The Study On The Electrocatalysts Of Oxygen Reduction Reaction Based On Carbon Nanotubes

The exploration of new energy has become an important challenge faced by all countries in the world with the depletion of fossil energy and severe pollution. Fuel cells is the most promising new green energy as its advantages of high energy conversion efficiency and low pollution. The air electrode, which is an important part of fuel cells, is a key bottleneck of controlling and affecting the cell performance. The oxygen reduction reaction(ORR) in air electrode has the characteristics of slow dynamics and multifarious reaction pathways, resulting in high current discharge to be very difficult. Looking for cheap and efficient fuel cell cathode catalyst to replace precious metal platinum based catalysts is the important development direction of fuel cell.In this work, the TM-N/C cathode catalyst was synthesized via cheap polyaniline and melamine co-modified carbon nanotubes. What still need to do is optimizing catalyst preparation conditions such as heat treatment time, heat treatment temperature and metal content and other factors. While LSV was used to evaluate the catalyst activity, and ORR polarization curves was used to survey catalytic mechanism of oxygen reduction reaction and stability, and amperometric I-t curves used to survey the methanol-tolerant performance, and the surface morphology and other characteristic were observed by SEM, XRD or XPS. The experimental results have shown that doping dual nitrogen sources has more advantages than that of doping one source, and the onset potential and the peak potential of N/C catalyst via high-temperature pyrolysis dual nitrogen doping carbon nanotubes at optimal conditions is-35 m V and-113 m V respectively; the metallic cobalt in the precursor can enhance catalytic performance, and the onset potential and the peak potential of Co-N/C-A is more positive 5 m V and 25 m V than that of N/C respectively and exhibites superior tolerance against methanol crossover effect. After the AAT, the losses of the onset potential and half-wave potential of Co/N/C-A are 23 and 10 m V, respectively. Notably, the decreases in the onset potential and half-wave potential for Pt/C catalyst are 68 and 20 m V, respectively. After the AAT, the current density of Co/N/C-A retained 99.6% of the initial current density at-0.4 V, whereas the Pt/C catalyst retained only 95.4% of the initial current density. These results suggest that the N/C and Co/N/CA catalytic electrodes have a much higher stability than the Pt/C catalytic electrode. Even more important, the adding of Co can make oxygen reduction reaction via efficient 4-electron transfer pathway, the the overall electron transfer numbers(n) for ORR at N/C and Co/N/C-A was calculated to be respectively ~2.7 and ~4.1, respectively. The factors such as the adding amount of Co, the temperature and time of heat treatment should be optimized to obtain the best catalytic performance, the optimal conditions is pyrolyzed the precursor in flowing N2 at 800 ℃ for 2 h with the 20% Co content.