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Engineers at the University of
Wisconsin-Milwaukee (UWM) have identified a catalyst that provides the same
level of efficiency in microbial fuel cells (MFCs) as the currently used
platinum catalyst, but at 5% of the cost.
Since more than 60% of the investment in
making microbial fuel cells is the cost of platinum, the discovery may lead to
much more affordable energy conversion and storage devices.
The material—nitrogen-enriched iron-carbon
nanorods—also has the potential to replace the platinum catalyst used in
hydrogen-producing microbial electrolysis cells (MECs), which use organic
matter to generate a possible alternative to fossil fuels.
“Fuel cells are capable of directly
converting fuel into electricity,” says UWM Professor Junhong Chen, who created
the nanorods and is testing them with Assistant Professor Zhen (Jason) He.
“With fuel cells, electrical power from renewable energy sources can be
delivered where and when required, cleanly, efficiently, and sustainably.”
The scientists also found that the nanorod
catalyst outperformed a graphene-based alternative being developed elsewhere.
In fact, the pair tested the material against two other contenders to replace
platinum and found the nanorods’ performance consistently superior over a
six-month period.
The nanorods have been proved stable and are
scalable, says Chen, but more investigation is needed to determine how easily
they can be mass-produced. More study is also required to determine the exact
interaction responsible for the nanorods’ performance.
The work was published in Advanced Materials.
The right recipe
MFCs
generate electricity while removing organic contaminants from wastewater. On
the anode electrode of an MFC, colonies of bacteria feed on organic matter,
releasing electrons that create a current as they break down the waste.
On the cathode side, the most important
reaction in MFCs is the oxygen reduction reaction (ORR). Platinum speeds this slow
reaction, increasing efficiency of the cell, but it is expensive.
Microbial electrolysis cells (MECs) are
related to MFCs. However, instead of electricity, MECs produce hydrogen. In
addition to harnessing microorganisms at the anode, MECS also use decomposition
of organic matter and platinum in a catalytic process at their cathodes.
Chen and He’s nanorods incorporate the best
characteristics of other reactive materials, with nitrogen attached to the
surface of the carbon rod and a core of iron carbide. Nitrogen’s effectiveness
at improving the carbon catalyst is already well known. Iron carbide, also known
for its catalytic capabilities, interacts with the carbon on the rod surface,
providing “communication” with the core. Also, the material’s unique structure
is optimal for electron transport, which is necessary for ORR.
When the nanorods were tested for potential
use in MECs, the material did a better job than the graphene-based catalyst
material, but it was still not as efficient as platinum.
“But it shows that there could be more
diverse applications for this material, compared to graphene,” says He. “And it
gave us clues for why the nanorods performed differently in MECs.”
Research with MECs was published
in Nano Energy.
