Catalytic activity of dual catalysts system based on nano-manganese oxide and cobalt octacyanophthalocyanine toward four-electron reduction of oxygen in alkaline media

Abstract

The electrocatalysis of the dual functional catalysts system composed of electrolytic nano-manganese oxide (nano-MnOx) and cobalt octacyanophthalocyanine (CoPcCN) toward 4-electron reduction of oxygen (O 2) in alkaline media was studied. Nano-MnOx electrodeposited on the CoPcCN monolayer-modified glassy carbon (GC) electrode was clarified as the nano-rods with ca. 10–20 nm diameter by scanning electron microscopy. The peak current for O 2 reduction at the dual catalysts-modified GC electrode increases largely and the peak potential shifts by ca. 160 mV to the positive direction in cyclic voltammograms compared with those obtained at the bare GC electrode. The Koutecký–Levich plots indicate that the O 2 reduction at the dual catalysts-modified GC electrode is an apparent 4-electron process. Collection efficiencies obtained at the dual catalysts-modified GC electrode are much lower than those at the GC electrode and are almost similar to those at the Pt nano-particles modified GC electrode. The obtained results demonstrate that the dual catalysts system possesses a bifuctional catalytic activity for redox-mediating 2-electron reduction of O 2 to HO 2 − by CoPcCN as well as catalyzing the disproportionation of HO 2 − to OH − and O 2 by nano-MnOx, and enables an apparent 4-electron reduction of O 2 at a relatively low overpotential in alkaline media. In addition, it has been found that the cleaning of the dual catalysts-modified electrode by soaking in 0.1 M sulfuric acid solution enhances its catalytic activity toward the reduction of O 2.