Preparation And Performance Study Of M-N-C Oxygen Reduction Catalysts

Our development vision is to achieve‘carbon peaking’by 2030 and ‘carbon neutrality’by 2060.The active development of hydrogen energy and fuel cell technology is an important step towards energy innovation and the achievement of the goals.However,the kinetics of the oxygen reduction reaction at the cathode of fuel cells is slow and the reaction mechanism is complex,and there is an urgent need to develop low-cost,high-performance catalytic materials.Based on the above background,the following work has been carried out in this thesis:（1）ZIF-8 was used as the main framework,and its cavity-limiting effect was used to separate iron acetylacetonate,while another metal,cobalt,was introduced to improve the oxygen reduction activity of the catalyst through the synergistic effect of the bimetal.In combination with the pore-forming effect of Zn,a carbon-based catalyst with a graded porous structure was prepared.After optimisation of the reaction conditions and calcination procedure,the Fe Co_5:1-N-C catalyst showed good catalytic activity and stability in the acidic electrolyte,with a half-wave potential of 0.815 V in 0.1 M HCl O₄,maintaining 95.5%of its original activity after 50,000 s timed current test,and good fuel cell device performance(peak power density 637 m W cm^-2).Further work was carried out on the macroproduction of precursors and catalysts,and the kilogram-scale production of non-precious metal catalysts was achieved through a process such as pelletizing and forming,combined with a fluidized bed high-efficiency calcination system,and the macroproduced catalysts have similar oxygen reduction properties and device performance to those obtained from the pilot scheme,which is expected to be produced on a large scale in the future.（2）By introducing another ligand to regulate the crystal growth environment during the reaction,a series of catalysts with controlled morphology and adjustable particle size were produced for the oxygen reduction reaction.A secondary pyrolysis strategy was also proposed to increase the specific surface area of the catalysts with a suitable graded porous structure by using the carbonised metal-organic skeleton derivatives as cobalt-doped precursors.The Fe Co-N/C_1:3 catalysts obtained after optimisation of the experimental scheme exhibit excellent electrochemical performance in both acid and alkaline electrolytes:in 0.1 M KOH,their half-wave potential is as high as 0.910 V,exceeding that of commercial platinum carbon;in 0.1 M HCl O₄,their performance is also comparable to that of commercial platinum carbon（half-wave potential of 0.825 V）.Assembled into a hydrogen-oxygen proton exchange membrane fuel cell,the peak power density of 801 m W cm^-2 exceeds that of most of the non-precious metal catalytic materials reported so far,which provides new ideas for the subsequent development and design of electrocatalysts with specific size structures.