(740h) Electrochemical CO2 Separation Using Membrane-Electrode Assemblies

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.