Synthesis of metal hydrides employing vapor deposition technologies

1. Synthesis of metal hydrides employing vapor deposition technologies Irmantas Barnackas, prof.L. Pranevičius Lithuanian Energy Institute 2006 01 20

2. Outline of the presentation • Hydrogen storage: metal hydrides (Mg2NiH4) • Experimental work • Conclusion

3. The main goal of the work To investigate the possibilities of formation of Mg-based alloys (Mg2NiH4), used for hydrogen storage, employing physical vapor deposition method.

4. 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 MgH2 The kinetics can be improved by alloying with Ni → Mg2Ni (the capacity to approx. 3.6 % and TDes ~ 553 K

5. Hydrogen Storage: Mg-Ni-H system • The phases of hexagonal Mg2Ni alloy: • α (Mg2NiH0.3) • β (Mg2NiH4) The Mg2NiH4 hydride has two crystallographic forms: • a low temperature (LT1 and LT2) modification • a high temperature (HT) modification For T > 510 K, Mg2NiH4 has a cubic structure (HT phase) which becomes monoclinally distorted below this temperature (LT phase).

6. Experimental technique: • to produce nanocrystalline Mg, Ni and Mg2Ni 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.

7. Experimental technique: Parameters of as-deposited Mg, Ni and MgNi films : IMg = 1 A, UMg = 400 V INi = 0.3 A, UNi = 450 V UBIAS = -100 V, IBIAS = 10-20 mA Deposition time - 5 min; Substrate temperature – 330 K Film thickness – 1 - 3μm Working gas – argon gas The scheme of experimental device of MgNi thin films for deposition and hydrogenation in hydrogen plasma

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

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

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

11. Plasma hydrogenation Parameters of hydrogenation: • Pressure – 100 Pa • Bias voltage – -300 ÷ -3000 V • Ion current from plasma – 70-400 mA • Temperature of sample holder 40 °C • Hydrogenation duration – 30-120 min. The schematic presentation of the plasma hydriding

12. Mg2Ni thin film saturated with hydrogen atoms

13. Mg2Ni films after plasma hydrogenation: - XRD and SEM analysis SEM micrograph of Mg2Ni film after plasma hydrogenation on quartz substrate (DC power supply) XRD diffractogram of Mg2Ni filmafter plasma hydrogenation using dc power supply

14. Mg2Ni films after plasma hydrogenation: - XRD and SEM analysis SEM micrograph of Mg2Ni film after plasma hydrogenation on quartz substrate (DC power supply) XRD diffractogram of Mg2Ni filmafter plasma hydrogenation using dc power supply

15. Mg2Ni films after plasma hydrogenation: - XRD and SEM analysis SEM micrograph of Mg2Ni film after plasma hydrogenation on quartz substrate (AC power supply) XRD diffractogram of Mg2Ni filmafter plasma hydrogenation using AC power supply

16. Mg2Ni films after plasma hydrogenation: - XRD and SEM analysis SEM micrograph of Mg2Ni film after plasma hydrogenation on quartz substrate (AC power supply) XRD diffractogram of Mg2Ni filmafter plasma hydrogenation using AC power supply

17. Reactive sputtering in Ar+H2 plasma SEM micrograph of MgNi film after reactive sputtering on quartz substrate XRD diffractogram of MgNi filmafter reactive sputtering on quartz substrate

18. Hydrogenation of MgNi thin films in high hydrogen pressure and temperature (p,T) Parameters of hydrogenation: • Pressure – 8 bar • Temperature – RT – 523 K • Hydrogenation duration – 30-120 min. The schematic view of the hydrogenation cell for the studies of the adsorption properties

19. Mg2Ni films after hydrogenation in high hydrogen pressure and temperature (p,T) : - XRD analysis

20. Mg2Ni 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.

21. Mg2Ni 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

22. Studies of de-hydrogenation kinetics of Mg2NiH4 thin films The schematic view of the de-hydrogenation cell for the studies of the desorption properties

23. De-hydrogenation kinetics of Mg2NiH4 thin films: SEM and XRD SEM analysis of Mg2NiH4 film after de-hydrogenation process XRD analysis of Mg2NiH4 film after de-hydrogenation process

24. Studies of de-hydrogenation kinetics of Mg2NiH4 thin films Basic parameters: T = 770 K,t = 30 min. GDOES analysis of desorption of Mg2NiH4 thin film

25. Conclusions • 1-3 µm Mg, Ni and Mg2Ni thin films were successfullydeposited on the quartz substrates using magnetron sputtering. • 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. • Formation of low temperature (LT) m-Mg2NiH4 thin films after hydrogenation of Mg2Ni in hydrogen plasma for 2 hours using AC power supplier is observed. • After the hydrogenation of Mg2Ni thin films in hydrogen atmosphere, in high pressure and high temperature, Mg2NiH4 thin films were successfully formed. • 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.