Mechanism of CO₂ Capture and Release on Redox-Active Organic Electrodes

Abstract

The mechanism of faradaic electro-swing for CO2 capture/release on a redox-active organic electrode is studied from the point of view of realizing a reversible process for CO2 separation. First, the cyclic voltammograms (CVs) of two redox-active organic monomers, anthraquinone (AQ) and 2,1,3-benzothiadiazole (BTZ), were measured under a CO2 atmosphere. The waveforms of CVs of the two redox-active organic monomers are altered under a CO2 atmosphere relative to a N2 atmosphere. There is a change in the number of redox waves from two to one for AQ and a change from reversible to irreversible waves for BTZ. To further understand the mechanisms of CO2 capture/release on redox-active organic compounds, redox-active polymer electrodes coated with polyanthraquinone (PAQ) and polybenzothiadiazole (PBTZ) were investigated using a spectroscopic analysis known as in situ attenuated total reflectance–surface-enhanced infrared absorption spectroscopy (ATR–SEIRAS) as well as density functional theory (DFT) calculations. The CVs measured with two redox-active polymer electrodes have more positive shifts of reduction potentials for PAQ and PBTZ under a CO2 atmosphere than under an N2 atmosphere, as measured versus Ag/AgNO3: −1.8 and −1.4 V → −1.4 and −0.9 V for PAQ and −2.5 V → −2.1 and −1.9 V for PBTZ. In addition, the oxidation current on the PBTZ electrode disappears only under a CO2 atmosphere. DFT calculations indicate that the positive shifts of reduction potentials in the two electrodes under CO2 conditions are due to an exergonic adsorption reaction of CO2 onto the redox-active organic compounds. To clarify the reaction behavior between CO2 and the redox-active organic electrode, an ATR–SEIRAS spectroscopic analysis was performed. Infrared peaks are observed at 2200 and 2100 cm–1 for PAQ and PBTZ electrodes, respectively, under a CO2 atmosphere, which have been confirmed by measurements under a 13CO2 atmosphere to have adsorbed CO2. The wavenumbers corresponding to the CO2 molecules adsorbed on the two electrodes are different. These findings indicate that one electron reduction and CO2 adsorption for each redox-active organic compound are occurring simultaneously. The calculated adsorption energy of CO2 for two redox-active organic electrodes indicates that the adsorption energies of two CO2 molecules for AQ and BTZ are −7.3 and −36.3 kJ/mol. The larger adsorption energy in BTZ than that in AQ is clearly related to the disappearance of the oxidation current. However, both adsorption energies indicating adsorption of CO2 onto organic units are less than the covalent bond energies of common organic compounds, indicating that such weak adsorptions are suitable for the faradaic electro-swing of CO2 capture/release on the redox-active organic units.

Organic Polymer Dots Photocatalyze CO2 Reduction in Aqueous Solution

“…As one PFBT can only be single‐electron reduced during photocatalysis, we simplified our analysis by representing one PFBT polymer using a repeating block unit. Moreover, guided by reports that reduced benzothiadiazole exhibits interaction with CO 2 as evident from IR spectra, [28] we adopted the perspective that benzothiadiazole could serve as the active site in Pdots, particularly because several recently reported heteroatomic organic molecules have shown electrocatalytic CO 2 reduction [29]…”

“…As one PFBT can only be single-electron reduced during photocatalysis, we simplified our analysis by representing one PFBT polymer using a repeating block unit. Moreover, guided by reports that reduced benzothiadiazole exhibits interaction with CO 2 as evident from IR spectra, [28] we adopted the perspective that benzothiadiazole could 12 CO 2 , (b) purging with 13 CO 2 . (c) Time-related PL decay of the PFBT Pdots in water when purging with Ar (green circle, noted as "PFBT + Ar"), CO 2 (yellow circle, noted as "PFBT + CO 2 "), and adding TEOA under Ar (purple circle, noted as "PFBT + TEOA").…”

Exploiting thiolate/disulfide redox couples toward large-scale electrochemical carbon dioxide capture and release

“…Moreover, the ECCR devices are easy to scale up or down, and thus offering opportunities to utilize the intermittent and decentralized electricity generated from renewbles. 14,15 To our best knowledge, three main types of organic redox-active molecules (Lewis bases) have been actively investigated to date, i.e., quinone, [16][17][18][19][20][21][22][23][24] bipyridine, 25,26 and phenazine 27 . Among them, quinone is the most extensively studied owing to its mild reduction potential and moderate CO2 binding affinity.…”