Investigation On The Performance And Stability Mechanism Of FeNC Oxygen Reduction Catalyst In Proton Exchange Membrane Fuel Cell

In recent years,people are eagerly seeking a cleaner energy source that can replace fossil fuels.Hydrogen energy has great potential as a non-polluting green energy source to solve the energy problems that the world is worried about.Hydrogen-oxygen fuel cell is an energy conversion device that converts chemical energy in hydrogen into electrical energy.Due to its advantages of clean and pollution-free products,high energy conversion efficiency,and low temperature start-up speed,it has attracted the attention of scientific research teams and technology companies.Fuel cells were first used in the field of aerospace and aviation,and now they have been vigorously developed in the field of commercial and civil vehicles.Fuel cell vehicles have become an inevitable trend in the development of new energy vehicles.However,due to the rare and expensive metal platinum used as the catalyst in the anode and cathode of the fuel cell,this accounts for almost 50%of the cost of the fuel cell.The high cost limits the commercial application of the fuel cell in a large range.Therefore,in order to promote the wider commercialization of fuel cells,the development and design of more efficient non-precious metal catalysts to replace expensive platinum-based catalysts will inevitably become the focus of research today.In this paper,the FeNC catalyst with the best performance in M-N-C（M:Fe,Co,Mn,etc.）is taken as the research object,and FeNC catalysts with different pore ratios are synthesized through literature research,and the fuel cell stability attenuation trends corresponding to different pore catalysts are compared;Four kinds of FeNC catalysts with the same structure were prepared,and the effect of nitrogen doping in the precursor iron source and nitrogen doping in the heat treatment ammonia atmosphere on the performance and stability of the fuel cell was explored;To study the change of the catalyst active site during the subsequent fuel cell stability test process,prepare FeNC catalysts with single-atom dispersion of iron active sites,optimize their oxygen reduction activity and apply them to fuel cells to study their discharge performance and stability trends.And all use conventional physical and electrochemical characterization methods to analyze the structure and performance of the catalyst.The specific research work is as follows:1.Use nano-silica as the hard template and etched with hydrofluoric acid to form a mesoporous structure for FeNC catalyst,and use Zn Cl₂as a pore-forming agent to volatilize to form a microporous structure during high-temperature pyrolysis.By adjusting the amount of these two materials added,three types of catalysts were prepared,mainly dominated by micropores,dominated by mesopores,and the ratio of mesopores was equivalent and their performance decline trend in the stability test of H₂-O₂fuel cells were compared.The experiment explored the effect of different aperture structures on the stability performance of the material.2.Two metal-organic frameworks of the same structure,namely MIL-101（Fe）without nitrogen element and NH₂-MIL-101（Fe）doped with nitrogen through its own amino group as the iron source precursor,were used to prepare FeNC catalysts.The fuel cell performance and stability trends of the catalysts obtained by pyrolysis in two different atmospheres of nitrogen and ammonia were compared again,and the effect of the doping of nitrogen in its own group and the doping of nitrogen in the external pyrolysis atmosphere on the performance and stability of the FeNC catalyst in the fuel cell test was studied.3.In order to further study the changes of active sites of FeNC catalyst during the fuel cell stability test,and avoid the research difficulties caused by the mutual interference between multiple active sites,we chose to prepare a FeNC catalyst as our research object with atomic dispersion of iron active sites.Through literature research,combining the nitrogen-and carbon-rich characteristics of g-C₃N₄with the important role of metal-organic frameworks in the preparation of single-atom catalysts,g-C₃N₄is wrapped on the surface of Fe-doped ZIF-8.The ammonia produced by high-temperature pyrolysis of g-C₃N₄can etch on the surface of the carbon support formed by the organic framework to form more defects and load more active sites,thereby improving the oxygen reduction activity.And then through the two-step pyrolysis under nitrogen and ammonia atmosphere,the FeNC catalyst with atomic dispersion of iron active sites with excellent oxygen reduction performance is obtained.