# Would a hydrogen/oxygen fuel cell be a good choice for energy storage and generation in H2 rich atmospheric environments?

So imagine an atmospheric probe sent to enter the atmosphere of a giant gas planet. There would be no need to store hydrogen since a compressor or an inlet with sufficient dynamic pressure would allow sufficient $\ce{H2}$ to enter the system in the upper atmosphere. The output would be basically limited by dynamic pressure and max output of the cells. $\ce{O2}$ would be delivered from a pressure vessel or cryogenic tank (seems possible, it's cold in the shade in space) and valve regulated.

Besides low operation temperature, what would be the drawbacks?

An "inverted" $\ce{H2/O2}$ fuel cell should work well, and be easier to maintain than one in an $\ce{O2}$ atmosphere, because there are a plethora of membranes to pass pure $\ce{H2}$ (e.g. hot platinum, plastics, ceramics...). That means that the cell would be less likely to be poisoned by trace gases.

It would also be possible to use methane, common on gas giants, in a fuel cell.

That said, carrying the oxygen in the probe from Earth to the target would take energy. A fuel cell might be useful for a short-lifetime probe, such as one penetrating deep into a gas giant's atmosphere, only to be crushed in a few days. For a longer lifetime, nuclear thermoelectric power (e.g. MMRTG) is more practical.