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Researchers Develop Model to Help Identify Optimal Hydrides for On-Board Hydrogen Storage
3 October 2007
Researchers at UCLA and Northwestern University have developed a model that could help speed up the development of hydrogen-fueled vehicles by identifying promising materials for hydrogen storage and predicting favored thermodynamic chemical reactions through which hydrogen can be reversibly stored and extracted.
The new method, published online in the peer-reviewed journal Advanced Materials, was developed by Alireza Akbarzadeh, a UCLA postdoctoral researcher in the department of materials science and engineering; Vidvuds Ozoliņš, UCLA associate professor of materials science and engineering; and Christopher Wolverton, professor of materials science and engineering at Northwestern University in Illinois.
A promising solution to the problem of hydrogen storage on-board a vehicle involves storing hydrogen within a material in the form of a chemically bound hydride—e.g., lithium hydride (LiH). Unfortunately, simple binary hydrides, in which hydrogen combines with light elements such as lithium, sodium, magnesium or others, do not adequately satisfy the requirements for on-board storage, as the hydrogen-yielding reaction requires heating the material to impractically high temperatures.
Because of this, researchers have turned to multicomponent hydride mixtures with higher volumetric and gravimetric densities, better operating temperatures and improved reaction rates for practical hydrogen storage. However, this flexibility comes at the price of drastically increased complexity associated with the large number of competing reactions and possible end-products other than hydrogen. Thus, predicting desirable hydrogen storage with multicomponent mixtures has proved difficult.
For example, the recently studied lithium hydride compound Li4BN3H10 was found to have as many as 17 hydrogen-release reactions, of which only three were found to be feasible—and none were in the desired range of temperatures and hydrogen pressures for practical on-board storage in hydrogen-powered vehicles.
The research team used modern quantum mechanical theories and computers to develop an algorithm that can automatically and systematically pinpoint phases and reactions that have the most favored thermodynamic properties—those that can release hydrogen at ambient temperatures using the waste heat from a proton exchange membrane (PEM) fuel cell.
The team tested the method on the well-studied Lithium-Magnesium-Nitrogen-Hydrogen system, predicting all experimentally observed pathways in the system. The researchers say this method can also be applied to other multicomponent hydrogen systems.
The development of an algorithm that goes beyond chemical intuition and finds all hydrogen storage reactions in silico is crucial and will help the scientific and engineering community to develop revolutionary new hydrogen-storage materials. This is a major achievement in the field, which can boost up the search for the best reversible solid-state hydrogen storage.
—Alireza Akbarzadeh
The research was funded by grants from the US Department of Energy.
Resources:
A. R. Akbarzadeh, V. Ozoliņš, C. Wolverton. “First-Principles Determination of Multicomponent Hydride Phase Diagrams: Application to the Li-Mg-N-H System” Advanced Materials Published Online: 21 Sep 2007 DOI: 10.1002/adma.200700843
October 3, 2007 in Hydrogen Storage | Permalink | Comments (5) | TrackBack (0)
Comments
Posted by: Jim G. | October 03, 2007 at 12:03 PM
The fundamental thing holding hydrogen back is that there is not efficient ways to make it compared to electricity. Why reform natural gas into hydrogen instead of just burning compressed natural gas? Why do electrolysis instead of just using the electricity directly to charge a battery? Why design a nuclear plant to produce hydrogen when electricity can be transmitted over long distances much cheaper and safely? Why capture sunlight (photons) to make hydrogen when you can make electricity directly at over 20% efficiency? If there is electricity generation in excess of the grid demand (e.g. windfarm), why generate hydrogen instead of pumping up a reservoir, or heating/chilling a water tank to supply an HVAc system? If there is a pathway to make hydrogen, store it, then convert into electricity, that is better than a using battery I'm all ears.
Posted by: mark | October 03, 2007 at 08:47 PM
Electric generation and delivery can be quite inefficient. Electrolysis in not inefficient, at 91% of energy output. If we use hydrogen on a mass scale it will be made from renewable energy sources, not natural gas. Natural gas is an excellent automotive fuel already.
Hydrogen holds the promise of a much higher energy density than batteries, that's why they are pursuing it.
Batteries do make a lot of sense though for cars, as the overall concept is so much more inexpensive and simple. And batteries are coming very close to being adequate for cars.
Posted by: Jay Tee | October 04, 2007 at 04:58 AM
Mark,
Hydrogen vehicles also offer the advantage of only emitting water. But yes the conversion process will need to be more efficient. Solar, wind, etc., which are intermittent, would benefit from a method to store surplus energy; with the proper conversion efficiencies hydrogen might fill that void as well, although ultracapacitors and flywheels are likely to get there sooner.
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Solid state hydride technology starts to resemble a battery where, instead of electricity going in and out, Hydrogen does. I've read some arguments (Rocky Mountain Institute for example) that hydrogen has a major advantage long term vis a vis batteries, as more batteries add significant weight to an EV, affecting speed & range adversely. But lithium batteries are lighter for the same power than Pb batteries; and I do wonder whether solid hydride storage adds significant weight to the vehicle. Perhaps these two technologies might end up meeting in the middle.