This image depicts the series of reactions by which water is separated into hydrogen molecules and hydroxide ions. The process is initiated by nickel-hydroxide clusters (green) embedded on a platinum framework (gray). Image: Argonne National Laboratory |
When it
comes to the industrial production of chemicals, often the most indispensable
element is one that you can’t see, smell, or even taste. It’s hydrogen, the
lightest element of all.
Researchers
at the U.S. Department of Energy’s (DOE) Argonne National Laboratory have
developed an extraordinarily efficient two-step process that electrolyzes, or
separates, hydrogen atoms from water molecules before combining them to make
molecular hydrogen, which can be used in any number of applications from fuel
cells to industrial processing.
Easier
routes to the generation of hydrogen have long been a target of scientists and
engineers, principally because the process to create the gas requires a great
deal of energy. Approximately 2% of all electric power generated in the United States
is dedicated to the production of molecular hydrogen, so scientists and
engineers are searching for any way to cut that figure. “People understand
that once you have hydrogen you can extract a lot of energy from it, but they
don’t realize just how hard it is to generate that hydrogen in the first
place,” says Nenad Markovic, an Argonne
senior chemist who led the research.
While a
great deal of hydrogen is created by reforming natural gas at high
temperatures, that process creates carbon-dioxide emissions. “Water
electrolyzers are by far the cleanest way of producing hydrogen,” Markovic
says. “The method we’ve devised combines the capabilities of two of the
best materials known for water-based electrolysis.”
Most previous
experiments in water-based electrolysis rely on special metals, like platinum,
to adsorb and recombine reactive hydrogen intermediates into stable molecular
hydrogen. Markovic’s research focuses on the previous step, which involves
improving the efficiency by which an incoming water molecule would disassociate
into its fundamental components. To do this, Markovic and his colleagues added
clusters of a metallic complex known as nickel-hydroxide. Attached to a
platinum framework, the clusters tore apart the water molecules, allowing for
the freed hydrogen to be catalyzed by the platinum.
“One
of the most important points of this experiment is that we’re combining two
materials with very different benefits,” says Markovic. “The
advantage of using both oxides and metals in conjunction dramatically improves
the catalytic efficiency of the whole system.”
According
to Argonne materials scientist George Crabtree, who helped to initiate the
establishment of Argonne’s energy conversion
program, the researchers’ success is attributable to their ability to work on
what are known as “single-crystal” systems—defect-free materials that
allow scientists to accurately predict how certain materials will behave at the
atomic level. “We have not only increased catalytic activity by a factor
of 10, but also now understand how each part of the system works. By scaling up
from the single crystal to a real-world catalyst, this work illustrates how
fundamental understanding leads quickly to innovative new technologies.”
This work, supported by the DOE Office of Science, is reported in Science.
