Can you store electricity with a fuel cell

[Abstract_Kerman]

do fuel cells only withdraw electricity or can you deposit power with the same hydrogen used to store it? 

[Dman979]

Moved to Science and Spaceflight, the subforum for all real sciencey and spaceflighty things.

[KSK]

Not sure I understand the question.

Taking a proton exchange membrane (PEM) cell as an example, it will combine hydrogen and oxygen to generate water and electricity. Basically you've got two catalytic electrodes separated by a membrane. The first electrode catalyses the conversion of hydrogen gas (H2) to protons (H+ ions) and electrons. The protons travel across the membrane (hence proton exchange membrane) to the second electrode, where they combine with oxygen molecules (O2) and electrons to give water. The two electrodes are connected via whatever external circuit you're driving with the fuel cell.

In principle I guess you could run the cell as an electrolyser to split water into hydrogen and oxygen. As a practical matter I'm not sure how well that would work - PEM cells are finicky beasts - simple in principle but engineering them to be robust, gas tight and cheap enough for the mass market is challenging (source - I was a patent examiner in a previous life and one of my subject matter areas was fuel cells and batteries) Along with the problems of storing reasonable quantities of hydrogen, it's the reason why fuel cells didn't really take off as vehicle powerplants, despite all the 'hydrogen economy' hype.

Take that with a slight grain of salt though - that previous life was quite some time ago and the state of the art in fuel cells may have moved on quite a bit since then.

Edited August 5, 2017 by KSK

[YNM]

Technically, you can - it's called hydrolysis. But I'm not sure about their efficiency.

 

EDIT : There might be a good reason why we use lithium nowadays - they're light and the oxide form doesn't stick too much. While water is even lighter, probably they bond more "strongly", and gaseous hydrogen AFAIK aren't the one usable for fuel cells.

Maybe, if we find some catalyst for breaking water, they'll be useful. Plants have done this for millenia.

Edited August 5, 2017 by YNM

[StarStreak2109]

I once took part in a study that investigated the use of hydrolysis to store energy during off-peak times and use it to provide energy during peak times. The efficiency is lousy, but it could work due to the changes in energy prices. Anyway, back to the question at hand: yes, you can use hydrolysis to store energy and release it again with the fuel cell, but it is overly complicated AFAIK and there are much more efficient ways to store energy...

[Abstract_Kerman]

7 hours ago, KSK said:

Not sure I understand the question.

a fuel cell takes power from the hydrogen can you put the power back in the hydrogen?

[Tex_NL]

14 minutes ago, Abstract_Kerman said:

a fuel cell takes power from the hydrogen can you put the power back in the hydrogen?

No, not with a fuel cell. It would be trying to 'un-burn' a log by compressing the smoke and ash back and expect to get wood.

But you can split the waste water produced by a fuel cell back into oxygen and hydrogen. It's called electrolysis.

[DDE]

1 hour ago, Abstract_Kerman said:

a fuel cell takes power from the hydrogen can you put the power back in the hydrogen?

To put it in another way, a fuel cell effectively burns hydrogen with oxygen (which isn't a problem on Earth, but in space...) to produce water as an exhaust. Not much functional difference from a hydrogen internal combustion engine, which is why the ACES will be using a small motor and not fuel cells.

Yes, it is quite possible to break that water back into hydrogen and oxygen. Electrolytic water-cracking is use to produce oxygen on the ISS, with hydrogen dumped overboard.

Edited August 5, 2017 by DDE

[wumpus]

I think what you want is a "flow battery".  I can't say they are ready for use.  A quick look at the wiki includes a graph that shows a bunch of types of batteries and the virtues of each, but has a lot of holes implying issues that keep such things from real use (and some certainly don't last for many cycles). https://en.wikipedia.org/wiki/Flow_battery

Hopefully these work better than trying to use electrolysis to drive a fuel cell.

[DDE]

And then don't forget yet another option - the momentum wheel.