Is it Possible to Build a Direct Borohydride Fuel Cell

[CrazyEgg]

Basically as the title says, is it possible to build a DB fuel cell stack? Something that could output 100W (to power a laptop or for power outages). I actually have access to a couple of kilos of sodium borohydride and while looking at what I can do with the stuff I came across this type of fuel cell. I'm guessing that it would be cheaper to build than an equivalent power hydrogen fuel cell because of not needing platinum catalysts right?

So have you guys got any advice for this project. Mainly if it is possible and if so how to build one and cost estimate.

Thanks

 

[Topher925]

Its very possible to build one and I recommend that you do as long as you know what you're doing. I believe (not 100% sure about this) DBFCs use liquid electrolytes consisting of a high molar alkaline solution such as potassium hydroxide so a lot of effort is going to be needed to find the right electrode materials and making sure the thing is safe to operate.

I'm not that familiar with DBFCs as I am with other FC technology but I think I have some good resources on how to construct and build one that I can post later. DBFCs are a relatively new and lightly studied technology to info about them is rather limited.

 

[Topher925]

It seems I was mistaken. DBFCs generally use nafion as an electrolyte. This is kind of surprising because I would think H202 formation would significantly shorten the life of a cell.

 

[CrazyEgg]

Can you give me some more info on these fuel cells, when I search for borohydride fuel cells the majority are for how to use sodium borohydride as a hydrogen storage medium.

How would I go about making one?

Also regarding hydrogen peroxide if I remember correctly they wanted to use that instead of atmospheric O2, but I would want to use oxygen, if I build one of these fuel cells.

 

[Topher925]

What kind of information do you require? Design, materials, fuel/oxidant delivery? Do you have a cost or performance target in mind? If you just want to make a DBFC that just works I would start by looking at how low temp AFCs and PEMFCs are designed since they are very similar in concept. DBFCs are a fairly new technology and haven't been heavily researched so information will be hard to come by. I've never built one myself (obviously)however I've built a few PEMFCs and am familiar with AFCs. I certainly don't know all the answers but will help you with what ever I can.

 

[CrazyEgg]

Sorry for not getting back to you sooner Topher.

Well for cost and performance, I have a budget of about $500 but I'm willing to go to $600 if I can make a fuel cell with an output of 100 watts.

Ideally, I would really like a list of the materials I would need and a set of instructions to actually build one as I have never built a proper fuel cell before.
The one I made a couple of months ago is in the link below, you can't get usable electricity from it and it uses hydrogen as fuel.
http://sci-toys.com/scitoys/scitoys/echem/fuel_cell/fuel_cell.html

Would a simple cell be a sandwich of electrodes with a layer of nafion in between them as this particular fuel cell doesn't need platinum?
Will a perforated metal sheet work as an electrode?

 

[Topher925]

To be honest, I don't really have a complete bill of materials for designing a DBFC. Most of my experience is only with PEM fuel cells which is a bit of a different breed although similar in concept.

I do know that you can use either a cation exchange membrane (like nafion) or an anion membrane depending on what ions you want to transport. I know most DBFCs use Nafion, mostly because its so readily available. There's a lot of different flavors of nafion and also some great nafion alternatives from companies like Fumatech: http://www.fumatech.com/EN/Onlineshop/fumapem-fuel-cells/

For monopolar/bipolar plates, corrugated or perforated stainless steel and maybe even nickel might probably work. I think NaBH4 is relatively inert but it is electrically conductive so you may want to do some research with what materials you want to use. I've mostly used sintered graphite for PEM and DMFC fuel cells as it works well and is cheap but can be difficult to machine if you're not experienced.

As for the electrodes, well that's the most difficult part. I can tell you what methods I have used before for making the electrodes for PEM fuel cells, and the same may work for DBFCs but I'm not sure. You can use Pt/C for the catalyst, and while it works the best, its not the only option. Iron tetramethoxyphenyl porphyrin (FeTMPP), Ag, and Ni have been shown to work well in DBFCs although I don't believe they perform as well.

As for your fuel cell size, if you're shooting for 100 watts of power you are most definitely going to want to go with a fuel cell stack unless you have a very good DC-DC converter or a load that likes to run at 0.5V and 200amps. Now this is where the serious engineering comes in. Because NaBH4 is electrically conductive, its can be very difficult to design a fuel cell stack that won't short itself out. A lot of thought will need to go into the manifolding and sealing in order to make sure the stack doesn't kill itself. You may even want to first try building a smaller low power FC stack or individual fuel cell to help with the learning curve.

 

[CrazyEgg]

I'm pretty sure I can get all the materials and maybe even some alternatives to see if there are any differences between each setup. As for lowering the power how about something that produces only 10 watts, would a single cell be able to produce this or will I need a stack even for this amount of power?

Could you tell me about the order the layers need to be arranged in?

 

[Topher925]

You could probably get 10W out a single cell but I think the smallest active area you could do it with is 50cm^2 probably.

The layers go something like;

end plate - current collector - mono/bipolar plate - diffusion media - electrode - membrane - electrode - diffusion media - mono/bipolar plate -current collector - end plate

 

[CrazyEgg]

The fuel cell idea is on hold at the moment, I've had a lot of coursework and exams to work on. That's why there has been a long delay in replying.

Also thanks for listing the layers that need to be in each cell but do you think that you can say what the material of each layer should be?
As for you mentioning using platinum-carbon catalysts, I thought that one of the advantages of using a DBFC is not having to use an expensive catalyst.

Is there a possibility for you to build a small one for me? Obviously, I could pay for the parts and labor.