Cobalt-porphyrin noncovalently functionalized graphene as nonprecious-metal electrocatalyst for oxygen reduction reaction in an alkaline medium

Cobalt 5,10,15,20-tetrakis(4-pyridyl)porphyrin (CoTPyP) micro/nanoparticles assembled on poly(sodium-p-styrenesulfonate) (PSS) modified reduced graphene oxide (PSS-rGO) as a nonnoble catalyst for oxygen reduction reaction (ORR) was prepared by an in situ solvothermal synthesis method. The CoTPyP/PSS-rGO micro/nanocomposite was characterized by UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM) techniques. Cyclic voltammetry (CV) measurement result disclosed that CoTPyP/PSS-rGO possesses quite high electrochemically accessible surface area, which was more than tripled as large as the bare glassy carbon (GC) electrode. Rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques were employed to study the catalytic activity and the ORR mechanism of as-synthesized CoTPyP/PSS-rGO catalyst in an alkaline medium. Linear sweep voltammetry (LSV) tests showed that the half-wave potential for ORR on the CoTPyP/PSS-rGO catalyst was found to be around -0.22 V vs. saturated calomel electrode (SCE), which was similar to that on Pt/C (-0.20 V vs. SCE). RRDE results displayed that the percentage of hydrogen peroxide yielded on the CoTPyP/PSS-rGO composite was less than 20 %, and the ORR process mainly proceeded via an almost direct 4-electron pathway. Moreover, the assembled CoTPyP/PSS-rGO catalyst possessed good stability and excellent tolerance to the crossover effect of methanol for ORR.