Influence of pH and supporting electrolyte on electrochemical reduction of CO2 using nickel(II) macrocyclic complex of 1, 3, 6, 9, 11, 14-hexaazacyclohexadecane as catalyst at HMDE

Electrochemical studies on the title compound using cyclic voltammogram (CV) and control potential electrolysis (CPE) techniques reveal that it reduces CO2 electrocatalytically at -1.36V/SCE at hanging mercury drop electrode (HMDE) in aqueous medium using LiClO4 as a supporting electrolyte. The products are found to be CO and H-2 in 3:2 mole ratio in the gaseous phase as detected using gas chromatography (GC) and trace amounts of formic acid in solution phase as detected using colorimetric technique. The I-k/I-d values (where I-k is the kinetic current measured in the presence Of CO2 and Id is the diffusion current measured in N-2 atmosphere) observed at various pH values show that pH 5.0 is best suited for CO2 reduction. In addition, the hydrophobicity/hydrophilicity near the electrode surface provided by the cation of the supporting salt and its influence on CO2 reduction is discussed.