Promoting Oxygen Reduction Reaction by Inducing Out-of-Plane Polarization in a Metal Phthalocyanine Catalyst

Metal phthalocyanine (MPc) material with a well-defined MN4 moiety offers a platform for catalyzing the oxygen reduction reaction (ORR), while the practical performance is often limited by the insufficient O-2 adsorption due to the planar MN4 configuration. Here, a design (called Gr-M-G-O-MPPc) is proposed, where the metal of MPc (M-P) is axially coordinated to a single metal atom in graphene (Gr-M-G) through a bridge-bonded oxygen atom (O), introducing effective out-of-plane polarization to promote O-2 adsorption on MPc. Manipulating the out-of-plane polarization charge by varying types of M-P and M-G (M-P = Fe/Co/Ni, M-G = Ti/V/Cr/Mn/Fe/Co/Ni) in the axial coordination zone of -M-G-O-M-P- are examined by density functional theory simulations. Among them, the catalyst of Gr-V-O-FePc stands out with the highest calculated O-2 adsorption energy, which is synthesized successfully and verified by systemic X-ray absorption spectroscopy measurements. Importantly, it delivers a remarkable ORR performance with half-wave potential of 0.925 V (versus reversible hydrogen electrode) and kinetic current density of 26.7 mA cm(-2). This thus demonstrates a new and simple way to pursue high catalytic performance by inducing out-of-plane polarization in catalysts.