Oxygen Generation by Carbon Dioxide Glow Discharge and Separation by Permeation Through Ultrathin Silver Membranes

A six Torr CO2 glow discharge in combination with a heated W mesh-reinforced ultrathin Ag membrane is used to generate molecular oxygen. The Ag membrane is a commercially available 25-mu m-thick Ag foil backed by a 25-mu m-thick W electroformed mesh. The permeation flux is inversely dependent on the membrane thickness and exponentially dependent on the membrane temperature. Calculations show that a pressure differential of 1 atmosphere can be supported by the W mesh/Ag foil membrane at temperatures up to 350 degrees C. In this work, a glow discharge for pressures between 2 and 15Torr CO2 and temperatures up to 500 degrees C were reported. The DC glow discharge was produced initially with a solid Ag rod cathode, 2 mm in diameter, and then with a 7-mm-diameter Ag rod machined into a hollow cathode, located 5mm from, and normal to, the Ag membrane anode. The voltage was varied from 440 to 620 VDC with currents up to 41 mA. A stable flux of 1.61x10(15)O(2)molecules.cm(-2).s(-1) is observed for a membrane temperature of 450 degrees C and a CO2 pressure of 6Torr. With similar to 4-m(2) surface area, this approach is competitive with the present mission qualified Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) system planned by National Aeronautics and Space Administration (NASA) for the 2020 Mars rover mission which generates approximate to 12g/hr O-2. The proof of concept technique presented herein can be substantially improved by further reduction of the membrane thickness, refinement of the cathode, and glow discharge plasma.