Could O2 be used in a fuel cell instead of H2, for example could we use electricity to extract O2 from CO2 and store it in a fuel cell (like Hydrogen). I guess O2 wouldn't be as powerful as H2 but would it be viable?
Fuel cells work by combining H2 with O2. If the fuel cell had only O2, what would you combine it with? But then the O2 would not be the fuel, it would be the oxidizer. Of course, many things will combine with O2. But to call it a fuel cell, it needs to make electricity directly, without any mechanical intermediate step. There are things that are more oxidizing that O2. Fluorine, for example. But they are all more dangerous than O2; and the system costs for any fuel cell using them would be very high. The nice thing about O2 is that it's free, you can get it from the air.
