Materials Science and Engineering Graduate Student Jin Suntivich (left) and Mechanical Engineering Graduate Student Kevin J. May (right) inspecting the electrochemical cell for oxygen evolution reaction experiment. Photo: Jonathon R. Harding |
A
team of researchers at Massachusetts Institute of Technology (MIT) has found one of the most effective
catalysts ever discovered for splitting oxygen atoms from water
molecules—a key reaction for advanced energy-storage systems, including
electrolyzers, to produce hydrogen fuel and rechargeable batteries. This
new catalyst liberates oxygen at more than 10 times the rate of the
best previously known catalyst of its type.
The
new compound, composed of cobalt, iron and oxygen with other metals,
splits oxygen from water (called the Oxygen Evolution Reaction, or OER)
at a rate at least an order of magnitude higher than the compound
currently considered the gold standard for such reactions, the team
says. The compound’s high level of activity was predicted from a
systematic experimental study that looked at the catalytic activity of
10 known compounds.
The
team, which includes materials science and engineering graduate student
Jin Suntivich, mechanical engineering graduate student Kevin J. May and
professor Yang Shao-Horn, published their results in Science on Oct. 28.
The
scientists found that reactivity depended on a specific characteristic:
the configuration of the outermost electron of transition metal ions.
They were able to use this information to predict the high reactivity of
the new compound—which they then confirmed in lab tests.
“We
not only identified a fundamental principle” that governs the OER
activity of different compounds, “but also we actually found this new
compound” based on that principle, says Shao-Horn, the Gail E. Kendall
(1978) Associate Professor of Mechanical Engineering and Materials
Science and Engineering.
Many
other groups have been searching for more efficient catalysts to speed
the splitting of water into hydrogen and oxygen. This reaction is key to
the production of hydrogen as a fuel to be used in cars; the operation
of some rechargeable batteries, including zinc-air batteries; and to
generate electricity in devices called fuel cells. Two catalysts are
needed for such a reaction—one that liberates the hydrogen atoms, and
another for the oxygen atoms—but the oxygen reaction has been the
limiting factor in such systems.
Other
groups, including one led by MIT’s Daniel Nocera, have focused on
similar catalysts that can operate—in a so-called “artificial leaf”—at
low cost in ordinary water. But such reactions can occur with higher
efficiency in alkaline solutions, which are required for the best
previously known catalyst, iridium oxide, as well as for this new
compound.
Shao-Horn
and her collaborators are now working with Nocera, integrating their
catalyst with his artificial leaf to produce a self-contained system to
generate hydrogen and oxygen when placed in an alkaline solution. They
will also be exploring different configurations of the catalyst material
to better understand the mechanisms involved. Their initial tests used a
powder form of the catalyst; now they plan to try thin films to better
understand the reactions.
In
addition, even though they have already found the highest rate of
activity yet seen, they plan to continue searching for even more
efficient catalyst materials. “It’s our belief that there may be others
with even higher activity,” Shao-Horn says.
Jens
Norskov, a professor of chemical engineering at Stanford University and
director of the Suncat Center for Interface Science and Catalysis
there, who was not involved in this work, says, “I find this an
extremely interesting ‘rational design’ approach to finding new
catalysts for a very important and demanding problem.”
The
research, which was done in collaboration with visiting professor
Hubert A. Gasteiger (currently a professor at the Technische Universität
München in Germany) and professor John B. Goodenough from the
University of Texas at Austin, was supported by the U.S. Department of
Energy’s Hydrogen Initiative, the National Science Foundation, the
Toyota Motor Corporation and the Chesonis Foundation.
A Perovskite Oxide Optimized for Oxygen Evolution Catalysis from Molecular Orbital Principles
This work identifies that the electronic configuration of metal ions can control the activity of metal oxides for oxygen evolution by at least 10,000 times, which serves as a “design principle” (a volcano plot) to screen metal oxide candidates and accelerate the development of water electrolyzer, metal-air batteries and other energy storage technologies. Image: Eva Mutoro, Jin Suntivich, Yang Shao-Horn |
