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WUSL team develops bifunctional catalyst for unitized regenerative fuel cells

A team at Washington University in St. Louis (WUSL) has developed a bifunctional catalyst for the oxygen electrode in a unitized regenerative fuel cell (URFC). A paper on their work is published in Proceedings of the National Academy of Sciences (PNAS).

Unitized regenerative fuel cells (URFCs) combine the functionalities of both electrolyzers and fuel cells in a single cell/stack, enabling lower weight, volume, and capital cost. URFCs theoretically offer a number of benefits for terrestrial, space and military applications, including low environmental impact and high energy density.

However, 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.

PNASRFC

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.

—Pralay Gayen, first author

The team ultimately identified and developed Pt-Pyrochlore (Pt-Pb2Ru2O7-x), a composite of platinum and a lead ruthenate pyrochlore, which yielded high bifunctionality.

The bifunctionality index (BI) is a measure of catalyst’s ability to facilitate both the forward and reverse direction of a reaction. The index should be low, said co-author 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 would be well suited for applications such as submersibles, drones, spacecrafts and space stations, as well as for off-grid energy storage.

Resources

  • Pralay Gayen, Sulay Saha, Xinquan Liu, Kritika Sharma, Vijay K. Ramani (2021) “High-performance AEM unitized regenerative fuel cell using Pt-pyrochlore as bifunctional oxygen electrocatalyst” Proceedings of the National Academy of Sciences 118 (40) e2107205118; doi: 10.1073/pnas.2107205118

Comments

Variant003

I know efficiency is not there yet, but a dream here is this;

fill tank with water and plug in to electricity (solar, grid, etc.) and produce the Hydrogen/oxygen to fill tanks. Use the "fuel" I just produced in a FC to power my electric car. Capture the water vapors for potable consumption or to return to electrolyzer to produce more "fuel"

Could in theory be a closed loop with only inputs being top off water and electricity.

Maybe a more realistic use case would be to install a system in your house and use the excess installed solar to produce Hydrogen/Oxygen during day, then switch over to FC mode to power home at night. Excess H/O could be used for car FC or just charge BEV car. Side benefit is using Hydrogen for heating and cooking gas in the home and pure H2O source for drinking water.

Jason

gryf

Home storage could work just don’t drink the water (it would have zero mineral content).
LAVO in Australia has a home storage unit of 40kWh using metal hydride storage (good idea). They use a separate alkaline electrolyzer, I.e. not Unitized and claim 50% RTE.
This system claims 75%RTE which is very good. It only depends on cost of manufacturing, particularly the platinum, ruthenate catalyst.

yoatmon

Let him drink it if he likes and I'm absolutely sure he'll make an experience he'll never forget if he survives.

SJC

Water misses the point of the article

GdB

This enables H2 FC E powered aircraft to regenerate and refuel during decent.

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