1. Hydrogen Storage An application-specific issue.

2. Physical storage of H2 Chemical storage of hydrogen New emerging methods Hydrogen Storage Overview Metal Hydride (“sponge”) Carbon nanofibers Compressed Cryogenically liquified Methanol Alkali metal hydrides Sodium borohydride Ammonia Amminex tablets DADB (predicted) Solar Zinc production Alkali metal hydride slurry

3. Compressed Volumetrically and Gravimetrically inefficient, but the technology is simple, so by far the most common in small to medium sized applications. 3500, 5000, 10,000 psi variants.

4. Liquid (Cryogenic) Compressed, chilled, filtered, condensed Boils at 22K (-251 C). Slow “waste” evaporation Kept at 1 atm or just slightly over. Gravimetrically and volumetrically efficient but very costly to compress

5. Metal Hydrides (sponge) Sold by “Interpower” in Germany Filled with “HYDRALLOY” E60/0 (TiFeH 2 ) Technically a chemical reaction, but acts like a physical storage method Hydrogen is absorbed like in a sponge. Operates at 3-30 atm, much lower than 200-700 for compressed gas tanks Comparatively very heavy, but with good volumetric efficiency, good for small storage, or where weight doesn’t matter

6. Carbon Nanofibers Complex structure presents a large surface area for hydrogen to “dissolve” into Early claim set the standard of 65 kgH 2 /m 2 and 6.5 % by weight as a “goal to beat” The claim turned out not to be repeatable Research continues…

7. Methanol Broken down by reformer, yields CO, CO 2, and H 2 gas. Very common hydrogen transport method Distribution infrastructure exists – same as gasoline

8. Ammonia Slightly higher volumetric efficiency than methanol Must be catalyzed at 800-900 deg. C for hydrogen release Toxic Usually transported as a liquid, at 8 atm. Some Ammonia remains in the catalyzed hydrogen stream, forming salts in PEM cells that destroy the cells Many drawbacks, thus Methanol considered to be a better solution

9. Alkali Metal Hydrides “Powerball” company, makes small (3 mm) coated NaH spheres. “Spheres cut and exposed to water as needed” H 2 gas released Produces hydroxide solution waste

10. Sodium Borohydrate Sodium Borohydrate is the most popular of many hydrate solutions Solution passed through a catalyst to release H 2 Commonly a one-way process (sodium metaborate must be returned if recycling is desired.) Some alternative hydrates are too expensive or toxic The “Millennium Cell” company uses Sodium Borohydrate technology

11. Amminex Essentially an Ammonia storage method Ammonia stored in a salt matrix, very stable Ammonia separated & catalyzed for use Likely to have non-catalyzed ammonia in hydrogen stream Ammonia poisoning contraindicates use with PEM fuel cells, but compatible with alkaline fuel cells.

12. Amminex High density, but relies on ammonia production for fuel. Represents an improvement on ammonia storage, which still must be catalyzed. Ammonia process still problematic.

13. Diammoniate of Diborane (DADB) So far, just a computer simulation. Compound discovered via exploration of Nitrogen/Boron/Hydrogen compounds (i.e. similar to Ammonia Borane) Thermodynamic properties point towards spontaneous hydrogen re-uptake – would make DADB reusable (vs. other borohydrates)

14. Solar Zinc production Isreli research effort utilizes solar furnace to produce pure Zinc Zinc powder can be easily transported Zinc can be combined with water to produce H2 Alternatively could be made into Zinc-Air batteries (at higher energy efficiency)

15. Alkaline metal hydride slurry SafeHydrogen, LLC Concept proven with Lithium Hydride, now working on magnesium hydride slurry Like a “PowerBall” slurry Hydroxide slurry to be re-collected to be “recycled” Competitive efficiency to Liquid H2

16. Storage Method Comparison Sodium Hydride slurry.91.0Must reclaim used slurry DADB.1 -.2.09-.1(numbers for plain “diborane”and sodium borohydride, should be similar) Amminex9.1.081 Zinc powderunsure US DOE goal9.0.081

17. Early Adoption of inefficient system Compressed Hydrogen is one of the least efficient both volumetrically and gravimetrically, but is currently the most common (because it’s a simple solution).

18. Credits http://psych.ucsc.edu/faculty/kg/H2Spirit/images2.htm http://www.photos.gov.ca.gov/essay20.html http://www.amminex.com/index_files/Page344.htm http://www.h2- interpower.de/deutsch/produkte/zubehoer.html#mhs20 http://www.h2- interpower.de/deutsch/produkte/zubehoer.html#mhs20 http://www.pnl.gov/news/notes/transportation05.stm http://www.safehydrogen.com/technology.html http://www.isracast.com/tech_news/090905_tech.htm http://www.h2fc.com/industry/infra/storage.shtml Fuel Cell Systems Explained, by James Larminie and Andrew Dicks