Automotive Engineering - March 2016 - 10

TECHNOLOGY REPORT

Basic membrane challenges Nafion
Several years ago the Delaware group developed a "Nafionequivalent" membrane for its alkaline fuel cell, a thin polymer
membrane that does for hydroxide ions what Nafion does for
protons. "We have a good handle on the hydroxide exchange
membrane," Yan asserted.
Technically, the prototype membrane is classified as "an efficient silver-phosphonium ionomer interface." Using a quaternary
phosphonium-functionalized polymer yields a material that is less
susceptible to swelling with water while providing excellent hydroxide exchange membrane fuel cell performance. According to
Yan, the material is a nanoscale patchwork of hydrophobic domains abutting hydrophilic water channels; it is via these tiny passages that hydroxide ions come streaming through.
The new membrane technology would also be cheaper because it would replace the PEM's high-priced fluorinated polymer membrane with a cheaper hydrocarbon material, another
boost to economic viability.
"Our real hope is that we can put hydroxide exchange membrane fuel cells into cars and make them truly affordable-maybe $23,000 for a Toyota Mirai," Yan speculated. "Once the cars
themselves are more affordable, that will drive development of
the infrastructure to support the hydrogen economy."
Yan recounted with amusement how he and his team's contrary R&D path somehow passed measure with Steven Chu,
the U.S. Department of Energy Secretary and notorious fuelcell skeptic, in 2009 and 2010. Despite a hard-eyed evaluation, Chu green-lighted Yan's group for funding.
If it wasn't the result of sheer spite on the part of the Nobel
Prize-winning physicist, perhaps it was the sheer audacity of
building a new kind of fuel cell that impressed the Secretary,
because it was one of only a few grants that Chu ever provided for hydrogen fuel cell technology.
Steven Ashley

10 March 2016

Secondary loop and heat pump climate
control under evaluation once more

Condenser

Evaporator

Cabin Air Flow

Expansion
Valve

Direct expansion
A/C (top) vs.
secondary loop.

Compressor
Engine Bay

Passenger Compartment

Pump

Condenser

Chiller

Cooler

Cabin Air Flow

Expansion Valve

Air Flow

those of platinum-group metals in an alkaline electrolyte.
The key remaining issue to address in the catalyst is the
comparative slowness of the alkaline reaction compared to its
acidic platinum counterpart. "It's a problem; the reaction occurs 100 times slower in basic conditions," Yan noted, "but we
have our ideas about how we can get the catalyst to do what
we want. Still, it's probably a couple of years away."

INTERIORS

Air Flow

Several years ago
Yan's University
of Delaware
team developed
an efficient
hydroxide
exchange
membrane for
fuel cells.

Compressor

Is secondary loop climate control about to make an engineering
splash? It got a close look for A/C when the industry was considering low-global-warming alternatives to R-134a, because it permitted confining a system using a refrigerant with safety/environmental issues to a safe underhood area. But once R-1234yf was
seen as a safe albeit mildly-flammable choice, usable with underdash circulation in a direct expansion cycle with existing technology, secondary loop went into mothballs. However, at the recent
SAE Thermal Management Systems Symposium (TMSS) it was
once again identified as a promising alternative.
Direct expansion vaporizes the liquid refrigerant in the under-dash heat exchanger-the evaporator-a single heat exchange loop. A carefully packaged secondary loop allows safe
use of R-152a, a low-cost, low-global-warming, modestly more
flammable refrigerant.
However, secondary loop requires an additional heat exchange circuit-from the refrigerant to an underhood coolant
chiller circulating water and antifreeze mixture into an underdash heat exchanger for cabin climate control. The second
circuit reduces overall system efficiency somewhat, of course.
So why would it be worth a new look?

Heat pump, thermal storage
Essentially reversing the refrigeration cycle (using control
valves) allows the compressor to operate as a heat pump, both
for electric vehicles (EVs) and fuel-powered cars. If the system-
A/C only or with heat pump circuitry-is a secondary loop, there
are potential fuel-economy benefits with an idle stop system.
The secondary loop is effectively "engine-off" liquid thermal
storage and can provide long periods of cabin comfort.
According to a study presented at TMSS by the Department
of Mechanical Engineering of the University of Maryland, the
AUTOMOTIVE ENGINEERING

Automotive Engineering - March 2016

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