Abstract: CoPy/C catalysts for the oxygen reduction reaction(ORR) were prepared with 40/60(mass ratio)(15%Co25%Py/C) using cobalt sulfate hepathydrate(CoSO₄·7H₂O) and pyridine(Py) as the Co and N precursors supported on Vulcan XC-72R followed by heat treatment in an inert atmosphere at different temperatures ranging from 600 ℃ to 900 ℃. The catalysts were characterized by TEM, XRD and SEM-EDS anlaysis. Their ORR activities as the function of heat treatment temperatures for catalyst synthesis were evaluated by cyclic voltammograms(CVs) and rotating disk electrode(RDE) measurements. The results show that high temperature treatment can greatly improve the ORR activity of CoPy/C catalyst, for which the catalyst synthesized at 800 ℃ exhibits the best ORR activity. The nanoparticles of the catalyst as-prepared, with a diameter of 17 nm, uniformly dispersed on Vulcan carbon(Vulcan XC-72R). XRD and EDS anlaysis indicate that the structure of CoPy/C is destroyed after high temperature pyrolysis, and changed as the different valence cobalt oxide and cobalt sulfide, which are with N and S as the active sites for ORR. In 3.0 mol/L KOH, 15%Co25%Py/C(in O₂) can produce the obvious ORR current, giving the onset potential at 0.026 V(vs. SCE) with a half-wave potential of -0.069 V. RDE results further reveal that 15%Co25%Py/C catalysts in 3.0 mol/L KOH solution catalyze the ORR via four-electron pathway, through which the molecular oxygen is directly reduced to H₂O.

Key words: CoPy/C catalyst, Heat-treatment, Cyclic voltammogram, Rotating disk electrode(RDE), Alkaline fuel cell, Oxygen reduction reaction