Proton coupled electron transfer mechanism in low-energy electrochemical CO2 desorption from Tiron-mediated amine solutions

Abstract

Electrochemical carbon capture offers a low-energy alternative to thermal desorption, yet remains limited by sluggish electron transfer and solvent–electrode mismatch. Herein, we address these challenges by integrating the proton-coupled electron transfer (PCET) mediator Tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt, QH2) with tertiary amines methyldiethanolamine (MDEA) and diethylethanolamine (DEEA), and systematically optimizing the electrode surface through heat treatment, acid treatment, and phosphorus doping. MDEA's compact structure enabled denser hydrogen-bonding and more uniform H⁺ distribution, thereby enhancing PCET kinetics, as supported by molecular dynamics (MD) simulations. Density functional theory (DFT) results further revealed that functional groups such as P–OH promoted interfacial charge transfer, reduced the work function, and improved solvent–electrode interactions. As a result, phosphorus-doped graphite felt (P-GF) in MDEA achieved a low desorption energy of 0.62 GJ per ton CO₂, nearly 60% lower than that of the untreated counterpart. This study demonstrates a viable pathway to enhance electrochemical CO₂ desorption through synergistic optimization of redox mediators, electrode interfaces, and solvent environments.