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 the 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.
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 laboratory 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.
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 |
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 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.
