oxygen generating hvac

10.30: gear/hvac/oxygen generation:
. instead of worrying about filtering air;
use daytime`solar to turn water into {oxygen, hydrogen},
then use hydrogen for night-time energy,
and inject oxygen whenever low .
. does it matter that co2 is high if oxygen is normal? .
. how does space get water if they are using it for oxygen ?
they could use plants instead,
and they use batt's for night-time .