Featured Research

from universities, journals, and other organizations

Calculations reveal fine line for hydrogen release from storage materials

Date:
July 17, 2012
Source:
University of California - Santa Barbara
Summary:
Scientists have shed new light on the kinetics of hydrogen release, or dehydrogenation, from aluminum hydride, a material that is highly promising for energy storage. Their computer simulations also illuminate the basic mechanisms governing these chemical reactions in general.

Hydrogen vacancy clustering in aluminum hydride (AlH3): The dark blue atoms represent the Al atoms in the regular AlH3 lattice, and the light blue atoms represent the Al atoms in the Al-rich region created by the clustering of hydrogen vacancies as hydrogen leaves the material.
Credit: Van de Walle Group

Hydrogen, the simplest and most abundant element on Earth, is a promising energy carrier for emerging clean energy technology. Hydrogen is the energy carrier that powers fuel cells in electric cars, and can be used to store energy generated by renewable sources at times of low demand.

A major challenge with hydrogen energy is meeting the dual goals of high storage density and efficient kinetics for hydrogen release when it is needed.

Scientists at the University of California, Santa Barbara, have shed new light on the kinetics of hydrogen release, or dehydrogenation, from aluminum hydride (AlH3), a material that is highly promising for energy storage. Their computer simulations also illuminate the basic mechanisms governing these chemical reactions in general.

"Aluminum hydride turns out to be promising because the binding energy for hydrogen is low, so that the release rate can be fast," explained Chris Van de Walle, a professor in the Materials Department and head of the Computational Materials group at UCSB. "At the same time, kinetic barriers are high enough to prevent the hydrogen release rate from being too fast."

Drs. Lars Ismer and Anderson Janotti in the Computational Materials group used computer simulations to investigate the microscopic mechanisms that drive hydrogen release from aluminum hydride. They performed cutting-edge, first-principles calculations to examine how individual hydrogen atoms diffuse through the aluminum hydride -- a process they found to be enabled by the creation of hydrogen vacancies. Their findings were detailed in a paper "Dehydrogenation of AlH3 via the Vacancy Clustering Mechanism" published in The Journal of Physical Chemistry.

Hydrogen vacancies are defects that play an important role -- they enable diffusion. If every atom is in place, none of the atoms would be able to move. If a hydrogen atom is missing, a neighboring hydrogen atom can jump into that vacancy, thus enabling motion of hydrogen through the material.

The group then extracted key parameters from these highly sophisticated calculations, and used them in Kinetic Monte Carlo simulations aimed at modeling how hydrogen is released, leaving clusters of aluminum atoms behind.

"This multi-scale approach allows us to take the highly accurate information obtained in the first-principles computations and employ it to model realistic system sizes and time scales," said Ismer. "We can monitor the nucleation and growth of the aluminum phase and the rate at which hydrogen is released."

An important feature of the simulations is that they allowed the researchers to identify the rate-limiting mechanism, which turned out to be the diffusion process. This result initially seemed to contradict conclusions from studies using the traditional interpretation of the observed S-shaped onset of the dehydrogenation curves, which ruled out diffusion as the rate-limiting factor. However, the UCSB team's simulations produced reaction curves in agreement with the measurements, while clearly indicating that the reaction is limited by diffusion of point defects.

"These concepts transcend the specific application to hydrogen-storage materials," said Van de Walle . "The broader lesson here is that caution should be exercised in drawing conclusions based solely on the shape of reaction curves. Those simple rules of thumb were developed back in the 1930s, when experiments were less sophisticated and computational studies were unheard of. Our present work strongly suggests that traditional assumptions based on the shape of reaction curves should be reexamined."

Professor Van de Walle's Computational Materials Group is affiliated with the Materials Department and the College of Engineering at UC Santa Barbara. The group explores materials for hydrogen storage and generation, complex oxides, nitride semiconductors, novel channel materials and dielectrics, and materials for quantum computing.

This research was supported by the U.S. Department of Energy.


Story Source:

The above story is based on materials provided by University of California - Santa Barbara. Note: Materials may be edited for content and length.


Cite This Page:

University of California - Santa Barbara. "Calculations reveal fine line for hydrogen release from storage materials." ScienceDaily. ScienceDaily, 17 July 2012. <www.sciencedaily.com/releases/2012/07/120717084904.htm>.
University of California - Santa Barbara. (2012, July 17). Calculations reveal fine line for hydrogen release from storage materials. ScienceDaily. Retrieved July 29, 2014 from www.sciencedaily.com/releases/2012/07/120717084904.htm
University of California - Santa Barbara. "Calculations reveal fine line for hydrogen release from storage materials." ScienceDaily. www.sciencedaily.com/releases/2012/07/120717084904.htm (accessed July 29, 2014).

Share This




More Matter & Energy News

Tuesday, July 29, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Baluchistan Mining Eyes an Uncertain Future

Baluchistan Mining Eyes an Uncertain Future

AFP (July 29, 2014) Coal mining is one of the major industries in Baluchistan but a lack of infrastructure and frequent accidents mean that the area has yet to hit its potential. Duration: 01:58 Video provided by AFP
Powered by NewsLook.com
Easier Nuclear Construction Promises Fall Short

Easier Nuclear Construction Promises Fall Short

AP (July 29, 2014) The U.S. nuclear industry started building its first new plants using prefabricated Lego-like blocks meant to save time and prevent the cost overruns that crippled the sector decades ago. So far, it's not working. (July 29) Video provided by AP
Powered by NewsLook.com
Lithium Battery 'Holy Grail' Could Provide 4 Times The Power

Lithium Battery 'Holy Grail' Could Provide 4 Times The Power

Newsy (July 28, 2014) Stanford University published its findings for a "pure" lithium ion battery that could have our everyday devices and electric cars running longer. Video provided by Newsy
Powered by NewsLook.com
The Carbon Trap: US Exports Global Warming

The Carbon Trap: US Exports Global Warming

AP (July 28, 2014) AP Investigation: As the Obama administration weans the country off dirty fuels, energy companies are ramping-up overseas coal exports at a heavy price. (July 28) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins