Intramolecular Hydrogen Bond-Stabilized Redox Mediator for Oxygen-Resistant Electrochemical CO2 Capture from Ambient Air

Abstract

Electrochemically induced direct air capture (DAC) has emerged as a compelling strategy for mitigating anthropogenic CO2 emissions. However, a critical bottleneck remains the O2 sensitivity of redox-active molecules, which directly degrades both capture efficiency and energy economy. Herein, we report a hybrid flow cell based on the proton-coupled electron transfer (PCET) of tribenzo[a,c,i]phenazine-10,15-dione (TBPDO) that drives pH-swing DAC. The O2 tolerance is enhanced by inducing intramolecular hydrogen bonds in the reduction product (r-TBPDOH2), which kinetically suppress O2 attack by lowering the local electron density at the oxygen center via intramolecular O–H···N═C interactions and extended π-conjugation, as confirmed by density functional theory (DFT) calculations. Consequently, this carbon capture system achieves a release/capture efficiency of 92%, a Coulombic efficiency of 81%, and an energy consumption of 149 kJ mol–1CO2. This work establishes intramolecular hydrogen bonding as a kinetic protection strategy against parasitic O2 oxidation, offering a molecular design principle transferable to other PCET-based electrochemical systems.