New flow battery stores power in simple organic compound

Date:
March 16, 2022
Source:
University of Groningen
Summary:
The intermittent supply of green electricity requires large-scale
storage to keep our power grids stable. Since normal batteries do
not scale very well, the idea of using flow batteries, which store
electricity in a fluid is attractive. Scientists have designed
a flow battery electrolyte that is cheaper and is based on an
organic compound, rather than a metal.



FULL STORY ==========================================================================
The intermittent supply of green electricity requires large-scale storage
to keep our power grids stable. Since normal batteries do not scale very
well, the idea of using flow batteries, which store electricity in a
fluid is attractive.

However, these batteries contain rare metals and are expensive. Scientists
at the University of Groningen, the Netherlands, have designed a flow
battery electrolyte that may solve both problems. Their results were
published in the Journal of the American Chemical Society on 8 March.


==========================================================================
Flow batteries are not very different from the everyday batteries that
we use.

The big difference is that the energy is stored in two separate fluids
with dissolved chemicals for charge storage. Electricity is stored (and
later released) by pumping these fluids through an electrochemical cell
that contains a membrane through which ions can be exchanged. The energy content of such a battery is scalable by simply using larger storage
tanks for the fluids.

Expensive China recently installed flow batteries to reduce the
variability in green electricity production. 'Large-scale storage
capacity is needed when intermittent sources, such as solar and wind
energy, become more prominent in the electricity mix, because the
grid might get destabilized,' says Edwin Otten, Associate Professor of Molecular Inorganic Chemistry at the University of Groningen. 'The type
of battery that the Chinese use was designed in the1980s and is based
on a solution containing vanadium.' This metal is only mined in a few
places on Earth. 'This means that the supply cannot always be guaranteed
and it is rather expensive,' Otten explains.

Furthermore, it requires a special membrane to separate the two fluids,
which also adds to the costs. That is why Otten's research group, together
with colleagues from the University of Eindhoven (the Netherlands)
and the Technical University of Denmark, set out to design a new kind
of flow battery material.

Blatter radical 'We wanted a symmetrical battery where both tanks
contain the same fluid,' says Otten. 'Also, we wanted it to be based
on an organic molecule rather than on a metal'. Both sides of the flow
battery generally hold fluids with a different composition. Symmetrical batteries have been designed by linking the molecules that are used on
both sides together and filling both tanks with the resulting hybrid
molecule. 'The drawback of this approach is that only one part of the
molecule is used on either side. And, during use, reactive radicals appear
that degrade over time. This makes stability a problem.' Otten and his
team used a different approach. They looked for a single molecule that
is stable and that can accept or donate electrons and could, therefore,
be used on both sides of the battery. The most promising compound was
a Blatter radical, a bipolar organic compound that can either accept or
donate an electron in a redox reaction. 'The molecule that we selected
was also intrinsically stable,' says Otten.

They tested the compound in a small electrochemical cell. It worked well
and remained stable over 275 charge/discharge cycles. 'We need to bring
this up to thousands of cycles; however, our experiments are a proof
of concept. It is possible to make a symmetrical flow battery that has
good stability.' The organic Blatter radical is relatively easy to make
and although it is currently not produced in industry, scale-up should
be possible.

Imbalance 'Another advantage of our symmetrical design is that it is not
a big problem if some of our compound crosses the membrane during use,' explains Otten. 'This could result in a slightly higher volume in one of
the tanks but any imbalance is easily restored by simply reversing the polarity.' During their tests, they have shown that this indeed works
as predicted. Other experimental designs of symmetrical batteries were
not stable enough to get the number of cycles needed to prove this.

The next step is to create a water-soluble version of the Blatter
radicals.

Most flow cells are designed for water-based fluids, since water is
cheap and not flammable. 'PhD students in my group are already working
on this.' A further step is to increase the stability and solubility of
the Blatter radical and test it on a larger scale. Otten: 'The crucial
test is to see whether our compounds will be stable enough for commercial applications.'

========================================================================== Story Source: Materials provided by University_of_Groningen. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jelte S. Steen, Jules L. Nuismer, Vytautas Eiva, Albert
E. T. Wiglema,
Nicolas Daub, Johan Hjelm, Edwin Otten. Blatter Radicals as Bipolar
Materials for Symmetrical Redox-Flow Batteries. Journal of the
American Chemical Society, 2022; DOI: 10.1021/jacs.1c13543 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220316115021.htm

--- up 2 weeks, 2 days, 10 hours, 51 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)