Electrocatalytic study of a 1,10-phenanthroline–cobalt(ii) metal complex catalyst supported on reduced graphene oxide towards oxygen reduction reaction

Abstract

A new class of oxygen reduction reaction (ORR) catalyst was fabricated by loading a 1,10-phenanthroline–cobalt(II) metal-complex onto reduced graphene oxide (rGO) surfaces by π–π interaction. The Co(II)–N₄ was the active center of the metal-complex catalyst and catalyzed the ORR via a highly efficient four-electron reduction pathway. The introduction of the nitro-group substituent in 1,10-phenanthroline highly boosted the catalytic activity of the metal complex in terms of half-wave potential (E_1/2) and kinetic current density (J_K), due to the downshift of the e_g-orbital energy level for central Co(II) resulting from the electron-withdrawing effect of the nitro group. Considering the configuration of the metal complex on rGO surfaces, a single cobalt center-mediated catalytic mechanism was proposed to elucidate the ORR process. Compared with the commercial Pt/C catalyst, the as-prepared metal-complex catalyst exhibited a superior methanol tolerance and catalytic durability for the ORR. Our study provides more information about the relationship between the molecular structure and catalytic activity towards the ORR.