Oct
31
Better Way to Split Water Developed
October 31, 2011 | 2 Comments
Many research teams have been searching for more efficient catalysts to speed the splitting of water into hydrogen and oxygen. The reaction is key to the production of hydrogen as a fuel for use in cars; to generate electricity in fuel cells, the operation of some rechargeable batteries, including zinc-air batteries; and for the industrial use of adding hydrogen to other materials. A lot of effort is being spent to outperform electrolysis.
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.
A team of researchers at MIT has found one of the most effective catalysts ever discovered for splitting oxygen atoms out from water molecules. The new catalyst liberates oxygen at more than 10 times the rate of the best previously known catalyst of its type. How much current is needed or the efficiency isn’t however noted. Meanwhile, the numbers are astonishing and the catalyst has no precious metals.
The MIT team says 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 compound’s high level of activity was predicted from the team’s systematic experimental study that looked at the catalytic activity of 10 known compounds.
Proposed OER Mechanism on Perovskite from MIT. Click image for more info.
The team’s results were published in Science on Oct. 28, 2011.
The research turned up other interesting clues. The MIT team 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. That aspect shows there may well be other catalyst compounds to discover.
Shao-Horn, the Gail E. Kendall (1978) Associate Professor of Mechanical Engineering and Materials Science and Engineering said, “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.”
MIT’s Daniel Nocera, is 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 including materials science and engineering graduate student Jin Suntivich, mechanical engineering graduate student Kevin J. May 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.
Shao-Horn says “It’s our belief that there may be others with even higher activity.” The team plans to continue searching for even more efficient catalyst materials. The new catalyst may be a leader for along time though, as the top choice was made from a new understanding to the basic operation of taking off the oxygen atom.
Splitting water to acquire free hydrogen is a demanding job. The water molecule has good bonds needing a lot of effort to break apart. Its one thing to just carve off a hydrogen atom leaving the HO and quite another to get all the way to fully freed hydrogen and oxygen.
Without a discussion of the energy involved a comparison with the practicing process in use now isn’t possible. That may be an oversight or simply not having good data or the catalyst demands inordinate power. It’s the information everyone is waiting to see.
MIT has the raw speed catalyst to spilt water now – which is no small feat. Lets keep an eye out for the power demands and hope the efficiency has a noteworthy improvement as well.
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I wonder what the implications of an artificial leaf are for space travel?
All these watter-splitting catalysts entirelly miss the point. The name of the game is not using sunlight to produce hydrogen, but to use nuclear-generated hydrogen as a substitute for photosynthesis. It’s the other way around!