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@rowow said in Using cnc router cut PVC foam boards as cell frame:
The long term goal and my personal next goal is to get into injection molding which of course is the best option.
At scale, definitely!
@rowow said in Using cnc router cut PVC foam boards as cell frame:
Ill see about uploading the cell fusion 360 model
A .step file would also be great so I could look at it in FreeCAD! I don't have a Fusion 360 license. I'd be curious to see if we could take a similar approach.
Nice find! Peter Allen has been at it for a while. I'd read his previous papers but not this one. A quick scan shows they are using an ion-exchange membrane, which @danielfp248 and I try to avoid if we can, since they are often the weak point of systems that rely on them.
Crossover of the mediators through the membrane will degrade performance. The possibility of this unwanted feature was examined by cyclic voltammetry on an electrochemical cell divided by the Fumasep FAS-50 anion exchange membrane in the 2 M KCl 20 % (v/v) EG AIB 3.0 electrolyte. The initial concentrations were 10 mM MV2+ in the left chamber and 10 mM ABTS2- in the right. A constant potential of 1.25 V was applied across the cell with 6.25 cm2 graphite electrodes for 24 h. This simulates the AIB 3.0 conditions. After the 24 h period CV was performed on catholyte to evaluate MV crossover and vice versa. We found no crossover through the membrane by the cyclic Voltammetry experiments.
I like how everything is commercially available at scale. There are quite a few organic flow battery startups that have tried to use methyl viologen as well like they do in this paper. I am curious what @danielfp248 thinks
@doho said in Upcoming improvements to the dev kit:
I have try-ed to download Your new files from github (.stl and .pdf), but the files all appeared as broken, even in github.
The files to sprint for the new endplates are here: https://codeberg.org/FBRC/RFB-dev-kit/src/branch/clampable-cell/CAD/exports
I haven't updated the new
You have to download them individually, unless you clone the repository with Git LFS set up---the large CAD files are handled with LFS and without LFS installed downloading the repository just downlaods a pointer/reference to the CAD file, not the actual file (at least that's how I understand it).
Let me know if this works for you!
Very nice work @doho ! It's great to see your setup.
@doho said in My Suction Luer Lock:
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?)
This is a good point, from what I've seen in other applications cells should generally clear air/produced gases by flowing against gravity from bottom to top, that is still possible with the new setup but the tubing from the pump outlet to cell inlet would have to be slightly longer. In my jig redesign I'll take this into account when writing the documentation.
Also, we have a "double-reservoir" part that contains an internal spillover passage for systems that have a lot of water/liquid transfer. Probably going to make a version with and without this and have it as the standard going forward, to simplify the tubing and jig setup for whatever version people want to use.
The double-reservoir with spillover is in use here
Oh, and we'll be trying to add Luer Lok twist connectors to make detaching the cell quickly from the rest of the setup faster/easier than undoing tight barbed fitting connections.
The new endplates are basically the same, just two alignment pins instead of four bolt holes.
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.
First off, @rowow , thanks for making your membrane approach open-source! Out of curiosity, is the patent application alongside it meant to prevent patent trolls from taking advantage of it?
@danielfp248 has looked into membranes quite a bit and I agree that the only way to know for sure about a membrane's chemical compatibility is to test it with the proposed electrolyte during operation, where it will be exposed to, to take our standard zinc-iodide cell as an example, zinc dendrites (which can puncture an IEM) and high concentrations of triiodide, which can be pretty aggressive and "weird", in the sense that it has attacks and goes through many polymers that are otherwise resistant to similar classes of chemicals.
So far we've used paper and Daramic (polyethlyene + silica microporous separators used in lead-acid cells) because our chemistries are meant to be symmetric (and can tolerate mixing) and they are generally quite chemically resistant and handle dendrites better than an IEM. We're not against IEM use by any means, but so far we haven't spent much time on them because of the previously mentioned problems, and it's not our main focus/skill set. We've had our hands full with electrolyte development and cell/system design, so we've essentially opted to keep the membrane "can of worms" (from our perspective) closed---that said, it would be really interesting to test your membrane approach in the dev kit with say, Zn-I, to see how it compares to Daramic---I just don't think we have the time right now to fabricate the membranes ourselves.
It seems you probably have most of the resources already to test your membranes with ZnI? The other thing that would be quite different in terms of membrane requirements for a battery vs. a refining process would be conductivity, I'm not sure if you've done measurements in terms of Ohm*cm² but this would be a harder target to reach for RFB applications.
Welcome @saphnich and @rowow ! Membranes are definitely something relevant to our work here, to date we have avoided ion-exchange ones like Nafion due to the high cost but having a low-cost and open-source option would be great. I'll hop into the thread @rowow started on DIY membranes.
@rowow said in New member introduction thread!:
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.
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.
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 
Video of the talk is now available here!
https://video.fosdem.org/2026/aw1126/3EEZZB-open-source-batteries.av1.webm
Did another leak test today with water, correctly with 2x ~12 mm plywood endplates each side. Saw no leaks through the edges which was great news, but the barbed connections on the cell showed signs. Also, the MP-6R pumps struggle with the current flow frame design, which has 0.8 mm wall thickness and a 1 mm internal channel (electrode area therefore 2x0.8 + 1 = 2.6 mm thick). I remade (and pushed to the repo) the flow frame with a 3 mm internal thickness, in order to alleviate this pressure drop.
Here is the test setup, I ran out of tubing (ordered 2m but they sent 1 m 
), so the connections aren't ideal but this time no kinks in the flow path. Note, I put these drain valves in, of course they are pointing the wrong way for now, will need to elevate the setup so they can point down in the future.
Because all the connections are on one side (in anticipation of stacking these cells), I also made "front" and "rear" versions of endplates, inner/outer current collectors, and gaskets in the FreeCAD files. This will make low-volume prototyping a bit more expensive but more robust against leaks, which no one wants!
This is the dimension that went from 1 mm to 3 mm to facilitate using MP-6R pumps.
We have the MP-6R now. It is the 6W high-flow version. the MP-10 is also 6W but lower flow / 50 % higher max pressure, then the MP-15R can do almost 3x higher pressure than the MP-6R but at 10 W.
@danielfp248 can hopefully print the 3mm flow frames and I can get them at FOSDEM, then try them out. If it turns out we need the bigger pumps, I'll order them from AliExpress:
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.
hey @DDM ! It's moving along slowly but surely. I had to move my lab around a couple times in the last months which has slowed things down a lot, just starting to get back to things!
Doing some initial leak tests with water, seems like we may need beefier centrifugal pumps than initially thought to get sufficient flow (and/or I did a poor job on designing the flow frame!). I'll be ordering the next couple sizes up of the same type of pump to see how much of a difference that makes.
Once we have good flow conditions the plan is to test the same Zn-I chemistry as the benchtop scale, but with about a liter of total electrolyte. Also need to get a battery cycler working for the larger currents needed at this scale, have two solutions for this right now, most likely is a MightyWatt electronic load I already have set up as a cycler (like here: http://kaktuscircuits.blogspot.com/2015/09/mightywatt-as-li-ion-charger.html).
Hi all, and apologies for the delay! This year has started off with quite a lot of administrative burden for me and I haven't had as much time for research as I anticipated.
@Santiago-Eduardo said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery:
Elektrolyte:
The group noticed that two slightly different electrolyte compositions are mentioned.
Sorry for the confusion, the correct mass composition can be found in the documentation here: https://fbrc.codeberg.page/rfb-dev-kit/electrolyte.html, the masses listed will prepare approximately 10 mL of electrolyte.
@Santiago-Eduardo said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery:
They assume an 880 ml volume for one single cell. Do you estimate this volume to maintain the obtained results until now? Is this the volume foreseen to achieve the 22 Wh/single large-format cell?
Yes this would be correct volume scaling for the large-format cell, although of course still a lot smaller than an eventual life-size system! It is basically t]e volume that we will end up using for our tests of the large-format cell (still to come).
@Santiago-Eduardo said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery:
The group is assuming the EE value to estimate this. This value does not include energy demand from pumps and electronics, correct?
Correct, these losses are often summed up in RFB literature as "balance-of-plant" or BoP if you want to search for some values.
@Santiago-Eduardo said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery:
Meaning: to store 1 Wh, 1.56 Wh needs to be taken from the grid (excluding electronics and pumps). Does this make sense, or are we oversimplifying here?
You've got it exactly!
@Santiago-Eduardo said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery:
Used electricity
For the same purpose of modelling the use phase, it is important to define from which country and what type of energy/electricity is being used to charge the electrolyte. Since the users of the FBRC battery can be anywhere, but are currently mostly centered in Europe, the group has decided to choose the European electricity grid mix data to represent the current FBRC reality.
This makes sense to me.
@Santiago-Eduardo said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery:
The separator, for instance, would be one of these peripheral impacts, since it would need to be replaced after some cycles (probably faster than the electrolyte). Since cycle durability of photo paper is still unknown, the group will model different scenarios from 10–100 cycles in steps of 30 cycles. Do you feel this is a reasonable range? Do you already now conditions such as density and flow rate the larger cell will work with? The group will assume 4 layers for the larger cell although in some parts are 3 layers stated.
While separators can be replaced, I am doubtful in an industrial system that they would, due to the labor costs. From my understanding, Li-ion lifetimes are often given as 2,000 cycles to 80% of initial capacity; for flow batteries, the data isn't as solid, but for VRFB the lifetime claims are more on the scale of 20,000 cycles or 20 years, whichever comes sooner (taken with a grain of salt...). We haven't done any testing that long-term, so don't have much for your to extrapolate, but RFB technoeconomic papers with operation and maintenance (O&M) costs incorporated would give you a good idea of membrane/pump replacement
frequency (if ever). I would increase the cycle range to much longer terms, with the upper end in the 1,000s at least.
We aren't yet locked-in on flow rates for the large cell as we are still settling on choice of pumps and flow field design.
@Santiago-Eduardo said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery:
The current BOM and building instructions do not provide specific links to purchase the necessary chemicals. To model the electrolyte production, including the transportation of each chemical, the group has assumed the following production locations based on market data and worldwide production trends. If your own experience differs in this, please do not hesitate to comment.
These assumptions all make sense to me; Daramic separator (which we also use in addition to paper depending on the test) can/is produced in the EU though not exclusively.
I hope this clears things up for you all somewhat, and again, sorry for the delay!
@gus said in Following your documentation – feedback & questions:
However, it is a more energy-consuming solution, so it doesn’t seem suitable as a final approach for a large battery system.
This "pulling through the cell" configuration is only possible with peristaltic pumps on the small scale, centrifugal pumps wouldn't handle this, due to net positive suction head/cavitation issues---this approach wouldn't end up in a real, real-world system, but we're going to recommend it for now at the benchtop scale to make testing easier!
Also, @Santiago-Eduardo mentioned you'd need parts by weight, manufacturing process, and material---this is certainly possible, though of course the design will evolve. I think it makes much more send to to this with our "large-format cell" (https://codeberg.org/FBRC/RFB-large-format-cell) as it is closer to a real system, than our dev kit (https://codeberg.org/FBRC/RFB-dev-kit), which is used to test new electrolytes and materials.
I think we can just build columns for weight, manufacturing process, and material, into the BOM of the project (which is currently in the README at https://codeberg.org/FBRC/RFB-large-format-cell). It will also eventually include tubing, pumps, reservoir, etc.
Rieke & the rest of your team,
First off, apologies for the delay! It's been quite a busy period, I'm sorry to keep you waiting.
I personally think Option 1 would be more useful in terms of research output. While end-scale RFBs will have systems to address potential leakage - and leakage can certainly happen (see https://fbrc.nodebb.com/topic/54/the-ultimate-demise-of-my-last-redflow-zcell) - leakage should not happen, at all, period. It is a design/system failure that should be extremely rare and controlled for, and systems will usually already have a form of secondary containment, so that leakage doesn't enter the local environment. It would be hard to quantify in the ways you ask, since normally if there's a leak, you stop everything, fix the source of the leak, and start over.
For Option 1, the electrolyte and membrane choice certainly do affect each other, but also strongly affect the system as a whole, independently. I think it would be hard to just isolate to their linked effects between electrolyte and membrane.
@Rieke-Huesmann said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery:
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
At FBRC, we have selected membranes that are easily available (ruling out exotic ion-exchange membranes), affordable (so no Nafion), and chemically compatible with the electrolytes we test (so, in neutral/acidic aqueous media, oxidizing/reducing conditions).
Purely in terms of material properties, a good membrane will have a high selectivity-it lets the ions you want (supporting electrolyte ions, e.g. potassium, chloride) through, and blocks ions you don't (e.g. charged triiodide molecules). Normally, an ion-exchange membrane (IEM) will allow either cations or anions through. Because there are no good cheap IEMs available for our use, we have just been using paper and other porous separators designed for batteries, like Daramic (designed for lead-acid systems). These are not very selective, but they are good enough for our use. A bonus of porous separators is that they are more conductive than IEMs, which leads me to...
Conductivity - this is just Ohm's Law, V = IR. You want the membrane's resistivity R to be as low as possible, so that the voltage drop across the membrane V, which is wasted energy, is as low as possible at a fixed current I. Resistivity is simply the inverse of conductivity. Again, we don't actively screen for this, because we find Daramic and paper to work well enough for testing - but it is because they meet our criteria. Nafion would certainly be more selective, and give us higher couloumbic efficiencies, but would be less conductive and cost way more (probably worse environmentally too, since it is fluorinated and has a complicated manufacturing process vs. porous separators).
So, to resume: availability, affordability, selectivity, conductivity (you want all of these values to be high!).
• Measured efficiencies of the current electrolyte-membrane selection
Here are the rough efficiencies for the system, they are likely slightly improved with some modifications we've made since this blog post: conditions, and results.
• Background on membrane selection in the development kit (e.g. which specific materials were chosen and why)
addressed above, I hope!
• How is the material wear currently counteracted (replacement only)?
Right now, we use a new membrane/separator for each test, in order to have repeatable results. It's possible to replace separators in a real stack but it would be very labor intensive/cost-prohibitive in a real stack. To my knowledge, I haven't heard of companies replacing membranes in the field, unless they have a big failure and they're under warranty - they probably just send the whole stack back to the factory and replace it with a new one, I'd wager.
• How is waste (wastewater, solid waste, co-products from chemical manufacture) disposed of?
Great question! We don't really have good answers on that. You'd have to look into the specifics of Nafion or lead-acid battery separator production (a very established industry). Also, for the chemicals we work with, they are all available at scale already: zinc chloride, potassium iodide, etc. I'd hope these are known already for their supply chains? I don't have knowledge here I'm afraid. Established chemical commodities like those probably don't have much waste, but could generate co-products as a result of their manufacturing. Iodine and zinc are both recycled, certainly.
At the end-of-life of an envisioned, full-scale RFB system - an inorganic electrolyte like Zn-I could be recycled with conventional chemical processing means (pH adjustment, precipitation, filtration - lots of techniques for aqueous inorganics). The reservoirs and stack could be recycled, but I doubt immediately reused. Metal current collectors, those are recycled easily. Plastic reservoirs, tubing, stack components - "recycled", as much as plastic is actually recycled - probably incinerated if we're looking at what happens nowadays... The used graphite felts may be able to be recovered or recycled - not sure. Used separators, again, possible to recycle. The main thing is, we don't know much about recycling of RFB stacks is - because not many of them have been built and actually reached end-of-life. They are, though, easy to take apart, which makes separating the constituent components very simple. And, for inorganic electrolytes, there are many established ways to recover the starting compounds, or to re-use in a new RFB system. This is an approach for vanadium RFB companies, some of which try to "lease" their electrolytes for periods of 20 years, because it effectively doesn't degrade (i.e., the vanadium isn't going anywhere).
I hope this helps, again, sorry for the delay! After the holidays/new year I will be much less busy (December was rough) and so I'll be able to answer more rapidly!
This is great sepi! A calibration wizard would be excellent, thanks for taking this on. I cloned your repo and was able to launch it on my PC, happy to help test in the future!
