Scientists discover new way to make water
Scientists at the
University of Illinois have discovered a new way to make water, and
without the pop. 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.
“We found that unconventional metal hydrides can be used for a chemical
process called oxygen reduction, which is an essential part of the process
of making water,” said Zachariah Heiden, a doctoral student and lead author
of a paper accepted for publication in the Journal of the American
Chemical Society.
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: 2H2 + O2 = 2H2O + 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 (2H2 + O2 = 2H2O + 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.
Source: University of Illinois at Urbana-Champaign
