Electrocatalytic four-electron reduction of oxygen with Copper (II)-based metal-organic frameworks

This communication describes the first demonstration on the use of metal-organic frameworks (MOFs) as electrocatalysts for oxygen reduction reaction (ORR). Copper (II) benzene-1,3,5-tricarboxylate (Cu-BTC, BTC = 1,3,5-tricarboxylate) was first synthesized and studied with respect to its electrocatalytic activity toward ORR. However, this kind of widely studied Cu(II)-based MOF was structurally unstable in aqueous media. We thus synthesized one kind of water-stable Cu(II)-based MOF, i.e., copper (II)-2,2'-bipyridine-benzene-1,3,5-tricarboxylate (Cu-bipy-BTC, bipy = 2,2'-bipyridine) as an alternative to Cu-BTC for the ORR study. In a phosphate buffer (pH 6.0), the synthetic Cu-bipy-BTC shows a couple of well-defined redox peaks at ca. -0.15 V. The presence of O-2 into the buffer clearly increases the reduction peak current, while decreases the reversed oxidation peak current of the redox wave. This property, along with the positive shift of the potential for ORR at the MOF-modified electrode compared with that at the bare GC electrode, demonstrates the electrocatalytic activity of the Cu-bipy-BTC MOF towards ORR. Rotating ring-disk electrode voltammetry reveals that this kind of MOF can catalyze the ORR through an almost four-electron reduction pathway. This study essentially offers a new approach to development of non-platinum ORR catalysts based on MOF materials. (C) 2012 Elsevier B.V. All rights reserved.