Bioinspired copper coordination polymer catalysts for oxygen reduction reaction

Abstract

Non–noble metal catalysts have recently emerged as promising alternatives to the expensive platinum catalysts for the oxygen reduction reaction (ORR). In this study, a new domain of materials, copper based coordination polymers, has been investigated as promising catalysts for ORR. The study was inspired by copper incorporating biomolecules, which efficiently catalyse the oxygen reduction reaction in nature. Two coordination polymers, [Cu2(μ−AcO)4Po)]n (shortened as[Cu–A]) and [Cu2(μ−BzO)4Po)]n (shortened as[Cu–B]), incorporating one–dimensional chains of Cu(II) paddle wheel units bridged with phosphineoxide ligands were combined with multi−walled carbon nanotubes (MCNTs) to prepare hybrid electrocatalysts for ORR. The electrochemical analysis demonstrates that [Cu–A] catalyses ORR with 3.24 numbers of electrons with Tafel slopes of 122/83 mV dec−1 while it is 2.37 numbers of electrons with Tafel slopes of 131/84 mV dec−1 for [Cu–B]. Rotating disk electrode measurements and evaluation of Tafel slopes reveal that acetate moieties attached to Cu site shift the onset potential of ORR anodically (ca. 40 mV) compared to the one with benzoate bridging groups. The effect of bridging ligands to the stability and activity of catalysts in alkaline media was also evaluated. This study opens a new perspective for the development of non–platinum ORR catalysts.