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

The O 2 sensitivity of electroactive organic quinone molecules in the field of electrochemical-mediated carbon capture (EMCC) restricts their electrochemical CO 2 capture/release process. In this work, 9,10-Phenanthrenequinone (PAQ) was chosen as a capture carrier to precisely regulate the half-wave potential E 1/2 (Q –1 /Q –2 ) and the CO 2 binding constant KCO 2 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 p K a 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 E 1/2 (Q –1 /Q –2 ) of PAQ anodically shifted to −0.85 V vs Ag/AgCl; simultaneously, an appropriate Log(KCO 2 ) (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 O 2 stability problem of quinone molecules with strong CO 2 complexation.