Double activation of oxygen intermediates of oxygen reduction reaction by dual inorganic/organic hybrid electrocatalysts

Abstract

Synergistic effects of dual homogeneous catalysts for chemical reactions have been reported. Double activation (chemical transformation process where both catalysts work in concert to activate reactants or intermediates) was often responsible for the synergistic effects of dual catalyst systems. Herein, we demonstrate the extension of the double activation from chemo-catalysis to electrocatalysis. The activity of low-cost cobalt oxide electrocatalysts for oxygen reduction reaction (ORR) was significantly improved by introducing secondary-amine-conjugated polymers (HN-CPs) as the secondary promoting electrocatalyst (shortly, promoter). It was proposed that HN-CPs activated neutral diatomic oxygen to partially charged species (O-2(delta-)) in the initial oxygen adsorption step of ORR. Electron donation number of HN-CP to diatomic oxygen (delta in O-2(delta-)) well described the order of activity improvement, i.e., polypyrrole (pPy) > polyaniline (pAni) > polyindole (pInd). The maximum overpotential gain at similar to 150 mV was achieved by using pPy with the highest delta. Also, it was confirmed that proton of HN-CP was transferred to single oxygen intermediate (*O) of ORR.