November 3rd, 2007
A new way to make water -- and fuel cells
You probably know that it is easy to combine hydrogen and oxygen to make water. After all, this chemical reaction is known for more than two centuries. But now, researchers at the University of Illinois at Urbana-Champaign (UIUC) have discovered a new way to make water. As states the UIUC report, ‘not only can they make water from unlikely starting materials, such as alcohols, their work could also lead to better catalysts and less expensive fuel cells.’ But be warned: don’t read the technical paper itself. It could win an obfuscated contest — if such a contest existed for scientific papers.
This project has been led by Zachariah Heiden, a doctoral student at UIUC and a member of the Thomas Rauchfuss’s research group. You can see Rauchfuss (left) and Heiden on the picture on the left. (Photo by L. Brian Stauffer for UIUC). Here is a link to a larger version of this picture.
Their work is summarized on this page about “Supramolecular Organometallic Chemistry in Separations and Catalysis” (scroll down to the “Metal-Amine-Hydrides as Prototype Catalysts for Fuel Cells” section). Fortunately, James E. Kloeppel, Physical Sciences Editor at UIUC, explains us what the researchers have found in a way we all can understand.
For example, he writes that the actual reaction to make water is simply — 2H2 + O2 = 2H2O + Energy — but he explains it. “In English, the equation says: To produce two molecules of water (H2O), two molecules of diatomic hydrogen (H2) must be combined with one molecule of diatomic oxygen (O2). Energy will be released in the process.”
What is important to note is that this equation also describes what happens inside a hydrogen fuel cell. “In a typical fuel cell, the diatomic hydrogen gas enters one side of the cell, diatomic oxygen gas enters the other side. The hydrogen molecules lose their electrons and become positively charged through a process called oxidation, while the oxygen molecules gain four electrons and become negatively charged through a process called reduction. The negatively charged oxygen ions combine with positively charged hydrogen ions to form water and release electrical energy.”
So what is the contribution of the two researchers to cheaper hydrogen fuel cells? “The ‘difficult side’ of the fuel cell is the oxygen reduction reaction, not the hydrogen oxidation reaction, Rauchfuss said. ‘We found, however, that new catalysts for oxygen reduction could also lead to new chemical means for hydrogen oxidation.’”
This is why they concentrated their efforts on new hydrogenation catalysts. [They] “focus exclusively on the oxidative reactivity of iridium-based transfer hydrogenation catalysts in a homogenous, non-aqueous solution. They found the iridium complex effects both the oxidation of alcohols, and the reduction of the oxygen. ‘Most compounds react with either hydrogen or oxygen, but this catalyst reacts with both,’ Heiden said. ‘It reacts with hydrogen to form a hydride, and then reacts with oxygen to make water; and it does this in a homogeneous, non-aqueous solvent.’”
This research work has been accepted for publication by the Journal of the American Chemical Society, where it appeared online on October 25, 2007 under the title “Homogeneous Catalytic Reduction of Dioxygen Using Transfer Hydrogenation Catalysts.”
Here is the beginning of this incredible abstract. “Solutions of Cp*IrH(rac-TsDPEN) (TsDPEN = H2NCHPhCHPhN(SO2C6H4CH3)-) (1H(H)) with O2 generate Cp*Ir(TsDPEN-H) (1) and 1 equiv of H2O. Kinetic analysis indicates a third-order rate law
(second order in [1H(H)] and first order in [O2]), resulting in an overall rate constant of 0.024 ± 0.013 M-2s-1. Isotopic labeling revealed that the rate of the reaction of 1H(H) + O2 was strongly affected by deuteration at the hydride position (kHH2/kDH2 = 6.0 ± 1.3) but insensitive to deuteration of the amine (kHH2/kHD2 = 1.2 ± 0.2); these values are more disparate than for conventional transfer hydrogenation.”
Would you like me to continue? Seriously, I’ve been reading scientific papers for many years now, but this one overwhelms me. I know it’s difficult to describe some chemical phenomena in plain English, but this abstract could win an obfuscated contest — if such a contest existed for scientific papers. Please drop me a line if you have already read such a obscure jargon.
Sources: University of Illinois at Urbana-Champaign news release, October 31, 2007; and various websites
You’ll find related stories by following the links below.
