Hydrogen Storage

An application-specific issue.

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

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.

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

Metal Hydrides (sponge)•Sold by “Interpower” in Germany•Filled with “HYDRALLOY” E60/0 (TiFeH2)•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

Carbon Nanofibers Complex structure

presents a large surface area for hydrogen to “dissolve” into

Early claim set the standard of 65 kgH2/m2

and 6.5 % by weight as a “goal to beat”

The claim turned out not to be repeatable

Research continues…

Methanol

Broken down by reformer, yields CO, CO2, and H2 gas.

Very common hydrogen transport method Distribution infrastructure exists – same as

gasoline

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

Alkali Metal Hydrides

“Powerball” company, makes small (3 mm) coated NaH spheres.

“Spheres cut and exposed to water as needed”

H2 gas released Produces hydroxide solution

waste

Sodium Borohydrate

Sodium Borohydrate is the most popular of many hydrate solutions

Solution passed through a catalyst to release H2

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

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.

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.

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)

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)

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

Storage Method Comparison

Sodium Hydride slurry .9 1.0 Must reclaim used slurry

DADB .1 - .2 .09-.1 (numbers for plain “diborane”and sodium borohydride, should be similar)

Amminex 9.1 .081

Zinc powder unsure

US DOE goal 9.0 .081

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).

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.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