Developing an open source technology and community around redox flow batteries

Kirk Pollard Smith, PhD

Flow Battery Research Collective

Daniel Fernandez Pinto, PhD

Flow Battery Research Collective

October 9, 2025

Flow Battery Research Collective?

• Community of researchers, energy storage users, and enthusiasts who want to help develop and democratize technologies for affordable, sustainable energy storage
• Motivated to develop an open-source flow battery for:
  • reproducible research
  • educational use
  • derisking future commercial systems
• All info at https://fbrc.dev

Our approach

• Open-source hardware¹: no patents, no licensing fees, free for commercial use (CERN OHL), modifications allowed, changes must be made public

• Cooperative, not competitive: trying to establish global community of contributors (eventually, users)

• Development published online in Git repository

1. Liu, J. et al. (2022). Aqueous Electrolytes Reinforced by Mg and Ca Ions for Highly Reversible Fe Metal Batteries. ACS Central Science. https://doi.org/10.1021/acscentsci.2c00293.

Why open-source?

• Lower barriers to entry = more iterations, with more brainpower, for lower cost

• Open-source provides valuable economic benefits: for €1 billion invested, €65 to 95 billion benefit to EU GDP¹

1. Blind, K. et al. (2021). The impact of Open Source Software and Hardware on technological independence, competitiveness and innovation in the EU economy. Final Study Report. European Commission, Brussels.

Open-source hardware from research communities

In EU/UK academia:

• French LAAS-CNRS lab creates open-source power electronics, commercializes them with company OwnTech (https://www.owntech.io/)

• From the UK: OpenFlexure community, open-source, lab-grade microscopes
  (https://openflexure.org)

Globally:

• Recyclable photovoltaic panels: https://www.biosphere.solar/

• Locally buildable small wind turbines: https://windempowerment.org/research-and-devlopment/small-wind-systems/the-piggott-turbine/, https://www.openafpm.net/

• Potentiostat/galvanostat¹

1. Irving, P. et al. (2021). MYSTAT: A compact potentiostat/galvanostat for general electrochemistry measurements. HardwareX. https://doi.org/10.1016/j.ohx.2020.e00163.

Our open-source community

• Community is essential to successful development of any open-source technology!
• Ours revolves around our forum: https://fbrc.nodebb.com/
• Currently 89 registered users, over 500 posts
• First independent replication of entire dev kit happened has occured
• Multiple people building our systems
• Consists of technology enthusiasts, PhD students, academics
• We invite you to participate!

Our forum is growing

Our (modified) roadmap

Current status: benchtop cell, “development kit”

Specified entire system: pumps, tubing, reservoirs, documentation etc. Low-cost, widely available, safe components/materials for ease of replication.

Certified Open-Source by OSHWA

https://certification.oshwa.org/fr000028.html

Current cell design

Flow frame design inspired by O’Conner, Bailey et al.¹

1. O’Connor, H, Bailey, J, et al. (2022). Sustainable Energy & Fuels.

Assembled cell

Simple power electronics

In the lab

The chemistry

Our initial chemistry is zinc-iodine (architecture inspired by Xie et al.¹ and electrolyte by Lee et al. ²), but we are exploring more varieties, such as: all-iron, zinc-iron, soluble iron-manganese (with chelates)

• Negative Terminal (Anode): \(\ce{Zn_{(s)} -> Zn^2+ + 2e-}\)

• Positive Terminal (Cathode): \(\ce{I3- + 2e- -> 3I- }\)

• Overall: \(\ce{Zn_{(s)} + I3- -> Zn^2+ + 3I-}, E^\ominus = 1.3 V\)

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

• Triethylene glycol is added to form soluble iodide complexes at higher SOCs

1. Xie, C. et al. (2018). A Long Cycle Life, Self‐Healing Zinc–Iodine Flow Battery with High Power Density. Angewandte Chemie. https://doi.org/10.1002/ange.201803122.

2. Lee, J. et al. (2023). Effective Enhancement of Energy Density of Zinc-Polyiodide Flow Batteries by Organic/Penta-iodide Complexation. ACS Applied Materials & Interfaces. https://doi.org/10.1021/acsami.3c09426.

Why Zn/I?

• Easy to source, low-cost reagents (vs. vanadium, chromium…)

• Compatible with cheap microporous membranes, such as paper

• Resistant to dendrites

• No appreciable hydrogen evolution

• Acceptable energy density (>20Wh/L)

• No strong acids or bases needed

• Lower toxicity (vs. vanadium, chromium…)

Current performance of Zn/I in the dev kit

2M KI, 1M ZnCl₂, 2M NH₄Cl with 5% triethylene glycol at 60mA/cm², Daramic AA-900, flow-through 3.2 mm graphite felt

Exploring all-iron, water-in-salt electrolytes (WiSE)

Based on Liu et al¹, all-iron hybrid RFB approach using highly concentrated divalent chloride salts, e.g. 4.5 M MgCl₂ or CaCl₂ alongside FeCl₂.

• Negative Terminal (Anode): \(\ce{Fe_{(s)} -> Fe^2+ + 2e-}\)

• Positive Terminal (Cathode): \(\ce{Fe^3+ + e- -> Fe^2+}\)

Hydrogen evolution greatly reduced.

Initial testing in progress, including approx. viscosity measurements: https://fbrc.nodebb.com/topic/44/only-fe-system/21

1. Liu, J. et al. (2022). Aqueous Electrolytes Reinforced by Mg and Ca Ions for Highly Reversible Fe Metal Batteries. ACS Central Science. https://doi.org/10.1021/acscentsci.2c00293.

Development of a 175 cm² cell

Development of a 175 cm² cell

175 cm² flow frame CFD

Design in FreeCAD, model in OpenFOAM

175 cm² flow frame CFD

Design in FreeCAD, model in OpenFOAM

Stacking the 175 cm² cell

Leak testing the 175 cm² cell

Current status

• Development kit is now stable and certified

• All-iron electrolyte exploration with development kit (water-in-salt)

• Completed leak-testing validation of 175 cm² cell

• Finishing control bench for testing 175 cm² cell

• Initial testing of 175 cm² cell with Zn/I chemistry

Acknowledgements

• Josh Hauser, Prof Sanli Faez & FAIR Battery team
• Daniel Fernández Pinto, chief chemist
• NLnet’s NGI0 Entrust fund

FAIR Battery

https://nlnet.nl/project/RedoxFlowBattery/

Get involved!

• Build a kit using our online documentation and designs, give feedback on instructions

• Benchmark and standardize more electrolyte chemistries with the development kit (ideally compatible with porous separators!)

• Help with CAD and FEM/CFD for our upcoming large-format flow frames

• Help design a battery monitoring system (BMS) including pump motor control for larger flow batteries

• Join with us on funding applications :)

Website, forum, development, build instructions at https://fbrc.dev/