Preparation And Electrocatalytic Performance Of Cobalt Based Nitrogen Doped Carbon Nanotubes

Nitrogen doped carbon nanotubes(NCNTs) coated Polypyrrole(PPy) were prepared using in situ chemical polymerization, and followed by carbonization. The effect of carbonization temperature on the structure, nitrogen content of NCNT microstructure and electrocatalytic properties were studied at the same time. The morphology, pore structure and chemical composition of NCNTs heat treated at 600 ℃, 800 ℃ and 1000 ℃, respectively, showed that higher carbonization temperature can increase specific surface area(SSA), but decreased the N content of NCNT due to nitrogen loss during the pyrolysis of polymer. The types and content of N containing functional groups of NCNTs are significantly affected by the preparations temperature. With increasing temperature the N containing functional groups convert from the pyrrolic nitrogen to the pyridine nitrogen and graphitic nitrogen. The NCNTs prepared at 1000℃ owns the highest ration of graphitic nitrogen despite of its lowest total nitrogen content. Electrochemical analysis shows that the NCNT1000 exhibit the best catalytic activity for oxygen reduction reaction(ORR) due to its largest graphite N(29.9 at%), SSA(276.09 m2/g) and microporous volume(0.105cm3/g) even though the fewest N amount, which supply more active sites for ORR.The electrocatalysts of cobalt loaded nitrogen-doped CNTs were prepared through the depositing cobalt oxides on the surface of PPy coated CNTs(PPy@CNTs) using liquid phase precipitation method, then treated in inert gas at high temperature. X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS) analysis shows cobalt oxide transform to low valence state of cobalt or cobalt simple substance, and the compounds containing the bond of Co-N are also found, which is probably attributed to redox reaction of cobalt oxides with carbon and nitrogen during the pyrolysis of polymer. Electrochemical analysis shows that Co-NCNT800 has more positive potential peak(-0.10 V) and higher current peak(-0.84 mA), and the catalytic activity can be kept 84.4% after 100 cycles, which is higher than Co-NCNT600(46.9%) and Co-NCNT1000(60.4%), respectively. The much better catalytic activity of Co-NCNT800 than Co-NCNTs and NCNT can be contributed not only by the highest SSA(204.10 m2/g) and largest loaded amount of Co(1.37%); the uniform dispersion of Co which can provide more active point; but also by the ORR synergistic effect of Co/Co compound and NCNTs...