Modeling Electrochemical Direct Air Capture of CO2 using Redox-Functionalized Electrodes

Abstract

Increasing research attention is being devoted to designing electrochemical systems that can capture CO2 from air and thus mitigate climate change, as decarbonization of the energy sector is occurring very slowly. The low concentration of CO2 in air however makes large scale, energy-efficient and rapid CO2 capture challenging. Understanding how the energetic cost of CO2 capture depends on operational and material parameters that describe electrochemical systems is important for designing practical and cost-effective devices.We have previously shown that electrochemical CO2 capture is possible using a pH swing cycle that is driven by proton-coupled electron transfer (PCET) involving organic molecules [1]. More recently, we have begun to consider a new design for electrochemical CO2 capture in which PCET-active species are conformally attached to the internal surface area of a highly porous electrode, and effect a reversible pH swing in an adjacent layer of aqueous electrolyte upon redox cycling. We develop a continuum reaction-transport model that simulates reactive CO2 capture into and release from the electrolyte layer, as well as transport of (bi)carbonate species, and protons, in response to an applied current or voltage. The model permits an assessment of the energetic cost of CO2 separation under various current densities and concentration gradients, and decomposition of that cost into thermodynamic, kinetic, mass transport-related and Ohmic contributions. We then highlight potential pathways to achieving an energetic cost of CO2 capture from air of 100 kJ/molCO2, and discuss preliminary results from an experimental prototype.[1] Jin. S, Wu M., Gordon R., Aziz M., Kwabi D., pH Swing Cycle for CO2 Capture Electrochemically Driven through Proton-Coupled Electron Transfer