https://www.youtube.com/watch?v=fk_YEXZgQ8E&list=WL&index=12

Not that great, only 74% @ 1000 cycles

This guy did some videos for an all iron static battery. Here is the final version video and info page:

https://www.youtube.com/watch?v=0eK5ouP8hNQ&list=PLYDTEjzfnaSUe4u0WKlIXLqpL3VmYcrxv&index=2&pp=iAQBsAgC

https://www.hardware-x.com/article/S2468-0672(25)00007-0/fulltext

There's a lot I would love to add to this community. I think the way traditional methodology for this technology needs to be reapproached. Firstly, by using my open sourced membrane recipe you can glue it directly into a PVC cell. Secondly, using foam core PVC sheets which are readily available and cheap from cabinet shops like imeca allows for complex flow cell designs to be easily and rapidly produced with a simple CNC router on various sizes. I have a flow cell design already I'll be glad to upload. I'm new here so sorry there's a lot I love to want to share and am doing things one thing at a time.

You can find more details on the membrane on the following GitHub https://github.com/Rowow1/Open-sourced-off-the-shelf-ion-exchange-membrane
However I started a separate thread specifically for this membrane topic.

@kirk said in New member introduction thread!:

This would be great to see! Feel free to start a thread in @general-discussion about your cell design. We had tossed around the idea of 2D-material milling/laser approaches to flow frames, but have stuck with 3D printed designs for now so that we can have internal geometries in the flow frames - 2D would certainly be easier and cheaper to make, but I was hesitant about the increased gasketing required/adhesives for sealing.

The key aspect of using the proposed PVC membrane recipe together with the pvc foam board actually completely eliminates the need for gaskets. You simply glue the membrane in place since its also made from pvc. Overall there's far less labor and requirements, forming a sealed (technically welded) bonded cell for a fraction of the price that 3d printing would cost. The long term goal and my personal next goal is to get into injection molding which of course is the best option.

Ill see about uploading the cell fusion 360 model soon depending on if people even care or not. But the point is the core principle idea of being able to use much cheaper pvc foam board material and mass produce these cells at a much better scale than one layer at a time with 3d printing. I was able to make unique geometries needed for flow cells with my 2d design.

As a comparison, you can buy these foam boards for $60-80 for 1/2" or 3/4" from imeca for a full 4x8ft sheet

Hi all, been planning some improvements to the dev kit that are underway, based on some ideas exchanged at a conference with some other open-source flow battery projects (Redoxino and the team at QUB).

It's mostly to improve ergonomics - there is now a case to hold the arduino and wires on the rear of the cell:

We also realized you can just clamp the cell shut with a 2-inch C-clamp instead of using the bolts, and it seals well:

Note, the new endplates here used are backwards-compatible with previous gaskets/graphite plates/brass current collectors, so no need to recut anything. Moving forward though, the design files for those components will change to reflect the need for only two alignment pin holes instead of the four bolt holes.

And based on Redoxino's presentation at the Nordic Flow Battery Network meeting, Gastronorm (GN) containers are a nice standard to use for secondary containment, it seems with some tweaks we could fit the entire kit into a GN 1/3 150 mm deep container, which are a standard for industrial kitchens worldwide (and available in polymers like PP and PC).

Need to make the reservoirs shorter or mounted lower somehow, and maybe make a holder in the jig for the C-clamp, so that it's in a fixed position.

Right now I'm working on these developments on the clampable-cell branch here: https://codeberg.org/FBRC/RFB-dev-kit/src/branch/clampable-cell

Let me know if you have feedback/ideas/suggestions! Docs are not yet updated for this configuration, I will do that before I merge it to main.

My individual changed construction

/FBRC-Redox-FLOW-Batterie/Fotos Projekt/IMG_7768.JPG

As I had to change the tubes in my pumps (they were the wrong tube type),(thanks @sepi) I also changed the connectors to Luer Lock .
Therefore it was necessary to enlarge the boreholes in the endplates and in the brass-plates to 10.5 mm to get the female Luer Lock part through.
And I changed my construction to sucking from the cells.

Some other thoughts:
@danielfp248 In your picture of 08.01.26 you put the pump for suction on the lower side of the cell, why?
In my opinion it would be better to connect the pump upper side to avoid air in the system as I did in my setup.

@kirk
your new approach for the test cell seems veri interesting. But for getting reproducible resultants the flow through the cell should be down to up, but not horizontal (how much would be air isolating in the chamber when changing parts?)

I do not have an idea for a reasonable physical layout for a really simple change of the test-chamber, but I will think over.

Printing materials I have used:
Parts not in contact with chemicals: PETG, works very well
PP: My 1st: (Yousu),all surfaces o.k, but all barbed broke. 2nd: Innovatefil PP GF worked very well, but the upper surface was rough, tests will come.

I just wrote a blog post sharing my first results testing the Zn-Br chemistry recently published by a Chinese group. Sodium sulfamate is not very easy to get, but I was able to source it from labdiscounter.nl in the EU. If any of you are in labs where you can also test this chemistry, I would be happy to hear about your thoughts and/or results.

A recent Chinese Nature paper showed how Sodium sulfamate can be used in Zn-Br batteries to sequester active Br₂ into an N-bromosulfamate that is much less aggressive, much more water soluble and even more easily electrochemically reversible than elemental bromine. I also wrote a recent post discussing the potential use of nicotinamide to achieve this (plot twist, it doesn’t work as the nicotinamide Zn complex is not very soluble). In today’s post I want to share with you my attempts at reproducing this chemistry of the Chinese paper using our open source flow battery dev kit.

The paper is very extensive and shares multiple formulations, they share a formulation for normal asymmetric cells as well as formulations to run the batteries using microporous Daramic membranes. Thankfully I have a bunch of 900um Daramic (thanks a lot to Daramic who donated these membranes to us for research). I bought some Sodium sulfamate (NaSA), Zinc bromide (ZnBr₂), Potassium bromide (KBr) and potassium acetate (KAc) and proceeded to run some tests.

My tests using the formulations that they disclose exclusively for daramic were not very successful. Formulations using only ZnBr₂, KAc and NaSA suffer from either lower capacities because of lower conductivity or issues with hydrogen evolution. This was specially the case when I tried the ZnBr₂ 1M, KAc 1.5M, NaSA1.5M formulation, which they suggest in the supporting information to reach >50Ah/L. However I think this is a typo and they meant 2M ZnBr₂. If you read that paragraph in the supporting information closely you’ll realize why this is the case (they previously refer to a ZnBr₂ 1M solution and then say this is basically 2x that, but still write it as ZnBr₂ 1M).

I then proceeded to test using some of the electrolytes they suggest for asymmetric cells, which were much more successful. In particular the 1M ZnBr₂, 2M KAc, 1M KBr and 1M NaSA was great, with high CE values and decent EE values (see graph above). I didn’t experience dendrites before reaching the Nernst limit of the cells when using the 900um thick Daramic, which suggests plating is not as aggressively dendritic as with other electrolytes. However dendrites are quite evident when using 300um Daramic, suggesting you need around 300um of Daramic for every 30mAh/cm². This might explain why the paper restricts most plating to below 90mAh/cm2 when using the 900um Daramic. I have yet to reproduce the Chinese group capacity or cycling stability values, but I believe I have validated the electrochemical principles well.

It is also worth noting that the Chinese group does some fancy functionalization of their felt with both nitrogen containing groups and carbon nanotubes, which aggressively boosts the conductivity and energy efficiency of the felt for the Br reactions. This is an important different that might justify why they get energy efficiencies closer to 75-80% while mine are just shy of 60%. I also haven’t optimized the compression ratio of my felt, which means that my felt might be under or over-compressed to extract the max EE in this setup. I also lack an oven to properly do air activation of the felt, so my felt is quite suboptimal and just used as-is.

Furthermore, the paper successfully tested a true flow battery setup using Ti-Br. I cannot easily buy TiOSO₄ but I decided to try to innovate and test this chemistry in a fully symmetric setup coupled with 0.5M of Fe-DTPA. While Fe-DTPA isn’t expected to be fully resistant to N-bromosulfamate, I figured it might last enough to provide me with some data. Given that the redox potential of the Fe-DTPA redox couple is quite lower than Fe²⁺/Fe³⁺, I figured it should give some appreciable voltage in an Fe-DTPA/N-Br-sulfamate battery. Fe-DTPA is also quite soluble and stable at the near neutral pH that favors the N-Br-sulfamate chemistry, so it should work nicely.

The results above, which have never been published before, show that this chemistry works to some extent. The low CE does suggest that a significant portion of the Fe-DTPA is somehow lost, perhaps to oxidation by atmospheric oxygen (I cannot purge my cells with N₂ or Argon at the moment), but also likely from just interactions with N-Bromosulfamate across the microporous membrane. With that said, it does show that the new stabilized bromosulfamate chemistry opens up the window to some very interesting options that just didn’t exist before. Perhaps I can test nicotinamide in this setup, where there is no Zn to cause it to precipitate out of solution.

Finally, I wanted to dedicate the above post to Robert Murray-Smith, a fellow chemist in the UK who passed away recently and was a key inspiration for the start of this blog. I know his passing has been very sad for a lot of us in the DIY community, the curiosity and inspiration he instilled in a lot of us will live on. Thank you Robert!

Hello, I recently open sourced a novel ion exchange membrane recipe using a high speed grinder on water softener resin and mixing with PVC cement. They can be produced for less than $1 a square yard with properties similar to other name brand ion exchange membranes. You can find more details on the following GitHub https://github.com/Rowow1/Open-sourced-off-the-shelf-ion-exchange-membrane

The patent in the GitHub describes more details, but I also made the following video where I released the files patent as a CCL1.0 license. I have lots of other ideas I would love to assist this community in but I hope this can demonstrate the significance change in scope of redox flow batteries.

https://youtu.be/c3tNXDlgE2M?si=ru-gOsw0ogBhBex2

Zinc bromide flow batteries have been researched very extensively during the past 30 years. There are many advantages to this chemistry, very high potential (~1.8V), high efficiencies, symmetric electrolyte and low reagent costs. Nonetheless, the disadvantages are also huge: zinc dendrites, hydrogen evolution, bromine corrosion, etc. Despite all the development, a lot of these disadvantages remain insurmountable.

A recent nature paper has disrupted the field by using sulfamate ions as a bromine scavenger. Unlike previously used complexing agents that sequestered Bromine as reactive Br^3- species, the new scavenging method sequesters Bromine as an N-bromosulfamate, which is stable in solution in the timescales necessary for energy storage. Furthermore, the N-bromosulfamate is chemically much milder than elemental Br² or Br^3-, making the use of cheaper gasketing materials possible and preventing a lot of issues associated with the high reactivity of elemental bromine species.

I have been very excited by these findings and have ordered some sodium sulfamate to test this chemistry myself in our FBRC development kit. However, the development of this technology is likely not open source and it is very likely that the people involved with it want to patent it and lock down the technology. This made me think about potential alternatives that could be used outside of the sulfamate family that could also exploit the mechanism of Br storage in N-Br bonds. Such a technology might be outside the scope of their original paper and therefore be exempt from intellectual property registration.

Thinking about the stability of N-Br compounds (usually not stable at all), I immediately think about NBS and analogous chemical compounds. These are very stable reagents that are routinely used in chemical synthesis, although their aqueous solubility is very low and therefore not useful in the creation of a ZnBr2 aqueous battery.

With that said, nicotinamide (vitamin B3) is a very water soluble and readily available material that also forms a stable N-Br compound in mildly acidic conditions. This 2007 paper describes how N-bromonicotinamide can be created using elemental bromine. While N-bromine compounds from amines like this would often go through a Hoffman rearrangement to yield the corresponding amine, this doesn’t happen under mildly acidic condition in the case of nicotinamide. In fact, the 2007 paper mentions that a concentrated solution of this N-Br compound was stored for months without degradation. The solubility of nicotinamide is also very high (5-6M), compared to sodium sulfamate’s solubility limit of 1.3M at 25C.

Furthermore, nicotinamide forms mono and dimeric complexes with Zn atoms through the nitrogen in their pyridine ring, which makes this nitrogen unavailable for potential deactivation with direct bromination of this N to yield the corresponding quaternary nitrogen salt (irreversible and undesirable in the context of a battery).

Given that vitamin B3 is very soluble, very low cost, already produced industrially, has a stable amide N-Br compound and is unlikely to undergo Hoffman rearrangement or similar decomposition modes, it is a great candidate to serve as a Br^₂ scavenger in a ZnBr₂ battery. I am going to buy some vitamin B3 to test this idea out. Stay tuned for some tests of this and the sodium sulfamate chemistry.

Available here: https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.10001658/v1

Code repo: https://github.com/mbarzegary/RfbFoam

Could be useful for improving the flow field design of the large-format cell.

Great project for someone to take on, without needing to do chemistry or wet-lab experiments

We will be presenting at FOSDEM 2026 and hope to see you there! Kirk and Daniel will be presenting at 12:30 on Saturday, January 31 in the Energy track in room AW1.126. Full details here, including the link to the livestream (talk should also be recorded and watchable later).

The title of the talk is "Scaling up open-source batteries: what's worth pursuing?". Here is the abstract:

Storing energy reversibly is useful. For clean energy, electrochemical batteries are one of the most attractive options. Most battery technology is proprietary, hard to recycle, and complicated to manufacture. What if that wasn't the case?

We will present our collective and individual efforts with the Flow Battery Research Collective (https://fbrc.dev/) to build open-source batteries for stationary storage applications. This includes our flow battery work, such as efforts to build a larger-format cell with simple manufacturing techniques like laser cutting and FDM printing, as well as our different experiments with flow battery electrolytes based on zinc, iodine, iron, and manganese.

We will also cover our individual efforts to build conventional, non-flow flooded batteries based on water and the above elements (including this work by the speaker Daniel: https://chemisting.com/2025/05/23/a-low-cost-open-source-cu-mn-rechargeable-static-battery/). We will discuss the economic hurdles facing practical implementations of these systems.

For the "large-format" cell, we'd like to target as large of a geometric area as possible, and ideally have the flow frame be useable both for single-cell and stack testing. This means it needs to possess adequate internal fluid manifolds and flow diffuser/spreading geometry. We must also consider shunt currents once we progress to stack testing, so we'd like to design the cell with that issue in mind upfront.

We plan to start with a flow-through design, as it is much, much simpler to design and manufacture than flow field-based approaches.

This thesis has some helpful figures - I haven't read it yet myself, but it looks quite useful. The author is now a professor at University of Padua.

https://global.discourse-cdn.com/free1/uploads/fbrc/original/1X/0f77c4b4b752d2c44bc56bc870b2ac407eb9f7ca.jpeg

Basically we want to make our own version of this. Ideally we could prototype it with polypropylene FDM printing... but in any real application it would be injection molded.

A good image showing the path of a shunt current, which leads to a drop in energy efficiency as well as uneven current distribution (and possibly plating, for hybrid RFBs):

Image from University of Padua researchers: https://iopscience.iop.org/article/10.1149/MA2024-0217mtgabs

Right now, we need a flow frame that:

1. Has the correct geometry for flow-through graphite felt electrodes (and possibly polymer felts/spacers, for hybrid chemistries)
2. Doesn't leak
3. Distributes flow evenly through the felts
4. Offers adequate pressure drop and shunt currents when implemented in a stack

References

PhD thesis: https://www.research.unipd.it/handle/11577/3422708

Optimization paper: https://doi.org/10.1016/j.electacta.2021.139667

Flow field optimization paper (we don't have flow fields, but the simulation framework/procedure is interesting): https://linkinghub.elsevier.com/retrieve/pii/S0378775321009563

Dear Flow Battery Research Collective,

as part of the CIRCLE project at the Bochum University of Applied Sciences, our student group is preparing to conduct a life cycle assessment (LCA) for the Flow Battery Research Collective’s open-source redox-flow battery. If possible, we would like to take a look on the upscaled cell/stack/battery.
During our Zoom meeting on 19. November 2025, you shared several ideas for meaningful LCA topics. Based on your input, we developed two possible options that could support the ongoing development of the battery. To proceed, we would like to know which option you prefer or where you can provide the most useful data.

Option 1: Electrolyte–Membrane interactions
This topic focuses on how the electrolyte composition and membrane material affect each other, especially regarding efficiency and degradation.
Goal:
To assess the environmental impact and technical relevance of electrolyte–membrane interactions, and to perform a screening comparison of membrane and electrolyte choices from production to end-of-life.
Information we would need (please provide as much information as possible):
• How the selected electrolyte interacts with different membrane materials and which parameters are considered for choosing the electrolyte-membrane pairing
• Measured efficiencies of the current electrolyte-membrane selection
• Background on membrane selection in the development kit (e.g. which specific materials were chosen and why)
• How is the material wear currently counteracted (replacement only)?
• How is waste (wastewater, solid waste, co-products from chemical manufacture) disposed of?

Option 2: Electrolyte Leakage
Leakage is an important practical and environmental concern, and understanding its causes could support improvements in design, sealing, and material choice.
Goal:
To analyse the environmental implications of electrolyte leakage, identify contributing factors, and explore what design or material changes might minimise it.
Information we would need (please provide as much information as possible):
• How frequently leakage occurs (per cycle/per kit/in what percentage of the kits)
• How leakage is currently detected (refill volume, reduced power output, emissions, etc.)
• Whether it is monitored proactively or noticed after cycle completion
• Estimated amount of electrolyte lost per cycle
-> If no data is available, could it be collected by measuring leakage over multiple cycles?
• Whether leakage becomes more common with aging or due corrosion
• Current methods or design choices used to minimise leakage (e.g. sealing, welding, bonding)

We also have some general questions. More questions will probably arise in the future.
General questions:
• How much energy supply does a RFB require (for one cycle/in total)?
• Which electricity mix is currently used to operate the battery (is there a proportion of green electricity)?
• Where are the materials purchased? From which countries are they delivered and how (train, car, ship)?
• In which country are the batteries assembled and tested?

We would be happy to work on either topic, and we aim to select the one that is most helpful for the FBRC team and for which the necessary data can be provided.

We look forward to hearing your thoughts and continuing our collaboration!

Kind regards,
Rieke Huesmann, Anita Thaqi, Stella Vucemilovic

I didn’t want to take over the “New member introduction thread” with my questions, so I’ve started a new one.

At this point, I already have the 3D printed components. I should receive the remaining parts later this month.

One thing I was missing in the documentation was information about the material for the "polymer endplate". In the photo, “PETG 100%” was written on the endplate with a marker, so I used that material and infill.

I have still not been able to test my cell because I wanted to make sure I had my mystat calibrated correctly. For this I wanted to implement a calibration wizard. Unfortunately I was not prepared to deal with the very large single file, single layer codebase of the mystat control software. I therefore had to start refactoring this code. My progress is visible here: https://codeberg.org/sepi/mystat/src/branch/feat-refactor-modular

The advantages of my refactor are amongst others the following:

• less global state, easier to understand code
• multiple smaller modules making it easier to find code
• layered architecture, separating concerns more cleanly
• "plugin" system for easier extension
• easier testing of both hardware code and gui code due to decoupling into layers. A mock hardware class could be implemented to test the gui or other Tabd could be implemented as new classes
• availability of decoupled hardware layer that can be used independently of the gui
• easier implementation of new "Tab plugins" by subclassing and using the hardware and gui layer.

This is still work in progress and probably pretty buggy. I tried not to touch any of the implemented logic but there afe surely some problems left. Once I'm done with the refactor, I would like to write a wizard for calibration hoping to make it obsolete to consult the original paper for reference.

I'm open for comments and suggestions now and help with testing once my branch has stabilised a bit.

In the hope that it will be useful to the future work of folks here, I've written up as much as possible about my experience patching up a failing ZCell and nursing it along. I've also included some further general notes about Redflow's hardware and software:

https://ourobengr.com/2025/12/what-happened-next/

Hello! I'll try to document my building experience here while I impatiently wait for parts to arrive. This is mostly to document and motivate myself to continue. Don't expect super interesting stuff in here.

After having ordered most of the material from aliexpress and amazon.de, I finally got around printing the endplates yesterday. I opted for PLA on my old ender 3. As described in the docs I went for the 60% infill and managed to produce some pretty decent parts. The layer height of 0.25 looks good too. Each plate took around 1h30 on this antique machine. There might have been a tiny bit of warping on one edge but I hope it won't be enough to cause issues.

Anyways, I still need to print the arduino case and the stand (which I might modify in order to use less material). On the ordering front, I still need to order most reagents from synthetica and some PP-filament.

Hello fellow flow battery enthusiasts! I bought 15m of Tygon Chemical tubing with PTFE lining suitable for the Zn/I chemistry as used in the devkit. I only need around 2m and someone else wanted to take 5m, that's 8m left to be distributed amongst people who need some. I ship in the whole EU and the price is 23€/m (thats what I paid incl. shipping). Just send me a PM if you're interested.

Hey Everyone. I designed and printed some PLA sleeves to go over M6 screws so that you don't need to use tape on the screws anymore with the kit. The tape is often hard to properly wrap around and imo has to be changed quite often, so this should improve the design. I printed these on a Prusa Core One using a 0.4mm diameter nozzle. The screws don't come into contact with active material, so you can use PLA for this (doesn't have to be PP, although this should also work).

You can get the STL here:

https://www.dropbox.com/scl/fi/r9h95p92dyt648aajktkm/sleeve_for_screws_kit.stl?rlkey=sxoenr3p8g1qe3ysgc0318j7z&dl=0

You can print these in "vase mode" so that you have no stitching marks. Let me know what your experience is with other printers!

Comments on the blog post at https://fbrc.dev/posts/october-2025-progress-update/