Study On The Influences Of Nitrogen Doping For Electrocatalytic Property Of Carbon Nanotube And Its Composites

At present,there are two technical problems hamper the commercialization of the direct methanol fuel cell?DMFC?.One is the sluggish kinetics of oxygen reduction reaction?ORR?the other is the methanol crossover.Although the platinum metal-based catalyst has the strongest activities about ORR,Pt used as electrode will add huge costs,and the Pt metal-based catalyst showed the poor methanol tolerant.Therefore it is significant to produce ORR catalyst with higher activity,lower cost and good methanol resistance.In this paper,the nitrogen doped carbon nanotubes?NCNT?were synthesized though the method of in situ doping and plasma modification using microwave plasma chemical vapor deposition?MPCVD?.Furthermore the AgCo₃/CNT was prepared by NaBH4 reduction methods followed with NH₃ plasma modification.The catalysts were characterized by TEM,Raman,XPS and the ORR properties was analyzed by electrochemical methods.According to the characterization and the electrochemical analysis,the influence of N-doped was revealed.In the method of in situ doping,the ORR ability of NCNT which was synthesized by different catalyst,microwave power and acid-processing was analyzed.The results are as follows:?1?The NCNT synthesized from Fe/Ca as catalyst have more complex structure,more disorder dgree and the higher nitrogen content.?2?With the microwave power increasing,the nitrogen content and the percentage of graphite-N show a downward trend.And the electrochemical measurement show that the lower microwave power,the better ORR ability the NCNT has.According to the test results,we can conclude that the graphite-N plays an important role in ORR.?3?The optimum time of acid treatment are 3 hours,the longer time of acid treatment can not improve the ORR ability.?4?The NCNT have a good resistance for methanol.The optimum processing condition is using Fe/Ca as catalyst,microwave power setting 400 w,acid treatment 3 hours.The onset potential and electron transfer number of the NCNT synthesized under the optimum processing condition are-137 mV and 3.3,respectively.The method of plasma modification was used to parpare NCNT.The results show that plasma modification can not change the morphology and increase the defects,but make the N doped into the lattice of CNT.The test of ORR shows that a small amount N can improve the ORR ability.The AgCo₃/CNT shows a good resistance for methanol tolerance.After the AgCo₃/CNT was modified by NH₃ plasma,the ORR ability of AgCo₃/CNT get some changes,after the plasma treatment the onset potential increase 38 mV,but the limited current density reduce to 3.96 mA/cm²,the electron transfer number has reduce.