Preparation And Performance Study Of Non-precious Metal Catalysts For Oxygen Reduction In Fuel Cells Applications

Over the past few decades,In the past decades,technicians have conducted a lot of research around the development of advanced electrochemical energy conversion devices to cope with the energy crisis and mitigate environmental pollution.Among them,proton exchange membrane fuel cells（PEMFCs）are a promising device that can achieve efficient conversion of chemical energy to electrical energy through a green and pollution-free electrochemical reaction.However,the slow kinetics of the cathodic oxygen reduction reaction of PEMFCs requires the extensive use of expensive and scarce Pt/C electrocatalysts,which severely limits their commercialization.Therefore,it is important to explore low-cost and high-activity non-precious metal oxygen reduction catalysts to accelerate the development of fuel cells.However,the electrocatalytic activity and stability of such catalysts are still difficult to meet the standards for commercial applications.Therefore,the continuous improvement of the activity and stability of non-precious metal catalysts has become a current research hotspot.In this paper,we prepared a series of bimetallic or diatomic-centered catalysts by rational active site design and structural modulation strategies to improve the performance and stability of non-precious metal catalysts.（1）Introduction of Co elements into metal-organic frameworks to improve the catalytic activity of Fe-N-C materials for the oxygen reduction in acidic media.Fe-N-C catalysts have been widely used in electrocatalysis due to their ability to catalyze oxygen reduction reactions effectively,but their single active site limits their development.In this chapter work,we used a stepwise pyrolysis strategy to construct active sites with Fe and Co bimetallic centers in nitrogen-doped porous carbon.Compared with Fe-N-C catalysts,Fe Co NC has more excellent catalytic activity for the oxygen reduction in acidic electrolytes.Our prepared catalysts have an onset potential of 918 m V and a half-wave potential of 801 m V in acidic media,which is attributed to the highly active bimetallic central site and the ideal porous structure.This bimetallic catalyst had ultra-high stability,possessing 96%current density retention after 70,000 s of operation at constant voltage under acidic conditions,and exhibiting a peak power density of 387 m W cm^-2in the H₂-Air fuel cell test.（2）A new approach to improve the oxygen reduction activity and stability of Fe-N-C catalysts by Fe-based nanoparticles was developed.To improve the oxygen reduction activity and stability of Fe-N-C catalysts,we achieved the goal by introducing a binuclear metal active center.The iron oxide nanoparticles were encapsulated within ZIF-8 during the precursor preparation,and Fe NPs and Fe NC composite active sites were formed by high temperature treatment under inert atmosphere.It was shown that Fe NPs could improve the oxygen reduction catalytic performance of the Fe Nx active site,and the optimized Fe _NP/Fe NC material had a significantly higher half-wave potential of 0.809 V compared with the Fe NC-NPC catalyst.Meanwhile,Fe NPs conferred a high stability,and the half-wave potential of the catalyst was basically unchanged after 15000 cycles.As a cathode catalyst for fuel cells,the peak power density reached 436 m W cm^-2at H₂-Air,2 bar.This provides a new idea for the design and synthesis of electrocatalytic materials with high catalytic activity and stability.