416931 Electrochemical CO2 Separation Using Membrane-Electrode Assemblies

Thursday, November 12, 2015: 3:36 PM
155B (Salt Palace Convention Center)
Nicholas R. Schwartz, Douglas Diez, Philip Cox and Justin J. Hill, Mainstream Engineering Corporation, Rockledge, FL

Chemical, biological, radiological, and nuclear (CBRN) environments pose a direct threat on military personnel, first responders, rescuers, and victims. Respirators and self-contained breathing apparatus (SCBA) equipment are used to protect against airborne contaminants by isolating the user from the surrounding environment by providing a contaminant-free source of breathing air directly to the face mask. Current SCBA systems use an isolated O2 source, a CO2 scrubber, and positive pressure for protection. Removal of CO2 is achieved by adsorption, which adds excessive heat and moisture to the circulating breathing gas loop. This makes the environment uncomfortable and can even become hazardous for the user. Smart, reliable, and high-performance CO2 removal is required to ensure protection without limiting the abilities of the operator.

A CO2 removal system using membrane electrode assembly (MEA) technology to electrochemically separate CO2 from an exhaled breathing within a breathing loop has been demonstrated. A catalyst-coated anion exchange membrane (AEM) was used to separate CO2 from a humidified breathing gas mixture. Pt was used as the CO2 reduction catalyst, which assists to convert CO2 into bicarbonate ions. These ions are transported by diffusion and the applied potential through the AEM. An oxidation catalyst, such as Ni, IrO2, or RuO2, can convert the bicarbonate ions into the rejected CO2. Removing CO2 with an MEA eliminates heat and humidity with standard adsorption beds and enables control using feedback from breath monitoring sensors.

Several membrane and electrocatalyst materials were evaluated for electrochemical CO2 separation. A Pt-Ni and Pt-RuO2 MEA were fabricated and demonstrated over a range of temperatures and CO2 concentrations to measure CO2 flux and efficiency. MEA polarization and electrochemical impedance response will be discussed under various environmental conditions. Under optimal conditions a Pt-Ni MEA achieved a flux of 1.10 L/m2·min using 10 mA/cm2 at 1.6 V. The Pt-RuO2 MEA held to 10 mA/cm2 maintained an average voltage of 1.03 V. Ion transport and charge transfer mechanisms pertaining to membrane and catalyst structure and composition will also be discussed.

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