A kinetic approach to electrochemical CO₂ capture 

Electrochemical CO₂ capture (eCCC) offers a scalable, low-cost route to CO₂ mitigation by exploiting redox-active organic mediators (RAOMs). While RAOMs enable efficient capture cycles, their reduced forms are highly sensitive to O₂, leading to performance limitations. Previous thermodynamic analyses suggest that increasing the redox potential decreases oxygen sensitivity, but also weakens CO₂ binding, revealing a fundamental tradeoff.  

We present a kinetic study of O₂ reactivity in phenoxazine-based RAOMs. Controlled electrochemical generation of the dianion species of phenoxazines enabled the direct measurement of its reaction rate with O₂, by using a dissolved oxygen probe and  initial-rate analysis. Results reveal that the O₂ reaction rate constant increases with pH (consistent with dianion dominance), providing strong evidence for the dianion being the underlying cause of O₂ sensitivity. Moreover, redox potentials correlated positively with O₂ rate constants, offering insight into the underlying mechanism involved in O₂ reactivity.

These findings highlight that potential tuning alone cannot resolve the O₂ sensitivity challenge, but rather a mechanistic, kinetic understanding of O₂ reactivity is essential for designing stable RAOMs for practical eCCC.