Page 56 - Plastics News April 2019

teChnoLogy

The right polymers for the job

esearchers from the University of Delaware have polymers consist of a long chain, or backbone, and a side
Rdeveloped the most powerful, durable hydroxide chain with a positively charged ion, or cation. In Yan's
exchange membrane fuel cell components on record, past work, the side chains used in hydroxide exchange
which they recently described in the journal Nature membranes contained very large positively cations,
Energy. The key ingredient are Membranes made from which made them stable but hindered their conductivity.
poly(aryl piperidinium) polymers. Fuel cells work by The backbone material, on the other hand, was inexpensive,
converting chemical energy into electricity, and they are a but not sufficiently stable. "The question was: how do you
promising source of power for eco-friendly vehicles. A few create a new polymer that is stable both for the organic
cation and the backbone at the same time, with a small
cation?" said Yan. Using poly(aryl piperidinium) polymers,
the team developed hydroxide exchange membranes and
ionomers with favorable properties, including good ion
conductivity, chemical stability, mechanical robustness,
gas separation and selective solubility.

When the team tested these materials in a system with
only a very small amount of platinum, the fuel cells fed
with air had a peak power density of 920 milliwatts per
square centimeter and operated in a stable manner at a
current density of 500 milliamperes per square centimeter
fuel cell vehicles already exist on the market, including for 300 hours in air at 95 degrees Celsius. These are
the Toyota Mirai, the Honda Clarity and the Hyundai the best power and stability stats yet for a hydroxide
Nexo, and more fuel cell cars are under development exchange membrane at above 90 degrees Celsius and the
worldwide. The fuel cells in automobiles require the use closest anyone has come to the 5000 operating hours that
of an expensive catalyst material, usually platinum, to would be required to use this technology in a car.These
hasten the chemical reactions inside. These are called are the best power and stability stats yet for a hydroxide
proton membrane exchange fuel cells, and they contain exchange membrane at above 90 degrees Celsius and
membranes made of a fluorinated polymeric material. For the closest anyone has come to the 5000 operating hours
nearly two decades, Yushan Yan, Distinguished Engineering that would be required to use this technology in a car.
Professor of Chemical and Biomolecular Engineering, has
been working to develop fuel cells that don't require The team developed a family of polymers, making this
platinum catalysts and instead employ cheaper metals, technology versatile. "There are a lot of knobs we can
such as silver or nickel. turn to deliver different properties," said Yan. "This is a
platform technology. The paper's first author is research
These fuel cells contain hydroxide exchange membranes, associate Junhua Wang, who has been working on this
which shift the environment within fuel cells from acidic project since 2011. "For this discovery to be made, he had
-- the current standard -- to alkaline. The membrane to be very patient," said Yan. "He is a wonderful scientist,
of the fuel cell is what determines the pH inside. "We very creative and diligent." The UD team also included
can make components much cheaper by switching from research associate Yun Zhao, postdoctoral associates Brian
proton exchange membrane fuel cells to hydroxide P. Setzler, Santiago Rojas-Carbonell, Lan Wang, Keda Hu;
exchange membrane fuel cells," said Yan. In order to doctoral student Lin Shi and adjunct professor Shimshon
make these membranes, Yan has been on a quest to Gottesfeld. They also collaborated with three colleagues
develop optimal, scalable materials. For this project, from Elbit Systems Limited, a fuel cell company based in
Yan enlisted the expertise of another electrochemistry Israel. The research is based on work supported by the
expert at UD -- Bingjun Xu, assistant professor of chemical U.S. Department of Energy, Advanced Research Projects
and biomolecular engineering. Hydroxide exchange Agency-Energy under Award No. DE-AR00000771.

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