"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 doctoral student Zachariah Heiden, who is the lead author of a paper posted online in the Journal of the American Chemical Society.
A water molecule is composed of two hydrogen atoms and one oxygen atom, but one cannot simply take two hydrogen atoms and stick them onto an oxygen atom. The actual reaction to make water is a bit more complicated, and is shown as 2H2 + O2 = 2H2O + Energy.
"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, professor of chemistry and the paper's corresponding author.
In a typical fuel cell, the diatomic hydrogen gas enters one side of the cell, while 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. Rauchfuss said that the "difficult side" of the fuel cell is the oxygen reduction reaction, not the hydrogen oxidation reaction.
"We found, however, that new catalysts for oxygen reduction could also lead to new chemical means for hydrogen oxidation," he said. During their research, the researchers focused 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. 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," Heiden said.
The researcher believes that the catalysts may lead to eventual development of more efficient hydrogen fuel cells, substantially lowering their cost.