Preparation Of Non-noble Metal Fe-N/C Catalysts For Oxygen Reduction Reaction

Energy is the material basis for human survival and social progress.In order to cope with the current energy crisis,it is of great significance to choose environmentally friendly and efficient renewable new energy fuel cells.Oxygen reduction reaction?ORR?is an essential step in this type of fuel cell for energy conversion and storage.So far,precious metal platinum and platinum-based materials are considered to be excellent electrocatalysts for catalyzing ORR in various environments,but the scarce reserves of precious metal catalysts and the high cost have greatly limited their large-scale commercial applications.Non-precious metal catalysts are inexpensive and have large room for performance improvement,and are expected to replace precious metal-based catalysts.This paper focuses on non-precious metal Fe-N/C catalysts,from the aspects of innovation in its preparation method,ceria doping,and co-catalysis with Pt,and investigates the relationship between their composition,structure and ORR catalytic performance.The main contents and conclusions are as follows:?1?The Fe-N/C supported CeO₂ catalyst was prepared by high temperature pyrolysis.Adding proper amount of CeO₂ during Fe-N/C synthesis can reduce the loss of nitrogen source,and effectively increase the active sites of oxygen reduction reaction such as Fe-N_x and C-N,which plays a decisive role in improving the catalytic performance of ORR.Under alkaline conditions,the Fe-N/C-CeO₂ catalyst prepared by adding 1 wt%CeO₂ exhibited superior ORR performance compared with Fe-N/C,and the half-wave potential shifted 50 mV forward to 0.862 V.The initial potential and limiting current are both significantly increased,which is close to commercial Pt/C catalysts.In addition,because CeO₂ can eliminate the intermediate product H₂O₂ generated in the reduction process,thereby protecting the active site in the Fe-N/C-CeO₂ catalyst from being destroyed and corroded,greatly improving the stability of the catalyst;10,000 cycles of the test afterwards,its half-wave potential only shifted negatively by 18 mV,which was far less than that of Fe-N/C catalyst?39mV?.?2?Using the Fe-N-C material prepared by the impregnation pyrolysis method as a carrier,a Pt-Fe-N-C catalyst with ultra-low Pt loading was synthesized.Pt clusters with a loading of as low as 0.5%are supported on the surface of Fe₃C and amorphous graphite carbon.The uniformly dispersed Pt clusters and Fe-N_x active sites play catalytic roles together,and the Fe-N_x active sites are coated by the amorphous carbon,effectively inhibiting the destruction and corrosion of the active site in the ORR process,which is conducive to improving the ORR performance of the Pt-Fe-N-C catalyst.Under alkaline conditions,the half-wave potential reaches 0.900V and the initial potential reaches 1.00 V.Its performance is significantly better than that of commercial Pt/C,and its mass activity reaches 42.6 times that of commercial Pt/C.It is also close to commercial Pt/C.In the application of zinc-air batteries,it shows a higher power density than Pt/C.?3?For the first time,a gelatin dispersion method was used to prepare a large specific surface area with highly dispersed,high-density Fe-N_x active site of FeNC porous catalyst.The catalyst exhibits excellent ORR performance.Under alkaline conditions,the half-wave potential can reach 0.930 V,the initial potential reaches1.07 V,and the kinetic current density at 0.9 V reaches 14.29 mA/cm².Until now,this FeNC porous catalyst show the best activity in non-precious metal catalysts,far exceeding commercial Pt/C catalysts.