Tuning the Half-Wave Potential and Binding Constant of PAQ Molecules for the Enhanced O ₂ -Tolerant Electrochemical CO ₂ Capture Process

The O2 sensitivity of electroactive organic quinone molecules in the field of electrochemical-mediated carbon capture (EMCC) restricts their electrochemical CO2 capture/release process. In this work, 9,10-Phenanthrenequinone (PAQ) was chosen as a capture carrier to precisely regulate the half-wave potential E1/2(Q–1/Q–2) and the CO2 binding constant KCO2 through intermolecular hydrogen-bonding networks between alcohols and reducing quinones. The electrochemical behavior of PAQ was systematically evaluated when different alcohol hydrogen-bond donors were introduced. A Hammett equation was constructed for alcohol hydrogen-bonding systems to quantify the theoretical relationship between electronic structure parameters and macroscopic electrochemical properties of alcohol alkyl groups. The experimental results indicated that proton donors with smaller pKa values and steric hindrance were more likely to form stable intermolecular hydrogen-bonding networks with reduced quinones. Density functional theory confirmed that hydrogen-bond networks obviously reduce the free energy of the inherent reaction system of PAQ, which is the main reason for achieving a better balance of the two key parameters. When the ethanol (EtOH) concentration was 0.66 M, the E1/2(Q–1/Q–2) of PAQ anodically shifted to −0.85 V vs Ag/AgCl; simultaneously, an appropriate Log(KCO2) (8.55) was still maintained at this time, and the estimated minimum energy consumption of the electrochemical system was 50.94 kJ/mol, which was significantly lower than that of the original electrolyte (73.43 kJ/mol). This suggested that constructing intermolecular hydrogen-bonding networks is beneficial for alleviating the O2 stability problem of quinone molecules with strong CO2 complexation.