Solar power on the Moon suffers from the month-long Lunar rotation which necessitates enough energy storage to last through the 2 week Lunar night.
An alternative to battery storage would be a closed-circuit hydrolysis/fuel cell with H2 storage.
Electrolyzers sometimes use proton-exchange membranes, as do fuel cells.
If a combined electrolyzer/fuel cell were paired with solar cells and metal hydride H2 storage, it could function as a “hydrogen battery”. For a given charging rate, the H2 battery capacity would be proportional to the H2 storage capacity. The longer the storage period, the more this is potentially a cost/weight advantage. There could also be benefits of integrating with other aspects of a Lunar “Hydrogen Economy” such as propellant production or use as a reducing agent in manufacturing.
Another potential application is on the long, inactive period in an interplanetary Cycler orbit.
Question: Do reversible proton-exchange membrane hydrolizer/fuel cells exist? Have they been incorporated into a “Hydrogen Battery”?
hydrolysis
tag then after thinking further I rolled back my edit because "water-splitting" is going to be an important thing in the future of spaceflight whenever one needs to make rocket fuel or keep those pesky humans alive! It's right up there with CO2 splitting, but I don't know a fancy/general name for that. But if we're serious about maintaining the tag, it would probably have to be added to a lot older questions. $\endgroup$