The continuous CO2 emissions caused by fossil fuel consumption have caused adverse effects on Earth’s climate. Different alternatives to mitigate these effects have been employed (e.g., solar and wind energy), but CO2 remediation is a viable option to reduce emissions and convert CO2 to value-added products. The high stability, facile synthesis, catalytic activity, and tunability of metal Schiff base (SB) complexes make them suitable for CO2 reduction reaction (CO2RR). This research presents two Pd and two Pt SB complexes that were characterized spectroscopically by UV-Vis, FTIR, 1H-NMR, and SC-XRD. The electrochemical properties of the complexes were determined using cyclic voltammetry under an inert atmosphere. All complexes exhibited a characteristic ligand-based oxidation process due to the non-innocent behavior of the ligands. Furthermore, the metal complexes CO2 reduction activity showed enhanced current density at the reduction peaks due to effective conversion of CO2. To create better catalysts, we added a hydroxy substituent in the diamine bridge of one of the SB ligands to direct the CO2 molecule towards the metal center. The hydroxy-substituted SB metal complexes showed a CO2 reduction at lower onset potentials, suggesting the positive effect of the hydroxy group. The addition of water as a sacrificial proton source further shifted the onset potential and increased the current density of reduction corresponding to the CO2RR. Current density values are greater than -0.5 mA/cm2 for all studied complexes at the CO2 reduction potential. The calculated HOMO/LUMO gap values are approximately 2.50 – 2.70 eV which are in good agreement with the DFT data.

Non-innocent Schiff base complexes of precious metals as electrocatalyst for CO2 reduction

ACS Spring 2022

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