My adventures building a DIY Mn/Fe flow battery

[Patrik L]

Good to hear and I am glad you explored another venue for the structure material. Super excited about the qualification of this separator and how it will compare to commercial grade. But, even if the time period between service is less compared to commercial separators, that might not matter since a new one can be manufactured

 

[danielfp248]

I replaced my old potentiostat with a mystat potentiostat from this paper (https://www.sciencedirect.com/science/article/pii/S2468067220300729). I had it made on pcbway and shared it on the site so anyone interested can order their own. (make sure to select PCB+assembly to get the full board) (https://www.pcbway.com/project/shareproject/MyStat_Potentiostat_9df57df2.html). Also make sure you read the description for notes on the power supply and cable needed for the electrodes.

This potentiostat has an extended potential range (-11 to 11V) and an extended current range (up to 200mA).

 

[cafuffu]

Daniel, i've been reading on your work and i'm mighty impressed, kudos to you! I've been recently wondering though about a flow battery chemistry that would use the O2 from the atmosphere, so that one half of the redox reaction is basically free, making the battery cheaper and more energy dense. Have you considered that option when deciding on the chemistry to use?
There's some literature on sulfide-air flow batteries but they seem to be problematic. I wonder if there are other options.

 

[danielfp248]

Daniel, i've been reading on your work and i'm mighty impressed, kudos to you! I've been recently wondering though about a flow battery chemistry that would use the O2 from the atmosphere, so that one half of the redox reaction is basically free, making the battery cheaper and more energy dense. Have you considered that option when deciding on the chemistry to use?
There's some literature on sulfide-air flow batteries but they seem to be problematic. I wonder if there are other options.

Thanks for posting and reading my content!

It is very difficult to create these batteries in a durable manner. There are mainly 2 issues faced by batteries that use O2. The first is that they require effective transport of oxygen containing species, which only happens under very basic conditions in water. This makes poisoning of the battery by CO2 from the air a huge problem. The CO2 forms carbonates, which are not electrochemically active and clog the battery.

Another is that these batteries will tend to form some insoluble oxide in the electrode, which is often poorly conductive. This makes the energy efficiency of the batteries lower and also generates "dead zones" in the cathode.

For the above reasons, I don't consider these chemistries, as they require material engineering beyond my DIY capabilities.

 

[danielfp248]

I have been doing some preliminary studies using the Fe-EDDHA/Mn-EDTA system using my current flow battery setup. So far it seems that it won't be a viable solution for DIY. I have written a blog post detailing some of the problems https://chemisting.com/2023/07/01/problems-with-the-fe-eddhamn-edta-flow-battery-system/.

 

[cafuffu]

Thanks for your reply, and sorry to read about the problems with the Fe-EDDHA. So the problems with an air breathing battery are due to the water, basically. I wonder if some other solvent could be used, i'll try to do some research.

 

[Patrik L]

oh no ...

 

[gnuorder]

I stumbled on your posts and found them interesting. I was hoping this would be a cheap renewable DIY project but I guess if it was, there would be more commercial options. Reminds me of making potato batteries in school. Maybe that deserves looking into. Hopefully with a byproduct of Vodka.

 

[danielfp248]

For anyone who was interested in this thread, you might be interested in my new thread on Zn-I flow batteries https://diysolarforum.com/threads/my-adventures-building-a-diy-zn-i-flow-battery.69145/. This now includes actual experimental results of flow batteries I've built.

 

[Vorg]

You talk about Iron Salt and Manganese salt, but call it a Manganese/Iron battery. I see a lot of talk about Iron/Salt flow batteries, but they seem to be saying salt water as in Sodium. Maybe it was mentioned some were in the pas 8 pages, but I take these are two different batteries. And if so, what was the reason for not going Iron/Salt?

 

[danielfp248]

You talk about Iron Salt and Manganese salt, but call it a Manganese/Iron battery. I see a lot of talk about Iron/Salt flow batteries, but they seem to be saying salt water as in Sodium. Maybe it was mentioned some were in the pas 8 pages, but I take these are two different batteries. And if so, what was the reason for not going Iron/Salt?

Pure Fe batteries are great in that the Fe is extremely cheap. There are however two main issues with them (for me):

1. They need very acidic electrolytes (HCl 3M), which are unsafe to keep and use at my house.

2. They have extremely high levels of H2 generation, which makes their CE really bad. Since I run the batteries in close loop systems, the H2 generation causes pressure buildups which end up causing big problems (mainly leaks) which are much worse in an acidic electrolyte.

 

[Vorg]

Ok, I was thinking it had something to do with using high salt levels since salt likes to eat a lot of metals.