Nitrogen Doped Carbon Nanotubes Loaded With Platinum Particles And Its Electrolytic Performance

In this study, the polypyrrole-coated nitrogen-doped carbon nanotubes wereprepared by in-situ chemical polymerization, and nitrogen-doped carbonnanotubes(NCCNT) were obtained through the carbonization of polypyrrole-coatednitrogen-doped carbon nanotubes. The effects of carbonization temperature on thetexture,structure and nitrogen contents of NCCNT as prepared were studied. As thesupports of platinum catalyst, the effects of texture and structural configuration ofNCCNT on deposition configuration and distribution of loaded catalysts, as well aselectro-catalytic properties, were studied. The main results are as follows:1. The texture, structure and nitrogen contents of NCNCT can be significantlyaffected by carbonization temperature, according to the morphology structure andchemical composition of NCNCT prepared at600℃,700℃and900℃. it issignificant to synthetise nitrogen-doped carbon nanotubes with high by the highercarbonization temperatures can result in the formation of NCCNT with the higherspecific surface area, but the lower nitrogen content. The NCCNT obtained at900℃has the highest specific surface area and the degree of graphitization, but the lowestnitrogen content. The NCCNT prepared at700℃(NCCNT700) and900℃(NCCNT900）has the hierarchical pore structure containing micropore, mesopore andmacropore, the NCCNT900contains more micropores.2. The XRD and TEM analyses show that platinum particles are uniformly depositedand distributed on the surface of NCNCTs. The particle sizes of platinum catalystsdeposited on the surface of NCNCT decrease in turn of NCCNT600, NCCNT700andNCCNT900. The particle size of platinum catalysts deposited on the NCCNT600andNCCNT700surface is about5nm and3nm, respectively. But the size of particles onthe surface of NCCNT900is less than2nm and platinum atomclusters less than1nmin size are also formed on the NCCNT. The distribution of platinum catalysts onNCCNT900are more uniformly than NCCNT600and NCNT700, which are mainlydue to the high specific surface areas and micropore volumes of NCCNT900.3. The electrocatalytic performance analyses show that the electrochemical activeareas of platinum catalysts loaded on NCCNT increases with NCCNT600,NCCNT700and NCCNT900in turn. The current density of oxygen reductionreaction (ORR) peak of Pt-NCCNT900is-93.3mA/g, which is significantly higherthan that of Pt-NCCNT600and Pt-NCCNT700(-73.8mA/g and-52.7mA/g), besides,the ORR peak potential of Pt-NCCNT900is0.54V vs SCE, which is more positivethan that of Pt-NCCNT600and Pt-NCCNT700（0.44V vs SCE）demonstrating thatPt-NCCNT900has better catalytic activity on ORR. At the same time, the cyclingstability of Pt-NCCNT900is also superior to that of Pt-NCCNT600andPt-NCCNT700. After200cycles, the decrease ORR peak current density ofPt-NCCNT900is19.1%, which is54.6%and32.8%for Pt-NCCNT600and Pt-NCCNT700,respectively. The good electrocatalytic performance of Pt-NCCNT900is mainly attributed to the high specific surface area of NCCNT900forplatinum particles deposition as the smaller size or atomclusters and uniformdistribution supplying more electrochemically active surface. The high degree ofgraphitization NCCNT900favors the transfer of electrons, meanwhile the hierarchicalpore structure of NCCNT is in favor of the mass transfer and diffusion of reactants.