Why I don't rely on Bismuth to fix my Battery problems

In my previous posts I have written a lot about the trident of problems with Iron-Chromium Redox Flow Battery, which are - 

  1. Hydrogen Evolution Reaction
  2. Slow Chromium Kinetics
  3. High operating temperature for the battery
Now if you ask an AI (Gemini in my case), one of the first answers it will give would be Bismuth as master solution to all 3. It stops Hydrogen evolution and makes chromium react faster, hence solving all the problems of the battery. It does that by acting as a catalyst. It forces the Cr3+ to accept electron quickly and react faster, and it has a more positive electrode potential (+0.32 V), as compared to chromium (-0.41 V), this stops water from splitting into hydrogen.


But first you need to understand how Bismuth is incorporated in the battery -

The Mechanisms-

In order to use bismuth or any other catalyst in a flow battery, you have 2 choices -
  1. Electrodeposition-  Dissolve bismuth chloride in the liquid electrolyte and when you apply voltage onto the battery, it temporarily plates onto the electrode (negative electrode in our case). 
  2. Permanent deposition- Dissolve bismuth chloride in acid and immerse the electrode (carbon felt) in let it soak for some time. Then put this in a furnace and heat it to 400°C, this will cause the bismuth to be deposited permanently on to the electrode. Acting as a catalyst forever in the battery.
I don't want to dismiss Bismuth as a catalyst, it was researched on extensively by NASA, and it is really effective it is one of the few catalysts well known as a solution to these problems. But I asked a few experts and read some research papers and here is what I found.
  • Electrodeposition has a certain voltage at which it happens, translation- sometimes bismuth does not always deposit, sometimes if the voltage fluctuates, it may not deposit, and well....... the battery may not charge. That's not good.
  • This research paper shows that thermally deposited bismuth has a tendency to form bismuth carbide while sticking with carbon felt long term, this is catastrophic, why ? Because it goes rogue, it does everything it had to prevent. It supports Hydrogen Evolution and reduces the voltage of the battery, that's worse than not having bismuth at all.
And these are the problems ASIDE from the gut wrenching price of Bismuth Chloride (Rs 3000 or $30 per 100g, if you are lucky).

So much money for a not so good of a solution. Really have to look for alternative catalysts, or what do you know  maybe I'll search around and come back full circle 😉😉.

None of this is AI generated, so feel free to fact check me and looking forward to your views and help. 

Mayank Jately

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