“It is simply to simple and easy to go with tried and true ways of ending life.”
The best method of execution is to simply put the perp in an airtight chamber and remove the air. It works like a charm and produces a euphoric feeling in the perp. Hell, give him/her a foofoo drink or a 6 pack. It only takes a tiny amount of time.
You are thinking of an air tight chamber and removing the CO2 as the perp uses up the O2.
The euphoria occurs as the brain becomes oxygen starved. Excess CO2 causes pain so removing the CO2 removes the pain of asphyxiation.