A water molecule (formally known as dihydrogen monoxide) is composed
of two hydrogen atoms and one oxygen atom. But you can�t simply take
two hydrogen atoms and stick them onto an oxygen atom. The actual
reaction to make water is a bit more complicated: 2
H2 + O2 = 2 H2O
+ Energy.
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.
�This reaction (2 H2 + O2
= 2 H2O + Energy) has been known for
two centuries, but until now no one has made it work in a homogeneous
solution,� said Thomas Rauchfuss, a U. of I. professor of chemistry
and the paper�s corresponding author.
The well-known reaction 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.
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.�
Rauchfuss and Heiden recently investigated a relatively new generation
of transfer hydrogenation catalysts for use as unconventional metal
hydrides for oxygen reduction.
In their JACS paper, the researchers focus exclusively on the
oxidative reactivity of iridium-based transfer hydogenation 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.�
The new catalysts could lead to eventual development of more efficient
hydrogen fuel cells, substantially lowering their cost, Heiden said.
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