Pt/FeNC Electrocatalyst Was Prepared By Using Polystyrene Microspheres As Template And Its ORR Performance

Oxygen reduction reaction（ORR）occurs at the cathode of proton exchange membrane fuel cell（PEMFCs）,which is a four-electron transfer process.The overpotential is high and the kinetic reaction is slow,so the demand for electrocatalyst is large.The most commonly used ORR electrocatalyst is Pt/C,but it is difficult to be commercialized on a large scale due to its disadvantages such as low reserve,high price and poor stability.Therefore,in order to achieve the large-scale application of PEMFCs,the introduction of non-precious metals and Pt combined to prepare Pt-based catalyst,the preparation of inexpensive,stable and efficient ORR electrocatalyst method has been widely concerned.Based on carboxyl polystyrene microspheres（PS）as the template,Fe（NO₃）₃·9H₂O and Zn（NO₃）₂·6H₂O as metal salt,2-methyl imidazole as ligands,using liquid phase synthesis of PS@Fe ZIF-8 precursor,in the high temperature calcination under N₂ atmosphere Fe NC-P,Pt/Fe NC-P electrocatalyst was prepared by reducing chloroplatinic acid with citric acid and its ORR performance was studied.Non-noble metal Fe was introduced to combine with Pt to produce synergistic effect,which improved ORR activity and reduced platinum dosage to reduce catalyst cost.The introduction of PS and the use of carboxyl groups on the surface of PS to anchor metal ions,disperse metal ions,prevent metal agglomeration,promote the formation of carbon nanotubes（CNTs）.The reaction conditions of Pt/Fe NC-P electrocatalyst were optimized.When the calcination temperature was 800℃,the molar ratio of Pt⁴⁺/(Zn²⁺+Fe³⁺)was 0.03,the amount of PS was 0.3 g,and the molar ratio of Zn²⁺/Fe³⁺was 3/1,the Pt/Fe NC-P electrocatalyst had better ORR performance.The main results are as follows:1)XRD results show that Pt/Fe NC-P is mainly composed of graphitized carbon and Fe₅C₂.Pt content is 0.32 wt%.There were self-growing CNTs with graphite carbon shells and Fe₅C₂encapsulated inside.The formation of more CNTs results in larger specific surface area and rich pore structure.2)ORR results showed that the initial potential,half-wave potential,stability and methanol resistance of Pt/Fe NC-P were 0.924 V,0.834 V,63.81%and 89.40%,respectively,which were higher than those of 20%Pt/C（0.903 V,0.817 V,45.30%and 59.20%）.3)XPS results showed that Pt was successfully loaded in Pt/Fe NC-P,and Pt and Fe NC acted synergistically.The introduction of Pt promoted the conversion of pyridine-N to Fe-N,increased the number of Fe N_xactive sites,and improved ORR performance.With the addition of PS,more CNTs were generated on the electrocatalyst,which promoted the conversion of pyridine-N into graphite-N,increased the number of graphite-N active sites,and further improved the ORR performance.This study provides new basic experimental data for the preparation and design of such catalysts and their application.