Which fuel cell fuels have been demonstrated in space?

Question

Combination of fuel cells and electric motors - whether it has been used as part of an electric pump-fed cycles? gives a short summary of fuel cells and lists the following energy-containing fuels that can be used to produce electrical power in cells which are optimized for them; I don't think you can just pour any fuel into any cell.

Fuel cells are very versatile in terms of fuels they can use (hydrogen, methane, hydrocarbons, hydrogen peroxide, hydrazine etc.)

Hydrogen fuel cells (together with batteries) were used for electrical power in the Apollo program, where it was recombined with oxygen on board to produce electricity.

Question: Beyond H₂ + 2O₂ → 2H₂O, which fuels have been "celled" to produce electrical power in space? Successful proof of principle demonstrations would certainly count.

I noticed that energetic materials like peroxide and hydrazine are mentioned above, so please include a simple summary of the reaction; hydrogen and hydrocarbons would require comparable quantities of an oxidizer, where as the others might be "monofuels" in the same way that they can perform as monopropellants.

related:

• Does the Soyuz spacecraft chemically stabilize its hydrogen peroxide (H₂O₂) to remain ISS-dockable for 200+ days?

Answer 1

The only actual missions I have found that used fuel cells have been Gemini, the Apollo service module, and the Space Shuttle. Perhaps there have been others (e.g. Russian), but they didn't show up in my searches. (Russian solar panels have worked well, so why change things?)

In each case, the reactants have been hydrogen and oxygen. This produces water as a product, which can be used for drinking water, rehydrating food, bathing, and cooling (coolant loops, evaporative cooling). There even was an experiment that fed monkeys water from a fuel cell for 14 days, to see if it was safe.

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As far as theoretical reactants, this paper evaluates rocket propellants as fuel cell reactants. In particular, they studied

1. Hydrazine
2. Hydrogen
3. Reformer gases
4. Oxygen
5. Nitric acid
6. Dinitrogen tetroxide
7. Hydrogen peroxide

Notice how the eventual choice of hydrogen + oxygen is covered by these options.

NTRS also has a 1966 PhD dissertation from MIT on a methanol-oxygen fuel cell. I've seen such a cell sold as a cell phone charger. Cute idea, but who keeps methanol around their home?

Most of the research on fuel cells has been about the electrodes, electrolytes, catalysts, and membranes. There are hundreds of papers, and a fair amount of information haphazardly scattered in this collection of articles, but Wikipedia's article is a better starting point.