CuII/CuI decorated N-doped carbonaceous electrocatalysts for the oxygen reduction reaction

Abstract

The oxygen reduction reaction (ORR) that for instance takes place at the cathode of fuel cells is one of the most examined model reactions of energy conversion. The ORR presents sluggish reaction kinetics, thus limiting the overall efficiency of these cells. Pt-based catalysts are still the widest choice though they exhibit important drawbacks such as long-term instability and intolerance to methanol crossover. In this context, engineering transition metals in the form of nano- and subnano-sites on carbonaceous supports has the potential of becoming an alternative to scarce noble metal-based catalysts. Herein, we describe a simple synthetic route towards Cu^II/Cu^I decorated N-doped carbonaceous ORR electrocatalysts. Cu^II/Cu^I nanosites are obtained by calcination in air of an ionic liquid derived noble carbonaceous support impregnated with copper(II) acetate. The strong interaction between the copper and the noble support foster the co-formation of Cu^II/Cu^I nanosites. Larger amounts of copper(II) acetate translate into larger amounts of Cu^I and lower Tafel slopes. The material with 4 wt% of copper catalyzes the selective reduction of oxygen through a 4-electron transfer pathway and exhibits a lower Tafel slope than commercial platinum, a minimal overpotential, and a higher limiting current density. Moreover, all materials show promising durability and high methanol stability, which makes them promising to replace noble metals for the ORR.