Nitrogen Or Sulfur Doped Carbon Nanotubes/Graphite Carbon Loaded Iron/Cobalt Towards Oxygen Reduction Reactions

Proton exchange membrane fuel cell?PEMFC?,as a new non-pollution energy source,is considered as one of the most promising technologies to solve the energy crisis due to its high energy conversion efficiency and unlimited sources of reactants.The cathodic reaction of the battery is oxygen reduction reaction?ORR?with slow reaction kinetics,and therefore it requires very efficient catalysts to speed up the reaction process.The commercialization of Pt catalysts can not achieve large-scale application in decade's continuous exploration because that the precious metal is expensive and poor stability in the electrolyte solution and easy to poisoning.Therefore,the development of cheap and efficient cathode non-noble metal catalysts is of great significance for the large-scale development of PEMFCs.Non-precious metal supported on carbon-based materials have attracted wide attention due to their large specific surface area,superior activity and stability.This work is based on graphitic carbon/carbon nanotubes loaded transition metals,and doped with N or S element as non-noble metal oxygen reduction catalysts.Firstly,in this work,IRMOF-3 is synthesized by hydrothermal method as a carbon support,mixing with ferric nitrate,sodium dodecyl benzene sulfonate,and melamine.After being pyrolyzed at 900 ^oC in N₂,N-doped carbon nanotube/graphite carbon loaded Fe₃C non-precious metal catalyst?MSF-900?is prepared.By changing components of the pre-pyrolysis precursor,catalysts with different components are obtained.Among them,the MSF-900 sample exhibits the highest activity,and the half-wave potential is 0.91 V,which is 10 mV higher than the commercial Pt/C catalyst.The transfer electrons number is 3.94 at 0.4 V.And the chronoamperometric current is also measured,the current density remains 94.7%of the initial value 10000 s,and the stability is much higher than that of Pt/C.The electrochemical activity is higher than that of most non-noble metal oxygen reduction catalysts up to date.The superior activity and stability mainly result from larger specific surface area,high nitrogen content,and carbon-coated Fe₃C structure.Secondly,in this work,precursors containing Co and S are prepared by solvent method,mixed with melamine at a certain ratio and then calcined at 800 ^oC in N₂,after pickling and drying,the sulfur-and nitrogen-codoped carbon nanotubes/graphitic carbon materials loaded Co are obtained?CoSMe-x-800?.By varying the ratios of cobalt and sulfur in the precursors,different sulfur-containing catalysts are obtained.Among them,CoSMe-2-800 exhibits the best catalytic activity and the half-wave potential is 0.85 V,which is 20 mV higher than commercial Pt/C.The transfer electron number is 3.96 at 0.7 V.And the current density still maintains 96.6%of the initial value after 10000 s chronoamperometry test.The half-wave potential has almost no negative shift after 5000 cycles,and its stability is much higher than commercial Pt/C.The superior activity and stability of CoSMe-2-800 are mainly attributed to high specific surface area,the co-doping of sulfur and nitrogen,and Co particles surrounded by carbon layers.