Electrocatalytic CO2 Reduction by [Re(CO)3Cl(3-(pyridin-2-yl)-5-phenyl-1,2,4-triazole)] and [Re(CO)3Cl(3-(2-pyridyl)-1,2,4-triazole)]

Abstract

The exploration of novel electrocatalysts for CO₂ reduction is necessary to overcome global warming and the depletion of fossil fuels. In the current study, the electrocatalytic CO₂ reduction of [Re(CO)₃Cl(N-N)], where N-N represents 3-(2-pyridyl)-1,2,4-triazole (Hpy), 3-(pyridin-2-yl)-5-phenyl-l,2,4-triazole (Hph), and 2,2'-bipyridine-4,4' dicarboxylic acidic (bpy-COOH) ligands, was investigated. In CO₂-saturated electrolytes, cyclic voltammograms showed an enhancement of the current at the second reduction wave for all complexes. In the presence of triethanolamine (TEOA), the currents of Re(Hpy), Re(Hph), and Re(bpy-COOH) enhanced significantly by approximately 4-, 2-, and 5-fold at peak potentials of -1.60, -150, and -1.69 V_Ag/Ag+, respectively (in comparison to without TEOA). The reduction potential of Re(Hph) was less negative than those of Re(Hpy) and Re(COOH), which was suggested to cause its least efficiency for CO₂ reduction. Chronoamperometry measurements showed the stability of the cathodic current at the second reduction wave for at least 300 s, and Re(COOH) was the most stable in the CO₂-catalyzed reduction. The appearance and disappearance of the absorption band in the UV/vis spectra indicated the reaction of the catalyst with molecular CO₂ and its conversion to new species, which were proposed to be Re-DMF ⁺ and Re-TEOA and were supposed to react with CO₂ molecules. The CO₂ molecules were claimed to be captured and inserted into the oxygen bond of Re-TEOA, resulting in the enhancement of the CO₂ reduction efficiency. The results indicate a new way of using these complexes in electrocatalytic CO₂ reduction.