New technique to make fuel cells more energy efficient

In a finding that could lead to better fuel cells and clean energy technologies, scientists have discovered that squeezing a platinum catalyst a fraction of a nanometre nearly doubles its activity.
A nanosize squeeze can significantly boost the performance of platinum catalysts that help generate energy in fuel cells, according to scientists at Stanford University in the US.
The team bonded a platinum catalyst to a thin material that expands and contracts as electrons move in and out, and found that squeezing the platinum a fraction of a nanometre nearly doubled its catalytic activity.
"In this study, we present a new way to fine-tune metal catalysts at the atomic scale," said Haotian Wang, a former graduate student at Stanford now at Harvard University.

"We found that ordinary battery materials can be used to control the activity of platinum and possibly for many other metal catalysts," said Wang.
The new technique can be applied to a wide range of clean technologies, Wang said, including fuel cells that use platinum catalysts to generate energy, and platinum electrolyzers that split water into oxygen and hydrogen fuel.

"Our tuning technique could make fuel cells more energy efficient and increase their power output," said Yi Cui, a professor of materials science and engineering at Stanford.
"It could also improve the hydrogen-generation efficiency of water splitters and enhance the production of other fuels and chemicals," said Cui.

Catalysts are used to make chemical reactions go faster while consuming less energy. The performance of a metal catalyst depends on its electronic structure - that is, how the electrons orbiting individual atoms are arranged.
The study focused on lithium cobalt oxide, a material widely used in batteries for cellphones and other electronic devices. The researchers stacked several layers of lithium cobalt oxide together to form a battery-like electrode.
"Applying electricity removes lithium ions from the electrode, causing it to expand by 0.01 nanometre. When lithium is reinserted during the discharge phase, the electrode contracts to its original size," Cui said.

For the experiment, the team added several layers of platinum to the lithium cobalt oxide electrode.
"Because platinum is bonded to the edge, it expands with the rest of the electrode when electricity is added and contracts during discharge," Cui said.
Separating the platinum layers a distance of 0.01 nanometre, or five per cent, had a significant impact on performance, Wang said.
"We found that compression makes platinum much more active. We observed a 90 per cent enhancement in the ability of platinum to reduce oxygen in water. This could improve the efficiency of hydrogen fuel cells," he said.
The findings were published in the journal Science.