Designing an Open-Source Flow Battery Kit

Kirk Smith

Flow Battery Research Collective

Daniel Fernández Pinto

Flow Battery Research Collective

Josh Hauser

Utrecht University/FAIR Battery Project

Sanli Faez

Utrecht University/FAIR Battery Project

April 9, 2024

Flow Battery Research Collective: Who are we?

Researchers who want to help develop and democratize technologies for affordable, sustainable energy storage

What did we do?

  • Built an affordable, complete kit which allows small-scale testing, using:

Why did we do it?

  • Commercial test kits are expensive
  • Existing academic designs aren’t yet accessible to non-experts: lacking documentation and everything needed to perform experiment
  • We want to see for ourselves if these technologies work

Commercial cells


Electrocell (cont.)

✅ Pros:

  • Highly configurable
  • Simple sealing principle
  • Internal manifolding

❌ Cons:

  • Machining of metal and specialized graphite material
  • Price

C-Tech Innovation

Pinflow Energy Storage > $ 7,000 USD > € 2,900

Note the internal manifolding

“ A-Cell, Redox Flow Battery Test Cell” (2024)

MTI Corporation: > $ 9,000 USD

Scribner > $ 5,000 USD

General observations of commercial test cells

  • Not cheap

  • Pricing not transparent (two exceptions)

  • Sturdy: thick metal plates

  • Requires machining of metal and graphite plates

  • Electronics/pumps not always included

Academic cells

Companies may buy those commercial cells, academic researchers often make their own.

Here are some of their designs.

QUILL cell

  • Tested with vanadium chemistry

  • Good overview of existing cell designs in Supporting Information

QUILL cell (cont.)

✅ Pros:

  • Open source!
  • 3D printable cell design
  • Improved performance vs. commercial C-Tech cell
  • Cell fabrication and assembly documentation
  • Ergonomic, closes with C-clamp
  • Minimal graphite machining needed
  • Flow enters electrodes in-plane with membrane/electrode1

❌ Cons:

  • Cell design cannot be milled (overhanging geometry)
  • Large cell pitch of ~8 mm (distance between current collectors)
  • Doesn’t include balance-of-plant
  • Couldn’t seal polypropylene cells (only ABS)

MIT Cell (Brushett Group)

MIT Cell (cont.)

✅ Pros:

  • Open-source!
  • Well-documented
  • Machinable from solid polypropylene
  • Capable of small interelectrode distances / cell pitch

❌ Cons:

  • Requires milling of specialized graphite plate material
  • Flow enters electrode perpendicular to electrode/membrane plane
  • Fixed size at ~2 cm2

Southampton Cell

Successful demonstration of 3D-printed cell components, using zinc-cerium chemistry. Similar approach to Electrocell (Arenas, Walsh, and León 2015)

General observations of academic test cells

  • Varying degrees of openness/documentation
  • Use of additive manufacturing methods common
  • Doesn’t include entire, reproducible system

Our design

Exploded view of current design

Exploded view of the current cell design

Affordable membrane

2,520 EUR/m2 vs. 6 EUR/m2 (Ion Power GmbH and Amazon UK)

Affordable current collectors

1,477 EUR/m2 vs. 66 EUR/m2 (FuelCellStore and Amazon US)

Our design: pros and cons

✅ Pros:

  • Off-the-shelf parts, including graphite foil used on top of copper current collector
  • 1 cm2 to 10 cm2 area configurable
  • Possibility for small interelectrode gap
  • Flow enters porous electrode in-plane with membrane

❌ Cons:

  • In practice, 3D-printable… but machined cell bodies are best
  • Precise fit required between copper current collectors and plastic cell body
  • Thick plastic required in absence of metal compression plates

Entire kit, front

Jig holds everything in place

  • Affordable diaphragm pumps
  • Flexible tubing and barbed fitting connections
  • 3D-printable reservoirs with integrated fittings, standpipe, and septum closure

Entire kit, back

Arduino and motor driver to control pump speeds (potentiostat not pictured)

Prototyping: FDM printing…

Resin printing

PP FDM-printed cell

Resin-printed cell

The fancy version you’re getting…

The software

The chemistry

  • Anolyte: \(\ce{3 Zn^2+ + 6e- -> 3Zn_{(s)} }\)

  • Catholyte: \(\ce{6I- -> 2I3- + 6e-}\)

  • Overall: \(\ce{3Zn2+ + 6I- -> 3Zn_{(s)} + 2I3- }, E^\ominus = 1.298 V\)

  • Parasitic reaction: \(\ce{6I- + O2 + 2 H2O -> 2I3- + 4OH- }\)

Why Zn/I?

  • Easy to source reagents

  • Low-cost reagents

  • Compatible with microporous membranes

  • Works with readily available paper as membrane

  • Dendrites are a non-issue with microporous membranes

  • No detectable hydrogen evolution

  • Acceptable energy density (>20Wh/L)

  • No strong acids or bases needed

  • Low toxicity (but don’t drink it)

Current performance

  • Coloumbic efficiency: 88%

  • Energy efficiency: 71%

  • Accessible energy density: 8.9 Wh/L

Avenues to explore

  • Hydraulic flow from anode to cathode across microporous membrane
  • Durability of separator membrane
  • Long term cycling
  • Use of other microporous separators (Daramic for example)
  • Modifications of microporous separator (PVA for example)

You can help!

  • Documentation
  • Cell design
  • Electrolyte design
  • Growing the community
  • Scale-up!


  • Josh “Bolt Breaker” Hauser, Sanli Faez & FAIR Battery team
  • Daniel Fernández Pinto
  • Conference organizers!


Arenas, L. F., F. C. Walsh, and C. Ponce de León. 2015. “3D-Printing of Redox Flow Batteries for Energy Storage: A Rapid Prototype Laboratory Cell.” ECS Journal of Solid State Science and Technology 4 (4): P3080.
“C-Tech Innovation: C-Flow 1×1 Electrochemical Cell.” 2024.
“Electrocell: Micro Flow Cell.” 2021.
Irving, P., R. Cecil, and M. Z. Yates. 2021. “MYSTAT: A Compact Potentiostat/Galvanostat for General Electrochemistry Measurements.” HardwareX 9 (April): e00163.
“Lab-Cell by Pinflow.” 2024.
Milshtein, Jarrod David. 2017. “Electrochemical Engineering of Low-Cost and High-Power Redox Flow Batteries.” PhD thesis.
“MTI Intl: Complete Testing Package for Vanadium Redox Flow Battery.” 2024.
O’Connor, Hugh, Josh J. Bailey, Oana M. Istrate, Peter A. A. Klusener, Rob Watson, Stephen Glover, Francesco Iacoviello, Dan J. L. Brett, Paul R. Shearing, and Peter Nockemann. 2022. “An Open-Source Platform for 3D-Printed Redox Flow Battery Test Cells.” Sustainable Energy & Fuels 6 (6): 1529–40.
“ A-Cell, Redox Flow Battery Test Cell.” 2024.
“Scribner: Redox Flow Cell Test Fixture.” 2024.


Can you put together a cell that doesn’t leak?