Guide to Making you own Iron Battery

So, when looking for a cheaper alternative to Vanadium batteries, I stumbled upon all iron chemistry,  the absolute cheapest battery chemistry possible, using only iron, the most mined element from Earth's crust. The metal so cheap that its literally the basis of human civilization. No need to heat the battery, no need to check supply chains, Iron is so abundant that you can find it wherever humans are.

I was convinced, Gemini gave me the broke college kid solution. So I ordered Iron chloride from the internet, you know how much lab grade 500g highest purity cost me ? Rs 800 ($8), that's pennies as compared to Vanadium. So before I give you step by step procedure of building you own Iron Redox Flow Battery we need to understand how it works.

Working of Iron Redox Flow Battery

Similar to Vanadium, Iron redox flow battery has iron on both sides, on both sides it is in Fe2+ state, when it charges on the positive side it converts Fe2+ to Fe3+ (loses 1 electron) and on the negative side it gains electron and Fe2+ converts into Fe 0, or solid iron is plated onto the negative electrode.
 
So when not charged, it is green on both sides, when charged, it is brown on one and faint light green  on another and results in charged voltage of 1.21 volts. In order to reach 1.21 volts, you need to provide extra electrical force (voltage), hence you need to use an AA battery with 1.5 volts of charge (or a current source if you have a lab or are rich 🤑🤑)

Source

Let's Build One

So here's what I did, what you will need, and what didn't really work. 
Search CAYREX on Youtube, he is one of the best guys to DIY this. He has explained every part of the battery properly, what grade of material to procure and has even assembled and dismantled his battery multiple times. Cayrex was one of the first videos I watched to understand what's going on. You can find his VRFB playlist here. 
Now we are operating under the assumption that Vanadium and Iron batteries are same, so for a DIY experiment, CAYREX designed stack will work. 

Here's what i ordered online, I found these items relatively cheaply in India, my whole 1 cell stack was built for around Rs 5000 ($50), due to small lab scale parts. Here's everything I used -
  1. 3d printed end plates- 2
  2. 3d printed flow plates - 2
  3. Graphitic carbon felt (5mm thick)
  4. Daramic or Celgard Separator
  5. M4 nuts and bolts- 10
  6. Peristaltic Pumps
  7. 6mm silicon tubing (OD)
  8. Scissors 
  9. Copper Sheet
  10. Neoprene Rubber Sheet (shore 70 A, 1mm thick)
  11. Thin graphite sheet or graphite foil
  12. A single AA battery
You can find the STL files for 3d printed plates here, I recommend using PETG as a material as it is the most chemical resistant and hard as compared to other filaments, print at 100% infill.

Preparing the electrolyte -
⚠Caution - Please use rubber gloves and wear a mask, these are corrosive substances that can cause staining and lung irritation.
First you have to decide the volume of electrolyte you require, I recommend starting with 100 mL each side at 1M concentration, so in order to prepare 200 ml electrolyte you need -
  1. 200 mL deionized or distilled water
  2. 16 grams of ferric chloride (FeCl3)
  3. 6 grams of Steel Wool (grade 0000)
  4. 5-10 mL hydrochloric acid
  5. Ascorbic Acid tablets (pure Vitamin C)
  6. Closed plastic bottle (I used PET bottle)
Don't use iron nails or mild steel filing, I wasted 2 weeks trying to dissolve them. Also the reaction is pretty slow, it will take around 2-3 days at room temperature, if you want to speed it up, I recommend heating the solution, but in a water bath and to not more than 50°C. Then also it took me around 2 days as I had to control heating and cooling.

#Note- If you leave the solution to heat and don't actively monitor temperature, it will start boiling and turn black, this means you need to put acid in it to restart the reaction .

Remember, we have to take the solution from brown to light green. Try to not stir the solution after initial mixing as black carbon precipitate will form at the bottom of the bottle and will have to be removed. Keep the bottle closed during the reaction as the solution reacts with oxygen very quickly and converts back into brown.

Once you have the green liquid, weigh it, if 100 ml of it weighs around 110 grams, you are good to go. I suggest you follow the assembly procedure and piping sequence as suggested by CAYREX. Before you start pumping the liquid electrolyte, I recommend doing a leak test with water.

Because after i put it all together, it leaked, very badly, so I did what any other guy with a leaking stack would do: ask AI to fix it 😁😁. So it started giving suggestions, one of them was using Anabond 666 RTV, its basically a gasket glue, if you put it between two surface and leave for 48 hours, it becomes soft silicon and stays there. Works beautifully. So I opened the stack, applied Anabond on all gaskets and flow plates and re-assembled it. Remember Anabond should not touch and active electrical components, graphite felt, membrane, current collector, apply it around the components on the gasket and plates.
After 48 hours, it finally stopped leaking. So i soldered wires onto current collectors and connected it to a AA cell, and it didn't work...... so i gave up, stopped the pumps and went to sleep.

AND IT WORKED !!!!!

How ? That's the next post. 
Iron Redox Flow Battery in charged state - 27th January 2026


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

Mayank Jately

If you want to follow this blog


Comments

Post a Comment

Popular posts from this blog

Introduction to the Blog

What's the one thing you cannot imagine modern life without ? Phones ? AI ? Social Media ? These are relatively modern inventions, commercialized in the last two decades. Let's go farther back - Cars, Trains ? Ships ? Planes ? still hardly a century old. Personally, my answer would be energy. From food you eat all the way to content you consume, everything is essentially some form of energy.  And i don't think any person reading this will need to be told that even today, most of humanity's energy comes from fossil fuels (petrol, diesel, crude oil etc), basically carbon that took 300 million years to form, which we dig up, process, and burn in seconds But energy is changing, fast and its happening at a historic pace, EVs, batteries, green hydrogen, solar, wind, hydropower, nuclear fission (hell maybe even fusion !!! ). Just to put that in perspective the amount of solar energy we deployed in the last 12 months (511 GW)is equal or may be more than the electricity demand o...
Read more

What exactly is a Redox Flow Battery ?

Image
We all know what a battery is, that same thing in almost every portable electronic device in your room has. Most batteries we use in our day to day are static batteries, i.e. once they are manufactured, their chemical composition doesn't really change. Now the chemicals used in a battery dictate everything about it, like its - 1. Cyclability  2. Efficiency 3. Safety 4. Supply chain constraints. Let me explain in a little more detail using examples - The AA and AAA batteries (chemical composition is Zinc and Manganese) normally used in T.V remotes are not rechargeable, they are single use. Once the energy inside them is used them, they are pretty much dead. They are mildly toxic, but safe to use, efficiency doesn't come into picture as they can't be recharged, energy density is ( 50-150 Wh/kg ) The Lithium Ion batteries in your phones and EVs are rechargeable (Duh !). Its of many types, i am aware of only two- a) NMC (Nickel Manganese Cobalt along with Lithium)  b) LFP (Lith...
Read more

Why Vanadium Leads Flow Batteries and Why I Didn't Build One.

Image
Search flow batteries anywhere on the internet, you'll find Vanadium's monopoly, ask any AI model about flow batteries and they'll assume vanadium and give you all the information. That's because Vanadium Redox Flow Batteries (or VRFBs in short) are already being commercialized, or at least they're trying their best.  I'll try to explain why, but before i move further, i forgot to explain the redox part in the last 2 posts. All Batteries are Redox Batteries- Batteries have 3 basic parts, positive side (cathode), negative side (anode) and a membrane or separator. So, when you connect a charger to your phone, the charger takes electrons from positive and gives it to the negative side, but if the positive and negative mix together they will neutralize each other, so they need to be separated by separator (or membrane). The word "redox" is made of two words : Reduction- gaining of electrons (by the negative side) Oxidation - loss of electrons (by the posit...
Read more