Molecular Catalysis of CO2 Reduction by [Zn(TPA)(H2O)]SO4: Electrochemical and Mechanistic Characterization

In this work, the coordination compound sulfate of aqua{tris(2-pyridylmethyl) amine}zinc(II) ([Zn(TPA)(H2O)]SO4) is investigated as a catalyst for the molecular reduction of CO2. The complex was synthesized and characterized by FT–IR, UV–Vis, TGA, and NMR spectroscopy. Cyclic voltammetry reveals irreversible electrochemical behavior, with two cathodic peaks at Epc = −1.72 V and Epc = −1.99 V vs. Fc/Fc+, respectively. Under a CO2 atmosphere, a catalytic wave appears at Epc = −1.87 V vs. Fc/Fc+, indicating catalytic activity toward CO2 reduction. This behavior was further confirmed by Foot-of-the-Wave Analysis (FOWA), which yielded a catalytic rate constant of (k = 1.352 × 103 M−1 s−1). Bulk electrolysis experiments combined with FT–IR analysis suggest that format is the main product of the CO2 reduction catalyzed by [Zn(TPA)(H2O)]SO4. Electrochemical impedance spectroscopy was used to examine the catalytic process at the electrode–electrolyte interface. In addition, density functional theory (DFT) calculations were conducted to analyze the interaction between the [Zn(TPA)(H2O)]SO4 complex and CO2.