Preparation Of Doped Carbon-based Electrocatalyst And Its Oxygen Reduction Performance

Fuel cells via electrochemical reaction direct converted chemical energy into electricity,which served as one of important next-generation energy technologies.In this reaction process,that is no emission of any hazardous molecule and company with high energy conversion efficiency.However,the oxygen reduction reaction?ORR?occurred in cathode have complex and sluggish kinetic reactions,which forced cathode need a large amount of ORR electrocatalysts to maintain the overall performances of fuel cells.In fuel cells,the most commonly electrocatalysts is precious metal platinum?Pt?,but its high cost and low abundant severe restrict the widespread commercialization of fuel cells.Therefore,developed Pt-free catalysts with low cost and high ORR performance to replace Pt-based catalysts is vital for the development of fuel cells.In various Pt-free electrocatalysts,doped carbon-based electrocatalysts have attracted lots of focus and researches due to its high ORR activities,favorable long-term stability and methanol tolerance.In this thesis,series of ORR electrocatalysts with high electrochemical activities were fabricated by a high-temperature treatment under mixtures of ammonia and argon for nitrogen using multi-cage carbon spheres with high specific surface area(1730 m²g^-1)as carbon support.The ORR catalytic mechanism and the effects of catalytic activities have been investigated based on their morphologies and microstructures,elemental compositions,and ORR performances.The main research contents were shown as follow:?1?Multi-cage carbon spheres?MCSS?were calcined under mixtures of ammonia?30 sccm?and argon?60 sccm?for nitrogen doping.When calcined time was 2 h,the N-MCSS-2 exhibited the best ORR performances.The electrochemical test indicated that N-MCCS-2 with high ORR activities,long-term stability and methanol tolerance in alkaline medium.The half-wave potential of N-MCSS-2 catalysts was 0.823 V?vs.RHE?,that was closed to Pt/C catalysts?0.828 V?and after 6500 cycles,it dropped27 m V.?2?Multi-cage carbon spheres contained iron precursor were calcined under mixtures of ammonia?30 sccm?and argon?60 sccm?for 2 h.The as-fabricated iron nitrogen co-doped multi-cage carbon spheres?Fe/N-MCCS-2?exhibited superior ORR performance,it should be mainly ascribed to the synergistic effects between iron and nitrogen atoms.Electrochemical test indicated that Fe/N-MCCS-2 exhibited superior ORR activities and methanol tolerance than commercial Pt/C catalysts.Its onset potential,half-wave potential and limit current density were 0.965 V,0.837 V?vs.RHE?and 5.68 m A.cm^-2,respectively,all surpass than that of Pt/C catalysts.After 8000 cycles,the half-wave potential of Fe/N-MCCS-2 drop 18 m V while Pt/C catalysts drop 15 m V,exhibited comparable long-term stability to commercia Pt/C catalysts.