Study On Preparation And Oxygen Reduction Performance Of Porous Carbon-Based Non-Noble Metal Catalysts

Promoting the development of hydrogen-oxygen fuel cells and metal-air batteries is a very important part to realize our country’s goals for carbon peaking and carbon neutrality.At present,the reaction kinetics of the cathodic oxygen reduction reaction(ORR)in these two devices is sluggish.Therefore,Pt-based noble metals are still needed as electrocatalysts to accelerate ORR.However,Pt is in short supply,which makes it very expensive.It is necessary to develop highly active catalysts from resource-rich non-precious metals.Fe-N-C catalysts with high density of Fe-Nx active sites are considered as one of the most promising non-noble metal catalysts due to abundant pore structure and high specific surface area of porous carbon as support.So far,there are still challenges in how to construct the most suitable pore structure in carbon support and how to control the microenvironment of Fe-N coordination to improve the catalytic performance of ORR.In this work,we use different methods to effectively control the structural characteristics of porous carbon-based catalysts and adjust their ORR activity by changing the external environment and microstructure of active sites.The hierarchical porous honeycomb-like Fe-DPC catalyst was constructed by the Kirkendall effect between Fe-doped 2,6-diaminopyridine and ZIF-8,which can effectively promote active sites accessibility and efficient reactant transport.In addition,a series of control experiments demonstrate the presence of moderate Fe and Fe3C nanoparticles in 5Fe-DPC,which can enhance ORR activity of Fe-Nx sites.In addition,a series of control experiments demonstrate that the presence of appropriate Fe and Fe3C nanoparticles in 5Fe-DPC can enhance the ORR activity of Fe-Nx.And the initial potential and half-wave potential of 5Fe-DPC are up to 1.01 V and 0.92 V,respectively.Zn-air battery assembled with 5Fe-DPC(power density is 254 mW·cm-2)as cathode catalyst showed excellent performance.Subsequently,combined with the spatial constraints of SiO2 microspheres and the regulation of ammonium chloride on active site of catalyst,porous carbon nanospheres with Fe-Nx active site were constructed to achieve rapid reactant transport and increase the exposure of active site.At the same time,the addition of ammonium chloride can also effectively regulate the crystallinity of Fe3C nanoparticles in catalyst,thereby optimizing its stability(95%)and ORR activity(half-wave potential is 0.88 V).Flexible zinc-air batteries assembled with this catalyst exhibited high power density(52.1 mW m-2)and stability.To further explore ways to improve ORR activity of catalyst,a dual-template method of SiO2 and ZnCl2 was used to synthesize a porous carbon-based Fe-N-C catalyst with interconnected pore structure,which maximizes the exposure of Fe-Nx sites and accelerates the reactant transport.Moreover,the effect of the introduction of S element on the internal structure and catalytic activity of Fe-Nx was also explored.These results lay a solid theoretical foundation for the development of inexpensive and efficient Fe-N-C oxygen reduction electrocatalysts.