Pyrolyzed Co-Nx/C Electrocatalysts Supported on Different Carbon Materials for Oxygen Reduction Reaction in Neutral Solution

Abstract

In this work, a non-noble metal material, i.e., 5, 10, 15, 20-Tetrakis(4-methoxyphenyl)−21H, 23H-porphine cobalt(II) (CoTMPP), is chosen as the metal complex which adsorbs on three different carbon support materials, namely, black pearls 2000 (BP), ordered mesoporous carbon (MPC) and single layer graphene oxide (GO), to form CoTMPP/BP, CoTMPP/MPC, and CoTMPP/GO catalyst precursors, respectively. These precursors are heat-treated at high temperatures to form Co-Nx/BP, Co-Nx/MPC, and Co-Nx/GO catalysts for ORR in neutral electrolyte solution, respectively. Several characterization methods including XRD, SEM/TEM and XPS are employed. Electrochemical methods such as cyclic voltammetry (CV), rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques are used to quantitatively measure the catalyzed ORR kinetic parameters. Effects of both carbon supports and heat-treatment temperature on the catalyst physical properties and catalytic ORR activities were also studied. Regarding the catalytic ORR activity, the activity order was measured as: Co-Nx/BP > Co-Nx/MPC > Co-Nx/GO. The overall electron transfer number catalyzed by Co-Nx/BP is measured to be 4, while those by Co-Nx/MPC and Co-Nx/GO catalysts are 2-electron transfer pathways. Based on these measurements and our analysis, an ORR mechanism is also proposed for facilitating further investigation and understanding.