Direct air capture of CO2via cyclic viologen electrocatalysis

Abstract

Electrochemical direct air capture (DAC) can leverage renewable electricity to reduce atmospheric CO₂ levels via energy-efficient organic redox couples. However, current organic systems are threatened by oxidative degradation when explosed to air. In this work, we propose an electrochemical process to regenerate hydroxide absorbents via cyclic viologen electrocatalysis (CVE). This strategy isolates the redox-active viologens from the alkaline absorbents to avoid oxidative degradation and vaporization loss. Tuning the viologen substituent is needed to facilitate fast reaction kinetics in the electric fields present under reductive and oxidative environments. We show that di-polar viologens, which contain both positively and negatively charged groups, can overcome electric field repulsion during reduction and oxidation. We demonstrate a minimum work of 0.82 GJ per tCO₂, calculated based on the cyclic voltammetry redox potentials, and a work as low as 3.8 GJ per tCO₂ in a practical two-electrolyser CVE configuration with over 200 hours of stable operation.