Preparation Of The Fe_xN/Nitrogen-doped Carbon Nanocomposite Catalysts And Their Electrocatalytic Performance For Oxygen Reduction Reaction

Fuel cells has a advantage of high energy conversion efficiency, environmental-friendly, etc, which is regarded as an ideal energy conversion device. As the cathodic reaction of fuel cells, oxygen reduction reaction?ORR? has great influence on the performance of the fuel cell. At present, Pt-based catalysts are widely used in fuel cells, but its expensive price severely limits the commercial applications of fuel cell. Therefore, the development of non-noble metal catalysts with low cost, high activity and stability, has become hot research in this field. Herein, we construct two types of N-doped nanocarbon-based catalyst with NH₃ as nitrogen source: “porous N-doped graphene?PNRGO? decorated with Fe_xN nanoparticles?Fe_xN/PNRGO?” and “mesoporous N-doped graphitic carbon spheres?MNGCS? decorated with Fe₂N nanoparticles?Fe₂N/MNGCS?”, which has low cost, high activity and excellent stability. The main contents of this work are as follows:1. Fe_xN/PNRGO: preparation and application in ORRFe₂O₃/NRGO had been prepared via hydrothermal self-assembly method of graphene oxide?GO? and Fe Cl3 mixed solution, then as-prepared composite was etched in NH₃ atmosphere for various time to form a series of catalysts?Fe_xN/PNRGO?t?t is the etching time in NH₃?.We investigated the effect of etching time on the crystal phase of Fe_xN particles, the content of PNRGO and microstructure to optimize the catalytic for ORR. The results showed that?Fe_xN/PNRGO?60 had the best ORR catalytic activity with crystal phase of Fe₂N,a content of PNRGO 24.6%,and the Eonset and E1/2 of?Fe_xN/PNRGO?60 was 0.94 and 0.81 V, respectively. The best catalyst had ORR activity nearly identical to that of the Pt/C and its methanol tolerant ability and stability were obviously better than that of Pt/C.2.?Fe₂N/MNGCS?: preparation and application in ORRIn Experiment 1, Fe₂N was the best crystal phase for ORR, but the content of PNRGO in?Fe_xN/PNRGO?60 was only 24.6%, so there were still some gaps for ORR catalytic performance between?Fe_xN/PNRGO?60 and commercial Pt/C. In order to further improve the electrocatalytic properties of Fe₂N/nitrogen doped carbon nanocomposite catalyst, We discussed the impact of the relative content of Fe₂N and nitrogen doped carbon and microstructure on ORR. Herein, we reported the fabrication of series of?Fe₂N/MNGCS?t?t is the acid etching time?, where ultra-small Fe₂N nanocrystals were incorporated into MNGCS to form efficient Fe-N/C catalytic active sites, and the Fe₂N/MNGCS electrocatalysts with difference Fe₂N contents and BET surface areas were obtained via altering the acid leaching time. The optimized ORR activity was achieved over?Fe₂N/MNGCS?4 with the Fe₂N content of 2.2 wt%, The?Fe₂N/MNGCS?4 reveals the positive half-wave potentials?0.881 V vs RHE? and onset potentials?0.96 V vs RHE?, excellent long-term stability?95.2 % of the initial current remaining after 60000 s of continuous operation? and good tolerance against methanol-crossover effect?94.9 % of the current retained prior to 4.0 M methanol injection? in alkaline media, which even was more superior to that of commercial Pt/C catalyst.