Electrochemical reduction of oxygen using a Metal-Organic complex of Cu²⁺

Energy storage and conversion electrochemical technologies usually employ expensive materials based on noble metals to catalyze the reactions. However, nature shows us, in enzymes, that it would be possible to get this catalysis with easily accessible components. The design and synthesis of metal-organic complexes (biphenyl structures) for transition metal cations of the p block, is an important section in this field due to their appreciable catalytic activity. Specifically, the cupric cation (Cu²⁺) complexes have an important function in the reduction of oxygen. In this work, a biphenyl-based copper complex was evaluated as electrocatalyst for the oxygen reduction reaction (orr), for a possible application as cathode material in fuel cells. To carry out this evaluation, the complex was supported on Vulcan carbon and deposited as a film on a glassy carbon rotating disk electrode by drop-casting a 1-mL drop of a suspension of carbon in a solution of the complex in DMSO containing Nafion as ionic conductive binder, and drying under vacuum. The cyclic voltammogram in 0.1 M NaOH solution showed voltammetric peaks between 0.8 and 1.0 V vs. Reference Hydrogen Electrode, which suggest the existence of electron transfer processes from/toward the ligand. The orr was tested in oxygen-saturated (1 atm) solution by linear sweep voltammetry, which showed significant orr current at relatively low overpotential (around -0.4 V), demonstrating the ability of the complex to efficiently electrocatalyze the orr. Complementary, the use of computational techniques to know the structural properties of this ligands and their complexation with M²⁺ cation is particularly interesting.