Preparation And Catalytic Performance Study Of Fe-based Nanoparticles For Oxygen Reduction Reactions

The threat of energy shortage and environmental pollution requires us to develop sustainable clean energy.With the development and progress of science and technology,researchers have made some progress in exploring and solving these two major problems.Clean new fuel cells have aroused people’s attention as a new energy source,and developing fuel cells to replace internal combustion engines as a new generation of power system can effectively alleviate resource shortages and environmental pollution problems.Besides,the oxygen reduction reaction（ORR）is a key factor that limits the performance of fuel cells,and high-efficiency ORR catalysts are the key to realizing the widespread application of fuel cells.However,the expensive ORR catalyst on the fuel cell cathode limits the wide application of fuel cells.In order to break the limitations of precious metal catalysts on the development of fuel cells,we investigated the ORR non-precious metal catalyst materials based on Prussian blue analogues（PBA）,and the research results obtained are as follows.（1）In view of the low boiling point of Zn metal（907℃）,while the melting and boiling points of Co and Ni metals are relatively high,it is easy to melt and volatilize during calcination.We prepared F_0.8Zn_0.2@MNC,Fe Co@NC,and Fe Ni@NC catalysts derived from Fe-Zn,Fe-Co and Fe-Ni PBA at 700℃calcination,respectively,and their ORR catalytic performance were compared.As a result,we found that due to the volatilization of Zn during the calcination of Fe-Zn PBA,the specific surface area,porosity and conductivity of the F_0.8Zn_0.2@MNC are higher than those of Fe Co@NC and Fe Ni@NC.And F_0.8Zn_0.2@MNC also showed better ORR catalytic activity than Fe Co@NC,Fe Ni@NC,and 20%Pt/C.Its onset potential and half-wave potential are0.965 and 0.820 V vs.RHE in 0.1 M KOH with 1600 r min^-1,respectively.In this regard,we believe that the volatilization of Zn plays an important role in regulating the structure and performance of Fe-N-C.（2）Based on the melting volatilization of Zn,we further explored the difference of morphology and composition of Fe_0.4Zn_0.6@NC-600,Fe_0.8Zn_0.2@MNC,Fe@MNC-800,and Fe@MNC-920 derived from Fe-Zn PBA at different calcination temperatures（600,700,800 and 920℃）,and compared their ORR catalytic performance.It is found that Fe_0.8Zn_0.2@MNC showed better ORR catalytic activity than Fe_0.4Zn_0.6@NC-600,Fe@MNC-800,and Fe@MNC-920.At the same time,we have drawn the following conclusions regarding how these differences in morphology and composition determine their ORR catalytic activity.We believe that:1)The increased specific surface and porosity due to Zn volatilization during the calcination of Fe-Zn PBA play a positive role in promoting ORR catalytic activity;2)The particle size and distribution of the catalyst affect the catalytic performance of ORR;3)A small amount of Zn atoms form a synergistic effect with Fe atoms and act as active centers together.In addition,the stability test results also show that Fe_0.8Zn_0.2@MNC has good ORR catalytic stability.After the durability test,the half-wave potential of Fe_0.8Zn_0.2@MNC is only negatively shifted by 3 m V,which is lower than 8 m V at 20%Pt/C.So,we believe that N-doped carbon shell layer in Fe_0.8Zn_0.2@MNC helps to improve the catalytic stability of ORR.This work can provide a constructive reference for the construction of mesoporous encapsulated structural materials to improve electron transfer,ion diffusion and the transfer rate of reactants.