid-state phase transformations. Composition gradients and diffusional fluxes are determined from local equilibrium and charge neutrality conditions at multiphase interfaces. The proposed theoretical framework can predict activation energies and distinguish between competing reaction morphologies. Applications to several prototypical hydrogen storage materials � alanates, amides, and borohydrides � will be demonstrated.

Kinetics of mass transport kinetics in complex metal hydrides

245th National Meeting (2013)

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