Noncovalent Immobilization of a Pyrene-Modified Cobalt Corrole on Carbon Supports for Enhanced Electrocatalytic Oxygen Reduction and Oxygen Evolution in Aqueous Solutions

Efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are the determinants of the realization of a hydrogen-based society, as sluggish OER and ORR are the bottlenecks for the production and utilization of H-2, respectively. A Co complex of 5,15-bis(pentafluorophenyl)-10-(4)-(1-pyrenyl)phenylcorrole (1) bearing a pyrene substituent was synthesized. When it was immobilized on multiwalled carbon nanotubes (MWCNTs), the 1/MWCNT composite displayed very high electrocatalytic activity and durability for both OER and ORR in aqueous solutions: it catalyzed a direct four-electron reduction of O-2 to H2O in 0.5 M H2SO4 with an onset potential of 0.75 V vs normal hydrogen electrode (NHE), and it catalyzed the oxidation of water to O-2 in neutral aqueous solution with an onset potential of 1.15 V (vs NHE, eta = 330 mV). Control studies using a Co complex of 5,10,15-tris(pentafluorophenyl)corrole (2) demonstrated that the enhanced catalytic performance of 1 was due to the strong noncovalent pi-pi interactions between its pyrene moiety and MWCNTs, which were considered to facilitate the fast electron transfer from the electrode to 1 and also to increase the adhesion of 1 on carbon supports. The noncovalent immobilization of molecular complexes on carbon supports through strong pi-pi interactions appears to be a simple and straightforward strategy to prepare highly efficient electrocatalytic materials.