Synthesis of metal hydrides employing vapor deposition technologies Irmantas Barnackas, prof.L. Pranevičius Lithuanian Energy Institute

Outline of the presentation Hydrogen storage: metal hydrides (Mg 2 NiH 4 ) Experimental work Conclusion

The main goal of the work To investigate the possibilities of formation of Mg- based alloys (Mg 2 NiH 4 ), used for hydrogen storage, employing physical vapor deposition method.

Hydrogen Storage  Compressed gas storage tanks  Carbon fibers and nanotubes  Metal hydrides Mg hydrides light weight low manufacture cost high hydrogen-storage capacity Limitations Slow adsorption kinetics High de-hydriding temperature (~573 K) Stability of the MgH 2 The kinetics can be improved by alloying with Ni → Mg 2 Ni (the capacity to approx. 3.6 % and T Des ~ 553 K Material H-atoms per cm3 (x 1022) % of weight that is hydrogen MgH Mg 2 NiH FeTiH LaNi 5 H

Hydrogen Storage: Mg-Ni-H system The phases of hexagonal Mg 2 Ni alloy: α (Mg 2 NiH 0.3 ) β (Mg 2 NiH 4 ) The Mg 2 NiH 4 hydride has two crystallographic forms: a low temperature (LT1 and LT2) modification a high temperature (HT) modification For T > 510 K, Mg 2 NiH 4 has a cubic structure (HT phase) which becomes monoclinally distorted below this temperature (LT phase).

Experimental technique: to produce nanocrystalline Mg, Ni and Mg 2 Ni thin film materials using magnetron sputtering; to hydrogenate MgNi thin films in hydrogen plasma and under high hydrogen pressure and temperature (p,T); to study MgNi thin films de-hydrogenation kinetics using GDOES techniques; to analyze MgNi thin films properties of as- deposited, after hydrogenation and de- hydrogenation using XRD, SEM and GDOES methods.

Experimental technique: The scheme of experimental device of MgNi thin films for deposition and hydrogenation in hydrogen plasma Parameters of as-deposited Mg, Ni and MgNi films : I Mg = 1 A, U Mg = 400 V I Ni = 0.3 A, U Ni = 450 V U BIAS = -100 V, I BIAS = mA Deposition time - 5 min; Substrate temperature – 330 K Film thickness – 1 - 3μm Working gas – argon gas

As-deposited Mg film: - XRD and SEM analysis XRD diffractogram of as-deposited Mg film on quartz substrate SEM micrograph of as-deposited Mg film on quartz substrate

As-deposited Ni film: - XRD and SEM analysis XRD diffractogram of as-deposited Ni film on quartz substrate SEM micrograph of as-deposited Ni film on quartz substrate

As-deposited MgNi film: - XRD and SEM analysis XRD diffractogram of as-deposited MgNi film on quartz substrate SEM micrograph of as-deposited MgNi film on quartz substrate

Plasma hydrogenation Parameters of hydrogenation: Pressure – 100 Pa Bias voltage – -300 ÷ V Ion current from plasma – mA Temperature of sample holder 40 °C Hydrogenation duration – min. The schematic presentation of the plasma hydriding

Mg 2 Ni thin film saturated with hydrogen atoms

Mg 2 Ni films after plasma hydrogenation: Mg 2 Ni films after plasma hydrogenation: - XRD and SEM analysis XRD diffractogram of Mg 2 Ni film after plasma hydrogenation using dc power supply SEM micrograph of Mg 2 Ni film after plasma hydrogenation on quartz substrate (DC power supply)

XRD diffractogram of Mg 2 Ni film after plasma hydrogenation using dc power supply Mg 2 Ni films after plasma hydrogenation: Mg 2 Ni films after plasma hydrogenation: - XRD and SEM analysis SEM micrograph of Mg 2 Ni film after plasma hydrogenation on quartz substrate (DC power supply)

XRD diffractogram of Mg 2 Ni film after plasma hydrogenation using AC power supply Mg 2 Ni films after plasma hydrogenation: Mg 2 Ni films after plasma hydrogenation: - XRD and SEM analysis SEM micrograph of Mg 2 Ni film after plasma hydrogenation on quartz substrate (AC power supply)

Mg 2 Ni films after plasma hydrogenation: Mg 2 Ni films after plasma hydrogenation: - XRD and SEM analysis XRD diffractogram of Mg 2 Ni film after plasma hydrogenation using AC power supply SEM micrograph of Mg 2 Ni film after plasma hydrogenation on quartz substrate (AC power supply)

Reactive sputtering in Ar+H 2 plasma XRD diffractogram of MgNi film after reactive sputtering on quartz substrate SEM micrograph of MgNi film after reactive sputtering on quartz substrate

Hydrogenation of MgNi thin films in high hydrogen pressure and temperature (p,T) The schematic view of the hydrogenation cell for the studies of the adsorption properties Parameters of hydrogenation: Pressure – 8 bar Temperature – RT – 523 K Hydrogenation duration – min.

Mg 2 Ni films after hydrogenation in high hydrogen pressure and temperature (p,T) : Mg 2 Ni films after hydrogenation in high hydrogen pressure and temperature (p,T) : - XRD analysis

Mg 2 Ni films after hydrogenation in high hydrogen pressure and temperature (p,T) : Mg 2 Ni films after hydrogenation in high hydrogen pressure and temperature (p,T) : - SEM analysis a b SEM micrograph of MgNi film after hydrogenation in high hydrogen pressure and temperature (p,T) on quartz substrate: a – after 30 min.; b – after 60 min.

Mg 2 Ni films after hydrogenation in high hydrogen pressure and temperature (p,T) : Mg 2 Ni films after hydrogenation in high hydrogen pressure and temperature (p,T) : - SEM analysis SEM micrograph of MgNi film at different magnification after hydrogenation in high hydrogen pressure and temperature (p,T) on quartz substrate

Studies of de-hydrogenation kinetics of Mg 2 NiH 4 thin films The schematic view of the de-hydrogenation cell for the studies of the desorption properties

XRD analysis of XRD analysis of Mg 2 NiH 4 film after de-hydrogenation process De-hydrogenation kinetics of Mg 2 NiH 4 thin films: SEM and XRD SEM analysis of SEM analysis of Mg 2 NiH 4 film after de-hydrogenation process

GDOES analysis of desorption of Mg 2 NiH 4 thin film Studies of de-hydrogenation kinetics of Mg 2 NiH 4 thin films Basic parameters: T = 770 K, t = 30 min.

Conclusions µm Mg, Ni and Mg 2 Ni thin films were successfully deposited on the quartz substrates using magnetron sputtering. 2.Observed formation of amorphous phase during plasma hydrogenation using DC power supply. It can be related to formation of the compressive stresses and defragmentation of the material. 3.Formation of low temperature (LT) m-Mg 2 NiH 4 thin films after hydrogenation of Mg 2 Ni in hydrogen plasma for 2 hours using AC power supplier is observed. 4.After the hydrogenation of Mg 2 Ni thin films in hydrogen atmosphere, in high pressure and high temperature, Mg 2 NiH 4 thin films were successfully formed. 5.SEM results show formation of “bubbles” on the surface during hydrogenation in (p,T). It can be related to the high temperature during hydrogenation and formation of the compressive stresses. These bubbles were lifted after de-hydrogenation and some parts of thin films were destroyed.