• New flow battery stores power in simple

    From ScienceDaily@1:317/3 to All on Wed Mar 16 22:30:42 2022
    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

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