Construction Of Transition Metal Modified Nitrogen-doped Carbon Materials And Investigations Of Their Electrocatalytic Prosperities

The development of modern society is closely linked to energy supply.And the sustainable energy supply plays an essential role in political stability and economic development.Due to the shortage of traditional fossil fuels and its adverse impact on the environment,it is urgent to develop new clean and sustainable energy sources to replace traditional fossil energy.Among the currently developed energy conversion and storage devices,fuel cells and metal-air batteries are regarded as the most promising new energy battery technology,owing to their high energy density,high conversion efficiency,and environmental friendliness.However,the kinetic sluggish of the oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?at the cathode necessitate noble metal catalysts such as Pt/C and RuO₂ to increase the reaction rate.The scarcity and high expense of precious metal materials make the new energy battery technology unable to achieve large-scale applications.Therefore,the development of non-precious metal catalysts is of great significance for the commercialization of new energy battery technology.With the in-depth understanding of the electrocatalytic mechanism and the rapid development of technology,the catalytic activity of non-noble metal electrocatalysts has been greatly improved.In this work,a wide range of environmentally friendly raw materials were selected using simple and efficient methods to prepare the carbon-based electrocatalysts.The electrocatalytic performance of carbon-based materials was optimized by adjusting nanostructure,heteroatom doping and transition metal compounds modification.The catalytic mechanism was investigated by various characterization combined with electrochemical performance tests.The main research contents are as follows:?1?The Fe₂O₃ nanoparticles modified two-dimensional N-doped porous graphene-like material?Fe?1.0?-N/C-800?was prepared by one-step pyrolysis using?-cyclodextrin as the carbon source,urea as the nitrogen source,and FeCl₃ as the ferric source.N doping can regulate the electronic structure of the C atoms and form a porous structure.Further introduction of Fe₂O₃ modification can not only catalyze carbon graphitization to achieve a two-dimensional layered structure,but also form Fe-N_x active sites with doped N in the carbon layer.Therefore,the asprepared Fe?1.0?-N/C-800 has desirable ORR catalytic performance in alkaline media(E_onset=0.937 V vs.RHE,E_1/2=0.832 V vs.RHE,j_L=-5.112 mA cm^-2),and excellent methanol tolerance and long-term stability.?2?Based on the above work,Fe-containing ionic liquids([C₁₆mim]₃[Fe?CN?₆])was performed as the carbon source and ferric source,and dicyandiamine as the nitrogen source.The[C₁₆mim]₃[Fe?CN?₆]was compounded with dicyandiamine by efficient ball-milling to prepare the Fe/Fe₃O₄ nanoparticles highly dispersed N-doped two-dimensional porous carbon material?Fe-N/C?C?-700?.Ball milling achieves uniform doping of N in the carbon skeleton.Ionic liquids with molecular template properties can induce the formation of highly dispersed metal nanoparticles and two-dimensional porous structures.The morphology and structure of the catalysts can be controlled by regulating the composition of the ionic liquids and ball-milling mass ratio of raw materials,so far to improve the electrocatalytic performance.Therefore,the asprepared Fe-N/C?C?-700 exhibits the comparable electrocatalytic ORR performance with the noble metal catalyst in the alkaline medium(E_onset=0.997 V vs.RHE,E_1/2=0.835 V vs.RHE,j_L=-6.087 mA cm^-2),together with outstanding methanol tolerence and cycling stability.?3?Based on the previous work,hard template was introduced into catalyst sythesis to adjust the nanostructure of the carbon material into a three-dimensional hollow spherical structure.Fe³⁺penetrated into the interior of the carbon sphere through the melt diffusion strategy of capillary force,which controls the in-situ growth of Fe₃O₄nanoparticles on the inner wall of the carbon sphere.N doping and Fe₃O₄ modification constructed more active sites and the special yolk-shell structure further ensured the stability of the catalyst.Fe₂₀@N/HCSs exhibits excellent bifunctional electrocatalytic ORR(E_onset=0.953 V vs.RHE,E_1/2=0.850 V vs.RHE,j_L=-5.750 mA cm^-2)and OER(E₁₀=1.519 V vs.RHE)performance,superior to commercial noble metal catalysts such as Pt/C and RuO₂.In addition,the Zn-air battery assembled with Fe₂₀@N/HCSs as the cathode achieved high open circuit voltage?1.57 V?,high power density(140.8mW cm^-2),and excellent long-term cycling performance?over 300 hours?,with superior performance compared to Pt/C+RuO₂-based battery.