@sepi If you have an assembled cell with everything except the pumps you can use a syringe to manually pump some liquid through and see if you have any obvious leaks. This is how I normally test cells before I put activate material inside them or cycle water through them using pumps.
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My build (very slowly progressing) -
Blog: czahl's build@czahl This is how I've done the sealing too. You have to press quite hard with your finger. Good thing is that the print must be good for this to work, otherwise it just won't seal, either because the edges are warped or because it escapes through the top or bottom.
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My build (very slowly progressing)@sepi Nicely done! Also don't forget to wrap your screws in packing tape before you assemble the device for testing, otherwise the screws will short the cell.
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My build (very slowly progressing)@kirk Thanks for clarifying kirk, I have the same issue, lol.
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My build (very slowly progressing)@sepi Great job starting to print PP! Your pieces look good! You don't have to remove the packing tape, if the tape stays on the piece when you put it inside the cell, it's fine, the PP tape is basically melted onto the piece and it's the same material, so it's chemically compatible with the electrolytes too. If you want a clean result without tape I would recommend either using the special PP surface from Prusa or buying a surface from PPPPrint (https://www.ppprint.de/en/produkt/surface/). Both of these solutions worked great for me.
Also, I would say the gasket can probably seal those surfaces well enough, provided the piece is water tight.
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Blog: czahl's build@czahl good work! Getting PP to seal is not very hard, but you must do a few things. For these prints it's important to
- Increase your number of horizontal shells to a large number (6-10). Vertical shells should be at least 5-6.
- Increase the extrusion multiplier slightly (1.05)
- Use outer and inner brims to make sure the inside part doesn't warp either.
- Increase the infill/perimeters overlap value to a higher value (I used 45-50%).
- Print at 100% infill.
- Use PP tape or use a surface specifically made for PP printing (I use the Prusa PP surface).
I attach my prusa slicer configuration bundle in case that's useful.
FF_config_bundle.txt -
Alternative Electrolytes@muntasirms Thanks for sharing. This is all very interesting. I have made several experiments with Zn/Fe fully symmetric cells (since Zn plates preferably over Fe), using glycine as a chelating agent to make sure Fe stays soluble at mildly acidic pH on the catholyte side. It hasn't really worked very well, I see big increases in ohmic resistance as a function of time, but I don't see any iron oxides forming on the cathode or on the membrane. I don't see full dissolution of the plated metal though, so I bet it has something to do with the oxidation of that metallic deposit (since probably some Fe+Zn alloy is depositing anyway).
I have never tried WISE electrolytes in flow batteries, and had actually never read the Fe+MgCl2 paper you mentioned. I just ordered MgCl2 and CaCl2, so I'll give that a try as soon as I have those salts! If we can get 1M FeCl2 work with MgCl2, then that would be amazing as a demonstration for the kit at both small and large scales.
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RFB University@sepi Let me answer your questions:
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Several modern batteries - Like Na/S - use ceramics as separators, so do several batteries in development, like solid Li-ion batteries. Ceramics are hard but they are also very brittle, the ionic conductivity of something like terracotta is also very low, so the way they increase ohmic resistance is very high. You might be able to create a very bad battery with one, but for anything close to practical, your common pottery sources are most likely not gonna cut it without heavy modification. For this reason ceramics used as separators that can support high current densities have to be extremely thin and have to be engineered to have high ionic conductivity. For a flow battery, where membranes require flexibility, they are not generally a good fit on their own. With that said, maybe you could try sandwiching a very thin layer of terracota between two photopaper layers, or just wetting the photopaper in a terracota suspension and drying it, see what you get.
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These flow channels are usually machined into an electrode, such as a graphite plate. This complicates the fabrication process significantly when compared with something like 3D printing. This is because the graphite has to be bipolar electrode material (cannot be regular graphite because liquids can leak through normal graphite plates) and usually gaskets are needed to properly seal these devices. This increases the cost and complexity to the point where it is only accessible to academic/industry players with significant resources or people with a lot of experience in machining. Services like Xometry will not do machining of graphite bipolar plate material.
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Yes, that's exactly what would happen. For a 2M solution charged to max SOC delivering around 250mWh of stored energy, 10mL of solution would heat up around 20C.
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The Nernst equation gives the electrode potential of a redox half-cell or cell under non-standard conditions, accounting for temperature and the concentrations of reactants and products via the reaction quotient. It’s a thermodynamic equation that relates to free energy, and while it doesn't describe reaction kinetics, it helps predict the direction and favorability of redox reactions. It is applicable away from equilibrium, and when the system reaches equilibrium. It doesn't predict or influence kinetics.
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Yes. The higher the overpotentials, the lower the voltaic efficiency.
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New member introduction thread!@czahl Welcome to the community Christian! We look forward to your fabrication journey. Please feel free to open up a thread to share your progress with us, that way it will be easier for you to ask questions as you advance and build a successful kit.
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All-copper@Vorg The reaction is not of elemental iodine with Zinc metal, it is of triiodide with Zinc metal. While this reaction is very exothermic, it is not explosive in this context because of a few reasons:
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While all the Zn is deposited at the same spot the oxidized iodine is distributed through the entire catholyte volume, so if the membrane ruptures it takes a while for the reaction to happen, it doesn't all happen at once.
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There is a lot of water here, which carries a lot of thermal load. While you can generate a lot of heat on membrane rupture, it isn't even enough to boil the solution at 100% SOC (from my experience). Per point 1, only a small fraction of iodine is able to react at any given point and for more to react flow must be present.
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Zn here is bulk Zn, it is not powedered or finely divided at all
I have seen this happen experimentally at high SOC at 2M KI using photopaper. The membrane ruptured at high SOC and what I saw was the volume all shift mostly to one side and the potential drop very quick. Nothing exploded, melted or anything that dangerous. Untreated photopaper is obviously not intended to be a long term use membrane, it is intended as a viable membrane to carry out short term testing that is very easily accessible. To use it long term it is necessary to increase its lifetime with a PVA coating or something along these lines.
The most dangerous scenario in my experience is solid iodine forming in the cathode, blocking flow and causing tubing to unhook, this then splashes charged electrolyte, which is a considerably greater hazard. The use of triethylene glycol seeks to mostly prevent this scenario, but it is still possible if very high currents are used or the cell is overcharged to high potentials (>1.6V).
With the above said, the anolyte and catholyte hold a lot of energy and mixing them obviously instantaneously discharges all that energy. At 10mL of total volume this is not much, around 250mWh but when using larger volumes this is a considerable risk and larger scale devices must be created and tested with this potential scenario in mind.
About the copper, oxygen in it would ruin the electrolyte because it would oxidize Cu+ to Cu+2 and this reaction would also increase the pH of the anolyte. This would eventually cause Cu hydroxide to fall out and kill the device. To recover the cell you would need to purge the electrolyte with Argon, cycle the solution over Cu metal to reduce the oxidized Cu2+ back to Cu+ and add hydrochloric acid to adjust the pH back to the proper level if necessary. To run a cell like this you need to make the system quite airtight and ensure the electrolyte is purged with Argon from the start.
An idea to test for a period under oxygen-present conditions is to keep a piece of sacrificial copper in the anolyte reservoir to make sure that any Cu2+ that is formed is reduced back, so that way you would only succumb to the slow pH up creep. However this means that the CE you measure isn't really fair, because you are not accounting for a huge chunk of active material present there. It can be useful however to cycle and perhaps get some insights into other sections of the system under a regular atmosphere. However I don't honestly know if this is good enough, as the reaction of Cu+ with oxygen is quite fast.
The copper chloride (I) initial electrolyte is usually prepared like this (under copper metal) to make sure there is no Cu2+ present when first loading the electrolyte into the device.
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