Synthesis And Study Of Porous Fe-based Materials As Oxygen Electrode Catalysts

With the quick development of our society,serious problems about environmental pollution and lack of resources have forced people to seek new types of alternative energy.Fuel cells and metal air batteries are popular among new energy due to convenience,non-pollution,reliable performance,and high energy density;electrolysis of water also develops quickly because it can product hydrogen through the clean and simple methods.However,the high overpotential and the slow kinetics of oxygen electrode hinder its commercial application.Therefore,it is very important to develop highly efficient catalyst for oxygen reduction reaction and oxygen evolution reaction to improve the working efficiency of battery.In this paper,a series of non-precious metal catalysts were prepared with the aim of designing cost-effective catalysts based on Fe-based catalysts.Furthermore,the relationship between ORR performance and structure of the catalyst was explored by combining with modern spectroscopy and electrochemical methods.The specific work is as follows:?1?A novel Fe₂P nanoparticles embedded N,P co-doped mesoporous carbon catalyst?Fe₂P/NPC?was designed and synthesized through directly pyrolyzing the o-methylaniline in the presence of FeCl₃?6H₂O,H₃PO₄,silica nanospheres,and hexadecyltrimethyl ammonium bromide?CTAB?micelle.Transmission electron microscopy,Brunauer-Emmett-Teller?BET?,X-ray diffraction and X-ray photoelectron spectroscopy measurements demonstrated that the obtained three-dimensional mesoporous Fe₂P/NPC catalyst possessed a considerable specific surface area of 785 m² g^-1 with high contents of Fe₂P nanoparticles,pyridinic N,and graphitic N species.Electrochemical results showed that the formed Fe₂P/NPC exhibited superior ORR performance to Pt/C in terms of comparable onset potential?-0.01 V?,about 20 mV higher half-wave potential,excellent stability and remarkable methanol tolerance in alkaline media.The synergistic effect of pyridinic N,graphitic N and Fe₂P species together with its three-dimensional porous structure are contributed to the impressive ORR performance.?2?o-Methylaniline was selected as the carbon source and nitrogen source,FeCl₃·6H₂O as the Fe source,HCl,H₂O,and NH₃?H₂O were used as pH modifier through directly pyrolyzing to obtain Fe-N-C_ac,Fe-N-C_ne,and Fe-N-C_al catalysts.Physical characterization results suggested that the obtained catalyst have significant differences in the bulk phase structure and surface structure,such as the content,distribution,and configuration.The catalyst which was prepared under neutral conditions has less content of Fe on carbon surface due to most of the metal particles encapsulated in the carbon layer.Electrochemical tests showed that the onset potential of Fe-N-C_ac?Fe-N-C_ne?Fe-N-C_al are-0.01 V,-0.05 V,and-0.06 V,respectively and Fe-N-C_ac catalyst shows remarkable stability?the catalyst maintained a relatively high current intensity of 95%of the initial value after a test of 1800 s at a constant potential?.?3?Using glucose as a carbon source,FeCl₃?6H₂O and Co?NO₃?₂?6H₂O as Fe source and Co source,g-C₃N₄ as C,N source and template with the stepwise pyrolysis process to obtain Fe_0.3Co_0.7,Fe₂O₃,and Co nanoparticles coated in N-doped carbon catalyst?Fe-Co@NC?.Physical characterization results indicated that the obtained catalyst have more active species such as Fe_0.3Co_0.7,Fe₂O₃,Co,Fe-N_x and Co-N_x and a higher specific surface area.The electrochemical results indicated that the obtained Fe-Co@NC catalyst shown both good ORR and OER performance??E=0.84 V?and excellent ORR and OER stability?Accelerated aging tests shown that the ORR curve and the OER curve of this catalyst change little after 8000continuous cycles and 2000 continuous cycles scanning tests,respectively?.