Automotive Engineering - March 2016 - 8

TECHNOLOGY
REPORT

POWERTRAIN | ENERGY

Rethinking the route to lower-cost fuel cells

This transmission electron microscope image shows a new
platinum-free fuel cell catalyst that Yan's team developed.
New fuel cell-powered cars and SUVs from
Toyota, Honda, Hyundai, and Mercedes-Benz
are capturing plenty of publicity on this year's
auto show circuit. But the first commercial models are expensive, in part because their fuel cell
stacks use costly platinum catalysts to speed
the key power-producing chemical reactions.
"The level of platinum use in fuel cells has
come down ten-fold in the last 20 years," observed Yushan Yan, chemical engineering professor at the University of Delaware in Newark,
"but I have a feeling that the platinum level will
stay where it is for some time to come."
Yan is skeptical that current fuel cell technology
can become truly affordable. About a decade ago
he and his colleagues turned away from current
proton exchange membrane (PEM) fuel cells in
favor of a type that needs no platinum at all.

corrosive, acidic operating environment. The
main issue was the other key component, the
membrane that passes protons (H+) between
the two electrodes.The ready availability of
DuPont's Nafion semi-permeable polymer film
was the game-changer, despite it looking like
ordinary plastic kitchen wrap.
Though the fluorinated polymer membrane
was itself premium-priced, researchers "felt like
that was it; they never wanted to work with
other technologies," Yan recalled. Rather than
settle on Nafion, he and his group at Delaware
bet that their hydroxide (OH-) exchange membrane fuel cell concept can offer high performance at an unprecedented low cost.
Opting for the high end of the pH range has
an advantage: it enables replacement of platinum catalysts with cheaper metals like nickel or
silver, Yan explained. "A basic operating environment is better," he said, "because many catalytic
metals are much more stable, while everything
dissolves in acid, including platinum."
Yan's team recently published an account of
their work on a hydroxide exchange membrane
fuel cell that uses a prototype low-cost nickelbased catalyst for the hydrogen oxidation reaction at the anode. (See www.nature.com,
January 14.) The composite catalyst, which
features nickel nanoparticles that are supported
on nitrogen-doped carbon nanotubes, exhibits
levels of hydrogen oxidation activity similar to

8 March 2016

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Acid versus base
When William Grove invented the principle of
the fuel cell in 1839, he used sulfuric acid as the
electrolyte. But it took another 100 years for
the alternative-the alkaline, or basic, fuel cell-
to be developed. The alkaline fuel cell used
KOH, or potassium hydroxide, as its electrolyte.
Yan noted that the reactions of both types are
similar at a high level-oxygen reduces on the
positive electrode, and the hydrogen oxidizes
on the negative electrode.
"But when you write down the chemical
reaction with the charge-carrying ions, it's different because you use an OH- instead of an
H+," he said.
In the 1990s when the auto industry focused
development on PEM hydrogen fuel cells, there
wasn't much concern about their extremely

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Professsor Yushan Yan's research team at the
University of Delaware has long worked to develop a
lower-cost alternative to conventional PEM fuel cells
for automotive use.

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Automotive Engineering - March 2016

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