How Can an Aluminum Air Fuel Cell Design Be Improved to Address Common Issues?

[hamiiiii]

TL;DR

New idea for an aluminum air battery

Hey everyone,

I had an idea for making an aluminum air battery that mitigates some of the problems. The draft is quite rough but I just made it now and I can improve it as I go along. So basically the idea is the aluminum will cut up into large grains/pellets in a fuel tank. The pellets will slide via gravity into a cone shaped well (which can be closed using a hatch when battery is not in use) where there sits a wire mesh (which is positively charged via an external power source) to keep them from falling into the electrolyte. Directly inside the electrolyte close to the well is another different mesh which is negatively charged. The idea is the voltage difference, combined with the proximity to the electrolyte, will break the electrons free from the aluminum atoms and cause them to dissolve into the electrolyte with minimal hydrogen evolution. The wire mesh in contact with the aluminum will carry the electrons out to the load into the cathode.

The aluminum ions react with ambient oxygen to form aluminum oxide, which drains from the cathode into a tank. To speed up the reaction and increase power, a compressor would feed air into the cathode where it would maintain pressure.

To avoid the issue of cathode clogging, there is a couple of solutions, one is to move the cathode around to shake loose the deposits (not sure if this idea would work, but putting it out there). Two is to have a separate type of liquid in the cathode, one that can dissolve the alumina deposits and conduct the OH- ions. An ion permeable separator could separate the electrolyte from the liquid to ensure mixing does not occur. Three is to pressurize the electrolyte to increase solubility (again. not sure how well this would work).

This is a rough idea I just thought of now, I'm curious to know what other people think.

 

[Baluncore]

Welcome to PF.

What needs to be added at a refilling station?
Does it consume both aluminium and electrolyte?

What is the exhaust from the process?
Does it produce a wet aluminium oxide cake?

Is there a rechargeable aspect to the chemical cell?

 

[hamiiiii]

 

[hamiiiii]

Welcome to PF.

What needs to be added at a refilling station?
Does it consume both aluminium and electrolyte?

What is the exhaust from the process?
Does it produce a wet aluminium oxide cake?

Is there a rechargeable aspect to the chemical cell?

Hi,

The idea is that the aluminum oxide would be drained and the aluminum pellets would be added at a fuel station, not recharged like a battery. It would be more like a gas car. The electrolyte would not be consumed as adding a new electrolyte every time you fuel up would be expensive.

Concerning the discharge products, I haven't finalized how exactly they will be drained into the discharge tank without draining the electrolyte, but yes, it would produce an aluminum oxide sludge.

 

[Baluncore]

I see separation of the Al₂O₃ as a dry biscuit would be a challenge. You would need to recover electrolyte from the wet mash, or purchase more electrolyte.

Aluminium is referred to as 'solid electricity', due to the large amount of electric power used in its production. I expect Al metal would be a relatively expensive fuel.

Have you considered ways that you might fuel the cell with empty aluminium beer cans, helically cut into a long thin strip, that can be fed into the cell at the required rate?

 

[hamiiiii]

Hi,

Yeah honestly the main premise of this whole design is mitigating the self corrosion issues by storing the fuel away from the battery. The pellets and feeding the fuel into a cone submerged in the electrolyte is honestly just one way of supplying the battery with the fuel but I don't see why it couldn't be done another way. The beer cans could be mashed together into foil and then slowly fed into the battery via a roller. That would ensure more surface area for the reaction to occur, the foil would have to be pressured against the wire mesh to maintain good current flow.

The electrolyte separation is an issue, I didn't really give a ton of thought to it yet. A possible solution would be to constantly pressurize the electrolyte via pumping through a filter that will filter out the solid Al2O3 and drop it into a tank? The constantly pressurized and swirling electrolyte would dissolve and wash away the deposits from the cathode and ensure it remains clean. The filter would pick up the alumina particles and this would be dropped into a tank. The electrolyte and filter could be changed every so often similar to the oil changes on a car (albeit not regularly).

 

[Baluncore]

With an aluminium strip feed, the electrode would not be a mesh. The electrode would be the aluminium strip fuel.

I believe the Al₂O₃ will be impossible to remove, without the loss of a great mass of electrolyte.

Chemical disposal may be expensive. What is the electrolyte?

 

[hamiiiii]

With an aluminium strip feed, the electrode would not be a mesh. The electrode would be the aluminium strip fuel.

I believe the Al₂O₃ will be impossible to remove, without the loss of a great mass of electrolyte.

Chemical disposal may be expensive. What is the electrolyte?

Ah I see what you are saying. I could place a slight positive charge across the aluminum strip to prevent hydrogen evolution and also allow the electrons to flow through it through the circuit. That would work pretty good.

I'm not too familiar with battery chemistry so I couldn't really say which particular electrolyte I had in mind, but I did see that aluminum air batteries use NaOh as the electrolyte so possibly I could use that?

So would filtering the Alo3 out from the electrolyte not work as the Alo3 is too hard to filter? What would the reason be?

 

[Baluncore]

Al₂O₃ is the hard mineral corundum.
As a big crystal, it is the gem ruby or sapphire.
It will be produced chemically in the form of a fine abrasive paste, saturated with hydroxide electrolyte. It will pass through fine filters, and will not dry out without an energy expensive process.
https://en.wikipedia.org/wiki/Corundum

 

[hamiiiii]

Perhaps I could use something similar to this setup then, with the aluminum foil feed system. As the aluminum is converted to AlOH3, it is fed out of the battery into a box.