You aren't taking into account the energy cost of separating substances from each other (understandable, since this isn't widely taught outside of chemical engi

You aren't taking into account the energy cost of separating substances from each other (understandable, since this isn't widely taught outside of chemical engineering). You can't get electricity by separating dilute carbonic acid from water, or CO2 from air. It's like trying to take the salt out of soup after you've oversalted it. Much better to stop before adding too much.