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Small But Terrible: Nanosize Squeeze Can Boost Fuel Cell Performance

Nov 26, 2016 04:48 AM EST

A team of Stanford scientists has discovered an unusual way to boost the performance of platinum catalysts that help generate energy in fuel cells: a nanosize squeeze.

In a study published in the Science journal, lead author Haotian Wang presented how he and his team bonded a platinum catalyst to a thin material that expands and contracts as electrons move in and out. They found that squeezing the platinum a fraction of a nanometer nearly doubled its catalytic activity.

"In this study, we present a new way to fine-tune metal catalysts at the atomic scale," said Wang. A former graduate student at Stanford who is currently at Harvard University, Wang believes their new technique can be applied to a wide range of clean technologies such as fuel cells that could generate energy. "We found that ordinary battery materials can be used to control the activity of platinum and possibly for many other metal catalysts."

"Our tuning technique could make fuel cells more energy efficient and increase their power output," added Yi Cui, a professor of materials science and engineering at Stanford and of photon science at the SLAC National Accelerator Laboratory and the study's co-author. "It could also improve the hydrogen-generation efficiency of water splitters and enhance the production of other fuels and chemicals."

Catalysts can be utilized to make chemical reactions more efficient by speeding them up and consuming less energy. "The electronic structure of a catalyst needs to match the molecule of interest in order to achieve the chemical reaction you want," Wang explained. "You can adjust the electronic structure of a catalyst by compressing the atoms or pulling them apart."

The study focused on lithium cobalt oxide, a material popularly used in batteries for 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 nanometer," Cui recounted. "When lithium is reinserted during the discharge phase, the electrode contracts to its original size."

According to Wang, separating the platinum layers a distance of 0.01 nanometer, or 5 percent, had a significant impact on performance. "We found that compression makes platinum much more active," he shared. "We observed a 90 percent enhancement in the ability of platinum to reduce oxygen in water. This could improve the efficiency of hydrogen fuel cells."

"Our technology offers a very powerful way to controllably tune catalytic behavior," Cui concluded. "Now, mediocre catalysts can become good, and good catalysts can become excellent."

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