Hydrogen Storage for Transportation Applications John J. Vajo, Ping Liu, Adam F. Gross, 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

2Outline 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 Source: U.S. DOE Energy Efficiency and Renewable Energy Office Proton Exchange Membrane Fuel Cell Solid polymer electrolyte sandwiched between two porous carbon electrodes containing catalyst H 2 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

4 Requirements for Hydrogen Storage Material System 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 H 2 release from storage material must be compatible with fuel cell operation (~80°C) Fast release and refueling times < 5 min refill time; H 2 supply to fuel cell must not be limited by H 2 release rate from hydride Material cost consistent with low overall storage system cost 2010 target: $133/kg-H 2 ; 2015 target: $67/kg-H 2 Durability (to maintain 80% capacity): 240,000 km

5 Hydrogen Storage Options REVERSIBLE CRYO- ADSORPTION LIQUID HYDROGEN COMPRESSED GAS PHYSICAL STORAGE Molecular REVERSIBLE CHEMICAL STORAGE Dissociated COMPLEX METAL HYDRIDES CONVENTIONAL METAL HYDRIDES LIGHT ELEMENT SYSTEMS NON-REVERSIBLE NANO STRUCTURE ADSORPTION DESTABILIZED LIGHT ELEMENT SYSTEMS Carbon Metal Organic Frameworks La Ni 5 Ti Fe LiAlH 4 NaAlH 4 LiBH 4 Mg(BH 4 ) 2 MgH 2 Mg Alloys LiH + Si MgH 2 + Al LiBH 4 + MgH 2 DECOMPOSED FUEL HYDROLYZED FUEL REFORMED FUEL

6 GasolineLiBH 4 LaNi 5 H 6.5 Liquid-H bar-H 2 Storage Material Volume (Liters) Volume of 8 kg Hydrogen in Different Storage Media (Compared with Gasoline) 8 kg hydrogen  300 mi range in GM Sequel (Assumes ICE 2x less efficient than fuel cell)

7 GasolineLiBH 4 LaNi 5 H 6.5 Liquid-H bar-H 2 (Assumes ICE 2x less efficient than fuel cell) Total Hydride Material Weight: 59 kg 570 kg Too Heavy Research Underway 8 kg hydrogen  300 mi range in Sequel Volume of 8 kg Hydrogen in Different Storage Media (Compared with Gasoline) Storage Material Volume (Liters)

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

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

10 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 … But Challenges Exist

11 Comparison Of Selected Hydrides with DOE System Requirements LiH ZrNiH 3 Mg 2 NiH 4 LiBH 4 VH 2 MgH 2 DOE 2010 System Target 30% system penalty 0% system penalty NaAlH 4 ZrMn 2 H Temperature (°C) LaNi 5 H 6.5 Existing hydrides do not meet DOE requirements Need either new material or method for altering existing hydrides Conventional (transition-metal) hydrides Light-metal hydrides

12 Strong Bonds in Light Metal Hydrides – Bond breaking (H 2 release) requires high temperature – Metal Hydride (MH) Metal (M) Hydrogen Gas High Temperature Conventional hydrides ENERGY (Heat) MH M + H 2 Dehydrogenated State Hydrogenated State High energy path

13 Hydride “Destabilization” by Alloy Formation Reduces Temperature for H 2 Release Metal Hydride Destabilizing Agent Alloy Hydrogen Gas Reduced Temperature Destabilized hydrides ENERGY MH + xA M + H 2 MA x + H 2 Dehydrogenated Stat e Alloy State Hydrogenated State Lower energy path Alloy gives tightly bound metal hydride a lower energy path to release H 2 Reduced energy demand means lower temperature for hydrogen release

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

15 Destabilization of LiBH 4 by Alloying with MgH 2 Reduces Temperature LiH ZrNiH 3 Mg 2 NiH 4 LiBH 4 VH 2 MgH 2 DOE 2010 System Target 30% system penalty 0% system penalty NaAlH 4 ZrMn 2 H Temperature (°C) LaNi 5 H 6.5 Significant reduction in H 2 release temperature with only small decrease in capacity (13.6 wt.%  11.4 wt.%) LiBH 4 /MgH 2 Conventional (transition- metal) hydrides Light-metal hydrides Destabilized light-metal hydride

16 LiH ZrNiH 3 Mg 2 NiH 4 LiBH 4 VH 2 MgH 2 DOE 2010 System Target 30% system penalty 0% system penalty NaAlH 4 ZrMn 2 H Temperature (°C) Summary of Destabilized Systems and Comparison with Known Hydrides Hydride destabilization is a versatile approach for reducing temperature However; reaction rates are much too slow for practical use LaNi 5 H 6.5 Calculated Demonstrated Conventional (transition- metal) hydrides Light-metal hydrides Destabilized light-metal hydrides

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

18 Inter-penetrating network of carbon nanopores (10-30 nm pore size) “Scaffold” serves as structure-directing agent for forming nano-scale hydrides Carbon Aeroge ls Carbon Aerogel “Scaffold” Hosts for Nanoscale Hydrides C-aerogel cubes Mix aerogel and LiBH 4 under N 2 Melt LiBH 4 (T=290 °C) Aerogel absorbs LiBH 4 Scrape to remove surface material Incorporate molten LiBH 4 into aerogel by “wicking” process

19 Faster Hydrogen Release from LiBH 4 in Nanoporous Carbon Scaffold LiBH 4  LiH + B + 1.5H 2 (13.6 wt %) Pore size distributions 13 nm 25 nm Graphite Rate for 13 nm aerogel ~60X rate for control sample Rate faster for smaller pore aerogel 13 nm 25 nm 300 °C

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