Electrochemically Facilitated Transport of CO₂ between Gas Diffusion Electrodes in Flat and Hollow Fiber Geometries

Electrochemically mediated CO₂ separations have drawn increasing attention as a possible route to modular, inexpensive, and low-energy carbon capture technologies. Two-stage electrochemical systems that combine activation with capture and deactivation with CO₂ release have the potential to operate close to the thermodynamic minimum for CO₂ separations. Cells based on supported liquid membranes between two gas diffusion electrodes are one of few examples that achieve this true two-stage operation. In this work, we demonstrate a multitubular electrochemical separation cell, where planar gas diffusion electrodes are replaced by porous, tubular electrodes. This cell can be designed with an array of anode and cathode tubes placed in varying arrangements and of different sizes, opening a vast design space to match the process chemistry to system design and potentially produce enhanced performance. Thus far, the only published examples of electrochemical membrane separation devices have utilized pH gradients or water splitting to drive their operation, though our group and others have long proposed the use of redox-active organic sorbents in ionic liquids to eliminate solvent loss. To perform our tubular cell demonstration, we first demonstrate at bench scale the continuous separation of CO₂ from 15% CO₂ in N₂ feed, with the release at 100% CO₂, utilizing a glyme-modified quinone (NQ-G2) that is infinitely soluble in many ionic liquids. This demonstration also illustrates the need for the design of future redox-active organic sorbents to focus on not just the reduction potential of the sorbent but also the separation from the oxidative wave. Combined, this work illustrates many important routes forward in electrochemically mediated CO₂ separations.