New catalyst helps combine fuel cell, battery into one device
The key is the 'bifunctionality index'

Date:
October 6, 2021
Source:
Washington University in St. Louis
Summary:
A team has developed a catalyst that can be used to both generate
fuel and provide power.



FULL STORY ==========================================================================
A single device that both generates fuel and oxidant from water and,
when a switch is flipped, converts the fuel and oxygen into electricity
and water, has a host of benefits for terrestrial, space and military applications. From low environmental impact to high energy density,
developing efficient unitized regenerative fuel cells, or URFCs as they
are called, has been in researchers' sights for years now.


==========================================================================
But to truly be efficient, an URFC needs bifunctional catalysts. This
means, in electrolyzer mode, catalysts should facilitate the breakdown
of water into hydrogen and oxygen, and, in fuel cell mode, facilitate
their recombination into water. Now, working in the lab of Vijay Ramani,
the Roma B. & Raymond H.

Wittcoff Distinguished University Professor, a team of researchers has
found an excellent bifunctional catalyst for the oxygen electrode.

Their work was published in the journal Proceedings of the National
Academy of Sciences.

"Unlike the hydrogen electrode, wherein platinum is an effective
bifunctional catalyst, it is very challenging to identify a suitable
catalyst for the oxygen electrode due to the sluggish kinetics of oxygen reduction and oxygen evolution," said Pralay Gayen, currently working
at Intel, who was a postdoctoral research associate in Ramani's lab at
the McKelvey School of Engineering at Washington University in St. Louis
and served as the paper's first author.

Sulay Saha, a postdoctoral research associate in Ramani's laboratory, and Gayen's research was guided by first principles -- taking into account
the fundamental properties of different substances before heading to
the lab to test potential catalysts.

Along with former undergraduate researcher and co-author Xinquan
Liu, the team ultimately identified and developed Pt-Pyrochlore, a
composite of platinum and a lead ruthenate pyrochlore, which yielded
high bifunctionality.

The "bifunctionality index" is a measure of catalyst's ability to
facilitate both the forward and reverse direction of a reaction. "We
want the index to be low," said Kritika Sharma, a PhD engineering
student. "Zero, ideally." This new catalyst has a bifunctionality index
of 0.56 volts -- very low compared with other catalysts reported. When
used in a URFC device developed by the laboratory, the catalyst enabled
a round-trip energy efficiency (RTE) of 75% - - the highest reported
round-trip efficiency in this type of URFC.

With such high efficiency, the URFCs developed are well suited for
applications such as submersibles, drones, spacecrafts and space stations,
as well as for off-grid energy storage.

========================================================================== Story Source: Materials provided by
Washington_University_in_St._Louis. Original written by Brandie
Jefferson. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Pralay Gayen, Sulay Saha, Xinquan Liu, Kritika Sharma, Vijay
K. Ramani.

High-performance AEM unitized regenerative fuel cell using
Pt-pyrochlore as bifunctional oxygen electrocatalyst. Proceedings
of the National Academy of Sciences, 2021; 118 (40): e2107205118
DOI: 10.1073/ pnas.2107205118 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211006160111.htm

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