Hydrogen Storage for Transportation Applications John J. Vajo, Ping Liu, Adam F. Gross, Sky L. Van Atta, Tina T. Salgu

1. Hydrogen Storage for Transportation Applications John J. Vajo, Ping Liu, Adam F. Gross, Sky L. Van Atta, Tina T. Salguero, Wen Li, Robert E. Doty HRL Laboratories, LLC Malibu, CA © 2008 HRL Laboratories, LLC. All Rights Reserved

2. Outline • Introduction to PEM fuel cells and hydrogen storage needs • Overview of hydrogen storage approaches • Solid state methods - advantages and challenges • Destabilized hydrides (addresses “thermodynamics challenge”) • Nanoengineering (addresses “kinetics challenge”) • Summary

3. Proton Exchange Membrane Fuel Cell • Solid polymer electrolyte sandwiched between two porous carbon electrodes containing catalyst • • H2 gas flows to anode– dissociates into protons and electrons • • Membrane only allows protons to pass • • Electrons follow external circuit to the cathode (e.g., powers motor) • • Electrons combine with oxygen from air and protons to form water (exhaust) • Each cell produces < 1 V  cells stacked in series to produce usable amounts of electrical energy Hydrogen must be available in quantities sufficient for fuel cell operation Source: U.S. DOE Energy Efficiency and Renewable Energy Office

4. • High storage capacity 2010 targets: System weight: >6 % hydrogen; System volume: >45 g/L hydrogen • Low energy investment to store and remove hydrogen Temperature for H2 release from storage material must be compatible with fuel cell operation (~80°C) • Fast release and refueling times < 5 min refill time; H2 supply to fuel cell must not be limited by H2 release rate from hydride • Material cost consistent with low overall storage system cost 2010 target: $133/kg-H2; 2015 target: $67/kg-H2 Durability(to maintain 80% capacity): 240,000 km Requirements for Hydrogen Storage Material System

5. Hydrogen Storage Options PHYSICAL STORAGE Molecular CHEMICAL STORAGE Dissociated REVERSIBLE NON-REVERSIBLE REVERSIBLE REFORMED FUEL HYDROLYZED FUEL DECOMPOSED FUEL CRYO-ADSORPTION COMPRESSED GAS LIQUID HYDROGEN NANO STRUCTURE ADSORPTION DESTABILIZED LIGHT ELEMENT SYSTEMS LIGHT ELEMENT SYSTEMS CONVENTIONAL METAL HYDRIDES COMPLEX METAL HYDRIDES • La Ni5 • Ti Fe • LiH + Si • MgH2 + Al • LiBH4 + MgH2 • Carbon • Metal Organic Frameworks • LiAlH4 • NaAlH4 • LiBH4 • Mg(BH4)2 • MgH2 • Mg Alloys

6. Gasoline LiBH4 LaNi5H6.5 Liquid-H2 700 bar-H2 Volume of 8 kg Hydrogen in Different Storage Media (Compared with Gasoline) 8 kg hydrogen  300 mi range in GM Sequel Storage Material Volume (Liters) (Assumes ICE 2x less efficient than fuel cell)

7. Gasoline LiBH4 LaNi5H6.5 Liquid-H2 700 bar-H2 Volume of 8 kg Hydrogen in Different Storage Media (Compared with Gasoline) 8 kg hydrogen  300 mi range in Sequel Total Hydride Material Weight: 59 kg 570 kg Storage Material Volume (Liters) Research Underway Too Heavy (Assumes ICE 2x less efficient than fuel cell)

8. Solid State Hydrogen Storage Process Hydrogen Released Hydrogen Material with no hydrogen Material with no hydrogen Material hydride with hydrogen stored Energy to remove hydrogen (high heat) Recycle To satisfy requirements, materials composed of light metal elements are needed

9. Light Metal Hydrides are Promising Candidates for On-Board H-Storage Potential for high weight (> 6 wt.%) hydrogen storage Enables 400 km driving range

10. … But Challenges Exist • Strong covalent/ionic chemical bonds in hydride • High temperatures (>200°C) needed for hydrogen release  thermodynamics challenge • Bonding is highly directional • Large barriers for atomic diffusion • Leads to prohibitively slow reaction rates (slow hydrogen uptake and release)  kinetics challenge These are the principal issues being addressed in the HRL hydrogen storage program

11. Comparison Of Selected Hydrides with DOE System Requirements LiBH4 DOE 2010 System Target LiH Conventional (transition-metal) hydrides 30% system penalty Light-metal hydrides MgH2 0% system penalty NaAlH4 Mg2NiH4 VH2 ZrMn2H3.6 ZrNiH3 LaNi5H6.5 500 400 300 200 100 20 Temperature (°C) • Existing hydridesdo not meet DOE requirements • Need either new material or method for altering existing hydrides

12. Metal (M) Hydrogen Gas High Temperature Metal Hydride (MH) Strong Bonds in Light Metal Hydrides – Bond breaking (H2 release) requires high temperature – Dehydrogenated State M + H2 High energy path ENERGY (Heat) MH Hydrogenated State Conventional hydrides

13. Hydride “Destabilization” by Alloy Formation Reduces Temperature for H2 Release Dehydrogenated State Alloy M + H2 Hydrogen Gas MAx+ H2 ENERGY Alloy State Reduced Temperature Lower energy path MH + xA Destabilizing Agent Hydrogenated State Metal Hydride Destabilized hydrides • Alloy gives tightly bound metal hydride a lower energy path to release H2 • Reduced energy demand means lower temperature for hydrogen release

14. LiH + B + H2 T=400°C LiH + MgB2 + H2 ENERGY Lithium borohydride Magnesium hydride Lithium hydride Magnesium boride Hydrogen T=225°C LiBH4 + MgH2 LiBH4/MgH2 Destabilized System – a promising candidate – 2LiBH4 + MgH2 2LiH + MgB2 + 4H2 (System with very high storage capacity (11.4 wt.%, 95 g/L) • System has been tested: 10 wt.% capacity demonstrated • Temperature for H2 release lowered 175°C by alloying with MgH2 Ref: J. J. Vajo, S. L. Skeith, F. Mertens “Reversible Storage of Hydrogen in Destabilized LiBH4”,J. Phys. Chem. B, vol. 109 (2005) pp. 3719-3722.

15. Conventional (transition-metal) hydrides Light-metal hydrides Destabilization of LiBH4 by Alloying with MgH2 Reduces Temperature LiBH4 DOE 2010 System Target LiH LiBH4/MgH2 30% system penalty MgH2 0% system penalty Destabilized light-metal hydride NaAlH4 Mg2NiH4 VH2 ZrMn2H3.6 ZrNiH3 LaNi5H6.5 500 400 300 200 100 20 Temperature (°C) Significant reduction in H2 release temperature with only small decrease in capacity (13.6 wt.%11.4 wt.%)

16. Conventional (transition-metal) hydrides Light-metal hydrides Destabilized light-metal hydrides Calculated Demonstrated Summary of Destabilized Systems and Comparison with Known Hydrides LiBH4 DOE 2010 System Target LiH 30% system penalty MgH2 0% system penalty NaAlH4 Mg2NiH4 VH2 ZrMn2H3.6 ZrNiH3 LaNi5H6.5 500 400 300 200 100 20 Temperature (°C) • Hydride destabilization is a versatile approach for reducing temperature • However; reaction rates are much too slow for practical use

17. <100 nm Issues: Enhanced Reaction Rates Using Nano-engineering Increase Hydrogen exchange rate by decreasing particle size Bulk Alloy Material Nanoparticles Long diffusion distances in bulk material:  slow H-exchange rate Short diffusion distances in nanoparticles:  fast hydrogen exchange rate Need efficient, low cost method for producing nanoparticles Sintering during hydrogen uptake and release can increase particle size – could be a big problem

18. C-aerogel cubes Mix aerogel and LiBH4 under N2 Melt LiBH4 (T=290 °C) Aerogel absorbs LiBH4 Scrape to remove surface material Carbon Aerogel “Scaffold” Hosts for Nanoscale Hydrides Carbon Aerogels • Inter-penetrating network of carbon nanopores (10-30 nm pore size) • “Scaffold” serves as structure-directing agent for forming nano-scale hydrides Incorporate molten LiBH4 into aerogel by “wicking” process

19. Faster Hydrogen Release from LiBH4 in Nanoporous Carbon Scaffold LiBH4 LiH + B + 1.5H2(13.6 wt %) Pore size distributions 25 nm 300 °C 13 nm 25 nm 13 nm Graphite • Rate for 13 nm aerogel ~60X rate for control sample • Rate faster for smaller pore aerogel

20. Summary • Hydrogen storage – a key hurdle in creating a hydrogen–based transportation system • Sufficient hydrogen can be stored on a vehicle to meet customer desires for range by either: • Changing the vehicle architecture to allow more room for fuel storage • Improving the capacity of the storage system • Light-metal hydrides are promising candidates for high capacity, on-board storage of hydrogen, but no existing material meets targets • High temperatures needed for hydrogen release • Release/uptake rates slow • Hydride destabilization being used to address the high temperature problem • Nano-engineering approaches are providing solutions to slow release/uptake Research efforts in these critical technology areas are on-going at HRL Labs in two projects sponsored by GM and U.S. DOE