Tech Briefs Magazine - January 2023 - 29

tion layer on the silicon surface. To predict
the ideal voltage at which the flow
batteries should run, the team developed
a new theoretical modeling method
that allowed them to select a pair of
chemicals in the flow battery that would
operate at the ideal voltage based on the
characteristics of the solar cell, maximizing
efficiency. The chemicals are organic
compounds, not expensive metals as in
traditional flow batteries, and are dissolved
in a benign water solution of table
salt rather than strong acids.
The resulting device maintained a
high efficiency over hundreds of hours
and hundreds of charge-discharge cycles
while retaining most of its capacity. That
lifespan was several times longer than
earlier devices.
For more information, contact Song
Jin at jin@chem.wisc.edu; 608-262-3571.
The integrated solar flow battery contains both a solar cell and chemicals to generate, store, and
redeliver renewable electricity from the Sun in one device. (Image: Wenjie Li)
Organic Redox Flow Battery
The large-capacity battery can be used to store energy from wind turbines and solar cells
and as a power bank for cars.
Linköping University, Linköping, Sweden
R
edox flow batteries are stationary batteries
in which the energy is located in
the electrolyte, outside of the cell itself, as
in a fuel cell. They are often marketed
with the prefix " eco " since they open the
possibility of storing excess energy from,
for example, the Sun and wind. It appears
that they can be recharged an unlimited
number of times; however, redox flow
batteries often contain vanadium, a
scarce and expensive metal. The electrolyte
in which energy is stored in a redox
flow battery can be water-based, which
makes the battery safe to use but results in
a lower energy density.
Researchers have produced not only a
water-based electrolyte but also electrodes
of organic material that increase the energy
density considerably. It is possible in
this way to manufacture completely organic
redox flow batteries for the storage
of, for example, energy from the Sun and
A model of the redox flow battery in the laboratory. (Image: Thor Balkhed)
Tech Briefs, January 2023
wind, and to compensate for load variation
in the electrical supply grid.
The team used the conducting polymer
PEDOT for the electrodes, which they
have doped to transport either positive
ions (cations) or negative ions (anions).
The water-based electrolyte consists of a
solution of quinone molecules, which can
be extracted from forest-based materials.
The high compatibility of quinones and
PEDOT means that the PEDOT electrodes
help the quinone molecules switch between
their oxidized and their reduced
states, creating a flow of protons and electrons.
The team also used a fundamental
phenomenon within electrocatalysis in
which one special ion in solution - in this
case, quinone ions - is converted to electricity.
The phenomenon is conceptualized
as ion-selective electrocatalysis and
most likely exists in other types of membrane
storage devices such as batteries,
fuel cells, and supercapacitors.
The organic redox flow batteries still
have a lower energy density than batteries
that contain vanadium but they are
inexpensive, completely recyclable,
safe, and perfect for storing energy and
compensating for load variations in the
electrical supply grid.
For more information, contact Mikhail
Vagin at mikhail.vagin@liu.se.
www.techbriefs.com
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Tech Briefs Magazine - January 2023

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