Kirk Pollard Smith

Accelerating Low-Carbon Innovation

The Chemistry of Redox‐Flow Batteries

<em>
 Towards the end of 2022 I drafted this, consider it a work in progress - it was before I had joined forces with Daniel to form the Flow Battery Research Collective
</em>
<strong>
 Motivation for an open-source flow battery
</strong>
<strong>
 This project aims to develop an open-source flow battery design suitable for mid-scale manufacturing by a well-equipped hackerspace or conventional machine shop.
</strong>

Motivation for an open-source flow battery

My collaborator Daniel shared an update on his blog about our the progress of our open-source flow battery kit, so I thought I’d do the same. This was motivated by my previous post (Smith 2024). We’ve been working together with Prof Sanli Faez and Josh Hausener at Utrecht University on their FAIR Battery Project, though the repository for my cell design and jig is currently here.

An open-source flow battery kit

Dual Power Supply

My collaborator Daniel shared an update on his
[blog](https://chemisting.com/2024/03/15/an-open-source-diy-flow-battery/)
about our the progress of our open-source flow battery kit, so I thought
I'd do the same. This was motivated by my previous post [(Smith
2024)]{.citation cites="smith2024"}. We've been working together with
Prof Sanli Faez and Josh Hausener at Utrecht University on their [FAIR
Battery Project](https://github.com/SanliFaez/FAIR-Battery), though the
repository for my cell design and jig is currently
[here](https://codeberg.org/kirkpsmith/RFB-dev-kit). Daniel and I are
contributing as independent scientists on our own time in our own
abodes.

I recently finished some preliminary renderings of the cell shown here:

::: {.quarto-figure .quarto-figure-center style="aspect-ratio: 1920 / 1080"}
<figure class="figure">
<p><img
src="https://dualpower.supply/posts/rfb-kit-workshop/images/exploded-1600w.webp"
class="figure-img"
srcset="images/exploded-1600w.webp 1600w, images/exploded-800w.webp 800w, images/exploded-400w.webp 400w"
decoding="async" width="800" alt="Exploded view of the cell" /></p>
<figcaption>Exploded view of the cell</figcaption>
</figure>
:::

::: {.quarto-figure .quarto-figure-center style="aspect-ratio: 1920 / 1080"}
<figure class="figure">
<p><img
src="https://dualpower.supply/posts/rfb-kit-workshop/images/front-1600w.webp"
class="figure-img"
srcset="images/front-1600w.webp 1600w, images/front-800w.webp 800w, images/front-400w.webp 400w"
decoding="async" width="800"
alt="Front view of the cell in jig with reservoirs, pumps, tubing" /></p>
<figcaption>Front view of the cell in jig with reservoirs, pumps,
tubing</figcaption>
</figure>
:::

::: {.quarto-figure .quarto-figure-center style="aspect-ratio: 1920 / 1080"}
<figure class="figure">
<p><img
src="https://dualpower.supply/posts/rfb-kit-workshop/images/back-1600w.webp"
class="figure-img"
srcset="images/back-1600w.webp 1600w, images/back-800w.webp 800w, images/back-400w.webp 400w"
decoding="async" width="800"
alt="Rear view of the jig showing fixtures for Arduino UNO R3 and a L298N motor driver" /></p>
<figcaption>Rear view of the jig showing fixtures for Arduino UNO R3 and
a L298N motor driver</figcaption>
</figure>
:::

Daniel has mostly worked on optimizing a suitable zinc-iodine chemistry
and choosing some widely available, affordable materials to build the
cell with. I've worked mostly on the cell design and CAD.

::: {.quarto-figure .quarto-figure-center style="aspect-ratio: 1024 / 576"}
<figure class="figure">
<p><img
src="https://dualpower.supply/posts/rfb-kit-workshop/images/paste-1-1024w.webp"
class="figure-img"
srcset="images/paste-1-1024w.webp 1024w, images/paste-1-800w.webp 800w, images/paste-1-400w.webp 400w"
decoding="async" width="800"
alt="Daniel&#39;s photo and caption: A polypropylene FDM printed prototype being tested with Mn/Fe chemistry. This particular test was done without reservoirs, on close circuit circulation to easily detect any leaking." /></p>
<figcaption>Daniel’s photo and caption: A polypropylene FDM printed
prototype being tested with Mn/Fe chemistry. This particular test was
done without reservoirs, on close circuit circulation to easily detect
any leaking.</figcaption>
</figure>
:::

::: {.quarto-figure .quarto-figure-center style="aspect-ratio: 1024 / 576"}
<figure class="figure">
<p><img
src="https://dualpower.supply/posts/rfb-kit-workshop/images/paste-2-1024w.webp"
class="figure-img"
srcset="images/paste-2-1024w.webp 1024w, images/paste-2-800w.webp 800w, images/paste-2-400w.webp 400w"
decoding="async" width="800"
alt="Daniel&#39;s photo and caption: Image of one of our latest prototypes. This features polypropylene FDM printed reservoirs, a resin printed cell body and a PLA FDM printed jig." /></p>
<figcaption>Daniel’s photo and caption: Image of one of our latest
prototypes. This features polypropylene FDM printed reservoirs, a resin
printed cell body and a PLA FDM printed jig.</figcaption>
</figure>
:::

For some scientists doing flow battery experiments in their respective
homes/apartments, we've got some solid preliminary results--- not bad in
terms of capacity and efficiency, in the sense that we are in the right
order of magnitude of real-world electrolytes here, and we're using
paper instead of an ion-exchange membrane!

::: {.quarto-figure .quarto-figure-center style="aspect-ratio: 770 / 938"}
<figure class="figure">
<p><img
src="https://dualpower.supply/posts/rfb-kit-workshop/images/paste-3-770w.webp"
class="figure-img"
srcset="images/paste-3-770w.webp 770w, images/paste-3-400w.webp 400w"
decoding="async" width="800"
alt="From Daniel&#39;s blog: Charge/discharge cycle using photopaper separators and the Zn-I chemistry using the open source flow battery design." /></p>
<figcaption>From Daniel’s blog: Charge/discharge cycle using photopaper
separators and the Zn-I chemistry using the open source flow battery
design.</figcaption>
</figure>
:::

From Daniel:

> Our design will be presented at the Flow4UBattery Event in Eindhoven,
> Netherlands, on April 8-9, 2024. [You can register here for
> free](https://www.eventbrite.com/e/flow4ubattery-event-pioneering-energy-storage-solutions-tickets-851447120257?aff=oddtdtcreator),
> which also includes complimentary lunch (so please make sure you
> intend to attend if you subscribe). Day 2 of the event will feature a
> workshop where participants can assemble a flow battery themselves
> using the design from our kit. Additionally, we'll be giving away 5
> complete kits during the event, each including mystat potentiostats.
> We'll also have a fully assembled kit doing cycling so that you can
> see the fully assembled kit in action!
>
> After this event, we will look into selling these kits online, with
> all proceeds going towards the development of higher capacity kits
> with the objective of reaching an open source flow battery stack
> within the next 2 years. We will also be publishing the full designs
> and bill of materials online, so that anyone can create their own too!

::::: {#references .section .level3}
### References {anchor-id="references"}

:::: {#refs .references .csl-bib-body .hanging-indent entry-spacing="0"}
::: {#ref-smith2024 .csl-entry}
Smith, Kirk Pollard. 2024. "Motivation for an Open-Source Flow Battery."
<https://dualpower.supply/posts/motivation-OSHW-RFB/>.
:::
::::

------------------------------------------------------------------------

*I am attempting the [100 Days To
Offload](https://100daystooffload.com/) challenge, and this is post
\#3.*
:::::

:::::: {#quarto-appendix .default}
::::: {#quarto-reuse .section .quarto-appendix-contents}
## Reuse {#reuse .anchored .quarto-appendix-heading}

:::: {.quarto-appendix-contents}
<div>

[CC BY 4.0](https://creativecommons.org/licenses/by/4.0/){rel="license"}

</div>
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:::::
::::::


*Towards the end of 2022 I drafted this, consider it a work in
progress - it was before I had joined forces with
[Daniel](https://chemisting.com/) to form the [Flow Battery Research
Collective](https://opencollective.com/fbrc)*

------------------------------------------------------------------------

:::::: {#motivation-for-an-open-source-flow-battery .section .level1}
# Motivation for an open-source flow battery

**This project aims to develop an open-source flow battery design
suitable for mid-scale manufacturing by a well-equipped hackerspace or
conventional machine shop. The design will incorporate principles from
the appropriate technology movement and derisk suitable flow battery
technologies from literature while communicating the science in lay
terms. Inspiration is taken from the Piggott small wind turbine design
and applied to stationary electrochemical energy storage.**

The energy transition is underway and demand for sustainable,
affordable, long-lasting energy storage capacity has never been higher.
Despite large individual and community-level interest in flow batteries
as a prospective technology that could address this demand, they have
largely failed to live up to their hype. Furthermore, unlike
lithium-ion, lead-acid, solar, and [small
wind](https://windempowerment.org/) technologies, flow batteries remain
outside the capabilities of enterprising individuals to design and build
their own energy infrastructure in an affordable fashion. This project
plans to change that and democratize flow battery technology, moving
specialized knowledge of their design and manufacture into the public
domain.

::: {#why-are-flow-batteries-worth-developing .section .level2}
## Why are flow batteries worth developing? {anchor-id="why-are-flow-batteries-worth-developing"}

Lead-acid and lithium-ion batteries are manufactured at the highest
industrial scale. The main use case envisioned for this project is
distributed stationary energy storage on the 10 kWh scale (roughly) for
off-grid use, load shifting, and arbitrage. Lead-acid and lithium-ion
are already fit for this purpose, so why bother with flow batteries?
Briefly, lead-acid batteries are affordable, and sustainable by some
metrics, but can require maintenance, and degrade within years of
regular deep cycling requiring tedious replacement procedures.
Lithium-ion is capable of more cycles at deeper depths-of-discharge than
lead-acid with zero maintenance, but at greater initial expense and
eventual capacity decline/replacement---and has concerns regarding
supply chain sustainability. Also, lithium-ion has flammability risks
whereas lead-acid does not.

Flow batteries, in this application of distributed, small-scale
stationary energy storage, could offer a cheaper initial capital
expenditure (*vs.* lithium-ion certainly), order of magnitude longer
cycle/service life, and sustainable supply chain. This project is
motivated by the promise of a cheap, long-lasting, sustainable,
appropriate technology solution to distributed small-scale stationary
energy storage.
:::

:::: {#why-you-cant-buy-a-flow-battery-today .section .level2}
## Why you can't buy a flow battery today {anchor-id="why-you-cant-buy-a-flow-battery-today"}

Flow batteries have existed for decades longer than the modern
lithium-ion battery, yet a regular consumer or small enterprise cannot
easily obtain a quote for one, much less go on to purchase one. Flow
batteries have been highly publicized in recent years, and like
hydrogen, fuel cells, fusion power, *etc*, many promoters of these
technologies have overpromised and underdelivered. Flow batteries have
not yet reached their promise of ultra-long-life, affordable energy
storage.

Furthermore, the technology development deadlines allowed and the
financial returns demanded by venture capital-backed startups in energy
storage have largely led to the abandonment of the residential market,
shifting focus to larger-scale commercial and industrial applications.
This is partly due to the higher proportion of soft costs inherent to
residential installations *vs.* commercial or industrial clients.
Additionally, to install such a chemical battery in a residential
setting would be subject to the strictest consumer health and safety
regulations, pushing early-stage stationary storage companies away from
the residential market and into telecoms and remote power applications
as their "beachhead market." Finally, the market "need" for grid-scale
electrochemical energy storage is still developing, and some commercial
attempts at flow batteries were simply ahead of their time and ran out
of financing runway (see 90s and early 00s-era iron-chromium commercial
attempts).

This failure to deliver as initially promised, however, is often not for
technological failure---market timing and business strategy are key to
proper execution, and firms attempting to commercialize emerging
technology must cope with many non-technical destabilizing factors while
simultaneously scaling up technological maturity. The market for
portable electronics provided ample resources for industry to develop
lithium-ion cells---both capital for R&D, and the relatively small
energy capacity of portable electronics allowing for many more "widgets"
to be produced. The instrinsic small size of batteries in portable
electronics allowed the lithium-ion battery industry's learning rate to
benefit from an "economy of volume," as discussed by [(Nussey
2021)]{.citation cites="nussey2021"}. Flow batteries, in contrast, have
suffered the same fate as nuclear energy, in the sense that their
respective industries have not been able to learn and improve over such
a high number of iterations; the technologies have been low-volume,
highly custom, and slow to build.

::: {.quarto-figure .quarto-figure-center style="aspect-ratio: 499 / 353"}
<figure class="figure">
<p><img
src="https://dualpower.supply/posts/motivation-OSHW-RFB/images/paste-1-499w.webp"
class="figure-img"
srcset="images/paste-1-499w.webp 499w, images/paste-1-400w.webp 400w"
decoding="async" width="600"
alt="Figure from Malhotra and Schmidt 2020, showing degree of design complexity vs need for customization" /></p>
<figcaption>Figure from Malhotra and Schmidt 2020.</figcaption>
</figure>
:::

[This
figure](https://www.cell.com/cms/attachment/bc1731bb-5bba-44de-9867-470f2d67d8d6/gr1.jpg)
from [(Malhotra and Schmidt 2020)]{.citation cites="malhotra2020"} shows
how flow batteries are currently still design-intensive and customized -
closer to a Type 3 technology than Type 1. This project will attempt to
push towards a standardized open-source design for at least some of the
component technologies.

Little academic research explores flow batteries above the benchtop
scale. Promising technological developments often get sucked into
universities' Technology Transfer Offices for opportunities to license,
spinout, and otherwise commercialize the work, even if the technology is
extremely early-stage. Many flow battery startups then, in
market-competitive, non-collaborative silos, simultaneously reinvent the
wheels of process scaleup, stack design, shunt current control, *etc*.
If they fail, the knowledge they gained often vanishes along with the
company.

The goal of this present effort is to pick a suitable flow battery
chemistry and develop it to the highest possible level in the most
transparent fashion. An ideal outcome would be delivering an appropriate
stationary energy storage solution into the lay, public domain---the
Piggott small wind turbine design is an aspirational example, though may
prove a difficult goal.
::::
::::::

::::::::::: {#which-chemistry-to-pick-applying-some-initial-constraints .section .level1}
# Which chemistry to pick? Applying some initial constraints

:::::::::: {#rigorous-justification-work-in-progress .section .level2}
## Rigorous justification (work-in-progress) {anchor-id="rigorous-justification-work-in-progress"}

There are many flow battery chemistries to choose from. The concept of
[appropriate
technology](https://en.wikipedia.org/wiki/Appropriate_technology) is
used here to help downselect from the many chemistries and component
options available. Some upfront design heuristics/principles result:

1.  safety is paramount: water-based, nonflammable electrolyte
2.  avoiding the requirement of a ion-exchange membrane
3.  no precious metals (ideally no need for catalysts at all)
4.  prioritizing elements in plentiful supply as defined by the
    [European Chemical
    Society](https://www.euchems.eu/euchems-periodic-table/)
5.  prioritizing passive over active design features
6.  designing for long cycle life
7.  designing for recyclability at end-of-life (compatability with the
    circular economy)
8.  minimize the use of heavy equipment for installation
9.  design for manufacturing by a regular machine shop

::: {.quarto-figure .quarto-figure-center style="aspect-ratio: 1197 / 849"}
<figure class="figure">
<p><img
src="https://dualpower.supply/posts/motivation-OSHW-RFB/images/paste-3-1197w.webp"
class="figure-img"
srcset="images/paste-3-1197w.webp 1197w, images/paste-3-400w.webp 400w, images/paste-3-800w.webp 800w"
decoding="async" width="600"
alt="EU Chemical Society periodic table of elements, considering sustainability" /></p>
<figcaption>EU Chemical Society periodic table of elements, considering
sustainability</figcaption>
</figure>
:::

[(Noack et al. 2015)]{.citation cites="noack2015"} provide a thorough
review of flow battery chemistries and presents the available
chemistries to choose from.

::: {#incomplete-list-of-explanations .section .level3}
### Incomplete list of explanations {anchor-id="incomplete-list-of-explanations"}

Nonaqueous approaches are excluded under heuristic 1. Vanadium, the most
common commercial chemistry, is not viable under heuristic 4.
"Air-breathing" chemistries---such as zinc-air or iron-air, which
utilize one or more oxygen electrodes---are also not possible without
technically risky and sometimes precious-metal catalyst structures, so
they are exluded based on heuristic 3. The iron-chromium chemistry is
also excluded based on limited availability of chromium based on
heuristic 4. Bromine and pure hydrogen are a safety concern.
:::

::::::: {#references .section .level3}
### References {anchor-id="references"}

:::::: {#refs .references .csl-bib-body .hanging-indent entry-spacing="0"}
::: {#ref-malhotra2020 .csl-entry}
Malhotra, Abhishek, and Tobias S. Schmidt. 2020. "Accelerating
Low-Carbon Innovation." *Joule* 4 (11): 2259--67.
<https://doi.org/10.1016/j.joule.2020.09.004>.
:::

::: {#ref-noack2015 .csl-entry}
Noack, Jens, Nataliya Roznyatovskaya, Tatjana Herr, and Peter Fischer.
2015. "The Chemistry of Redox-Flow Batteries." *Angewandte Chemie -
International Edition* 54 (34): 9776--9809.
<https://doi.org/10.1002/anie.201410823>.
:::

::: {#ref-nussey2021 .csl-entry}
Nussey, Bill. 2021. *Freeing energy: how innovators are using
local-scale solar and batteries to disrupt the global energy industry
from the outside in*. s.l.: Mountain Ambler Publishing.
:::
::::::

------------------------------------------------------------------------

*This concludes my draft motivation/manifesto for an open-source flow
battery. It's currently a side project of mine. I am attempting the [100
Days To Offload](https://100daystooffload.com/) challenge, and this is
post \#1.*
:::::::
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::::::::::: {#quarto-appendix .default}
::::: {#quarto-reuse .section .quarto-appendix-contents}
## Reuse {#reuse .anchored .quarto-appendix-heading}

:::: {.quarto-appendix-contents}
<div>

[CC BY 4.0](https://creativecommons.org/licenses/by/4.0/){rel="license"}

</div>
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::::::: {#quarto-citation .section .quarto-appendix-contents}
## Citation {#citation .anchored .quarto-appendix-heading}

<div>

::: {.quarto-appendix-secondary-label}
BibTeX citation:
:::

``` {.sourceCode .code-with-copy .quarto-appendix-bibtex}
@online{pollard smith2024,
  author = {Pollard Smith, Kirk},
  title = {Motivation for an Open-Source Flow Battery},
  date = {2024-02-26},
  url = {https://dualpower.supply/posts/motivation-OSHW-RFB},
  doi = {10.59350/fknwy-k7a54},
  langid = {en}
}
```

::: {.quarto-appendix-secondary-label}
For attribution, please cite this work as:
:::

::: {#ref-pollard smith2024 .csl-entry .quarto-appendix-citeas}
Pollard Smith, Kirk. 2024. "Motivation for an Open-Source Flow Battery."
February 26, 2024. <https://doi.org/10.59350/fknwy-k7a54>.
:::

</div>
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