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I apologize if this is a silly question. The reason I ask is I'm wondering if it would be possible to build a fuel cell that runs on body fat. I know ones for butane exist, could they work for this? If not, is there any good reason it isn't possible?

Basically I'm imagining some kind of flexible inductive charger in your hand, or wrist for a smart watch, and connected to a fuel cell that's connected to the circulatory system and runs off body fat.

It just seems silly to lug external batteries along on long on bike rides when the whole point of the ride is to get rid of excess chemical energy anyway.

I obviously don't have the skills to pursue this, but I just want to know if the dream is silly. :)

Thanks!

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It is certainly possible to oxidize fats electrochemically, but there are a few problems with the idea that I can think of:

  • Triglycerides do not flow freely through the blood as they are too hydrophobic and are instead carried by lipoproteins that would have to be removed. Similarly, free fatty acids are transported bound to serum albumin.
  • The blood concentration of triglycerides and fatty acids is relatively low most of the time in healthy individuals.
  • Existing fuel cells that work on fatty acids seem to be mostly microbial fuel cells, which are quite slow.

I think it would be more practical to use glucose from blood instead, using an enzymatic fuel cell, as blood glucose levels are relatively high and the oxidation is easier to accomplish (though there are still a lot of technical challenges to be resolved—biofouling, efficiency, device lifetime, etc.).

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  • $\begingroup$ Thanks a glucose based fuel cell looks like something that is in active development. Very exciting! $\endgroup$ – netsplit Oct 1 '15 at 19:18
  • $\begingroup$ Glycerol might make a good fuel for fuel cells. There is currently a glut of it on the market. $\endgroup$ – iad22agp Oct 1 '15 at 19:29

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