METAL-SALEN DERIVATIVES FOR ELECTRO-REDUCTION OF CARBON DIOXIDE

Abstract

Copper(II) salen, salophen-based ligands, and their corresponding copper complexes were prepared and utilized for the electrocatalytic reduction of carbon dioxide. Controlled-potential electrolysis of copper(II) salen electrocatalyst with carbon dioxide in non-aqueous solution was investigated to obtain the optimized electrolysis condition including the applied potential and proton donor quantity. With the applied potential of –2.10 V, carbon monoxide (3.50-16.30%) was obtained as the only product in gas phase. Methane was additionally found with the addition of proton donor and its maximum percentage (0.39 ± 0.00%) were obtained from the electrolysis with 25.00 mM proton donor and 2.00 mM copper(II) salen. Moreover, salophen and its derivatives as well as corresponding copper complexes were successfully synthesized, characterized, and applied as homogeneous electrocatalysts for the electro-reduction of carbon dioxide. Salophen-based ligands and complexes presented possibilities in electrochemically catalyzing the carbon dioxide reduction. Among all salophen-based compounds, copper(II) bromo-salophen showed the best electrocatalytic efficiency with the highest current enhancement (360%) in cyclic voltammetric experiment. Similar to the copper(II) salen–carbon dioxide electrolysis, the electrolysis of carbon dioxide by electrogenerated copper(I) salophen and its derivatives gave carbon monoxide as gaseous product (5.90-8.87%), whereas methane was additionally found (0.57 ± 0.00%) when a proton donor was added.