Alkali Metal Ion Tuning of a Crown Ether-Appended Porphyrin for Electrocatalytic CO2 Reduction

Iron-porphyrin systems are among the best catalysts to reduce selectively CO2 to CO. Electronic modification of the porphyrin skeleton by substituents can enhance the catalytic efficiency of the complexes. In this work, we modified the iron porphyrin complex with crown-ether auxiliaries and tested the effect of complexation with alkali metals on their electrocatalytic properties for CO2 reduction. The presence of Na+ or K(+ )resulted in a positive shift of the onset potential by 210 mV while not compromising the catalytic current. This effect was maintained after the immobilization at the vulcanized carbon support, and the catalyst showed the Faradaic efficiency above 90 % for CO2 to CO reduction in aqueous solution of NaHCO3 or KHCO3 in a wide range of overpotentials. Hence, host-guest chemistry at the periphery of the CO2 reduction catalysts can tune the electronic properties of the catalysts and thereby increase the catalytic efficiency.