(22f) 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. Thermodynamic analyses indicate that two-stage electrochemical systems combining 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 multi-tubular electrochemical separations cell, where planar gas diffusion electrodes are replaced by porous, tubular electrodes. This cell can, in principle, be designed with an array of anode and cathode tubes placed in varying arrangements and of different sizes, opening a large design space to match the process chemistry to system design and potentially produce enhanced performance. We demonstrate at small scale the continuous separation of CO₂ from a 15% CO₂ in N₂ feed to the anodic fiber, with release to a 100% CO₂ sweep stream in the cathodic fiber, utilizing a glyme-modified quinone (NQ-G2) that is infinitely soluble in many ionic liquids. The quinone is reduced at the anode, where it complexes with the CO₂, before diffusing to the cathode where, on oxidation, it releases the CO₂ to the sweep stream. The preparation and characterization of the electrodes will be discussed, as will the need for 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.