Non-negligible Axial Ligand Effect on Electrocatalytic CO₂ Reduction with Iron Porphyrin Complexes

Abstract

Iron(III) porphyrin complexes have been demonstrated as one of the efficient molecular catalysts for the electrochemical reduction of CO 2 . However, the role of axial ligands coordinated with a metal center in the complex on the electrochemical CO 2 reduction activity has not been fully explored yet. Herein, iron(III) tetraphenylporphyrin thiocyanate (FeTPP-SCN) is synthesized from a commercially available catalyst of FeTPP-Cl by a counteranion exchanging reaction. Cyclic voltammetry measurements showed that the catalytic activity of FeTPP-SCN is noticeably suppressed in the DMF solutions. The structural dynamics of the axial ligand in FeTPP-SCN are further examined by the FTIR and ultrafast IR spectroscopies, where the SCN ligand is employed as the local vibrational probe. Vibrational relaxation measurements showed that the reorientational dynamics of SCN ligands was strongly restricted in DMF solution, suggesting that the subtle electrostatic interaction between the ligands and metal center in the complex can have a non-negligible effect on its catalytic activity.

Further Understanding the Roles of Solvent, Brønsted Acids, and Hydrogen Bonding in Iron Porphyrin-Mediated Carbon Dioxide Reduction

“…Further investigation of the influence of electrolytes on CO 2 reduction in different solvents will be useful. We also note that a range of FeTPP complexes in DMF and in MeCN have Faradaic efficiencies over 90% for CO production, 43,49,60 which we assume to be the case here.…”

Customization from Single to Dual Atomic Sites for Efficient Electrocatalytic CO2 Reduction to Value‐added Chemicals

“…As expected, the experimental results indicated that with the introduction of the electron‐absorbing group cyano, the electron density of the Ni metal center was reduced, while the electrocatalytic CO 2 RR efficiency was greatly improved after the electron‐rich methoxy modification. Similarly, the catalytic activity of FeTPP modified by strong electron‐absorbing cyano groups was significantly lower in DMF solution compared to FeTPP−Cl [75] . However, the active site modified by electron‐absorbing groups can also promote the conversion of CO 2 to CO at a certain voltage.…”

“…Similarly, the catalytic activity of FeTPP modified by strong electron-absorbing cyano groups was significantly lower in DMF solution compared to FeTPPÀ Cl. [75] However, the active site modified by electron-absorbing groups can also promote the conversion of CO 2 to CO at a certain voltage. li et al reported a À COOH-modified carbon nanotube-loaded CoPc heterogeneous molecular catalyst, in which the electronabsorbing group À COOH promoted the formation of Co(I), which can be used as the active site for CO 2 RR.…”

Unveiling the Structural and Dynamic Characteristics of Concentrated LiNO3 Aqueous Solutions through Ultrafast Infrared Spectroscopy and Molecular Dynamics Simulations

“…Ultrafast infrared (IR) spectroscopy has emerged as a powerful tool for elucidating structure and dynamics in the condensed phases. − Monitoring the intrinsic probe of OH stretching offers insights into hydrogen-bonding dynamics, typically achieved by employing isotopically diluted solutions (e.g., 2% D 2 O dissolved in H 2 O) to avoid resonance vibrational energy transfer. , This strategy is crucial for studying vibrational relaxation dynamics that are sensitive to the local environment, which have been extensively utilized in investigations ranging from electrolyte solutions to biological studies. , As the vibrational spectra of the OH stretching band are not sensitive to the presence of Li + , extrinsic probes with longer vibrational lifetimes are employed to directly reflect the solvation dynamics of Li + in concentrated solutions. − Combined with MD simulations, this approach promises to unravel the underlying mechanisms of Li + transport and factors contributing to the widening of the electrochemical stability window in aqueous LiNO 3 solutions.…”