Metal hydride formation and hydrogen storage in AlLi

Metal hydride formation and hydrogen storage in Al-Li alloys IRI Symposium May 22, 2003 A. Rivera Defects in Materials, IRI, TUDelft Work supported by the Delft Institute for Sustainable Energy (DISE) Contributors at DM: A. van Veen (head), F. Labohm, J. de Roode, W. J. Legerstee, K. T. Westerduin, S. W. H. Eijt, H. Schut. External contributors (Materials Science Faculty, TUDelft): R. Delhez, N. van der Pers

World energy consumption To reduce oil dependency Hydrogen

How to store hydrogen? l A 1000 kg car consumes – 5 -6 kg fuel/100 km l The same car would consume – 2 kg H 2/100 km in combustion mode or – 1 kg H 2 /100 km in fuel cell mode However, at room temperature and atmospheric pressure 1 kg H 2 occupies 11 m 3 l Storage: l – Pressurised vessels – Liquified H 2 – Sorbed at surface or bulk materials

Contents l Material requirements – Examples Non-transition light metal hydrides l Experimental developments l Al-Li materials l Conclusions and further work l

Material requirements l l l l Storage capacity > 5 wt. % Fast reaction kinetics H 2 release: 100 k. Pa at T < 200 ºC Reversibility in the range 0 – 200 ºC Resistance to degradation Cost Safety

Sources of inefficiencies Hysteresis between absorption and desorption l Hydride stability l Limited kinetics l – Poor heat conduction – Small diffusion constant – Surface reactions Necessity for initial hydriding activation l Sensitivity to air, impurities or other gases l Volume expansion l Decrepitation into fine powder l

Storage and release Hydrogen in solution: α-phase l Hydrogen in hydride: β-phase l Formation of hydride: α & β l – M + ½x. H 2 MHx + ΔQ – Isotherm flat l More plateaux can appear Desorption isotherm is lower due to stress l This is undesired for hydrogen storage l Formation enthalpy can be obtained l

Kinetics E. g. Mg. H 2 at 600 K l Slow diffusion l 1 μm / s

Hydrogen storage materials

Key properties

Non-transition light metal hydrides Li. Al. H 4, Na. Al. H 4 (in water irreversible full H 2 release) l High capacities (10 and 5 wt. %, respectively) l No reversible due to decomposition l – 3 Li. Al. H 4 Li 3 Al. H 6 + 2 Al + 3 H 2 – Li 3 Al. H 6 + 2 Al 3 Li. H + 3 Al + 1. 5 H 2 – 3 Li. H + 3 Al. Li + 1. 5 H 2 Slow kinetics l Catalysts, as Fe, Ti and Zr l – Make some steps reversible – Improve the kinetics [150 -175 o. C] [180 -220 o. C] [387 -425 o. C]

Our approach Objective: to develop nanostructured light weight alloys for hydrogen storage l Choice: Al-Li compounds l Preparation l – Sputtering of Al-Li alloy or Li. Al. H 4 – Laser ablation of Al-Li alloy or Li. Al. H 4 – Cathodic charge, ion implantation gas or plasma exposure + annealing l Characterisation – Volumetric analyses, Permeation, TDS, XRD, NDP, PBA – Occasionally ERDA, SEM, TEM

Gas analysis techniques l Hydra – – l Hydrogen absorption and desorption experiments Desorption detection limits 1013 - 1022 H 2 molecules Dynamic measurements give direct information on kinetics Appropriate for thin films Permeation – of solved molecules or electrochemically introduced atoms – in situ after sputtering will become available soon l Sensitive thermal desorption spectrometry – Detection limit as low as 1011 H 2 molecules – Significantly lower for D 2

Hydra

Hydra Mix volume Expansion volume M 1 10 -2 -10 Pa M 2 10 -105 Pa M 0 0. 1 -6 MPa Gas inlet To pumps Pd filter Mass analyser Cell (90 -900 K)

Hydra (static) Mix volume Expansion volume M 1 1015 -1017 H 2 M 2 1017 -1022 H 2 M 0 0. 1 -6 MPa Gas inlet To pumps Pd filter Mass analyser Cell (90 -900 K)

Hydra (dynamic) Mix volume Expansion volume M 1 M 2 M 0 0. 1 -6 MPa Gas inlet To pumps Mass analyser 1012 -1015 H 2/s 1013 -1016 H 2 Pd filter Cell (90 -900 K)

Hydra software

Desorption of Li. Al. H 4 l 0. 4 mg Li. Al. H 4, 0. 1 K/s l Total H 2: 1. 5 x 1022 g-1 l Total gas: 3. 9 x 1022 g-1 l 0: Hydroxide l 1: Li. Al. H 4 l 2: Li 3 Al. H 6 l 3: Li. H

Sputter deposited Al-Li: SEM l SEM evidences the formation of columnar structures in the nm range, size increases with distance from substrate Pd Al Li ~1 µm sputter deposited Pd layer ~1 µm sputter deposited Al-Li at room temperature, the layer contains 5 at. %Li (NDP)

Sputter deposited Al-Li: Hydrogen l Dynamic measurements: – High sensitivity – Easy background estimation – Peaks indicate kinetics processes Around 0. 5 at. H% l Recharging results in low T peak of 0. 3 at. H% l

Conclusions and further work l Effort to fulfil material requirements l Successful H 2 detection techniques l Successful creation of samples by – Sputtering – Laser ablation l Currently: – High Li content samples from Li. Al. H 4 targets – Study of samples with high porosity – Fundamental study of Li nanocrystals in c-Al

Further information l Contact – A. Rivera: – A. van Veen: Rivera@iri. tudelft. nl Av. Veen@iri. tudelft. nl