Preparation Of Iron-based Nanocatalysts And Their Electrocatalytic Oxygen Reduction Performance

Oxygen reduction reaction（ORR）is the cathode key reaction for energy conversion devices such as zinc-air batteries.Particularly,Pt/C is a benchmarking electrocatalyst in oxygen reduction reaction.Due to the cost,scarcity,and poor durability of Pt,the search for non-noble metal-based catalysts with low cost,high activity,high stability and strong resistance to methanol poisoning has become an important research theme.In this thesis,Fe/NC-900 and Fe/BNC catalysts with excellent ORR activity and high stability were prepared by high temperature pyrolysis strategy and host-guest strategy,respectively.The main contents of the thesis are as follows:1.A high temperature pyrolysis strategy was proposed to prepare Fe-based nano-catalyst Fe/NC-900 using g-C₃N₄-derived nitrogen-carbon material.After high temperature carbonization,the iron particles are wrapped in the carbon layer.The iron particles exist in the form of Fe₃C/Fe composite particles,and the Fe₃C itself has certain ORR activity,which can produce a synergistic effect with Fe-N_x active center,thus leading to an efficient oxygen reduction reaction.The ORR results show that the half-wave potential of Fe/NC-900 reaches0.91 V under alkaline conditions,which is 50 mV higher than that of Pt/C.At a potential of0.85 V,the kinetic current density reaches 23.86 mA cm^-2,which is about 2.5 times of Pt/C.After 10000 CV potential cycles,half wave potential attenuated only 13.2 mV.The electrocatalyst prepared by this method has high activity and excellent stability,along with a strong potential application perspective.2.A host-guest strategy was described to prepare Fe-B@ZIF-8 by introducing Fe and B species within ZIF-8.This was followed by high temperature pyrolysis to obtain nitrogen and boron co-doped iron catalyst（Fe/BNC）.Fe/BNC retained part of the original regular dodecahedron structure of ZIF-8,along with the formation of carbon nanotubes.The Fe particles in Fe/BNC were wrapped with carbon layers,which facilitates the ORR reaction process.Since the electronegativity of boron（2.04）is lower than that of carbon（2.55）,B is an electron-deficient atom relative to C.The introduction of B into the lattice structure of carbon can regulate the d-band center of Fe,thus modulating the electronic structure of the catalyst and synergizing with the Fe-N_x active site to enhance the ORR activity.The results show that the half-wave potential of Fe/BNC under alkaline condition is 0.90 V,which is 50 mV higher than that of Pt/C.After 10000 CV cycles,the half wave potential attenuated 26.1 mV.Overall,the nitrogen and boron co-doped iron catalyst in the present study demonstrated high activity,excellent cycling stability,and strong resistance to methanol poisoning.