Fuel
cells are inefficient because the catalyst most commonly used to
convert chemical energy to electricity is made of the wrong material, a
researcher at Case Western Reserve University argues. Rather than
continue the futile effort to tweak that material—platinum—to make
it work better, Chemistry Professor Alfred Anderson urges his colleagues
to start anew.
“Using
platinum is like putting a resistor in the system,” he said. Anderson
freely acknowledges he doesn’t know what the right material is, but he’s
confident that researchers’ energy would be better spent seeking it out
than persisting with platinum.
“If
we can find a catalyst that will do this [more efficiently],” he said,
“it would reach closer to the limiting potential and get more energy out
of the fuel cell.”
Anderson’s analysis as well as a guide for a better catalyst have been published in a recent issue of Physical Chemistry Chemical Physics and in Electrocatalysis online.
Even
in the best of circumstances, Anderson explains, the chemical reaction
that produces energy in a fuel cell like those being tested by some car
companies ends up wasting a quarter of the energy that could be
transformed into electricity. This point is well-recognized in the
scientific community, but to date efforts to address the problem have
proved fruitless.
Anderson
blames the failure on a fundamental misconception as to the reason for
the energy waste. The most widely accepted theory says that impurities
are binding to the platinum surface of the cathode and blocking the
desired reaction.
“The decades-old surface-poisoning explanation is lame, because there is more to the story” Anderson said.
To
understand the loss of energy, he used data derived from
oxygen-reduction experiments to calculate the optimal bonding strengths
between platinum and intermediate molecules formed during the
oxygen-reduction reaction. The reaction takes place at the
platinum-coated cathode.
He
found the intermediate molecules bond too tightly or too loosely to the
cathode surface, slowing the reaction and causing a drop in voltage.
The result is the fuel cell produces about .93 V instead of the
potential maximum of 1.23 V.
To
eliminate the loss, calculations show, the catalyst should have bonding
strengths tailored so that all reactions taking place during oxygen
reduction occur at or as near to 1.23 V as possible.
Anderson
said the use of volcano plots, which are a statistical tool for
comparing catalysts, has actually misguided the search for the best one
“They allow you to grade a series of similar catalysts, but they don’t
point to better catalysts.”
He
said a catalyst made of copper laccase, a material found in trees and
fungi, has the desired bonding strength but lacks stability. Finding a
catalyst that has both is the challenge.
Anderson
is working with other researchers exploring alternative catalysts as
well as an alternative reaction pathway in an effort to increase
efficiency.
Source: Case Western Reserve University