Flow Battery Research Collective

Posts

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  Only Fe system
  D danielfp248

  Did a few cycles at low SOC and then attempted to cycle at 10Ah/L.

  

  Catholyte (left) anolyte (right) below:

  

  pH of catholyte was 0.24 and anolyte was 4.7. As you can see on second cycle to 10Ah/L the CE dropped from 93% to 83% and then capacity continued to decrease. On disassembly a lot of unreacted passivated iron remained on the anode, likely due to the pH increase. As Fe deposits water activity likely increases, which increases HER, which increases pH and leads to Fe passivation.

  I am going to run a test adding 1M ZnCl2 to the electrolyte, to see how the additional salinity changes water activity and metal passivation.

  Electrolyte Development

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  Only Fe system
  D danielfp248

  I prepared a bulk amount of solution to have a more standard mix. This is 90g MgCl2, 32g FeCl2.2H2O, 2.5mL 15% HCl, 0.75g of Ascorbic acid. Volume to a total 200mL using a volumetric flask, then transferred to store here.

  Initial MgCl2 addition was done in a 1L beaker over around 150mL of reverse osmosis water, added HCl after, then Fe, then ascorbic, then waited to cool, transferred to volumetric flask to finalize vol, then put into storage.

  If you prepare this be very careful as MgCl2 reacts very exothermically with water. Cool the water in an ice bath and add slowly.

  Final solution is perfectly clear.

  The above correspond to molar concentrations of around 0.98M Fe and 4.7M Mg.

  The HCl is to ensure complete dissolution of any Fe3+ hydroxyde/oxide contamination and the ascorbic acid is to reduce any present Fe3+ into Fe2+. Excess ascorbic has to react on initial charge, so it will eat into a tiny bit of the SOC.

  

  Electrolyte Development

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  New member introduction thread!
  D danielfp248

  @StevenHickey Awesome to have you here! Very excited to see someone here with so much experience in flow batteries. Since you have so much experience in Zn-Br I wanted to ask if you have had any chance to test the Zn+Na sulfamate chemistry that was published not long ago. I tried it with some success, but had some stability issues https://chemisting.com/2026/03/23/zn-br-sulfamate-battery-stability/. Would love to hear your opinion on that subject.

  General Discussion

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  You Tuber Video on an open source all Iron battery
  D danielfp248

  The cost per kWh of this is too high, the use of organic materials and ion exchange membranes puts this closer to what people do in academia and further from the cells that can be reasonably fabricated using DIY approaches. The use of an ion exchange membrane likely reduces the lifetime of this cell a lot. For a static cell, I think the sulfuric acid Cu/Mn battery we have discussed before is far more promising. That chemistry requires no exchange membranes, uses only commodity inorganic materials and cycles to 30-40Wh/L.

  For pure Fe batteries I am much more inclined to the Fe flow batteries.

  General Discussion

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  New Zn-Br chemistry using Na sulfamate
  D danielfp248

  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.

  Electrolyte Development

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  My Suction Luer Lock
  D danielfp248

  Thanks for sharing your pictures! It always makes us very happy to see anyone reproducing the kit independently.

  You can see my current setup below:

  

  I am testing the double reservoir with spill-over communication (that's why the reservoirs look different and are at the center). My pumps are connected in a suction configuration and they enter and exit the cell on their sides. When you have pumps in a push-through configuration having the flow going from bottom to top is important to push air out, but when you suck through the cell the vacuum will push all air out and fill the entire cavity, almost regardless of how you pump. I haven't seen any air being trapped there (no bubbles are evident when shaking or moving the cell so that the flow is in either direction).

  As you can see I have changed some connections to luer locks, except the connections for the pumps. I however like how you've made them ALL luer locks, much simpler to disassemble.

  As you can see I'm also testing the new clamp-compatible end-plates and clamp. This works SO much easier than the screws, since the compression is centered I am also experiencing fewer problems with the cell and slightly better energy efficiencies since the felt compression seems to be more uniform. Opening and closing this cell is a breeze compared to the screws. I used PLA with 80% infill to print the end plates but I am sure PETG will work great too.

  About the PP, it is a bit tricky to find the PP and printer settings that work best for water tight results. I am using the Ivor white PP from smart 3d, which has worked well on the prusa core one. In any case, let me know if there's anything I can help you with.

  General Discussion